The largest comet ever discovered was traveling toward the sun more than a million years ago, and its gigantic scale is shedding light on the mysterious objects that make up one of the largest structures in our solar system.
at New study, astronomers used the Hubble Space Telescope to confirm that the solid center of the giant comet C/2014 UN271 (Bernardinelli-Bernstein) is the largest comet nucleus ever discovered. It measures an astonishing 50 times larger than most known comets, and is about 140 kilometers (about 85 miles) wide.
However, this strangely large size – or rather the apparent strangeness of it – may tell us more about us and our limited concept of comets than anything else.
C/2014 UN271 descended from Oort cloud: a giant spheroidal dispersal of icy bodies proposed to enclose the Sun in the deepest and most distant extensions of our solar system (far, in fact, thought to extend at least a quarter of the way toward the next closest star system, Alpha Centauri).
It looks pretty big, doesn’t it? Theoretically. However, the Oort cloud is so far away and difficult to detect, it is essentially a huge hypothetical mystery, although astronomers consider it one of the largest structures in our solar system.
Every once in a while, something appears from this mysterious mass, gravitationally drawn towards the Sun from the far reaches of the cosmic hinterland.
Compare the size of the comet nucleus. (NASA/ESA/Zina Levi, STScI)
C/2014 UN271 is one of those things, and it tells us a lot about the existence of the frozen “original” blocks that make up the Oort cloud. It is believed to have formed early in the inner solar system, before falling to its outer edges under the gravitational effects of giant planets such as Jupiter and Saturn.
“This comet is literally the tip of the iceberg of several thousand comets that are too faint to be seen in the farthest parts of the Solar System,” Says Astronomer David Jewett of the University of California.
“We have always suspected that this comet must be large because it is so bright at such a great distance. Now we confirm that it is.”
In the new analysis, Jewett and fellow researchers led by first author Man Tu Hui of the Macau University of Science and Technology, calculated the volume of C/2014 UN271 with the highest accuracy to date. that they Based on previous estimates Using Hubble observations and modeling to isolate the nucleus from the coma of a comet – the long tail of ice that sublimes into gases in a comet’s wake.
“We confirm that C/2014 UN271 is the largest long-range comet ever discovered,” the team Writing in their new paper.
(NASA / ESA / Man To Hui, Macau University of Science and Technology / David Jewett, UCLA / Alissa Pagan, STScI)
Above: A sequence showing a Hubble image of a comet, its typical coma, and an isolated nucleus.
The discovery of C/2014 UN271 was announced last year, after it was found hidden in a batch of observational data captured by Dark Energy Survey Between 2014 and 2018. Subsequent follow-up analyzes revealed that C/2014 UN271 was indeed captured as early as 2010.
However, even that early glimpse doesn’t begin to cover the astounding length of a comet’s flight. It follows an elliptical orbit of about 3 million years around the Sun, and its shape means it has been slowly approaching the Sun for more than a million years.
It is due to reach its closest approach to the sun – known as rock bottom – In 2031, at this point, Bernardinelli-Bernstein will still be about a billion miles from the Sun, before bending outward on its elliptical path.
That means we have nearly a decade of improved observational opportunities ahead, to learn more about C/2014 UN271 and the like as the comet approaches, before it quietly slips into the dark again.
The results are reported in Astrophysical Journal Letters.