the exceptional 2021.09.13 Jupiter impact flash
Discovery and observations
by Marc Delcroix
last updated 2021.09.16

Here is a summary of the discovery of this impact, and all observations which could be recovered afterwards. This impact occurred on 2021.09.13 around 22:39:30 UT, in very good conditions for detection and observations: Jupiter was close to meridian from Europe, hence around its highest altitude (even if maximum altitude was not so high for central Europe, e.g. 26° from Paris). It was even more favorable from part of the American continent, from example at 55° high from Sao Paulo, Brazil. Timing was also favorable, close to opposition (24 days after opposition), hence with a large apparent diameter (48 arcsec), a period when usually the most amateur observations are done.


As of now, we consider that 5 amateurs discovered independently the impact (following order is not important) !

Maciej Libert (Bremerhaven, Germany)

Maciej was capturing videos of Jupiter on his 350mm Schmidt-Cassegrain. Between two shots, he took a break for what he calls himself as the "blackest coffee of his life": when getting back to the PC, he saw through the screen the flash live (red filter was on) but capture was not running! He took other capture afterwards to look for traces (in methane absorption band filter) but could not find any, and posted the information on his facebook page after the observations.

Simone Galelli (Villachiara, Italy)

Simone, visual observer, could watch the flash at the eyepiece (with binoculars) of his 300mm Dobsonian, for about 1 second, and posted the information on his facebook page after the observation.

Harald Paleske (Langendorg, Germany)

Harald captured the flash through is 408mm Newtonian. He alerted the German-speaking community afterwards on a famous forum (, and also posted  the information on the cloudynight forum.

José Luis Pereira (Sao Paulo, Brazil)

Weather conditions that night for José Luis were not good with a lot of fog and bad seeing. But as a highly motivated participant in the Jupiter and Saturn impact detection "DeTeCt" program I run, he decided to continue to attempt impact detection. During his first video, while he was tweaking capture parameters, he saw something temporary brightening on Jupiter, but thought it was due to the very bad and varying seeing and transparency conditions. After his observation run, he launched the DeTeCt software as usual on his video, and went to bed. Next morning when checking the results of the software analysis, he realized the software identified a very high probability of an impact on this first video. He then contacted me to confirm the situation, and realizing right away that this was an impact looking at the video, I issued a large alert to the whole international planetary amateur community (emails, groups, forums, social media) and inform the professional community interested in the topic, starting with Ricardo Hueso whom I have been working with for many years. The alert was very largely shared, and lead to put in light the other discoverers, and made three other observers check their videos.

Jean-Paul Arnould (Villey-le-sec, France)

Jean-Paul while capturing the giant planet that night, saw a brief flash on the PC screen. He wondered what it was but continues his acquisitions. When done, he checked his videos and was quite happy to see the phenomenon, while still doubting it was coming from Jupiter. The day after, he shared his finding with another amateur astronomer, who heard of the alert concerning José Luis discovery. He then shared his impact flash observation with the French Astronomical Society, who transferred it to me as the person responsible for the planetary observations section.

Observations recovered after the discoveries

As of now, we had two other captures of the phenomenon, which were recovered after the captures, thanks to the alert issued

Didier Walliang, Thibault Humbert, Stéphane Barré, Alexis Desmougin (AstroQueyras, Saint-Véran observatory, France)

Having seen on twitter the day after the alert issued, a team of French amateur astronomers observing through a 620mm Cassegrain in the high altitude observatory of AstroQueyras realized they could have caught the impact flash. They used the DeTeCt software to confirm it after having looked at the video.
This observation is quite important for the scientific study of the phenomenon, having been done through a large telescope, under average conditions (but better than the other observations).

Michel Jacquesson (Sévigny-Wallepe, France)

Michel, another major contributor to the DeTeCt project, is a regular amateur observer experienced in Jupiter (he used to be measurer for the Jupos organization). Having heard of the alert, he checked his videos of that night and could luckily recover the impact flash on one of those! He then transfered it to me naturally. 

Cosmin Sandu Val (Romania)

Cosmin saw something when capturing with his 280mm Schmidt-Cassegrain, but only understood that it was an impact on Jupiter when seeing the alert issued the day after.

Jean-Christophe Griveau (Mothern, France)

Jean-Christophe read the alerts in a french forum and realized that he caught the flash, with his 280mm Schmidt-Cassegrain and a ZWO290MC.


First check of the available videos show that this impact flash could be the brightest one observed by amateurs (not including the one from C/Shoemaker-Levy 9 in 1994). We looked for a possible trace left by the impact in different images taken right after, like one excellent from Damian Peach in RGB, or others in methane absorption band but could not find any. This will be helpful to constrain the size limit of a body hitting Jupiter to leave a trace.
The amount of energy released, the dynamic of the impact, the physical characteristics of the body will be looked for by careful scientific study of the lightcurves of the event derived from the amateur videos.

The DeTeCt software/project permitted a second discovery of an impact (the one from José Luis Pereira, after the one from Ethan Chappel in 2019) which if it would have missed could have not lead to a fast issue of a wide alert to the amateur and professional community. This alert was efficient thanks to a vast sharing, making us aware of other discoveries/observations, and allowing the gathering of captures of the events which will be of great use for the scientific study of those rarely obsereved events. Aside Comet Shoemaker-Levy 9 impacts in 1994, never an impact was so well covered!

If you suspect you have an observation of this event, do not hesitate to contact Marc Delcroix and/or Ricardo Hueso, your video could prove to be of high scientific value !!!

And if you observe Jupiter or Saturn for pleasure, do not hesitate to use the software (even on archived videos!) and participate the DeTeCt project which could allow you to retrieve an impact flash you would have missed while observing, or even if this is not the case just contribute to an exciting collaborative professional - amateur project to estimate the frequency of impacts on the giant planets!

Many thanks to every amateur who was implied in this event, whether discovering it, observing it, looking for it in his capture without finding it, or spreading the alert (there were hundreds of shares).
Special thanks to the amateurs of the French astrosurf forums who helped me a lot to find out information on discoveries or new observations.
We amateurs demonstrated our force as a community, showed our motivation, dedication and experience through this great event!