This sequence shows how the nucleus of Comet C/2014 UN271 (Bernardinelli-Bernstein) was isolated from a vast shell of dust and gas surrounding the solid icy nucleus. On the left is a photo of the comet taken by the NASA Hubble Space Telescope's Wide Field Camera 3 on January 8, 2022. A model of the coma (middle panel) was obtained by means of fitting the surface brightness profile assembled from the observed image on the left. This allowed for the coma to be subtracted, unveiling the point-like glow from the nucleus. Combined with radio telescope data, astronomers arrived at a precise measurement of the nucleus size. That's no small feat from something about 2 billion miles away. Though the nucleus is estimated to be as large as 85 miles across, it is so far away it cannot be resolved by Hubble. Its size is derived from its reflectivity as measured by Hubble. The nucleus is estimated to be as black as charcoal. The nucleus area is gleaned from radio observations. Credits: NASA, ESA, Man-To Hui (Macau University of Science and Technology), David Jewitt (UCLA); Image processing: Alyssa Pagan (STScI)
The behemoth comet, C/2014 UN271 (Bernardinelli-Bernstein) is barreling
this way at 22,000 miles per hour from the edge of the solar system. But not to
worry. It will never get closer than 1 billion miles away from the Sun, which
is slightly farther than the distance of the planet Saturn. And that won't be
until the year 2031.
The previous record holder is comet C/2002 VQ94, with a nucleus estimated
to be 60 miles across. It was discovered in 2002 by the Lincoln Near-Earth
Asteroid Research (LINEAR) project.
"This comet is literally the tip of the iceberg for many thousands of
comets that are too faint to see in the more distant parts of the solar
system," said David Jewitt, a professor of planetary science and astronomy
at the University of California, Los Angeles (UCLA), and co-author of the new study in The Astrophysical Journal Letters. "We've always suspected this comet had to be big because it is so
bright at such a large distance. Now we confirm it is."
Comet C/2014 UN271 was discovered by astronomers Pedro Bernardinelli and
Gary Bernstein in archival images from the Dark Energy Survey at the Cerro
Tololo Inter-American Observatory in Chile. It was first serendipitously
observed in November 2010, when it was a whopping 3 billion miles from the Sun,
which is nearly the average distance to Neptune. Since then, it has been
intensively studied by ground and space-based telescopes.
"This is an amazing object, given how active it is when it's still so
far from the Sun," said the paper's lead author Man-To Hui of the Macau
University of Science and Technology, Taipa, Macau. "We guessed the comet
might be pretty big, but we needed the best data to confirm this." So, his
team used Hubble to take five photos of the comet on January 8, 2022.
The challenge in measuring this comet was how to discriminate the solid
nucleus from the huge dusty coma enveloping it. The comet is currently too far
away for its nucleus to be visually resolved by Hubble. Instead, the Hubble
data show a bright spike of light at the nucleus' location. Hui and his team
next made a computer model of the surrounding coma and adjusted it to fit the
Hubble images. Then, the glow of the coma was subtracted to leave behind the
starlike nucleus.
Hui and his team compared the brightness of the nucleus to earlier radio
observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in
Chile. This combined data constrains the diameter and the reflectivity of the
nucleus. The new Hubble measurements are close to the earlier size estimates
from ALMA, but convincingly suggest a darker nucleus surface than previously
thought. "It's big and it's blacker than coal," said
Jewitt.
This diagram compares the size of the icy, solid nucleus of comet C/2014 UN271 (Bernardinelli-Bernstein) to several other comets. The majority of comet nuclei observed are smaller than Halley’s comet. They are typically a mile across or less. Comet C/2014 UN271 is currently the record-holder for big comets. And, it may be just the tip of the iceberg. There could be many more monsters out there for astronomers to identify as sky surveys improve in sensitivity. Though astronomers know this comet must be big to be detected so far out to a distance of over 2 billion miles from Earth, only the Hubble Space Telescope has the sharpness and sensitivity to make a definitive estimate of nucleus size. Credits: Illustration: NASA, ESA, Zena Levy (STScI)
The comet has been falling toward the Sun for well over 1 million years. It
is coming from the hypothesized nesting ground of trillions of comets, called
the Oort Cloud. The diffuse cloud is thought to have an inner edge at 2,000 to
5,000 times the distance between the Sun and the Earth. Its outer edge might
extend at least a quarter of the way out to the distance of the nearest stars
to our Sun, the Alpha Centauri system.
The Oort Cloud's comets didn't actually form so far from the Sun; instead,
they were tossed out of the solar system billions of years ago by a
gravitational "pinball game" among the massive outer planets, when
the orbits of Jupiter and Saturn were still evolving. The far-flung comets only
travel back toward the Sun and planets if their distant orbits are disturbed by
the gravitational tug of a passing star – like shaking apples out of a
tree.
Comet Bernardinelli-Bernstein follows a 3-million-year-long elliptical
orbit, taking it as far from the Sun as roughly half a light-year. The comet is
now less than 2 billion miles from the Sun, falling nearly perpendicular to the
plane of our solar system. At that distance temperatures are only about minus
348 degrees Fahrenheit. Yet that's warm enough for carbon monoxide to sublimate
off the surface to produce the dusty coma.
Comet Bernardinelli-Bernstein provides an invaluable clue to the size
distribution of comets in the Oort Cloud and hence its total mass. Estimates
for the Oort Cloud's mass vary widely, reaching as high as 20 times Earth's
mass.
First hypothesized in 1950 by Dutch astronomer Jan Oort, the Oort Cloud
still remains a theory because the innumerable comets that make it up are too
faint and distant to be directly observed. Ironically, this means the solar
system's largest structure is all but invisible. It's estimated that NASA's
pair of Voyager spacecraft won't reach the inner realm of the Oort Cloud for
another 300 years and could take as long as 30,000 years to pass through it.
Circumstantial evidence come from infalling comets that can be traced back to this nesting ground. They approach the Sun from all different directions meaning the cloud must be spherical in shape. These comets are deep-freeze samples of the composition of the early solar system, preserved for billions of years. The reality of the Oort Cloud is bolstered by theoretical modeling of the formation and evolution of the solar system. The more observational evidence that can be gathered through deep sky surveys coupled with multiwavelength observations, the better astronomers will understand the Oort Cloud's role in the solar system's evolution.
Hubble determined the
size of the largest icy comet nucleus ever found. And, it’s big! With a
diameter of approximately 80 miles across, it’s about 50 times larger than
typical comets. Its 500-trillion-ton mass is a hundred thousand times greater
than the average comet. Credits: NASA's Goddard Space Flight Center; Lead
Producer: Paul Morris
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.
Source: Hubble
Confirms Largest Comet Nucleus Ever Seen | NASA
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