2008TC3:

 

This object was discovered by R.A. Kowalski of the Mount Lemmon Survey (MPC G96) at 06:40UT on 2008 Oct. 06 at a distance of 0.00329AU. A report was made soon after discovery that this small object, with H=30.673 according to the JPL ephermeris, corresponding to a diameter of a few metres, could impact the Earth early on October 7th. This was not the first prediction of this kind to have been made, but as the orbit improved it rapidly became obvious that the initial assessment was correct and a trajectory termination point could be determined, giving a presumed impact in Northern Sudan at 02:46UT. The object was in Pisces/Pegasus, well positioned for observation from Europe at nightfall. As word spread of the impending impact, an increasing number of observers started to follow the object, leading to the MPC putting out an unprecedented 21 MPECs during the night, with more than 500 observations being reported to the MPC over about 8 hours. More than 200 observations have been reported from five sites, despite two of them being severely affected by poor weather.

 

MPC Code

Name

Site

First

Last

No. astrometry

No. Photometry

213

Ramón Naves &

Montse Campàs

Barcelona

20:22

00:11

50

50

J47

Gustavo Muler

Lanzarote

21:08

23:13

125

125

J51

Juan Antonio Henríquez

Tenerife

21:56

21:58

3

3

J53

Rafael Benavides

Cordoba, Spain

21:44

01:24

15

15

J95

Peter Birtwhistle

Great Shefford, UK

19:20

23:44

16

13

Total

 

 

19:20

01:24

209

206

 

 

In total the asteroid was followed for 6h4m from the five sites. The observations by J51 were curtailed by cloud, whilst J95 suffered from cloud interruptions. J53 reported that the velocity of the asteroid was too high at the end to allow reliable photometry to be taken from the images. The light curve from the data can be seen below. Significant scatter is seen at the beginning and the end due to the difficult conditions of observation. Initially the asteroid brightened relatively slowly, from R=16.6 at 19:29UT to R=15.3 at 23:10UT (0.35 mags/h), before accelerating to R=13.5 at 01:23UT when the last observations were made (1.5 mags/h). We see that the observed CCD light curve in R is about 0.9 magnitudes brighter than the JPL geocentric ephemeris in V, part of which is due to the observers being on the surface of the Earth and not at it centre and part due to the (V-R) colour index of the asteroid, although it does genuinely seem a little brighter than the assumed absolute magnitude.

 

 

Given the object’s small and rapidly decreasing geocentric distance, parallax became an important effect for observers, even separated by relatively small distances. Of the five sites that have reported data here, one was in southern England, one in the north-east of the Iberian Peninsula, one in the extreme south and two in the Canary Islands, giving a total separation of approximately 3000km between sites. This led to there being large differences in the measured astrometry between sites, due to parallax. Even allowing for the slight differences in the exact time of the measures, the differences are obvious in this table and became larger as the evening progressed. In the plot the position is show for each reported astrometric measure, as well as the geocentric ephemeris from 19:00-01:05UT.

 

06/10/2008 21:50

23

33

41.76

8

8

17.7

15.6

R

J53

06/10/2008 21:50

23

35

21.28

8

30

44.2

15.9

C

J47

06/10/2008 21:52

23

32

31.51

7

59

31.4

15.7

R

213

 

06/10/2008 22:42

23

33

58.29

8

2

50.6

15.6

R

213

06/10/2008 22:42

23

37

11.45

8

42

10.5

15.6

C

J47

06/10/2008 22:45

23

35

27.03

8

14

32.8

15.5

R

J53