The European Space Agency (ESA) has released the first awaited images of the close passage of the interstellar comet 3I/ATLAS to the planet Marsalone 30 million km away. ESA attempted to image the comet using all the instruments on board the ExoMars and MarsExpress probes, normally used to study the surface of the red planet. From the first analysis of the data, it seems that only the ExoMars probe was able to image the comet, thanks to the ability of its camera to perform long exposure shots. The released images only show the comet comaformed by gas and dust, since the tail is too weak to be able to be identified by the instruments on board the probes, while the core too small to be able to be distinguished from that distance. Even the NASA ha attempted to observe 3I/ATLAS using the Rover Perseverance on the Martian surface. However, NASA images only show a apparently cylindrical objectthe result of the combination of 30 second exposures. Probably it’s not even 3I/ATLAS, but Phobosthe moon of Mars. Due to the American government shutdown, NASA has not yet commented on the images released so confirmation that it is not the comet will have to wait, hopefully just a few more days.
ESA images of the comet
The probes ExoMars and Mars Express ESA attempted to capture images of the interstellar comet 3I/ATLAS between October 1st and October 7th, that is, in conjunction with close passage of the comet to Mars, which occurred at approximately 30 million km away. The two probes used both cameras and on-board spectrographs, in an attempt to determine the shape and chemical composition of the interstellar comet.
The image above was obtained from the tool Color and Stereo Surface Imaging System (CaSSIS) by ExoMars. This has been thesingle tool capable of producing clear images of the comet (the diffuse object to the right of the image), thanks to the possibility it has of taking pictures long exposure photo. This is a noteworthy achievement, as the comet is 10,000-100,000 times fainter than the Martian surface normally analyzed by the probe.
The image is one composition of multiple 5 second exposures. What we see is the hair of the comet, one thin atmosphere of gas and dust generated by the sublimation of the cometary nucleus. The latter is indistinguishable from the coma due to its size of about one km which, seen from 30 million km away, is equivalent to try to photograph a cell phone on the Moon from the surface of the Earth. Furthermore, you can’t even see the in the image tail of the comet, not because it is not present, but because too weak to be able to be imaged with ExoMars tools.
The Mars Express instruments and the spectrographs of both Mars Express and ExoMars do not appear to have been able to obtain images of the comet due to its weak brightness, but data analysis will continue in the coming months to try to extract every last photon from the data. Furthermore, next month the Juice probe (Jupiter Icy Moons Explorer)traveling to Jupiter, will resume 3I/ATLAS immediately after perihelionwhen the comet is expected to be much more active than it currently is. ESA thus hopes to understand more about this interstellar visitor which, according to some studies, could be there oldest comet ever observedeven three billion years older than the Solar System, which is 4.6 billion years old.
The controversial NASA images
In addition to the ESA probes, also the small Rover Perseverance from NASA tried to obtain an image of comet 3I/ATLAS, but this time from the surface of Mars. As you can see from the image below, taken on October 4the rover took a object that appears to have a cylindrical shape. Due to the American government shutdown, the image was only published and not officially commented on by NASA, thus leaving room for the most imaginative interpretations of the cylindrical shape of the comet.
In reality what you see in this image is the resulting from the combination of a series of 30-second snapshots each. The Perseverance rover does not move its camera following the motion of the sky (since that is not the scientific objective for which it was built), consequently at each exposure the object has changed his position slightly in the sky and once the images are combined the result is a “scrawled” effect . You can also obtain it with a camera by taking a long exposure shot of the starry sky that is longer than 20/30 seconds.
In addition, most likely the item in the photo it’s not even the comet, but Phobosthe moon of Mars. By correlating the shooting data with the celestial maps of a planetarium such as Stellarium, one can notice how the position of the crawled object coincides precisely with that of the natural satellite of Mars. Furthermore, as can be seen from the photo above, in the previous days the comet had been imaged by Perseverance and it appeared as a faint whitish patchcertainly not an elongated object. Even Avi Loeb, the Harvard astronomer who supported the thesis of the extra-terrestrial nature of the interstellar comets discovered so far, was critical in the interpretation of the cylindrical shape of 3I/ATLAS. In any case, we will have to wait for the end of the shutdown to have a comment on the nature of these images from NASA.
