“Strange” comet ATLAS could be a remnant of a former visitor
The “bizarre” comet ATLAS, which lit the sky in 2020 and succumbed to an untimely death later that same year, was a broken piece of a larger comet that swung through the Sun 5,000 years ago, according to scientists studying this unusual icy space visitor. .
It is suspected that around 5,000 years ago, towards the end of the Stone Age, the civilizations of Eurasia and North Africa were treated to a spectacular sight as a large comet swept within 37 million kilometers (23 million miles) from the Sun – an orbit closer to the innermost planet than Mercury does.
But not much is known about this sighting, so how do astronomers know that such a visitor to space made an appearance all those years ago? The answer is comet ATLAS (C / 2019 Y4).
Discovered by its namesake in December 2019, the ATLAS (Asteroid Terrestrial-impact Last Alert System), a robotic astronomical surveying system based in Hawaii, Comet ATLAS was considered one of the brightest comets to have swept the Earth. over the past two decades.
However, after lighting up the sky for a few months, the object started to darken and the telescopes quickly noticed that ATLAS was starting to disintegrate.
“It’s really exciting – both because events like this are super cool to watch and because they don’t happen very often,” said Quanzhi Ye, leader of a Hubble observation team observing the breaking up last year.
By mid-April, it was confirmed that Comet ATLAS had fragmented into at least 25 to 30 pieces each about the size of a house. But not before German amateur astronomer and comet expert Maik Meyer noted that its orbit closely resembles that of another long-period comet (LPC) known as the Great Comet, or C / 1844 Y1 .
According to a second-hand report by François Arago in March 1845 in the Proceedings of the Academy of Sciences, the Great Comet was first observed in Guyana at dusk on December 16, 1844, although no information on the discovery actual was not mentioned. .
It turns out that Meyer was right, because after analyzing the data from the space telescope, Ye, who is based at the University of Maryland, confirms that ATLAS follows the same orbital “railroad” as C / 1844 Y1 and that both most likely once belonged to a mother comet that shattered several centuries earlier.
Only two families of long period comets (LPCs) have been unambiguously identified: the famous Kreutz sungrazing family of comets which contains more than 4,000 known fragments as well as the Liller-Tabur-SWAN group, say Ye and colleagues in their article. published in the Astronomical Journal.
And it’s not just the fact that it’s relatively rare that makes Comet ATLAS special; it’s also because it’s “weird,” Ye said.
Unlike its supposed former parent comet, ATLAS disintegrated when it was further from the Sun than from Earth, at a distance of over 161 million kilometers (100 million miles).
It was much farther than the distance his parent passed the Sun. “It underscores its strangeness,” Ye says.
“If it broke 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 adds. “It’s 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.”
Clues as to why this might be the case can be gathered from how he broke up. Comets are traditionally thought of as fragile agglomerations of dust and ice, but one piece of ATLAS disintegrated within days, while another piece lasted for weeks. “It tells us that one part of the core was stronger than the other,” Ye says.
The cause of the initial fragmentation is still undetermined, Ye says, but it could have been caused by streamers of ejected matter that spun the comet so quickly that centrifugal forces tore it apart. Alternatively, the so-called super-volatile ice gases simply detonated the room like exploding aerial fireworks. “The behavior of comet ATLAS is interesting but difficult to explain.” Ye concludes.
Astronomers will wait a long time before testing other theories about Comet ATLAS’s familial connection to its surviving brother, as C / 1844 Y1 won’t return to our corner of the sky until the 50th century.