Comet ATLAS May Have Been Part Of A Prehistoric Comet

Some 5,000 years ago, a brilliant comet may have stunned our ancestors as it appeared in the sky. How do experts even know that such a prehistoric comet even existed? The now-disintegrated Comet ATLAS and its sibling may provide the clues.

Comet ATLAS (C/2019 Y4) was discovered on Dec. 29, 2019, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Hawaii and soon sparked the interest of many for possibly becoming "one of the most spectacular comets" of the last 20 years. However, it ended up getting dimmer instead of brighter, and observations eventually confirmed it had indeed broken apart.

Now, more than a year after the breakup of the comet, it is still proving to be quite interesting. In fact, NASA noted in a news release this week that comet ATLAS may actually have been a piece of the prehistoric comet.

The clue, NASA said, is the fact that comet ATLAS actually followed the same "railroad track" of a comet that was seen in 1844.

"The link between the two comets was first noted by amateur astronomer Maik Meyer," NASA said.

According to the agency, which cited a study by the University of Maryland's Quanzhi Ye, this suggests the two comets came from the same parent comet. In this case, they likely came from the comet that passed 5,000 years ago.

"The belief is that comet at least split into two pieces, which would not return to the Sun along the same orbital track until 5,000 years later," Hubblesite noted. "This forensic evidence can be linked to the great comet of 1844 that was nearly as bright as the brightest naked-eye star, Sirius."

So what happened to these siblings? As we now know, comet ATLAS disintegrated when it passed around the sun in 2020. Ye called this event rather "weird" as it disintegrated farther from the sun than its possible parent comet did. Specifically, it disintegrated some 100 million miles away from the sun when its "hypothesized" parent comet likely broke apart some 23 million miles away, which the agency noted to be even closer than Mercury.

"If it broke up this far from the Sun, how did it survive the last passage around the Sun 5,000 years ago? This is the big question," Ye said in the NASA news release. "It's very unusual because we wouldn't expect it. This is the first time a long-period comet family member was seen breaking up before passing closer to the Sun."

In a study, recently published in the Astronomical Journal, Ye and colleagues reported that while a part of comet ATLAS disintegrated within days, another part lasted for longer, suggesting that one part was stronger than the other.

In the case of its sibling, it survived passing around the sun, but NASA noted that it won't come back "until the 50th century."