Gérard FAURE  -  DESCRIPTION OF THE SYSTEM OF ASTEROIDS AS OF MAY 20, 2004
		( Previous full description on 31-December-03 )
		English translation : Richard MILES
When I began observing asteroids in 1975, I knew hardly anything about them and data about them was not readily available to the amateur.
The research I undertook allowed me to discover their large number (several thousand at that time) and their orbital diversity within the Solar System.
It was thrilling to learn that these tiny and mysterious travellers wandered between and across the planets, crossing regions unknown to man.
I took an avid interest in them and in observing them as much as possible and learning the most about them.
Until the middle of the 1990s, each discovery, especially that of an Earth-Grazer was a notable event, and one could continue to have a good idea of the
composition of the minor planets on account of the limited number of new objects discovered annually.
When the era of automatic observation began and discoveries were made at an ever increasing rate, it was no longer possible to have a complete
knowledge of the structure and above all the composition of these tiny Liliputian worlds.
In September 2000, for the Meeting of the internet list of Alphonse Pouplier in the south-east of France, I had prepared an article presenting the asteroids, based
largely on numbered objects.
I had wanted to carry out a more complete analysis including unnumbered objects and the principal acquired knowledge on these asteroids.
This was done at the end of April 2002, in French and English.
Two updates followed : one partial one in French in August 2002, then a full and more comprehensive one at the end of 2003, translated into English by Richard Miles.
Lastly, for the presentation of this dossier at MACE 2004 ( Meeting on Asteroids and Comets in Europe ) in Frasso Sabino near Rome, I have proceeded to
update the data through to 20-May-2004.
Always with the help of the very useful spreadsheet Microsoft Excel, my personal and up-to-date library and the very useful MPCORB file from the Minor Planet
Center website, I have again spent a large part of my free time preparing, over a total period of 3 weeks, this "Description of the System of Asteroids"
in our Solar System to  20-May-2004.
214044 minor planets have been taken into account and I have processed, sorted, analysed and reanalysed nearly 3 million items of numerical data.
I have also newly drawn on information from dozens of recent professional articles and websites, for which references are given at the end of the analysis.
Due to a lack of time, the majority of statistics have not been updated since 2003.
For the first version in 2002, difficulties encountered had principally been :
Determining definite dynamical families and groupings within the Belt N°1 (notably the Nysa-Hertha, Griqua and Flora ones)
Assigning the TNOs to known or suspected families
The limiting zones of the variously-determined families and groups based on the orbital elements of the asteroids.
Updating the basic files as and when new MPECs (Minor Planet Electronic Circulars) are published.
For update at the end of 2003, which comprised numerous new categories, the difficulties were primarily :
Understanding and putting in summarised form current knowledge about the taxonomy and surface mineralogy of the minor planets.
Taking into account the advances in the knowledge of the structure of the Kuiper Belt.
Setting up files automating the various statistics presented in this file.
Updating all the precise orbital data for asteroids having often changed over 20 months at the level of tenths or hundreths of astronomical units,
sometimes even for definitively-numbered minor planets.
I have constructed the first analyses so as to give the largest possible number of readers, even those not fascinated by the asteroids, an accurate picture
of the various components making up the World of Minor Planets.
The initial pleasure has transformed itself into a very interesting work, requiring much research and allowing me to learn again and always, in spite of
the large number of years of reading already done.  It is also true that our knowledge about the asteroids is perpetually evolving…
As an Observer, I also take advantage of this work, which enables one to spot interesting objects to observe in the future.
Finally, certain analyses and statistics allow one to specify the limits and real extent of observational problems, bringing about a better appreciation
of planned work, sometimes contradicting previous ideas.
Of course, in spite of my attention, some errors or omissions have been made in the production of this work, which is published on the website of AUDE ( Association
des Utilisateurs de Détecteurs Electroniques, i.e. "Electronic Detectors Users' Association") , in that part reserved for the Magnitude Alert Project (MAP), jointly
managed by "The Minor  Planet Section  of the ALPO" (Association of Lunar and Planetary Observers) and by AUDE.
I would be grateful to you, if the case arises, if you would like to let me know by a message addressed to <gpmfaure@club-internet.fr> since it all adds something
useful. Thanks in advance.
I want to thank my friend Richard MILES (rmiles@baa.u-net.com), who at the MACE 2003 meeting in Mallorca offered his help for future English translations
of this dossier and its updates.
His very valuable contribution enables the near-simultaneous publication of the French and English versions, close to the very update of the scientific data included.
Lastly, I would like to draw your attention to the very interesting website of the Czech astronomer, Petr Scheirich, which can be found at the address :
" http://sajri.astronomy.cz/asteroidgroups/groups.htm "
A visit to his webpage "Asteroid Groups" enables, with the help of very fine images and graphics, to visualise many groups with various characteristics complementing
the account of the "System of Minor Planets" described below.
Good reading !
Gérard Faure
Asteroids taken into account
				Number on 31-Dec-03		Number on 20-May-04
The 85117 asteroids definitively numbered by the Minor Planet Center.				73636		85117
All other unnumbered asteroids from the MPCORB (MPC) file and/or the various lists on the MPC website				129966		128919
Certain probable NEAs dating from before 1990 and the possible Apohele 1998 DK36 (various sources)				8		7
The largest Plutino, Pluto				1		1
Particularly new discovered objects and notified in MPECs later than the download of the last used MPCORB file				2684		0
				206295		214044
NB: On 31-Dec-03, the MPC possessed 232740 asteroid orbits, of which 203605 were available in the MPCORB database and/or in the lists on the MPC website.
Those missing from MPCORB and the MPC lists are those of the most uncertain orbits. The objects concerned are effectively lost for the present.
Each day, new asteroids are discovered and orbits improved.
This update comprises 7749 minor planets additional to those at the end of 2003 and 58039 more than for the previous update to 28-April-2002.
NB: Satellites of asteroids are not counted in addition to the primary asteroid
Last remark before getting into the nitty-gritty of the subject: For practical reasons involving Excel (lack of space in certain tables, particular uses of brackets on
a French keyboard of a laptop PC, etc…), the official name format of definitively-numbered asteroids involving parentheses has not often been adhered to.
TERMS USED IN THE DESCRIPTION OF THE SYSTEM OF ASTEROIDS
a	Semi-major axis of the orbit or the mean distance from the Sun in AU
albedo	Percentage of sunlight that an object reflects from its surface.
e	Defines the degree of ellipticity of the orbit, from 0.0 (Circle) to >1.0 (Hyperbola)
family	A family is formed from asteroids having very similar values of "a", "e" and/or "i"
G	Defines the reflection of sunlight by the asteroid as a function of phase angle
group	A group is formed from asteroids situated in the same region of the Solar System having quite similar values of "a", "e" and/or "i"
H	The brightness in the V-band of an asteroid if at a distance of 1 AU from the Sun and 1 AU from the Earth
i	Inclination of the asteroid orbit from the Ecliptic in degrees
gap	Region of the Solar System devoid of asteroids owing to perturbations by a large planet (in particular resonance zones)
orbit	Path in space followed by a celestial body
P	Time required to complete one revolution of the orbit, in terrestrial years
Lagrangian Point	Stable orbital zone at 60° ahead of or behind the same orbit of a large planet ( zone "L5" westwards and zone "L4" to the east )
q	Perihelion or point in the orbit closest to the Sun, in AU
Q	Aphelion or point furthest from the Sun, in AU
resonance	The natural frequency of a physical system in the regions where the orbital period of the asteroids are at certain fractions of the
	period of a large planet.
AU	Astronomical Unit = approximately the Earth-Sun distance = 149 597 870 km.
NB: Other orbital elements exist. They are less descriptive but are indispensable for working out positional Ephemerides and the brightness of asteroids in the sky.
Examples : The "Longitude of the Ascending Node" of the orbit measured from the Vernal Equinox, the "Mean Anomaly" ( mean motion of the asteroid and the interval of time
since the asteroid passed perihelion), "the argument of perihelion" ( angle between the ascending node and the perihelion measured in the direction of the motion ), etc..
System of asteroid identification
Currently, new asteroid discoveries are subject to a 4-stage identification procedure, from the discovery to the definitive numbering :
In brief, the 4 stages are :
Stage 1 : Following discovery, the Discoverer assigns it a provisional designation ( Example : J002E3, P00ACE, SS-291, etc…)
Stage 2 : When the existence of the asteroid is confirmed, the MPC assigns it a provisional designation comprising the year of discovery, followed by
a letter, which defines the half-month in which the discovery was confirmed, and a second letter, usually accompanied by a number, defining
the sequential order of confirmation ; (examples : 1937 UB, 1980 AA, 2000 WR106, 2003 WT42, etc…).
Stage 3 : When the orbital elements become certain, the MPC assigns it a definitive number, which is indicated before the provisional designation.
Example: (20000) 2000 WR106
Stage 4 : Once definitely numbered, the Discoverer can name it.  Example: asteroid (20000) 2000 WR106 has become (20000) Varuna.
NB:  All asteroids have not followed these naming stages in the past and several provisional designations can be involved for the same object when it has been lost several times.
It is therefore, generally, the provisional designation that has yielded the definitive identification that is kept.
LARGE PLANETS:  Table of Minimum, Mean and Maximum Distances from the Sun
	q in AU	a in AU	a in millions of km	Q in AU		P in years
MERCURY	0.307	0.387	57.8	0.466		0.241
VENUS	0.718	0.723	108.1	0.728		0.615
EARTH	0.9833	1.000	149.5	1.0167		1.0
MARS	1.381	1.5236	227.9	1.6662		1.881
JUPITER	4.947	5.202	778.2	5.456		11.862
SATURN	9.030	9.578	1432.8	10.125		29.458
URANUS	18.171	19.129	2861.6	20.087		84.015
NEPTUNE	29.683	29.955	4481.2	30.227		164.788
(PLUTO)	29.620	39.496	5908.5	49.372		247.7
HISTORY of Minor Planets to 20-May-2004
16th Century		6 planets known, orbiting around the Sun:
		Planet                     Dist. in AU               Mean Dist. in millions of km
		MERCURY                      0.39                                       57.9
		VENUS                           0.72                                      108.1
		EARTH                           1.00                                      149.6
		MARS                            1.52                                       227.9
		JUPITER                         5.20                                      777.9
		SATURN                         9.54                                     1433.9
1596	Johannes KEPLER	The existence of a planetary body between Mars and Jupiter first mooted
		(Adaptation of Plato's Theory. Crystalline spheres of Ptolemy on 5 geometric solids
		each supporting a sphere.  One of these solids, the Tetrahedron, must support a sphere
		comprising a planet between the orbits of Mars and Jupiter.)
1766	Johannes TITIUS and	Titius-Bode Law : (n+4)/10 where "n" is an element from the series; 0, 3, 6, 12,...
	Johann BODE
		Planet                     Dist. in AU               Titius-Bode Prediction
		MERCURY                      0.39                        0.4
		VENUS                           0.72                        0.7
		EARTH                           1.00                        1.0
		MARS                            1.52                        1.6
		????                                                             2.8
		JUPITER                         5.20                        5.2
		SATURN                         9.54                      10.0
		There must therefore be a planet between Mars and Jupiter....
1781	William HERSCHEL	Discovery of the Planet URANUS located on average 19.2 AU from the Sun, that is 2.887 billion km.
		The Titius-Bode Law is again obeyed:  19.2 AU cf. 19.6 AU according to the law.
1785 to 1800	Baron Von ZACK (Hungary)	Search for the missing planet and start of the Zodiacal star catalogue in 1800.
31-Dec-1800	Guiseppe PIAZZI	Star in Taurus recorded on a chart at Palermo Observatory
01-Jan-1801	Guiseppe PIAZZI	Discovery of CERES followed until mid-February 1801.
		Thanks to calculations of Carl GAUSS, VON ZACH relocates Ceres on 07-Dec-1801
28-Mar-1802	Wilhem OLBERS	OLBERS fortuitously discovers PALLAS, having prepared star charts for observing Ceres.
01-Sep-1804	Karl HARDING	Olbers, thinking that Ceres and Pallas are two pieces from the same planet, asks for assistance.
		Karl HARDING finds JUNO on 01-Sep-1804.
29-Mar-1807	Wilhem OLBERS	Wilhem OLBERS finds VESTA on 29-Mar-1807.
1815		Search abandoned.  The Solar System is thus considered to comprise 11 planets.
		The word "asteroid" coined by William HERSCHEL in 1802 was used only after 1845.
08-Dec-1845	Karl HENCKE	Discovery of ASTRAEA after 15 years of solitary searching.
		Relaunch of the search for asteroids by the astronomical community, principally by amateurs.
23-Sep-1846	J.G. GALLE and	Discovery of NEPTUNE orbiting on average some 29.955 AU from the Sun, that is 4.481 billion km.
	U.V. LE VERRIER
End of 1849		10 asteroids are known. They are from now on called "asteroids" or "minor planets"
July 1868		100 asteroids are known.
		Daniel KIRKWOOD explains the gaps devoid of asteroids at certain average distances from the Sun as a
		result of the resonant action of Jupiter on the orbits of minor planets in the Asteroid Belt.
13-Jun-1873	James WATSON	Discovery of 132 AETHRA which at perihelion reaches the aphelion distance of Mars.
End of 1891		322 minor planets have been found, all visually.
		The record is held by Johann PALISA with 83 discoveries resulting from comparing the observed sky with
		that star charts extending sometimes to 15th magnitude !
20-Dec1891	Max WOLF	First photographic discovery of an asteroid : 323 BRUCIA
13-Aug-1898	Gustav WITT	Discovery of 433 EROS, first Earth-approaching asteroid, reaching 0.13 AU, that is 19.9 million km
Start of 1900		452 asteroids are known. Their orbits and their ephemerides are still derived by hand ...
		Data centres established at Berlin and Kiel.
24-Dec-1905		First Photographic Discovery by an amateur Joël H. METCALF ( 581 Tauntonia)  Taunton (USA) .
22-Feb-1906	Max WOLF	Discovery of 588 ACHILLES , first Trojan orbiting with Jupiter, at a Lagrangian point ( L4 )
20-Oct-1920	Walter BAADE	Discovery of 944 HIDALGO, which at aphelion reaches the vicinity of Saturn, at 9.54 AU.
1923		1000 asteroids recorded.
19-Feb-1930	Clyde TOMBAUGH	Discovery of PLUTO, the first trans-Neptunian object, orbiting at an average distance of 39.44 AU
		from the Sun (namely 5,900 billion km), but crossing the orbit of Neptune near perihelion.
24-Apr-1932	Karl REINMUTH	Discovery of 1862 APOLLO, first asteroid crossing the orbits of the Earth and Venus.
28-Oct-1937	Karl REINMUTH	1937 UB alias "HERMES" passes  733,000 km from the Earth.
1947		Minor Planet Center set up by the IAU under the direction of Paul HERGET.
		Start of the publication, "Ephemerides of Minor Planets" by the Institute of Astronomy, Leningrad
26-Jun-1949	Walter BAADE	Discovery of 1566 ICARUS, which approaches some 0.18 AU from the Sun, closer than Mercury.
05-Dec-1954	G.ABELL	Recovery of 1954 XA, the first ATEN asteroid orbiting on average closer to the Sun than the Earth.
10-Aug-1972		The Earth is skimmed at an altitude of 58 km by the "Montana Bolide" (USA) which returned to space.
11-Nov-1977	Charles KOWAL	Discovery of 2060 CHIRON, the first CENTAUR, having an orbit ranging from 8.43 to 18.84 AU ( that is
		2.8 billion km, not far from Uranus).
30-Jun-1978		The Minor Planet Center set up in Cambridge (USA) under the direction of Brian MARSDEN.
1989		Start of SPACEWATCH telescope operations on Kitt Peak, searching for asteroids making close approaches to Earth.
09-Jan-1992	Spacewatch - Kitt Peak	5145 PHOLUS, new Centaur discovered, situated at 32.2 AU, further than the average distance from the
		Sun of Neptune.
30-Aug-1992	D. JEWITT and J. X. LUU	Discovery of 1992 QB1, first TNO (Trans-Neptunian Object) not crossing the orbit of Neptune and
		orbiting at an average distance of 43.80 AU, namely 6.55 billion km from the Sun.
Sep-1992		First CCD discovery of an asteroid by an amateur: 1992 RA by N.KAWASATO
09-Dec-1994		1994 XM1 passes 112000 km from Earth, to date the closest Earth-crosser passage observed telescopically
09-Aug-1996	Palomar/NEAT and	Discovery of 1996 PW reaching 528 AU from the Sun, i.e. 79 billion km !
	Gareth WILLIAMS of the MPC
1997		Start of operation of the first LINEAR telescope (New Mexico) systematically combing the sky
Mar-1999		10000 numbered asteroids... Not including Pluto ( following discussions on the the status of this small
		planet or large asteroid )
29-Jul-2000	Cerro Tololo Observatory	Discovery of 2000 OO67 attaining a distance of 1016 AU from the Sun, that is almost 152 billion km !
		Its orbital period around the Sun is 11808 terrestrial years !
28-Nov-2000	McMILLAN and LARSEN	2000 WR106 is discovered by Spacewatch. This is the largest TNO discovered to date ( 900 km diameter )
Jan-2001		The 20,000th asteroid is numbered : 2000 WR106, which becomes (20000) Varuna
04-Jun-2002	TRUJILLO and BROWN	A very large TNO (1250 km diameter) 2002 LM60 is detected, visible to amateurs using CCDs.
	(Palomar/NEAT)
Nov-2002		50,000 numbered asteroids !!  2002 LM60 becomes known as (50000) Quaoar
11-Feb-2003	LINEAR	2003 CP20 is the first asteroid discovered orbiting entirely within the Earth's orbit.
21-Aug-2003	Deep Ecliptic Survey team	Confirmation of discovery of first Neptune-Trojan, 2001 QR322
15-Oct-2003	Brian SKIFF	After 66 years of searching, 1937 UB alias "Hermes" is found once more !
19-Feb-2004	(Palomar/NEAT)	2004 DW is a new TNO apparently larger than (50000) Quaoar, with an orbit of the Pluto type.
15-Mar-2004	BROWN et al	Announcement of the discovery of 2003 VB12 ( Sedna ), larger than 2004 DW and orbiting at 509 AU from the Sun !
	(Palomar/NEAT)
18-Mar-2004		The Aten 2004 FH pulverises the record for closest approach to the Earth, at 0.00033 AU, or 49367 km.
05-May-2004		The MPC has 251,002 asteroid orbit identified, of which 85,117 comprise definitively numbered objects.
		It is estimated that the number of asteroids exceeding 1 km in diameter reaches several million ....
		The hunt for new asteroids is thus far from over ....
SOURCES						Ref.G.Faure
Michel-Alain Combes		Deux siècles de découvertes d'astéroides - L' Astronomie Vol.115 janvier-février 2001				-
Tom Gehrels		History and Future - Asteroids -1979 T.Gehrels				<GF:FO>
Richard A. Kowalski		A Brief History of Minor Planet Research: The importance of the Amateur - Minor Planet				-
		Amateur/ProfessionalWorkshop 1999.
Minor Planet Center		Various data on asteroids ( http://cfa-www.harvard.edu/iau/mpc.html )				-
Syuichi Nakano		List of the first asteroids discovered by amateurs using CCDs
Frederick Pilcher and Jean Meeus		Tables of Minor Planets 1973				<GF:BK>
		TABLE OF THE SYSTEM OF MINOR PLANETS AS OF MAY 20, 2004
				Total	Total Identified		Number
GROUPS/FAMILIES	Orbital	Characteristics	Remarks	Numbered	as of 20-May-2004		Estimated
				1 to 85117	Number	Date	> 1 km
Within the Earth's orbit				0	3
VULCANOID	a < 0.22 AU	Q < q Mercury	Family still hypothetical	0	0	20-May-04	max. 900
APOHELE	a < 1.00 AU	Q < 1.00 AU	Orbit entirely within that of the Earth	0	2	20-May-04	20 ?
			1 (uncertain) = 1998 DK36		+ 1 ?
Near Earth Asteroids				339	2821	20-May-04	max.1200
ATEN	a < 1.00 AU	Q >1.00 AU	Aphelion external to q Earth	16	220	20-May-04
APOLLO				154	1354	20-May-04
APOLLO 1	q < 1.00 AU	a =1.00 to 1.524 AU	Crosses the Earth's orbit	74	594	20-May-04
APOLLO 2	q < 1.00 AU	a =1.524 to 2.12 AU	Crosses the Earth's orbit	48	433	20-May-04
APOLLO 3	q < 1.00 AU	a = 2.12 to 3.57 AU	Crosses the Earth's orbit	32	325	20-May-04
APOLLO 4	q < 1.00 AU	a > 3.57 AU	Crosses the Earth's orbit	0	2	20-May-04
AMOR				169	1241	20-May-04
AMOR 1	q < 1.30 AU	a =1.00 to 1.524 AU	Does not cross the Earth's orbit	22	225	20-May-04
AMOR 2	q < 1.30 AU	a =1.524 to 2.12 AU	Does not cross the Earth's orbit	66	422	20-May-04
AMOR 3	q < 1.30 AU	a = 2.12 to 3.57 AU	Does not cross the Earth's orbit	80	588	20-May-04
AMOR 4	q < 1.30 AU	a > 3.57 AU	Does not cross the Earth's orbit	1	6	20-May-04
NEA (uncertain)					6
Inside Belt N°1				1376	6790
MARS-CROSSER	q = 1.30 to 1.6662 AU	( a, i and e very varied )	Crosses Mars' orbit	638	3387	20-May-04
MARS-TROJAN EAST	a  ~ 1.524 AU	i > 16°	Lagrangian point L4 of Mars	0	1 ?	20-May-04	Total
MARS-TROJAN WEST	a  ~ 1.524 AU		Lagrangian point L5 of Mars	1	4 ?		50 ?
HUNGARIA	a = 1.76 to 2.06 AU	i = 12° to 36° /  e < 0.17	Between resonances 1:5 and 1:4	736	3375	20-May-04
Pre-Main-belt Objects	a = 1.88 to 2.06 AU	low i	Hungaria zone	1	23	20-May-04
BELT N°1	a = 2.10 to 4.02 AU			82417	201774	20-May-04	1 000 000
							to
			excl. Griquas, Cybeles, Hildas  =	81680	200179		1 400 000
							maximum
ZONE I  (INNER)	a = 2.065 to 2.501 AU		Between resonances 1:4 and 1:3	32221
Flora   (family?)	a = 2.12 to 2.27 AU	e = 0.04 to 0.21 / i < 8°	Between resonances 1:4 and 2:7		(3021)	2002
Phocaea (group)	a = 2.23 to 2.50 AU	e > 0.1 and i = 18 to 32°	Between resonances 2:7 and 1:3			(Morbidelli)
Vesta   (family)	a = 2.349 to 2.374 AU	e < 0.16 and i = 5 to 8°	Between resonances 2:7 and 1:4		(5575)	2002
Nysa-Hertha (family?)	a = 2.41 to 2.50 AU	e = 0.12 to 0.21 /  i < 4.3°	Between resonances 2:7 and 1:5		(6614)	2002
ZONE II (CENTRAL)	a = 2.501 to 2.820 AU		Between resonances 1:3 and 2:5	27179
Eunomia  (family)	a = 2.563 to 2.670 AU	e =0.07 to 0.21/ i =11 to 15°	Between resonances 1:3 and 2:5		(6162)	2002
ZONE III (OUTER)	a = 2.825 to 3.279 AU		Between resonances 2:5 and 1:2	22280
Koronis   (family)	a = 2.828 to 2.939 AU	e < 0.12 and  i < 3.5°	Between resonances 2:5 and 3:7		(2663)	2002
Eos         (family)	a = 2.988 to 3.046 AU	e < 0.13 and  i = 8 to 12°	Between resonances 3:7 and 4:9		(5188)	2002
Themis   (family)	a = 3.047 to 3.219 AU	e < 0.22 and  i < 3°	Between resonances 4:9 and 1:2		(2739)	2002
Hygiea   (family)	a = 3.108 to 3.217 AU	low "i" and moderate "e"	Between resonances 4:9 and 1:3		(1703)	2002
Griqua  ( Group ? )	a = 3.20 to 3.35 AU	e > 0.35 and i > 17°	In resonance 1:2 with Jupiter	5	20	20-May-04
CYBELE	a = 3.28 to 3.67 AU	e < 0.35 and i < 26°	Between resonances 1:2 and 3:5	357	702	20-May-04
HILDA	a = 3.74 to 4.02 AU	quite high e and i < 26°	In resonance 2:3 with Jupiter	375	873	20-May-04
Beyond Belt N°1				6	23
THULE	a = 4.28 AU	i = 2.3°	In resonance 3:4 with Jupiter	1	1	20-May-04
Internal Jupiter-crosser	a between 3.6 to 5.0 AU	high e ; isolated objects	Crossing towards Q the orbit of Jupiter	5	22	20-May-04
Jupiter-Trojans				877	1667		<2 million
JUPITER TROJAN EAST	a  = 4.90 to 5.37 AU	e < 0.30 and i < 40°	Lagrangian point L4 of Jupiter	525	1039	20-May-04
JUPITER TROJAN WEST	a  = 4.96 to 5.36 AU	e < 0.28 and i < 44°	Lagrangian point L5 of Jupiter	352	628	20-May-04
Beyond Jupiter				21	79
External Jupiter-crosser	a  > 5.1 AU	q < 5.1 AU and high e	Crossing towards q the orbit of Jupiter	5	25	20-May-04
CENTAUR	a = 5.5 to 29 AU	q > 5.2 AU / i < 35° / high e	"a" between Jupiter and Neptune	16	53	20-May-04
NEPTUNE-TROJAN EAST	a = 30.1 AU	e = 0.02  and i = 1.3°	Lagrangian point L4 of Neptune	0	1	20-May-04
NEPTUNE-TROJAN WEST	a ~ 30 AU		Lagrangian point L5 of Neptune	0	0	20-May-04
KUIPER BELT			( Discoverable if q < 52 AU )	81	887	20-May-04	millions ?
KBO Inner I	a = 30 to 35 AU	high e / q close to Uranus	q governed by Uranus ?	3	9	20-May-04
KBO 5:4	a = 35.0 AU	q < or = Q Neptune; i ~ 20°	Resonance 5:4 with Neptune	1	3	20-May-04
KBO Inner II	a= 36 to 38 AU	e<0.07-0.13 / q >Q Neptune	Inner Belt + Resonance 4:3 with N.	6	18	20-May-04
PLUTON+CHARON	a = 39.496 AU	q < Q Neptune	Resonance 3:2 with Neptune	0	1	20-May-04
PLUTINO	a ~ 39.5 AU	q near Q Neptune; i ~ 20°	Resonance 3:2 with Neptune	20	152	20-May-04
CUBEWANO	a = 40 to 47 AU	q >38 AU ; low "i" et "e"	( = Classical KBO )	27	450	20-May-04
KBO 5:3	a = 42.2 AU	high "e"	Resonance 5:3 with Neptune	2	7	20-May-04
( TNO uncertain )		TNO with"a"+"e" unknown			141	20-May-04
KBO 7:4	a = 43.9 AU	e > 0.2	Resonance 7:4 with Neptune	1	5	20-May-04
KBO 2:1	a ~48 AU	high "e" > 0.3	Resonance 2:1 with Neptune	2	10	20-May-04
Scattered Disk Object	a > 48 AU ?	q < 40 AU  and high "e"	( = SKBO )  ; q governed by Neptune	13	80	20-May-04
KBO 5:2	a ~ 55 AU	very high "e" > 0.4	Resonance 5:2 with Neptune	5	9	20-May-04
Extended Scattered Disk	a > 48 AU ?	q > 40 AU and high "e"	Existence still hypothetical	1	2	20-May-04
OORT CLOUD	a > 2000 AU ?	e > 0.9 and very large "Q"	a ~ 2000 to 10000 AU ?	0	0	20-May-04
							( 5 to 10
				85117	214044	20-May-04	million ? )
Remarks:
The assignment of each asteroid to a group is made following the official classifications :
*Majority from the position of their orbit relative to that of the Earth or of Mars, until and including the Mars-crossers, not taking into account their
semi-major axis.
*For distant objects, it is the position of their orbit relative to Jupiter and/or Neptune depending which dominates.
*I have classed Earth-crossers on the basis of the Earth's semi-major axis being equal to 1.000 AU, without taking into account the annual evolution of the Earth's orbit
between 0.983 and 1.017 AU.  In that, I have followed the rule employed by the Minor Planet Center.
I have not departed from the official nomenclature except for those types of object which are more or less unclassified at present :
*In the absence of a definitive nomenclature for those asteroids with orbits internal to that of the Earth, I have kept the designation "Apohele" which permits having a
fourth name for the 4th type of Earth-crosser orbit in addition to the Aten, Amor and Apollo.
Besides, Apohele allows one to adhere to the naming series based on the letter "A" for Earth-crossers.
Some minor planets of low inclination and eccentricity, located in the Hungaria zone, have nearly the orbital characteristics of the nearby Objects located in the inner edge
of the Belt N°1. I have called them "Pre-Main-belt Objects".
*Asteroids situated in the largely empty zones between the Hildas and Jupiter and crossing the Jovian orbit are called "Internal Jupiter-crossers".
*Unclassified asteroids beyond Jupiter, but crossing its orbit, have been named "External Jupiter-crossers".
*For the inner part of the Trans-Neptunian zone, I have split the present TNOs into "KBO Inner I" and "KBO Inner II", separated by the 5:4 resonance.
NB: The limiting zones of the families and groups within the Belt N°1 are based on the known limits for members clearly named in astronomical articles.
Evolution of the total numbers since the end of April 2002
Groups	end-April 2002	To 20 May 2004	Last update by the MPC	Increase in 25 months
Vulcanoids	0	0	20-May-2004	0
Apohele	1 ?	3?	20-May-2004	1
Atens	145	220	20-May-2004	75
Apollos	874	1354	20-May-2004	480
Amors	854	1251	20-May-2004	397
Mars-crossers	2396	3387	20-May-2004	991
Mars-Trojans	6	5 ?	20-May-2004	1
Hungarias	2227	3375	20-May-2004	1148
Belt N°1 ( excl. C and H )	146442	200179	20-May-2004	53737
Cybeles	509	702	20-May-2004	193
Hildas	568	873	20-May-2004	305
Jupiter-Trojans West	520	628	20-May-2004	108
Jupiter-Trojans East	787	1039	20-May-2004	252
Thule + Jupiter-Crossers	31	48	20-May-2004	17
Centaurs + Neptune-Troj.	34	54	20-May-2004	20
Internal KBO to CKBO	531	796	20-May-2004	265
SDO	74	89	20-May-2004	15
ESDO	1	2	20-May-2004	1
Oort	0	0	20-May-2004	0
Other Names of families and of groups of Minor Planets
Alinda	Asteroid undergoing libration in the 1:3 gap ( "a" ~ 2.5 AU, in the1:3 resonance with Jupiter )
CKBO	Second name for asteroids in the Kuiper belt, situated near 42 AU and with a low eccentricity, not crossing the orbit of Neptune.
Damocloid	Group derived from the Oort group of objects, with large "e", "i" and "a" reaching the interior part of the Solar System, often with "i" >90°
EGA	Asteroid which passes closer than 0.100 AU to the Earth's orbit
Earth-Grazer	Old name frequently used prior to that of "NEA".
Earth-crosser	An asteroid crossing the orbit of the Earth ( strictly Apollos or Atens ).
Griqua	Object on the outer edge of the Belt N°1, near 3.27 AU, with "i"  > 17° and e > 0.35 (resonance 1:2 with Jupiter)
IEO	Inner Earth Object = Object with orbit completely internal to that of the Earth. Another name for "Apohele"
KBO	Kuiper Belt Object
Kubewano	First name given to asteroids from the Kuiper Belt, located at about 42 AU and with a low eccentricity, not crossing the orbit of Neptune.
MBO	Belt N°1 Object
NEA	Near Earth Asteroid  = Asteroid approaching the Earth with q < 1.30 AU
NEO	Near Earth Object = Asteroid or comet approaching the Earth with q < 1.30 AU
Oort cloud object	Damocloid object
PHA	Potentially Hazardous Asteroid ( potentially dangerous ), with H < 22.0 and passing closer than 0.05 AU to the plane of the Ecliptic, at r = 1.0 AU
SDO	Scattered Disk Object = SKBO = Objects scattered from the Kuiper Belt, with "a" > 48 AU and "q" < 40 AU
SKBO	Scattered KBO = SDO = Objects scattered from the Kuiper Belt, with "a" > 48 AU and "q" < 40 AU
TNO	Trans-Neptunian Object = theoretically those situated beyond the orbit of Neptune
Vestoid	Small asteroid making up part of the dynamical family, Vesta, and exhibiting very similar spectral characteristics to those of 4 Vesta.
V-type	Asteroid exhibiting spectral characteristics similar to those of 4 Vesta, without being a member of the Vesta family.
Vulcanoid	Asteroide from a hypothetical belt, located within the orbit of Mercury, from 0.09 AU to 0.21 AU from the Sun.
	Recent studies indicate the possible existence of 300 to 900 Vulcanoids of more than 1 km diameter ( max. 25 km ),
	situated at a solar elongation of 4° to 12°, they will be difficult to detect, if they do indeed exist ….
Estimates of total asteroid numbers
All asteroids with:
Diameter > 1.0 km	> 3 million
Diameter > 0.1 km	billions
Earth-crossers:	( Spaceguard Data )
Diameter > 1.0 km	2 100
Diameter > 0.5 km	9 200
Diameter > 0.1 km	320 000
Diameter, 40 to 100 m	2 000 000
Diameter > 10 m	150 000 000
Following more recent estimates, the total number of Earth-crossers with diameter > 1 Km oscillates between 855+/-110 ( Morbidelli et al. en 2001) and 1200
( MPML 23-Jul-02 - Marsden data ). They are expected to comprise;  2% Atens, 23% Amors and 75% Apollos.
W.Bottke et al. indicate in their view a composition of; 6% Atens, 32% Amors and 62% Apollos, for NEAs with H < 22.
Those NEOs of mag < 18 would number 960 +/-120.
The NEA Search Report of NASA of Sep-2003 estimates at 1100 the number of NEAs > 1 km diameter, and at 500,000 those from 50 to 100 m in diameter.
Belt N°1:	( ISO Data )
Diameter > 1.0 km	1.1 to 1.9 million
The most recent estimates based on the Sloan Digital Sky Survey (SDSS) corrects for observing selection bias ( Asteroids III ) and indicates :
H < 12.0 = Actual	2858
H = 12	4600
H = 13	16000
H = 14	50000
H = 15	130000
H = 16	278000
H = 17	518000
Total > 1 km	1.0 to 1.4 million	( until H ~ 18.25 )
Kuiper Belt:
Diameter > 100 km	25,000 Plutinos	( David Jewitt data )
	45,000 Cubewanos	( David Jewitt data )
	>10,000 objects in the Extended Scattered Disk ( Data from B.Gladman et al. )
There should be, at the last estimates, around 100,000 TNOs greater than 100 km in diameter between 30 and 50 AU.
The recent estimates made at Kitt Peak National Observatory ( MPML 29-May-02 ) arrive at an inventory of 34 objects of the size of Charon and 4 the size of Pluto
which should be discoverable amongst the various TNOs.
Asteroids having changed family since definitive numbering (1985 to 2003) - Examples
1660 Wood	ex-Mars-Crosser	Belt N°1 ( Phocaea )	q Asteroid at the limit for Q of Mars
4015 Wilson-Harrington	ex-APOLLO 3	new AMOR 3	q Asteroid at the limit of "a" for the Earth; Comet.
4222 Nancita	ex-Belt N°1	new Mars-crosser	q Asteroid oscillates at the limit for Q of Mars
4587 Rees	ex-Mars-Crosser	new AMOR 3	q Asteroid oscillates at the boundary between the Amors and the Mars-crossers
5251 1985 KA	ex-Belt N°1 ( Phocaea )	new Mars-crosser	q Asteroid oscillates at the limit for Q of Mars
6263 1980 PX	ex-Belt N°1	new Mars-crosser	q Asteroid oscillates at the limit for Q of Mars
6454 1991 UG1	ex-Belt N°1	new Mars-crosser	q Asteroid oscillates at the limit for Q of Mars
6489 Golevka	ex-Amor 3	new APOLLO 3	q Asteroid at the limit of "a" for the Earth.
7747 Michalowski	ex-Mars-Crosser	Belt N°1	q Asteroid at the limit for Q of Mars
8722 Schirra	ex-Belt N°1	new Mars-crosser	q Asteroid oscillates at the limit for Q of Mars
18751 1999 GO9	ex-Belt N°1	new Mars-crosser	q Asteroid oscillates at the limit for Q of Mars
30555 2001 OM59	ex-Belt N°1 ( Phocaea )	new Mars-crosser	q Asteroid oscillates at the limit for Q of Mars
40310 1999 KU4	ex-Amor 3	new Mars-crosser	q Asteroid oscillates at the boundary between the Amors and the Mars-crossers
Comets numbered as asteroids
2060 Chiron	=	P/Chiron (95P)	Discovered as an asteroid in 1977, but considered to exhibit cometary activity in 1988
4015 Wilson-Harrington	=	P/Wilson-Harrington (107P)	Discovered as an asteroid but orbitally linked with a comet by B.Marsden in 1992
7968 Elst-Pizarro	=	P/Elst-Pizarro (133P)	"Comet" of dust with a stellar nucleus, orbiting in the Main Asteroid Belt.
NB: The asteroid-comet "Elst-Pizarro" is an exceptional object. This asteroid, from the dynamical "Themis" family, has shown cometary activity in 1996,
but was seen as stellar in 1979. The observation of a dust tail was repeated in 2002 thereby eliminating the possibility of a temporary dust tail in 1996, caused by a possible
collision. The two outbursts seem however to have been at a similar point in its orbit, perhaps indicating that a small part of the surface of the object, seasonally warmed
by the Sun, is responsible for the dust activity.
2201 Oljato, having an orbit similar to comet P/Encke has been suspected of gaseous emission similar to that of a comet in 1979 and in 1983.
Numerous other asteroids are suspected of being ancient comets, notably those possessing a comet-like orbit ( high eccentricity and inclination, …)
Examples:
5335 Damocles	Mars-crosser	a = 11.831 AU and e = 0.867	Halley-type orbit	H = 13.3
1996 PW	Oort  ?	a = 265.479 AU and e = 0.990	Oort Cloud origin ?	H = 14.0
Quite a large number of NEAs could be ancient extinct comets, sometimes linked with meteor streams.
According to estimates, the percentage of extinct comets amongst the NEOs ranges between 10 and 40%, with the greater likelihood being in the range, 25 to 40%.
There are about a dozen Earth-crossers which appear to be linked with meteor streams.
3200 Phaeton, an Apollo-type asteroid, is the nucleus of an extinct comet, associated with the Geminid meteors of the 14th December.
2101 Adonis and 1995 CS ( H ~ 25 ), having a similar orbit for the last 30,000 years, seem to be associated with 4 active meteor streams located in the
constellations of Capricornus and Sagittarius
(5496) 1973 NA has been associated with the Quadrantid meteor stream, but it is 2003 EH1 which appears to be the extinct parent body (IAU Circular 8252).
Meteor streams appear to contain small bodies several tens of meters in diameter.
In 2001, 17 objects from several meters to several tens of meters passed within several million km of the Earth having been found in the proximity of
the meteor radiants during the period of activity of the Capricornids,  Coma Berenicids, Leonids and Perseids.
APOHELE asteroids found or probable as of  20-May-2004
The first definite "Apohele" was discovered on 11-Feb-2003 :
Two Apoheles have been discovered to date :
2003 CP20	H = 16.5	a = 0.741 AU	q = 0.502 AU  and  Q = 0.9798 AU	e = 0.322	i = 25.61°	LINEAR
2004 JG6	H = 18.8	a = 0.633 AU	q = 0.294 AU  et   Q = 0.9723 AU	e = 0.633	i = 19.215°	LONEOS
These are the first asteroids known, for which the orbit is entirely contained within the Earth's.
Venus and Mercury are the only other known bodies in the Solar System orbiting closer to the Sun than the Earth.
2004 JG6 even has a semi-major axis smaller than that of Venus !
One other possible Apohele yet to be confirmed has been observed in 1998 :
1998 DK36	H = 25.0	a = 0.693 AU	q = 0.407 AU  and  Q = 0.980 AU	e = 0.413	i = 2.03°	(David THOLEN)
Around 20 Apoheles greater than one kilometer in diameter should exist, according to recent estimates.
The total number of Apoheles would be equivalent to only 2% of the total NEAs, according to Bottke et al..
An Earth-crosser can evolve dynamically to become an Apohele or IEA, names which have not yet been adopted by the MPC having classed 2003 CP20 and 2004 JG6 as Atens.
The terms Amor, Apollo and Aten specifically designate types of orbit close to the Earth: it would be regrettable not to set up a fourth orbital type.
NEAR EARTH ASTEROIDS  - Various Data
In the main, NEAs originate from five sources namely the resonances v6 and 1:3 ( Alindas ), the outer zones of the Belt N°1, Mars-crossers and the
family of comets perturbed by Jupiter and originating from the Kuiper Belt.
The main sources look to be the dynamical families from the Belt N°1 and the more distant TNOs or from the Oort Cloud.
Collisions between asteroids and moreover, the "Yarkovsky Effect" feed resonances capable of injecting new NEAs over several million years into
the inner Solar System.
Bottke et al. estimate that 61% of NEOs of H < 22 originate from the inner part of the Belt N°1, 24% from the central region, 8% from the outer zone
and 6% from the Jupiter family of comets.
TheYarkovsky Effect is a very weak thermal impulse when asteroid surfaces are heated by the Sun.  The effect particularly affects small asteroids, less than 10 km in diameter.
Certain Earth-crossers such as 1996 AJ1 ( Apollo 1 with a = 1.308 AU ) have 8 very close possible approaches (to less than 0.050 AU) to the Inner Planets of the Solar System.
Their lifetime is estimated to be very short.
The Amor  (6178) 1986 DA is in an orbit which permits a collision with Mars.
Some NEAs are in resonance with the Earth ; Examples :
887 Alinda	Resonance 3:1	'Leader' of a certain number of asteroids in 1:3 resonance with Jupiter, in the 1:3 gap
1221 Amor	Resonance 8:3	…and also in 2:9 resonance with Jupiter which with Earth govern the complex secular orbital variations
1627 Ivar	Resonance 11:28
3753 Cruithne	Resonance 1:1	Horseshoe orbit ("a" always between 0.997 and 1.003 AU with a cyclic variation in its orbital elements of 770 years)
NB: Other Earth-crossers could become "co-orbiters" to the Earth in the future, such as: 10563 Izhdubar, 3362 Khufu and 1994 TF2.
There could however be small asteroids (H > 20) in 1:1 resonance with the Earth. Very faint and dispersed across the sky, they would be very difficult to detect.
2002 AA29 ( a 100-m diameter asteroid ) travels along an orbit similar to that of the Earth, and has even been a satellite of the Earth in the past (around 550 AD
lasting 50 years).  It will do so anew in 2600 and 3880 AD !			a = 0.9975 AU / e = 0.012 / i = 10.74° / H = 24.3
Furthermore, certain asteroids such as 1991 VG and 2000 SG344 could be remnants from space vehicle launches, owing to the very strong resemblance of their orbital
elements to those of the Earth. The only definite case to date is J002E3 ( discovered by the amateur Bill Yeung ), which must be the third stage of the Saturn V rocket
from the launch of the Apollo 12 mission in 1970.  Other data are available at the web address: "http://www.projectpluto.com/probes.htm"
NEAs having common origins (a, e, i, related)
trio	433 Eros	1943 Anteros	1991 JR
pair	1566 Icarus	5786 Talos	( pieces from a broken-up parent comet ? )
pair	1620 Geographos	10115 1972 SK	( Asteroid pair, non-cometary origin )
pair	2101 Adonis	1995 CS	Linked with 4 active meteor streams => Joint cometary origin
pair	4015 Wolf-Harrington	1992 UY4	( pieces from a broken-up parent comet ? )
pair	6318 Cronkite	6322 1991 CQ
pair	1989 UP	1989 VB
pair	2201 Oljato	P/Encke	( fragments from an hypothetical Centaur named HEPHAISTOS ? )
NB: 2212 Hephaistos and 5143 Heracles could be fragments from an enormous Centaur which ventured into the Inner Solar System following a decrease
in its semi-major axis. It would have given birth to numerous NEAs or comets of which P/Encke is one, with "e" ~ 0.70-0.85 and low "i" (between 0 and 12°).
Nearly thirty NEAs belonging to this group could be found.
Examples of NEAs and numbered Mars-crossers of the type "Alinda" (i.e. "a" ~ 2.501 AU, in the 1:3 resonance zone with Jupiter)
887 Alinda	a = 2.485 AU	Amor 3	Type V = Fragment of Vesta ?	Resonance 4:1 with Earth
2608 Seneca	a = 2.503 AU	Amor 3
4179 Toutatis	a = 2.511 AU	Apollo 3
6318 Conkrite	a = 2.508 AU	Mars-crosser	q =1.341 AU
6322 1991 CQ	a = 2.515 AU	Mars-crosser	q =1.324 AU
6489 Golevka	a = 2.498 AU	Apollo 3	Type V = Fragment of Vesta ?
6491 1991 OA	a = 2.502 AU	Amor 3
7092 Cadmus	a = 2.523 AU	Apollo 3
13551 1992 FL1	a = 2.527 AU	Mars-crosser	q =1.459 AU
19356 1997 GH3	a = 2.492 AU	Amor 3
NEAs in resonance with Jupiter - Examples:
1221 Amor	Resonance 2:9	a = 1.919 AU	Amor 1	P = 2.659 years
6178 1986 DA	Resonance 2:5	a = 2.809 AU	Amor 3	P = 4.707 years
8567 1996 HW1	Resonance 1:4	a = 2.047 AU	Amor 2	P = 2.929 years
NEAs of Type 4 ( a > 3.57 AU beyond the Belt N°1 )
2003 WE42	Amor 4	a = 3.630 AU and e = 0.696	q = 1.101 AU and Q = 6.159 AU	H = 18.2	i = 34.9°
2001 XQ	Amor 4	a = 3.641 AU and e = 0.713	q = 1.043 AU and Q = 6.239 AU	H = 19.5	i = 28.99°
1982 YA	Amor 4	a = 3.707 AU and e = 0.697	q = 1.123 AU and Q = 6.291 AU	H = 16.5	i = 34.60°
1997 SE5	Amor 4	a = 3.730 AU and e = 0.666	q = 1.244 AU and Q = 6.215 AU	H = 14.8	i = 2.60°
2002 RN38	Amor 4	a = 3.799 AU and e = 0.674	q = 1.235 AU and Q = 6.362 AU	H = 17.3	i = 3.84°
5025 P-L	Apollo 4	a = 4.201 AU and e = 0.895	q = 0.439 AU and Q = 7.962 AU	H = 15.9	i = 6.20°
3552 Don Quixote	Amor 4	a = 4.232 AU and e = 0.712	q = 1.216 AU and Q = 7.248 AU	H = 13.0	i = 30.8°
1999 XS35	Apollo 4	a = 7.945 AU and e = 0.946	q = 0.421AU and Q = 15.468 AU	H = 17.2	i = 19.4°
The largest NEAs and their closest-approach distances to the Earth
NEA	Magnitude H	Diameter in km	Type of object	Closest Approach
1036 Ganymed	9.45	39	Amor 3	0.341 AU
433 Eros	11.16	33 x 13 x 13	Amor 1	0.124 AU
4954 Eric	12.6	12	Amor 2	0.194 AU
1866 Sisyphus	13.0	8	Apollo 2	0.102 AU
3552 Don Quixote	13.0	19 (very low albedo)	Amor 4	0.301 AU	( Extinct comet ? )
Frequency of passage by Earth-crossers close to the Earth
1 Earth-crosser 400 meters in size passes every 50 years at less than twice the Earth-Moon distance. ( MPML 03-Sep-02 )
1 or 2 Earth-crossers of 100 meters diameter pass by closer than the Moon each year ( Jim Scotti, MPML 24-Jun-02 )
NB: For the 'Earth-crossing' Comets, 180 of them of more than 1 km diameter cross the Earth's orbit each century (Spaceguard data ).
Some 2,400 or more 'lilliputians' of around 10 meters diameter pass closer than the Earth-Moon distance each year.
Very few of them are observed, as they reach magnitude 14 within 200,000 km of the Earth.  They shift very quickly across the sky and are bright for only a few hours.
For example, the large rock named 2003 XJ7 of H mag = 26.5 (~30 m) reached mag 13.4 on 06-Dec-03 at 0.0010 AU from the Earth, yet it only spent 8 hours when
it was brighter than magnitude 16.0, passing from an RA and Dec of 05h 41m and +45°, to 09h 36m and -67° !
From future predictions, it should be noted that 2000 WO107 ( H = 19.4 with diameter ~ 610 m ) could reach magnitude V + 5.0 in December 2140 !
Collisional frequency of NEAs with the Earth
These vary in the time and depend on the source of the estimates :
In 1979, Shoemaker estimated one collision of an object of 100 m diameter every 2,000 to 12,000 years or so.
20 to 40% of NEAs might be expected to collide with the Earth at some time in the future (Estimates: Wetherhill, 1979, and Shoemaker et al, 1990)
From 1975 to 1992, American spy satellites registered 136 explosions of mini-asteroids ranging from a few meters to 10 meters across in the atmosphere, even
though the instrumentation was only able to detect 10% of the explosions statistically-speaking.
A.Morbidelli et al. in 2001 estimated one collision with an Earth-crosser of H = 20.6 every 63,000 +/- 8,000 years. NEAs discovered to date only represent about 18%
of the potential impactors.  82% of them ( excl. Oort objects ) remain to be discovered …
Energy released	Impact interval	H equivalent	% of impactors yet to be discovered	Diameter
1000 megatonnes	63,000 +/- 8,000 yr	20.63	82	277 m
10,000 megatonnes	240,000 +/- 30,000 yr	18.97	63	597 m
100,000 megatonnes	925,000 +/- 121,000 yr	17.3	51	1287 m
1 impact of an NEA 50 meters in size occurs every century on Earth ( Jim Scotti, MPML 24-Jun-02 ).
2 impacts of an NEA some 100 meters in size occur every 1000 to 2000 years on Earth ( Jim Scotti, MPML 24-Jun-02 ).
In August 2003, some English and Russian researchers estimated that one body > 200 m in diameter would hit the surface every 160,000 years.
Their results relied on a study of the characteristic behaviour of the impactor during its travel through the atmosphere.
The NEA Search Report of NASA of September 2003 indicated an impact frequency of 1 object of 50-100 m every 1,000 years and of 1 object of 1 km
size every 500,000 years.
The same month, J.Scott of MIT announced in his view that one collision takes place with a 50-meter body every 2,000 to 3,000 years, and every 600,000
years for a body 1 km in diameter.
These results come from statistical analyses, which are in effect dependent on the magnitudes H and albedos of Earth-crossers, and also on the rate of formation
of craters in the lunar seas.
For dormant comets of the "Halley" type and those dormant for a long period, the collisional probability ( 2002 ) is respectively once every 370 and 780 million years.
On the 16th March 2880, (29075) 1950 DA has a 1 "chance" in 300 of entering into a collision with the Earth, according to the known stable orbital elements.
It should also be pointed out that currently, there are about 50,000 meteorites which fall to earth each year (MPML 24-Sep-02).
The oldest NEAs lost from 20 years ago or more
5025 P-L	Apollo 4	H = 16.9	a = 2.255 AU and q = 0.625 AU	Palomar Leiden Survey in September 1960
6344 P-L	Apollo 3	H = 21.5	a = 2.379 AU and q = 0.949 AU	Palomar Leiden Survey in September 1961
1972 RB	Amor 3	H = 19.7	a = 2.149 AU and q = 1.105 AU	Gehrels - 49-day arc
1977 VA	Amor 2	H = 19.0	a = 1.864 AU and q = 1.130 AU	E.Helin - 93-day arc
1979 QA	Apollo ?	?	a =  ? AU and q < 1.0 AU ?	Palomar
1979 QB	Amor 3	H = 17.4	a = 2.329 AU and q = 1.296 AU	E.Helin - 67-day arc
1979 XB	Apollo 3	H = 19.0	a = 2.262 AU and q = 0.649 AU	K. S. Russell
1980 QA	NEA ?	H = ?	?	?
1981 JD	NEA ?	H = ?	?	?
1982 CA	NEA ?	H = ?	?	?
1982 EA	NEA ?	H = ?	?	?
1982 YA	Amor 3	H = 16.5	a = 3.707 AU and q = 1.123 AU	F. Dossin
1983 LB	Amor 3	H = 16.5	a = 2.287 AU and q = 1.194 AU	E. F. Helin, R. S. Dunbar - 56-day arc
1983 LC	Apollo 3	H = 19.0	a = 2.632 AU and q = 0.766 AU	E. F. Helin, R. S. Dunbar
1983 SN	NEA ?	H = ?	?	?
1983 VA	Apollo 3	H = 16.5	a = 2.609 AU and q = 0.800 AU	IRAS Satellite - 189-day arc
The oldest lost NEAs recovered since 2000
719 Albert	Amor 3	H = 16.0	a = 2.584 AU and q = 1.188 AU	Found on 03-Oct-1911
	= 2000 JW8	H = 15.8	a = 2.637 AU and q = 1.184 AU	recovered on 01-May-2000
1937 UB   Hermes	Apollo 2	H = 18.0	a = 1.639 AU and q = 0.616 AU	observed in 1937 (4-day arc)
(69230)		H = 17.5	a = 1.654 AU and q = 0.621 AU	recovered on 15-Oct-2003
1950 DA	Apollo 2	H = 15.9	a = 1.683 AU and q = 0.838 AU	observed in 1950 (17-day arc)
(29075)	= 2000 YK66	H = 17.0	a = 1.699 AU and q = 0.837 AU	recovered on 31-Dec-2000
1954 XA	Aten	H = 18.5	a = 0.687 AU and q = 0.261 AU	1st Aten, observed in 1954 (6-day arc)
	= 2003 UC20	H = 19.2	a = 0.781 AU and q = 0.517 AU	recovered on 21-Oct-2003
4788 P-L	Amor 3	H = 16.9	a = 2.612 AU and q = 1.153 AU	Palomar Leiden Survey of September 1960
	= 2003 SV84	H = 16.7	a = 2.629 AU and q = 1.155 AU	recovered on 20-Sep-2003
1978 CA	Apollo 1	H = 18.0	a = 1.125 AU and q = 0.883 AU	observed for 32 jours in 1978
		H = 17.1	a = 1.123 AU and q = 0.883 AU	recovered on 11-Jan-2003
1975 XA	Apollo 3	H = ?	a =  ? AU   et q < 1.0 AU ?	Wroblewsky - Mag.11 seen - December 1975
	= 2004 JN13	H = 14.6	a = 2,868 AU et q = 0,867 AU	recovered on 23-Apr-2004
MARS-CROSSERS with large "a" and "e"
Mars-crossers are probably produced by various resonances caused by Jupiter ( resonances v6 or 3:1 for example ), Mars and also by the combined
pair of Jupiter-Saturn.
These resonances slowly increase the eccentricities of the asteroids in the Belt N°1 until their perihelia reach the orbit of Mars,
The Mars-crosser population also evolves as a function of the variations in the eccentricity of Mars itself ( 0.01 to 0.12 ) over 2 million years.
Thus objects having a q ~ 1.6 AU to 1.78 AU are able to cyclically become Mars-crossers.
Certain asteroids such as 5335 Damocles (q = 1.572 AU, a =11.831 AU, Q=22.091 AU) could be called a Mars-crosser (based on q), Jupiter-crosser,
Centaur (based on "a"), Saturn-crosser and Uranus-crosser (based on Q). Certain of these are no doubt ancient comets.
1997 MD10 is even a Neptune-crosser !
The 3 examples of Mars-crosser having large "a" are:
5335 Damocles	q = 1.572 AU	a = 11.831 AU	Q = 22.091 AU
1998 WU24	q = 1.425 AU	a = 15.216 AU	Q = 29.006 AU
1997 MD10	q = 1.545 AU	a = 26.581 AU	Q = 51.618 AU
Possible MARS-TROJANS as of 20-May-04
5261 Eureka	Lagrangian point L5	H = 16.1	r = 1.425 to 1.622 AU	First Mars-Trojan discovered in 1990
1998 VF31	Lagrangian point L5	H = 17.4	r = 1.371 to 1.677 AU
1999 UJ7	Lagrangian point L4	H = 17.0	r = 1.465 to 1.584 AU	Doubtful, being at 11H in R.A.of Mars at end-2003
2001 DH47	Lagrangian point L5	H = 19.7	r = 1.468 to 1.572 AU
2001 FG24	Lagrangian point L5	H = 21.3	r = 1.319 to 1.717 AU
2001 FR127	Lagrangian point L5	H = 19.0	r = 1.354 to 1.692 AU
2003 SC220	Lagrangian point L4	H = 20.1	r = 1.331 to 1.710 AU	Doubtful, being at 1.5H in R.A.of Mars at end-2003
NB: The existing list in October 2003 ( prior to the recent case, 2003 SC220 ) has been put in doubt by the MPC who will only reintroduce Mars-Trojans when these objects
are confirmed by long-term integrations using good orbits.
Nearly 50 or so Mars-Trojans larger than a kilometer could exist.
Trojan orbits near to Mars are very stable.
Photometric and spectroscopic studies of 3 of the Mars-Trojanshave not revealed any striking similarities between them ( 5261 Eureka, 1998 VF31 and 1997 UJ7 )
There must therefore not have been a common origin for these objects.
5261 Eureka and 1998 VF31 are however of a rare mineralogical type ( Sr/A ) not common in Belt N°1.
2003 OX7 ( a = 1.5293 AU ) is virtually on the same orbit as Mars, but is not a Mars-Trojan.
It made its closest approach to Mars on 4 July 2003 at 0.045 AU, at least for the period 1800-2200  (MPML 02/09/03).
MAIN BELT  ( or BELT N°1 ) : Data and various remarks
One personal remark to begin with : The discovery of many large asteroids of mag H < 4.5 in the Kuiper Belt, and the fact that the First (trans-Martian) Belt only
contains 3 may be considered to render the name "Belt N°1" obsolete for this first region of asteroids.
The dimensions and divisions of the Belt N°1 are principally due to gravitational perturbations created by Jupiter.
The total mass of this trans-Martian belt is estimated to be about 18 X 10^-10 of the solar mass.
The zones in resonance with Jupiter are either empty of asteroids (Kirkwood gaps) or stable zones populated by groups of asteroids.
More than 99% of primordial asteroids would have been ejected in one million years from the Solar System through perturbations from the larger embryonic planets.
TheYarkovsky Effect ( thermally-induced impulse from solar heating of the asteroid surface ) shifts the small objects ( e.g., by 0.04 AU in 100 million years
for those of 1 km diameter in the Flora zone ) and contributes to emptying the Solar System of those small asteroids, which enter a resonance zone,
finishing by either hitting the Sun or a planet, or by being ejected from the Solar System.
With the Yarkovsky Effect, passage close to one of the large asteroids in the Belt can also cause a variation in the orbit of small bodies (0.00075 AU in the case of (1) Ceres).
At the end of 1997, those asteroids of mag H < 12.75 , 12.25 and 11.25 (inner, middle and outer regions of the Belt N°1) were considered to have been all found.
In 2002, nearly all asteroids from the Belt N°1 up to H = 13.0 had been discovered.
At least one third of asteroids from the Belt N°1 are part of asteroid families arising from the fragmentation of larger asteroids following collisions.
It is with the aid of the "proper" orbital elements ( a' , e' and sin i ' ) valid over a million years that dynamical families are determined.
As time passes, the families become diluted and are less recognisable, following possible collision,  and evolution of the proper elements of the asteroids.
There may be about 64 groupings of asteroids, of which 32 dynamical families are certain.
9 Metis and 113 Amalthea, which exhibit near-identical spectrophotometric data, probably arose from the same parent body of 300 to 600 km size.
The most recent family identified is the "Karin" family ( 13 objects with the parent, 832 Karin of 20 km diameter ) which came about as a result of the fragmentation
of an asteroid of 27 km in size, 5.8 million years ago.
The "Flora" family :
It is composed of different sub-families owing to successive collisions arising most probably 500 million years ago ( 900 million years ago at most).
Various non-members have already been identified by their different taxonomic type to type S of Flora : 298 Baptistina, 2093 Genichesk, 4278 Harvey, etc..
The parent body of the "Floras" would have had a mass 1.75 times larger than (8) Flora itself with a diameter of 164 km.
8 Flora could be the major constituent part from the central region of a large fragmented asteroid.
8 Flora (136 km in diameter) and 43 Ariadne (66 km) appear to be the two biggest members of the Floras, the others being hardly 30 km across or less.
951 Gaspra, visited by the space probe Galileo, is most likely a fragment from the Flora parent body (same type S and similar orbital elements).
With a semi-major axis of 2.256 AU from the Sun and resonances with Jupiter (2:7) and Mars (9:4), there would have been a significant loss of small "Floras" to the
Mars-crossers.
The "Flora" family would have lost 3% of its members over a 100 million-year period, to the benefit of the Mars-crossers.
The Flora and the Phocaea families situated at the inner edge of the Belt N°1 and the v6 resonance would be the main source of the Mars-crossers which after become NEAs.
The Phocaea group
Located in a region having the 3:1 resonance, their orbits have a large inclination and eccentricity.
This group, having particular proper elements, is quite isolated in an 'islet' of stability with limits defined by the action of the main or secular resonances.
They never make close approaches to Mars.
It is not possible to know whether Phocaeas comprise members of a group having similar orbital elements or members of a family originating from the break-up of a
large asteroid.
The "Vesta" family :
It is composed of 4 Vesta and various small asteroids in similar orbits and of a near-identical reflectance spectral type V, related to Pyroxene and close to that of
basaltic HED ( Howardite, Eucrite and Diogenite) meteorites. These small objects are called "Vestoids" and may be pieces of the crust of Vesta, torn away
by collision.  Together, the Vestoids are believed to be equivalent in volume to a crater 100 km across and 7 km in depth.
In 1997, the Hubble Space Telescope (HST) found on the globe of Vesta, a formation which could be the sign of a very large crater.
Furthermore, 2579 Spartacus may have a spectral signature similar to the mineral, Olivine, and which could be regarded as a mixed piece of "mantle and
crust" of 4 Vesta.
1929 Kollaa ( the largest Vestoid with d = 15 km ) could arise similarly from the deep layer of Eucrite from 4 Vesta
However, other asteroids also exhibit type V even though they are distant from Vesta.  They might be the survivors from another fragmented basaltic asteroid.
The Yarkovsky Effect, which can alter the semi-major axis by 0.0001 AU each million years, could be the main cause for the diffusion of the Vesta family.
The ejection velocity of the fragments from Vesta or their subsequent acceleration through dynamic evolution could also have directed them close to resonances injecting
them into other zones of the Solar System, such as the region of the NEAs.
Several examples of non-Vestoid asteroids of type V :
809 Lundia ( the biggest non-Vestoid V-type known : d = 9.1 Km ) and 4278 Harvey ( d = 3.3 km ), situated in the Flora zone
1459 Magnya of 30 km diameter, situated at a = 3.14 AU in the outer region of the Belt N°1, quite far from 4 Vesta and the only large object of type V in that area.
The "Eunomia" family :
15 Eunomia represents 70% of the initial mass of the parent body estimated at 284 km in diameter.
We know of 110 members larger than 11 km making up the Eunomia family.
The "Adeona" family :
The age of this family appears to be around 600 million years.  It is large having 648 members as of 2002.
The "Gefion" family :
The age of this family appears to be around 850 million years.  Located in the central part of the the Belt N°1 ( a =  ~ 2.78 AU ), it comprises 37 known members
as of 1995, and 973 members as of 2002, but remains a minor family within the Belt N°1.  The asteroid 1 Ceres orbiting in this zone does not make up part of the Gefion family.
The "Eos" family :
The "Eos" family seems to have arisen from successive collisions between asteroids dating from more than a billion years ago.
Several rings of dust have been found by the space probe, IRAS, notably in proximity to the Eos and Themis families.
The small members (H>13) of this family will feed the closeby 7:3 resonance, as a result of the Yarkovsky Effect.
The "Koronis" family :
The "Koronis" family seems to have arisen from successive collisions between asteroids.
The age of this family is estimated at 1.5 billion years, based on crater counts on 243 Ida imaged by the space probe Galileo in 1993.
The Koronis parent body looks to have been decimated, in that 158 Koronis is estimated to make up only 4% of the initial mass of the parent body of diameter, 119 km.
As with the Eos family Eos, the small members ( H>13) of this family will feed the closeby 7:3 resonance, as a result of the Yarkovsky Effect.
2953 Vysheslavia, a member of the Koronis family, very close to the outer edge of the 2:5 resonance, could be ejected from the Solar System during the next 10 million years.
A recent study of the rotational axes of nearly a dozen members of the Koronis family, 25 to 45 km in size, has shown that the axial alignments fall into two groups of 4 and 6
asteroids, according to whether rotation is prograde or retrograde.
In spite of the random primordial distribution of rotational axes following on the initial collision, orbital resonances with Saturn and the Yarkovsky Effect together will have forced
an axial realignment for these Koronis objects (the so-called "Slivan state").
Thermal pressure arising diurnally at the asteroid surface could also ( depending on the nature of the shape, surface and rottation of the asteroid) have realigned the
axes of the Koronis objects. This long-term effect is named YORP after the name of its discoverers ( Yarkovsky, O'Keefe, Radzievsky and Paddick )
These objects also appear to possess, on average, a larger lightcurve amplitude than other objects from the Belt N°1.
The "Themis" family :
The family named "Themis" appears to be the result of the break-up of one of the large asteroids ( originally one 380 km in diameter ), some 2 billion years ago.
Given that the cometary asteroid 7968 Elst-Pizarro belongs to the "Themis" dynamical family, it could be that the parent body of the "Themis" family had been of mixed
nature (part-asteroid, part-comet) such as a large body displaced from the Kuiper Belt. Soon after fragmentation, the numerous pieces must have generated cometary activity.
The Griqua group :
The asteroids of the Griqua type, located at the limit of the outer sub-belt, near 3.28 AU ( to be found between 3.10 and 3.27 AU ) is only distinguished from the rest of
nearby asteroids through their high eccentricities exceeding the (arbitrary ?) limit of 0.35.
The Griquas are close to the 1:2 resonance with Jupiter and are protected from planetary interaction by librations about this resonance.
Their remaining in this resonance will only last between 1,000 and 1 million years.
Some amongst them could be ancient Centaurs.
Personal remark : On analysing orbital elements of asteroids situated in the region, a = 3.0 to 3.5 AU, asteroids are found having eccentricities and inclinations,
which are weakly spaced out, up until the Griquas and even beyond. Potential Griquas having very high eccentricity find themselves becoming Mars-Crossers.
If from the elements of the Griquas themselves it is not possible to differentiate them from other objects in this zone, then they probably do not form a separate group….
Principal resonances with Jupiter  ( x:y  means: "x" revolutions of Jupiter for "y" revolutions of the asteroid in the same time)
Solar Distance	Resonances	Kirkwood Gaps	Groups found:	P in years
a = 1.778 AU	1:5			2.372
a = 1.908 AU	2:9		Hungaria
a = 2.065 AU	1:4	Resonance v6		2.965
a = 2.256 AU	2:7	(NB: Also corresponds to a 9:4 resonance with Mars)
a = 2.501 AU	1:3	Hestia Gap	Alinda	3.954
a = 2.706 AU	3:8
a = 2.825 AU	2:5	Gap
a = 2.956 AU	3:7	Gap	(Between Koronis and Eos families)
a = 3.030 AU	4:9	-
a = 3.278 AU	1:2	Hekuba Gap	Griqua	5.931
a = 3.700 AU	3:5	Gap	(between Cybeles and Hildas)
a = 3.969 AU	2:3	-	Hilda	7.908
a = 4.03 to 4.29 AU		Empty zone	(between Hildas and Thule)
a =  4.293 AU	3:4	-	Thule	8.896
a = 4.29 to 4.90 AU		Empty zone	(between Thule and Trojans)
a =  5.203 AU	1:1	-	Jupiter-Trojans	11.862
NB: Other less marked resonances exist such as those of 5:9, 7:4, 5:8, 7:12, etc…
All these resonances are so-called "mean motion resonances", which can be misleading in that orbital
variations can take place over a short time-scale, of the order of 1000 years.
There also exist so-called "secular resonances", connected with the precession of the orbits of bodies interacting.  A small body in secular resonance with a large
planet sees it's orbit precess in the same manner as a planet's orbit.
These secular resonances act over very long periods of over a million years, and produce changes to various orbital elements such as eccentricity and inclination.
The v6 secular resonance ( pronounced "nu 6") is a resonance which acts when the rate of precession of longitudes of perihelia of asteroids correspond with those of Saturn.
This resonance delineates the inner edge of the Belt N°1.
This v6 resonance and that of 3:1 should be the most prolific in generating new NEAs ( 100-160 objects and 40-60 objects with H<18 respectively ).
The orbital elements of perturbing planets evolve with time, such that resonances shift in interplanetary space.
Resonances are not necessarily empty. The 7:3 resonance actually contains at least 23 asteroids temporarily trapped through the action of the Yarkovsky Effect.
They are all small asteroids with the exception of 677 Aaltje (diam. 30 km), perhaps having been pushed into the resonance through the proximity of 1 Ceres.
Personal remark:
In the various articles on resonances explored, one comes across two types of representation for the same resonances, involving Jupiter.
For example: the 3:2 or 2:3 resonance, the 9:2 or 2:9…..
To ensure conformance between resonances involving Jupiter and those of the TNO zone, I have therefore standardised on the description of resonances
by using the following format : " x revolutions of the major Planet : y revolutions of the Asteroid"
Therefore, the "3:5" resonance defines the gap separating the Cybeles and Hildas (3 orbital revolutions of Jupiter for 5 of an object at 3.7 AU) and the resonance "5:3"
defines that located in the CKBO zone near 42 AU (5 revolutions of Neptune for 3 of a KBO, hence 5:3)
Number of members of the main dynamical families in the Belt N°1, in 1995 and in 2002
Families	HCM Method 1995	WAM Method 1995	Estimated number of objects diam. > 5 km		Morbidelli et al 2002
Flora	604	575	709		3021
Nysa / Hertha	381	374	?		6614
Vesta	231	242	402		5575
Ceres/Minerva	89	88	?		-	Family not sure
Maria	77	83	654		1776
Adeona	63	67	1430		648
Dora	77	79	310		419
Eunomia	439	303	2748		6162
Hygiea	103	175	> 10000		2663
Koronis	325	299	729		2663
Eos	477	482	4131		5188
Themis	550	517	9825		2739
HCM Method	= Hierarchical Clustering Method  (Zappala et al.)				See references
WAM Method	= Wavelet Analysis Method (Bendjoya et al.)				See references
Morbidelli et al 2002	= HCM method used with 106284 minor planets having proper elements ( Knezevic and Milani )				See references
NB: The Nysa zone is populated by various families depending on the author: Nysa, Hertha, Polana, etc…
The Hertha and Nysa families are apparently distinguished by a narrow void and a distinct difference in orbital inclination.
The "Maria" family is situated on the edge of the strong 3:1 resonance and may furnish the NEA zone with large Earth-crossers.
Numbers and H magnitudes of the 4 main members of the principal dynamical families from the asteroid belt :
The number and composition of the members of each family differ according to the authors of the studies, the assignment of an asteroid to one or other family is not
still 100% certain. From a study by P. Bendjoya, the largest 4 asteroids for sure for each of the principal dynamical families are :
Family
Flora	8 Flora  ( H = 6.49 )	43 Ariadne  ( H = 7.93 )	367 Amicitia  ( H = 10.7 )	770 Bali  ( H = 10.93 )
Nysa + Hertha	44 Nysa  ( H = 7.03 )	135 Hertha  ( H = 8.23 )	1493 Sigrid   ( H = 11.99 )	1650 Heckmann  ( H = 11.56 )
Vesta	4 Vesta  ( H = 3.20 )	63 Ausonia  ( H = 7.55 )	2346 Lilio  ( H = 11.9 )	2086 Newell  ( H = 12.4 )
Maria	170 Maria  ( H = 9.39 )	472 Roma ( H = 8.92 )	660 Crescentia ( H = 9.14 )	714 Ulula ( H = 9.07 )
Eunomia	15 Eunomia ( H = 5.28 )	1275 Cimbria ( H = 10.72 )	1329 Eliane ( H = 10.90 )	1503 Kuopio ( H = 10.6 )
Koronis	158 Koronis ( H = 9.27 )	167 Urda ( H = 9.24 )	208 Lacrimosa ( H = 8.96 )	462 Eriphyla ( H = 9.23 )
Eos	221 Eos ( H = 7.67 )	579 Sidonia ( H = 7.85 )	639 Latona ( H = 8.20 )	653 Berenike ( H = 9.18 )
Themis	24 Themis ( H = 7.08 )	62 Erato ( H = 8.76 )	90 Antiope ( H = 8.27 )	171 Ophelia ( H = 8.31 )
Families of 50 to 100 members and groups known ( in 1995 ) :
Phocaea	a = 2.23 to 2.50 AU	e > 0.1 and i = 18 to 32°	grouping of objects from the Inner Belt having high orbital inclination
Polana	a ~ 2.4 AU	Family of the 'clan', Nysa	Dynamical family, by the WAM method (102 members known in 1994)
Alinda	a ~ 2.50 AU	1:3 resonance with Jupiter	Earth-crossers in libration with Jupiter
Pallas	a = 2.50 to 2.82 AU	i = 33 to 38°	Dynamical family	(More than 10 members found as of 1994)
Maria	a =2.526 to 2.591 AU	e< 0.11 and i < 27°	Dynamical family	(74 members found as of 1994)
Adeona	a =2.661 to 2.688 AU	e< 0.18 and i < 21°	Dynamical family	(61 members known for certain by 1994)
Dora	a =2.763 to 2.813 AU	e< 0.20 and i < 14°	Dynamical family	(75 members known for certain by 1994)
NB: The Phocaea group distinguish themselves from other asteroids of the inner Belt N°1 by high inclinations and extend as far as the Mars-crossers, which differ from
Phocaeas only by their larger eccentricity to cross the orbit of Mars.
The Hilda group
Situated in the 2:3 resonance with Jupiter, these asteroids reach aphelion passing in front of the Lagrangian points of Jupiter or in being in opposition with Jupiter,
thereby avoiding capture by Jupiter.  They pass perihelion facing Jupiter or at 120° of longitude to the giant planet.
Thus the Hilda group define a triangle in rotation with Jupiter around the Sun.
The Hildas, which have less stable orbits than the Jupiter-Trojans, are expected to be the principal source of cratering of the Galilean satellites.
Numbered "internal Jupiter-crossers" with a < a of Jupiter and q > Q of Mars from the 85117 numbered asteroids
5164 Mullo	a = 3.645 AU	Q = 5.486 AU
6144 1994 EQ3	a = 4.785 AU	Q = 6.520 AU
20898 Fountainhills	a = 4.226 AU	Q = 6.192 AU	"a" similar to 279 Thule, but "e" and "i" larger
32511 2001 NX17	a = 5.053 AU	Q = 7.212 AU	"a" similar to Trojans West, but the asteroid is far from Point L5
52007 2002 EQ47	a = 4.262 AU	Q = 5.208 AU
NB: 37384 2001 WU1 with Q = 4.9295 AU does not cross Jupiter's orbit.
JUPITER-TROJANS
The Jupiter-Trojans form two populations of isolated objects, at the L4 and L5 Lagrangian points, 60° preceding and following Jupiter in its orbit.
They are placed in a very stable zone.
Levison et al. have estimated that around 2 million asteroids greater than one kilometer in size could be found at Jupiter's L4 and L5 points.
The two Trojan groups situated at the L4 and L5 Lagrangian points are not alike :
The L4 group of Trojans-East are larger in number than those of the Trojans-West near Point L5 ( 1039 for Point L4 compared to 628 for Point L5 ).
The dynamic families are more numerous for Point L4.
Of the larger asteroids, for Point L4 there are : 93 of mag H < 10 compared with only 56 for Point L5.
Orbits are more inclined for Point L5 ( 14.7° against 11.4° for Point L4)
Trojan Families having more than 10 members arising from collisions:
Melenaus	41 members in 2001	Lagrangian Point L4
Epeios	30 members in 2001	Lagrangian Point L4
Podalirius	22 members in 2001	Lagrangian Point L4	ex-(4086) 1986 WD
Oysseus	15 members in 2001	Lagrangian Point L4
(5119) 1988 RA1	23 members in 2001	Lagrangian Point L5
On average, collisions would have been more numerous for the Trojans than for the Belt N°1.  Consequently, the lightcurve amplitudes are
higher on average.
Numbered "external Jupiter-crossers" with a > a of Jupiter and q > Q of Mars from the 85117 numbered asteroids
944 Hidalgo	a = 5.746 AU	q = 1.950 AU	H = 10.77
15504 1999 RG33	a = 9.390 AU	q = 2.140 AU	H = 12.1
20461 Dioretsa	a = 23.759 AU	q = 2.386 AU	H = 13.8	1999 LD31
37117 2000 VU2	a = 6.924 AU	q = 3.092 AU	H = 13.2
65407 2002 RP120	a = 56.094 AU	q = 2.473 AU	H = 12.3
Personal remark:
External Jupiter-crossers are not named "Centaurs" but their semi-major axes "a" are similarly situated between Jupiter and Neptune.
It is only the Centaurs that have high eccentricity …..
CENTAURS
Centaurs have orbits entirely between those of Jupiter and Neptune, in a zone where - due to strong planetary perturbations - the orbits are very
chaotic ( lifetimes of less than 10 million years ).
The region between Jupiter and Saturn is virtually empty, owing to perturbations from these two giant planets, similarly for the region between Uranus and Neptune.
Save for two narrow zones at 7.02 and 7.54 AU and a zone situated between 24 and 27 AU, in which an orbit having very low "e" and  "i" can remain stable, only
a few resonance zones can be temporarily occupied.
The majority of them are situated beyond the orbit of Saturn in a region some 24 to 27 AU from the Sun.
Centaurs may be objects derived from the Kuiper Belt  in transit towards the inner Solar System, prior to becoming, probably, short-period comets.
Some of them stay trapped in resonances linked to a single giant planet during about 1,000 to 10,000 years.
Those resonances involving two or three planets at a time can hold them for even longer, more than 100,000 years.
There may exist more than 10 million Centaurs greater than 2 km in diameter, of which a hundred may exceed 100 km in diameter.
30 to 40% of them do not migrate towards the inner Solar System on cometary orbits
These could end up in the region of the Hildas (2:3 resonance with Jupiter) or the Griquas (1:2 resonance with Jupiter).
10199 Chariklo is the largest Centaur known to date ( 273 to 302 km in diameter ).  Water has been detected on its surface.
2060 Chiron, the first Centaur discovered in 1977, is also considered to be cometary ( 95P/Chiron ).
Its cometary activity has been recognised since the end of 1987, at which time a surprising increase in its H magnitude was noted.
By contrast, the comet C/2000 B4 LINEAR, which is present amongst the Centaurs, has become inactive. If it had been discovered later on then it would have been classed
as a Centaur.
Other than Chiron, 7 comets are known having Centaur-like orbital characteristics :
Comets with Centaure orbits		q in AU	a in AU		Q in AU
29P/Schwassmann-Wachmann 1		5,721	5,992		6,263
39P/Oterma		5,471	7,242		9,013
1986XIV-Shoemaker		5,457	5.473		5.489
P/1997 T3 Carsenty-Nathues		6,846	11,264		15,681
C/2001 T4 NEAT		8,555	14,140		19,724
C/2000 B4 LINEAR		6,819	18,123		29,428
C/2001 M10 NEAT		5,298	26,710		48,123
P/2004 A1 LONEOS		5,463	7,896		10,330
NEPTUNE-TROJANS
If, from strong initial perturbations, Saturn-Trojans and those of Uranus have not been able to survive at the relevant Lagrangian points, those of Neptune
must in part have been able to do so.
50% of Neptune-Trojans could still remain at the Lagrangian points of Neptune, that is 6,000 to 17,000 objects of mag V = 22 ( d = 110 km ) to V = 25 ( d = 30 km ).
One sole Neptune-Trojan is known to date.  Discovered in 2001, it has been confirmed during early 2003 :
2001 QR322	H = 7.3  ( Diam ~ 160 Km )	a = 30.1138 AU	e = 0.025	i = 1.327°
TRANS-NEPTUNIANS
Apart from Pluto found in 1930, the second trans-Neptunian discovered was 1992 QB1 (Asteroid 15760), in January 1992.
In spite of observational difficulties, more than 850 TNOs have been discovered as of the end of 2003, but a lot of these have been lost after being followed for a short time.
About half of known TNOs have been observed for less than 6 months, which is less than 1% of their orbit, the semi-major axis of which can be in error by dozens of AU !
Even the most well-known TNOs have travelled only a small part of their orbit since their discovery or since identification on old photographic plates.
( Pluto 35% of its orbit and 20000 Varuna 16% ).
Therefore we still do not have very precise data for the new Kuiper Belt and its members, given that the current means of observation allows one to hardly go beyond 50 AU.
Only large objects orbiting or reaching their perihelion within this distance can currently be found.
Nevertheless, two large populations have been discerned that is to say the Plutinos having orbits similar to the largest amongst them, Pluto, and a population of objects
near 42 AU which does not transect the orbit of Neptune.
1992 QB1, an object of the 2nd type, takes its "phonetic" pronunciation from the group called "Cubewanos".
This group could be made up of two dynamically-distinct populations, which are differentiated by their inclinations and absolute magnitudes.
Over 12 years, the accumulation of discoveries has enabled us to have a better idea of the structure of the Kuiper Belt.
There exists a small population of objects for which the semi-major axis is situated between Neptune (a = 30 AU) and the Plutinos (a = 39 AU).
It seems that this "inner" zone between 30 and 38 AU must be occupied by those TNOs separated by the 5:4 resonance ( a = 35.0 AU )
Between 30 and 35 AU, there is a population of objects having high eccentricities, which often leads them in the vicinity of the orbit of Uranus near 20 AU.
Between 36 and 39 AU, one has principally TNOs with low eccentricities that do not traverse Neptune's orbit and which are close to or in the zone of
the 4:3 resonance ( a = 36.6 AU )
In my table, I have therefore named these two zones "KBO Inner I" and "KBO Inner II".
Coming now to the Plutinos ( a ~ 39 AU ) and Pluto.  They are trapped in the 2:3 resonance with the mean motion of Neptune and often cross the orbit of
the planet near their perihelia, but never approaching the planet itself.  Pluto never gets nearer than 17 AU to Neptune.
A large number of secular and mean motion resonances exist in the zone occupied by TNOs, and these impart a complex structure to the Transneptunian Belt between
39 and 41 AU. This region between the Plutinos and 41 AU is not well-populated.
The Belt of the Classical Cubewanos", also named "CKBOs" (Classical Kuiper Belt Objects) by Jewitt, occupies a region comprising between a = 40 to 47 AU.
The Cubewanos do not intersect the orbit of Neptune and have low eccentricities and inclinations.  They are in a very gravitationally-stable part of the Solar System.
(50000) Quaoar is the largest TNO presently found in the CKBO belt.
A third group of TNOs having high eccentricity with a semi-major axis located beyond 50 AU, has now been found.
This is the SDO (Scattered Disk Object) with perihelia less than or close to 40 AU and subject to the influence of Neptune.
The origin of this group seems to have been through the external migration of Neptune at the beginning of the Solar System. The orbits of SDOs would have become very elliptical.
Only beyond the KBO objects of large eccentricity in the 5:3, 7:4 and 2:1 resonances, we find the beginning of the SDO or SKBO (Scattered Kuiper Belt Objects) zone
of which we can currently discover only those objects having large eccentricities with their perihelia within 50 AU.
Kuiper-belt objects should be composed of ices of H2O, CO and CO2 together with dust, and should be the origin of the short-period comets.
Certain TNOs are susceptible to cometary activity such as the SKBO (29981) 1999 TD10 when close to perihelion.
One estimate dating from 2000 put forward the possible existence of 800 million objects greater than 5 km in diameter.
Yet, between 90 to 99% of the initial mass in the trans-Neptunian zone would have been lost following perturbations by Neptune and the many collisions between
the innumerable initial TNOs.
However,a search for small TNOs carried out with the Hubble satellite found only 3 small TNOs of 25 to 45 km in diameter (mag 26 to 28), when 60 small TNOs were expected
in the studied zone. This lack of small TNOs has not yet been explained.
One more recent estimates made at Kitt Peak National Observatory ( MPML 29-May-02 ) put forward the existence of 34 objects of the size of Charon and 4 of the size of
Pluto, which are yet to be discovered in the Kuiper Belt. These as-yet-undiscovered objects would be very faint and therefore distant ….
According to a very recent hypothesis of 2003, it could be that the current Kuiper Belt has been formed from objects repelled by Neptune at the time of its outer
initial migration, rather than from the presence of a proto-planetary disk beyond 30 AU.
Mean-motion resonances of TNOs with Neptune:
Main Resonances	Solar Distance	Currently numbered TNOs	Currently unnumbered TNOs	Remarks
Resonance 5:4	a ~ 35.1 AU		1999 CP133, 2003 FC128, 2002 GW32
Resonance 4:3	a ~ 36.6 AU	(15836) 1995 DA2	2000CQ104, 1998 UU43	Inner zone of the Kuiper Belt
Resonance 7:5	a ~ 37.7 AU	(42355) 2002 XW93 ?	2002 XW93 ?	Region empty of TNOs ?
Resonance 3:2	a ~ 39.4 AU	Pluton and the Plutinos		Plutinos zone
Resonance 5:3	a ~ 42.1 AU	(59358) 1999 CL158, (15809) 1994 JS and 2002 VA131, amongst others
Resonance 7:4	a ~ 43.8 AU	(60620) 2000 FD8	2000 OP67, 1999 KR18
Resonance 9:5	a ~ 44.6 AU		2000 QM51 ?
Resonance 2:1	a ~ 47.8 AU	(40314) 1999 KR76, (20161) 1996 TR66, (26308) 1998 SM165, 1997 SZ10, amongst others
Resonance 5:2	a ~ 55 AU	(26375) 1999 DE9, (38084) 1999 HB12, (60621) 2000 FE8, amongst others
Resonance 11:2	a ~ 92 AU
Resonance 15:2	a ~ 115 AU
The actual or possible presence of TNOs in the resonances 1:1, 5:4, 4:3, 3:2, 5:3, 7:4, 9:5, 2:1 and 5:2 has recently been confirmed on the basis of theoretical calculation.
Save for the Neptune-Trojans (resonance 1:1), those TNOs in resonances are all of high orbital eccentricity or inclination.
NB: There are several secular resonances present which cross the inner resonances of the Kuiper Belt.
PLUTO = Major Planet or big Asteroid ?
Pluto is twice as small as the other solid planets located very close to the Sun
Pluto crosses the orbit of another Giant Planet and is in a 2:3 resonance with it, and thus remains under its influence.
Its diameter is less than that of many natural satellites such as the Moon.
Its orbit is similar to those of the very numerous trans-Neptunians "controlled" by Neptune.
Its round shape and (likely) internal differentiation already exist for the largest asteroids.
Some satellites notably Titan have an atmosphere thicker than that of Pluto.
Other asteroids possess their own satellite, such as the Earth-crosser 69230 Hermes, 243 Ida in the Belt N°1, the Kuiper object 1998 WW31, etc....
A comparative table of main data shows the great difference between the inner planets and the three biggest TNOs :
	EARTH  VENUS    MARS     MERCURY    PLUTO      SEDNA   2004 DW
Mass	1           0.81         0.11          0.06            0.0017           ?              ?
Diameter in Km	12742    12104     6792         4879            2300        1600?      1300?
Density in d/cm3	5.515       5.24       3.94           5.43              2.05             ?             ?
Orbit shaped by :	Sun        Sun        Sun          Sun            Neptune       Sun       Neptune
	+  Sun                         + Sun
Continuing to include Pluto as one of the Large Planets which shape their own environment seems at present to be a little daring ….
There is nothing which distinguishes Pluto from the other Plutinos with the exception of its size as the largest TNO currently known.
Some yet-unknown objects in the Kuiper Belt may perhaps also be as big as Pluto ?
In comparison to Ceres, which was rightly relegated from its position as a "Planet" after 45 to 50 years during the 19th Century, Pluto in proportion
is hardly much bigger than the plutino 2004 DW in relation to what Ceres is towards the other very large asteroids of the Belt N°1.
To relegate Pluto from its status as a Major Planet would take nothing away from its title as the largest Plutino nor from the credit of the discoverer, Clyde Tombaugh.
One might also claim that there is an injustice at present concerning Giuseppe Piazzi, discoverer of 1 Ceres, the largest main-belt asteroid ...
It is still regrettable that an out-moded chauvinism can at present get the upper hand over a scientific fact accepted by the majority of the International
Astronomical Community.
The inclusion of definitively-numbered objects also allows less room for distorting the statistics, work and analyses done on these objects …