A comet so large that it was mistaken initially for a dwarf planet is currently on an inward-bound path from the outer Solar System.
There's no reason to worry C/2014 UN 271 (Bernardinelli-Bernstein), as the comet is called, will approach no closer to the Sun than just outside the orbit of Saturn. Its size and relative proximity will allow for rare opportunities to observe a pure object from Oort Cloud and gain new information about the formation and evolution of the Solar System.
"We have the privilege of discovering perhaps the largest comet ever observed or at least larger than any other well-studied one, and we caught it early enough to allow people to observe it evolve as it approaches." Gary Bernstein, co-discoverer and Astronomer from the University of Pennsylvania stated earlier this year.
"It hasn't visited the Solar System for more than 3,000,000 years."
The outer Solar System is, in general, a mysterious place. It is far away and very dark. The objects within it are also small. Therefore, finding out what lies beyond Neptune's orbit can be quite difficult.
Although we have an idea of the space's architecture, the Kuiper Belt is made up of small icy bodies and the Oort Cloud, which are spread over greater distances, the details are more difficult to determine.
However, we are now getting more information from an unanticipated source: The Dark Energy Survey (DES) which ran from August 2013 to January 2019.
The telescope scanned the southern sky in near-infrared over several hundred nights. It studied objects like supernovae, galaxy clusters, and other stars to determine the acceleration of the Universe's expansion. This was thought to be due to dark energy.
The survey was very accurate in identifying objects in outer Solar System beyond Neptune's orbit, which is approximately 30 astronomical units away from the Sun. A team of astronomers discovered 461 objects in the outer Solar System that were previously unknown in DES data earlier this year.
One of those objects, spotted by Bernstein and fellow University of Pennsylvania astronomer Pedro Bernardinelli, was C/2014 UN 271 (Bernardinelli-Bernstein). They and their colleagues now describe the comet in more detail in a paper that was accepted into The Astrophysical Journal Letters.
"We conclude that C/2014 UN 271 (Bernardinelli-Bernstein) is a 'new' comet in the sense that there is no evidence for previous approach closer than 18 au to the Sun since ejection into the Oort Cloud," the researchers write.
"Indeed this may be the cleanest comet we've ever seen, as it has been detected before Uranus' orbit and may not have done so previously."
According to the team's analysis, C/2014 UN 271 (Bernardinelli-Bernstein) started its inward journey at a distance of around 40,400 astronomical units from the Sun. This is Oort Cloud territory. It's a vast sphere of icy objects that stretches from approximately 2,000 to as far away as 100,000 astronomical unit.
The comet was located at an approximate distance of 29 astronomical units to the Sun when it was first discovered. The closest approach to the Sun is expected in 2031. It will be at a distance 10.97 astronomical unit from the Sun. Saturn's orbit has an average distance distance of 9.7 astronomical units.
At a size of 155 kilometers (96 miles) in diameter, C/2014 UN 271 (Bernardinelli-Bernstein) is an absolute chonker, but even so, will not be visible to the naked eye at that distance.
However, scientists will make every effort to observe it with telescopes. They believe that by learning more about its structure, we will be able learn more about the early Solar System and its distant reaches.
This is because icy rocks found at the fringes of our Solar System are believed to have remained relatively unchanged since their formation, which was around 4.5 billion year ago. Therefore, volatiles in the comet's liquid ices could contain information about the composition of the outer Solar System at the time it formed.
Scientists have already detected signs of a "coma", the cometary atmosphere that occurs when a comet approaches the Sun. Increased warmth melts ices on the surface of the comet, resulting in visible comas and, at close range, cometary tails. Spectral analysis of these features will tell us a lot about what's inside C/2014 UN 271 (Bernardinelli-Bernstein).
Since we know very little about the Oort Cloud and the objects therein, C/2014 UN 271 (Bernardinelli-Bernstein) represents a very rare window into this enigmatic region of our home in space.
The Astrophysical Journal Letters has accepted the research and it is now available on arXiv.
