by Agency Writers
Baltimore MD (SPX)
The majority of comet nuclei observed are smaller than Halley's comet. They are typically a mile across or less.
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
The nucleus is about 50
times larger than found at the heart of most known comets. Its mass
is estimated to be a staggering 500 trillion tons, a hundred
thousand times greater than the mass of a typical comet found much
closer to the Sun.
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.
It was discovered in 2002 by the Lincoln Near-Earth Asteroid Research (LINEAR) project.
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.
So, his team used Hubble
to take five photos of the comet on January 8, 2022.
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.
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.
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 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.
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 348º Fahrenheit.
Yet that's warm enough
for carbon monoxide to sublimate off the surface to produce the
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.
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
multiwave-length observations, the better astronomers will
understand the Oort Cloud's role in the solar system's evolution.