Doomed comet ATLAS has a long history with Earth

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Now, observations made while the comet, named ATLAS, was still intact have shed light on the comet’s “family”, which dates back thousands of years.

Comet ATLAS was first detected by the Terrestrial-impact Asteroid Last Alert System, or ATLAS, which is operated by the University of Hawaii on December 28, 2019.

Quanzhi Ye, an astronomer at the University of Maryland, observed the comet using the Hubble Space Telescope. Ye and his colleagues used their observations to determine that Comet ATLAS was actually a remnant of the one that likely crossed our skies 5,000 years ago. This ancient comet was found within 23 million kilometers from the sun, closer than Mercury to our star, and Stone Age civilizations across North Africa and Eurasia have probably witnessed the heavenly sight. The study was published in July in the Astronomical Journal.

There is no record of this sighting, but studying comets the way Ye and his team analyzed comet ATLAS is helping them trace the origins of comets. In fact, ATLAS’s orbit around the sun followed a similar path to that of a comet observed in 1844, suggesting that these two comets were “siblings” from a mother comet that s’ is separated centuries ago.

Comet ATLAS and the 1844 comet were originally linked by an amateur astronomer Maik Meyer.

It is not uncommon for a comet to separate into a “family”. Several telescopes, including Hubble and even the Galileo spacecraft, focused on Jupiter in July 1994 when comet Shoemaker-Levy 9 was torn apart by the gas giant’s gravitational pull. He formed a “train of comets” made of pieces of the comet that formed a line.

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The disappearance of the comet had been predicted by astronomers. They watched pieces fall into Jupiter, creating a spectacular fireball and leaving massive scars on the planet that were visible for months afterward.

Comet ATLAS is different, having disintegrated when it was further from the Sun than Earth, unlike its parent comet, which was closer to the Sun when it separated.

“If it separated so far from the Sun, how did it survive the last pass around the Sun 5,000 years ago? That’s the big question,” Ye said in a statement. “This is very unusual because we weren’t expecting it. This is the first time that a member of the long-lived comet family has been seen to shatter before approaching the Sun.”

When astronomers watch a comet shatter into pieces, they can also determine how it formed in the first place. Comets are gigantic dirty snowballs made of dust and ice that originate from the edge of the solar system.

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Part of comet ATLAS shattered within days, while another fragment survived for weeks.

“It tells us that one part of the core was stronger than the other,” Ye said.

It is possible that the comet was torn apart by the material it ejected, or that it collapsed like fireworks.

“It’s complicated because we are starting to see these hierarchies and the evolution of comet fragmentation. The behavior of comet ATLAS is interesting but difficult to explain,” Ye said.

Meanwhile, the sister of comet ATLAS, the one observed in 1844, will no longer be visible in our skies until the 50th century.



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