A doomed celestial visitor could have been a piece of a prehistoric comet

Comet Atlas may have been a blast from the past

When our very first ancestors colonized the Nile Valley 5,000 years ago at the dawn of civilization, it is likely that a bright comet appeared in the sky before dawn. There is no direct evidence of this visitor as the start of recorded history was still a few centuries away.

The belief is that the comet at least split into two pieces, which would not return to the Sun along the same orbital path until 5,000 years later. This forensic evidence can be linked to the large comet of 1844 which was almost as bright as the brightest star with the naked eye, Sirius. The second fragment, called comet ATLAS, appeared around the beginning of 2020.

Unlike his brother who survived passing around the Sun in 1844, ATLAS met untimely death while still 100 million kilometers from the Sun. It completely disintegrated as photographed by the The Hubble Space Telescope.

It is suspected that about 5,000 years ago, a comet swept within 23 million kilometers of the Sun, closer than the innermost planet, Mercury. The comet could have been a spectacular sight for the civilizations of Eurasia and North Africa at the end of the Stone Age.

However, this unnamed space visitor is not recorded in any known historical narrative. So how do astronomers know there was such an interplanetary intruder?

Enter comet ATLAS (C / 2019 Y4), which first appeared in early 2020.

Comet ATLAS, first detected by the University of Hawaii’s Earth Asteroid Impact Alert System (ATLAS), quickly met an untimely death in mid-2020 when it s ‘is disintegrated into a cascade of small icy pieces.

In a new study using observations from NasaThe Hubble Space Telescope, astronomer Quanzhi Ye of the University of Maryland at College Park, reports that ATLAS is a fragment of this ancient visitor from 5,000 years ago. Why? Because ATLAS follows the same orbital “railroad” as that of a comet seen in 1844. This means that the two comets are probably the sisters of a mother comet which separated several centuries earlier. The link between the two comets was first noted by amateur astronomer Maik Meyer.

Such families of comets are common. The most dramatic visual example was in 1994 when doomed comet Shoemaker-Levy 9 (SL9) was reduced to a series of pieces by Jupitergravitational pull. This “train of comets” was short lived. It fell piece by piece into Jupiter in July 1994.

But Comet ATLAS is just “weird,” says Ye, who observed it with Hubble at the time of the rupture. Unlike its supposed parent comet, ATLAS disintegrated when it was further from the Sun than from Earth, at a distance of over 100 million miles. It was much farther than the distance his parent passed the Sun. “It underscores its strangeness,” Ye said.

“If it shattered 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. “It’s very unusual because you wouldn’t expect it. This is the first time that a member of the long-period comet family has been seen to break apart before approaching the Sun. “

Observing the breaking up of the fragments offers clues as to how the mother comet was formed. The misconception is that comets are fragile agglomerations of dust and ice. And, they can be lumpy, like raisin pudding.

In a new newspaper from Astronomical Journal, after a year of analysis, Ye and his co-investigators report that one fragment of ATLAS disintegrated within days, while another lump lasted for weeks. “It tells us that one part of the core was stronger than the other part,” he said.

One possibility is that streamers of ejected matter spun the comet so quickly that centrifugal forces tore it apart. Another explanation is that it has so-called super volatile ice cream that just blew up the room like an exploding aerial firework display. “It’s complicated because we’re starting to see these hierarchies and the evolution of comet fragmentation. The behavior of comet ATLAS is interesting but difficult to explain.

The surviving brother of comet ATLAS did not return until the 50th century.

Reference: “Decay of long period comet C / 2019 Y4 (ATLAS). I. Hubble Space Telescope Observations ”by Quanzhi Ye, David Jewitt, Man-To Hui, Qicheng Zhang, Jessica Agarwal, Michael SP Kelley, Yoonyoung Kim, Jing Li, Tim Lister, Max Mutchler and Harold A. Weaver, July 21, 2021 , Astronomical Journal.
DOI: 10.3847 / 1538-3881 / abfec3