First reddishthen with a halo greenish and now looking slightly blue. New observations of the interstellar comet 3I/ATLAS indicate that it has begun to show a faint bluish tone, which would be its second chromatic variation since it was detected 4 months ago.
3I/ATLAS is the third interstellar body to be discovered and, probably, the oldest of them all, with an origin outside the Solar System estimated to be more than 7,000 million years ago. When it was seen for the first time at the beginning of July, it was moving about 210,000 kilometers per hour towards the Sun and reached its perihelionthe point closest to it, the past October 29. As it passed on the other side of the Sun with respect to the Earth, the comet lost visibility for a few weeks and It could no longer be observed by terrestrial telescopes.although it was still within reach of other observation instruments in space.
One day before, on October 28, the researchers Qicheng Zhangfrom the Discovery Telescope at Lowell Observatory, and Karl Battamsfrom the United States Naval Research Laboratory, who analyzed data from instruments that could still observe 3I/ATLAS, revealed that The comet had brightened by several orders of magnitude after disappearing from viewsomething that cannot be fully explained by its proximity to the Sun.
In the same study, the authors point out that 3I/ATLAS shows ‘noticeably bluer than the Sun’a characteristic hitherto unpublished and which suggests the release of gases different from those observed in previous phases, possibly carbon monoxide or ammonia. At the moment, these conclusions are preliminary. The work has not undergone peer review and other observation campaigns have not yet confirmed the bluish tone.
It should be noted that this blue color refers to the ‘fingerprint’ spectra of the comet and is detected with photometry instruments. It is not necessarily ‘blue’ in appearance and is probably not visible to the human eye without optical aid due to its low projected luminosity.
According to the researchers, this new nuance contrasts with the reddish phase recorded in July, attributed to large amounts of dust expelled from the core, and with the brief greenish episode observed in September, related to dicarbon or cyanide emissions present in the coma. However, these color changes have only been temporary, and for now it is unclear why. Only time and continued observations will determine whether the comet’s new color will stick.
In the coming weeks, the comet will become increasingly most visible to sky watchers in the northern hemisphere as it moves north in the sky. However, it cannot be seen with the naked eye, so it will be necessary a telescope or astronomical binoculars to observe it.
3I/ATLAS will reach its point closest to our planet on December 19standing at a minimum distance of 270 million kmabout 1.8 times the Earth-Sun distance. Researchers will then have a closer view of the comet and will be able to study it better.
This interstellar object has shown several unusual features since its discovery, including aabundance of carbon dioxide, high levels of water loss and an enigmatic tailback. Researchers also believe that its icy shell may have been altered by billions of years of cosmic ray bombardmentwhich could make it difficult to analyze the original material from its home star system.