A huge comet with a solid center that is more than twice as wide as Rhode Island is on an orbit that will swing it inside our cosmic neighborhood, astronomers say.
The icy intervener travels 22,000 mph from the edge of the solar system toward the sun. In a study published Tuesday in The Astrophysical Journal Letters, scientists said the comet is no cause for concern because it will not pass anywhere near Earth.
Even as the comet approaches the sun, in 2031, it will remain at least 1 billion miles away, said a co-author of the study, David Jewitt, professor of planetary science and astronomy at UCLA.
“It will not even cross Saturn’s orbit, so it is certainly no threat to us,” he said. The comet, officially known as Comet C / 2014 UN271, is the largest such object ever observed by astronomers, Jewitt said.
Its core – the solid center, which typically consists of ice, rock and dust – is about 85 miles across. That makes it about 50 times larger than most known comets, with a mass estimated to be 100,000 times larger than a typical comet, according to the study.
“It’s a huge amount of material just in one body,” Jewitt said.
Astronomers used the Hubble Space Telescope to observe the colossal comet and determine the size of its core. Hubble took five images of the icy object on January 8, revealing its bright core shrouded in a glowing cloud of dust and gas, known as a coma.
“This is an amazing object considering how active it is when it’s still so far from the sun,” said the study’s lead author, Man-To Hui, an assistant professor at Macau University of Science and Technology, in a statement to Space Telescope Science Institute, which administers Hubble.
The researchers used a computer model developed from previous observations of the comet through terrestrial and space-based telescopes to look past the dusty coma and map the nucleus.
In addition to its enormous size, astronomers have found that the surface of the comet’s core is darker than previously thought.
“Only 3 percent of the light that hits its surface bounces off,” Jewitt said. “It’s a really, really dark surface. It’s more black than coal.”
More research is needed to understand why the core is so dark. Jewitt said it is possible that prolonged exposure to high-energy cosmic rays may have “boiled” the surface and coated it with carbonized material resembling charcoal.
Comet C / 2014 UN271 was first discovered in 2010 by astronomers Pedro Bernardinelli and Gary Bernstein when it was 3 billion miles from the sun. Although scientists have spent more than a decade studying the comet, the new study is the first to confirm its enormous size.
Jewitt said it probably formed more than 4 billion years ago when the solar system was in its infancy. It is possible, he said, that it evolved in the area between Jupiter and Neptune and grew along with the beginning planets.
“As it grew, and as the planets grew simultaneously, we believe the gravity of the planets was able to fling the comet out of the planetary orbit,” Jewitt said.
He added that the displaced comet and other similar objects probably ended up in what is known as the Oort cloud, an area outside Pluto where astronomers believe that icy objects orbit the solar system in a spherical bubble.
Occasionally, gravitational forces from passing stars can bump into distant comets in the Oort cloud and “kick them into the solar system,” Jewitt said.
Comet C / 2014 UN271 is less than 2 billion miles from the sun, according to the study. And in a few million years, it will migrate back to the Oort cloud, Jewitt said.
Astronomers hope to continue observing the comet leading to its nearest approach in 2031. Jewitt said that studying such objects could reveal insights into the solar system and help solve enduring mysteries in the cosmos.
“It’s a reminder that the outer solar system is not a very well-known place,” he said. “When you walk far away from the sun, everything out there is so faint that all sorts of things are waiting to be discovered.”