A giant comet from the outskirts of our solar system has been discovered in
six years of data from the Dark Energy Survey. Comet Bernardinelli-Bernstein
is estimated to be about 1000 times more massive than a typical comet,
making it arguably the largest comet discovered in modern times. It has an
extremely elongated orbit, journeying inward from the distant Oort Cloud
over millions of years. It is the most distant comet to be discovered on its
incoming path, giving us years to watch it evolve as it approaches the Sun,
though it's not predicted to become a naked-eye spectacle.
A giant comet has been discovered by two astronomers following a
comprehensive search of data from Dark Energy Survey (DES). The comet, which
is estimated to be 100–200 kilometers across, or about 10 times the diameter
of most comets, is an icy relic flung out of the solar system by the
migrating giant planets in the early history of the solar system. This comet
is quite unlike any other seen before and the huge size estimate is based on
how much sunlight it reflects.
Pedro Bernardinelli and Gary Bernstein, of the University of Pennsylvania,
found the comet—named Comet Bernardinelli-Bernstein (with the designation
C/2014 UN271)—hidden among data collected by the 570-megapixel Dark Energy
Camera (DECam) mounted on the Víctor M. Blanco 4-meter Telescope at Cerro
Tololo Inter-American Observatory (CTIO) in Chile. The analysis of data from
the Dark Energy Survey is supported by the Department of Energy (DOE) and
the National Science Foundation (NSF), and the DECam science archive is
curated by the Community Science and Data Center (CSDC) at NSF's NOIRLab.
CTIO and CSDC are Programs of NOIRLab.
One of the highest-performance, wide-field CCD imagers in the world, DECam
was designed specifically for the DES and operated by the DOE and NSF
between 2013 and 2019. DECam was funded by the DOE and was built and tested
at DOE's Fermilab. At present DECam is used for programs covering a huge
range of science.
DES was tasked with mapping 300 million galaxies across a 5000-square-degree
area of the night sky, but during its six years of observations it also
observed many comets and trans-Neptunian objects passing through the
surveyed field. A trans-Neptunian object, or TNO, is an icy body that
resides in our solar system beyond the orbit of Neptune.
Bernardinelli and Bernstein used 15–20 million CPU hours at the National
Center for Supercomputing Applications and Fermilab, employing sophisticated
identification and tracking algorithms to identify over 800 individual TNOs
from among the more than 16 billion individual sources detected in 80,000
exposures taken as part of the DES. Thirty-two of those detections belonged
to one object in particular—C/2014 UN271.
Comets are icy bodies that evaporate as they approach the warmth of the Sun,
growing their coma and tails. The DES images of the object in 2014–2018 did
not show a typical comet tail, but within a day of the announcement of its
discovery via the Minor Planet Center, astronomers using the Las Cumbres
Observatory network took fresh images of Comet Bernardinelli-Bernstein which
revealed that it has grown a coma in the past three years, making it
officially a comet.
Its current inward journey began at a distance of over 40,000 astronomical
units (au) from the Sun—in other words 40,000 times farther from the Sun
than Earth is, or 6 trillion kilometers away (3.7 trillion miles or 0.6
light-years—1/7 of the distance to the nearest star). For comparison, Pluto
is 39 au from the Sun, on average. This means that Comet
Bernardinelli-Bernstein originated in the Oort Cloud of objects, ejected
during early history of the solar system. It could be the largest member of
the Oort Cloud ever detected, and it is the first comet on an incoming path
to be detected so far away.
Comet Bernardinelli-Bernstein is currently much closer to the Sun. It was
first seen by DES in 2014 at a distance of 29 au (4 billion kilometers or
2.5 billion miles, roughly the distance of Neptune), and as of June 2021, it
was 20 au (3 billion kilometers or 1.8 billion miles, the distance of
Uranus) from the Sun and currently shines at magnitude 20. The comet's orbit
is perpendicular to the plane of the solar system and it will reach its
closest point to the Sun (known as perihelion) in 2031, when it will be
around 11 au away (a bit more than Saturn's distance from the Sun)—but it
will get no closer. Despite the comet's size, it is currently predicted that
skywatchers will require a large amateur telescope to see it, even at its
brightest.
"We have the privilege of having discovered perhaps the largest comet ever
seen—or at least larger than any well-studied one—and caught it early enough
for people to watch it evolve as it approaches and warms up," said Gary
Bernstein. "It has not visited the solar system in more than 3 million
years."
Comet Bernardinelli-Bernstein will be followed intensively by the
astronomical community, including with NOIRLab facilities, to understand the
composition and origin of this massive relic from the birth of our own
planet. Astronomers suspect that there may be many more undiscovered comets
of this size waiting in the Oort Cloud far beyond Pluto and the Kuiper Belt.
These giant comets are thought to have been scattered to the far reaches of
the solar system by the migration of Jupiter, Saturn, Uranus and Neptune
early in their history.
"This is a much needed anchor on the unknown population of large objects in
the Oort Cloud and their connection with early migration of the ice/gas
giants soon after the solar system was formed," said NOIRLab astronomer Tod
Lauer.
"These observations demonstrate the value of long-duration survey
observations on national facilities like the Blanco telescope," says Chris
Davis, National Science Foundation Program Director for NOIRLab. "Finding
huge objects like Comet Bernardinelli-Bernstein is crucial to our
understanding of the early history of our solar system."
It is not yet known how active and bright it will become when it reaches
perihelion. However, Bernardinelli says that Vera C. Rubin Observatory, a
future Program of NOIRLab, "will continuously measure Comet
Bernardinelli-Bernstein all the way to its perihelion in 2031, and probably
find many, many others like it," allowing astronomers to characterize
objects from the Oort Cloud in much greater detail.
This research was reported to the Minor Planet Center.
Reference:
MPEC 2021-M53 : 2014 UN271, Minor Planet Electronic Circular:
minorplanetcenter.net/mpec/K21/K21M53.html
Tags:
Space & Astrophysics