A 4 billion-year-old relic of the early solar system is heading our way

(ORDO NEWS) — The huge comet – about 130 km across, more than twice the width of Rhode Island – is moving towards us at a speed of 35,500 km per hour from the edge of the solar system. Fortunately, it will never get closer to the Sun than 1.5 billion km, which is a little further from the Earth than Saturn; this will happen in 2031.

Comets, one of the solar system’s oldest objects, are icy bodies that were unceremoniously ejected from the solar system in a gravitational pinball game among the massive outer planets, says David Jewitt.

The UCLA professor of planetary science and astronomy has co-authored a new comet study in the Astrophysical Journal Letters. The expelled comets have settled in the Oort cloud, a vast collection of distant comets that surround the solar system for many billions of kilometers in deep space, he said.

A typical comet’s spectacular tail, several million kilometers long, which makes it look like a rocket, hides the fact that at the center of the fireworks is a solid core of ice mixed with dust – in fact, a dirty snowball. This huge comet, named Comet C/2014 UN271 and discovered by astronomers Pedro Bernardinelli and Gary Bernstein, can be up to 130 km across.

“This comet is literally the tip of the iceberg for the many thousands of comets that are too dim to see in the more distant parts of the solar system,” Jewitt said. “We always suspected that this comet must be large because it is so bright at such a great distance. We now confirm that it is.”

This comet has the largest comet nucleus ever observed by astronomers. Jewitt and his colleagues determined the size of its core using NASA’s Hubble Space Telescope. Its nucleus is about 50 times larger than most known comets. Its mass is estimated at 500 trillion tons, which is one hundred thousand times the mass of a typical comet, which is much closer to the Sun.

“This is an amazing object considering how active it is while still so far away from the Sun,” said study lead author Man-To Hui, who received his PhD from the University of California in 2019 and is now at the Macau University of Science and Technology in Taipa. Macau. “We assumed that the comet might be quite large, but we needed the best data to confirm it.”

Therefore, the researchers used Hubble to take five photographs of the comet on January 8, 2022, and included radio observations of the comet in their analysis.

The comet is now less than 3 billion kilometers from the Sun and will return to its nest in the Oort cloud in a few million years, Jewitt said.

Comet C/2014 UN271 was first spotted by accident in 2010 when it was 4.8 billion kilometers from the Sun. Since then, it has been intensively studied by ground-based and space telescopes.

The problem with measuring this comet was how to isolate the solid core from the huge dust coma – a cloud of dust and gas that envelops it. The comet is currently too far away for Hubble to visually determine its nucleus.

Instead, the Hubble data shows a bright burst of light at the core’s location. Hui and his colleagues then created a computer model of the surrounding coma and fitted it to the Hubble images. They then subtracted the glow from the coma, leaving only the core.

Hui and his team compared the core’s brightness to earlier radio observations from the Atacama Large Millimeter/Submillimeter Array, or ALMA, in Chile. The new Hubble measurements are close to earlier ALMA size estimates, but strongly suggest a darker core surface than previously thought.

“It’s big and blacker than coal,” Jewitt said.

The comet has been flying towards the Sun for over 1 million years. The Oort Cloud is believed to be a nesting site for trillions of comets. Jewitt believes that the Oort Cloud extends from several hundred times the distance between the Sun and Earth to at least a quarter of the way to the nearest stars to our Sun in the Alpha Centauri system.

According to Jewitt, Oort cloud comets were ejected from the solar system billions of years ago by the gravity of the massive outer planets. According to the professor, distant comets return to the Sun and planets only if their orbits are disturbed by the gravitational pull of a passing star.

First put forward in 1950 by the Dutch astronomer Jan Oort, the Oort cloud is still a theory because the comets that make up it are too faint and far away to be observed directly. This means that the largest structure in the solar system is virtually invisible, Jewitt said.

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