When comet C/2019 Y4 (ATLAS) disintegrated earlier this year, there were mixed feelings from the comet community.
On the one hand, hopes of viewing the comet from Earth with the naked eye were literally shattered, but on the other hand, its spectacular fragmentation offered a rare opportunity for astronomers to probe ATLAS’ remnants. In doing so, an international team of astrophysicists have discovered that Comet ATLAS’ coma (the dusty envelope surrounding the comet’s nucleus) and tail contained high levels of carbon.
“ATLAS was expected to be the brightest comet of 2020, visible from the Earth with a naked eye,” Ekaterina Chornaya, a postgraduate student at Far Eastern Federal University, Russia, said in a statement. “However, instead of observing the comet itself, we witnessed its disintegration.
“Luckily, we had begun photometric and polarimetric studies before the process started, and because of that, we are able to compare the composition of the coma before and after the disintegration,” Chornaya continued. “In the course of disintegration we noticed a dramatic growth of the positive polarization branch which, according to modeling, is consistent with a high concentration of carbonaceous particles."
As ATLAS was a long-period comet, it rarely approached the Sun, which allowed it to prevent its ancient elements, such as carbon, from succumbing to the Sun’s warming influence. Therefore, using the evidence from ATLAS, the researchers believe that carbon levels in other comet comas could be used to estimate the time they have spent in the Solar System. A lower carbon content would indicate a shorter period comet that has spent more time in close proximity of the Sun, and vice versa.
In ATLAS’ case, as described in Monthly Notices of the Royal Astronomical Society, the ability of dust particles in its coma to absorb, refract, and polarize light gave away the comet’s carbon secret. In fact, these measurements from ATLAS were similar to one of the brightest comets in history – Comet Hale-Bopp (C/1995 O1).
Even though the solid, icy ATLAS failed to survive its trip around the Sun, another rock on the block has restored comet-hunter’s 2020 hopes. Now visible to the naked eye just after sunset, Comet NEOWISE will be visible in the North-West for over an hour in the evening and visible for about an hour in a North-Easterly direction before sunrise.