This pair (see below for other images) of Hubble Space Telescope images of Comet C/2019 Y4 (ATLAS), taken on April 20 and April 23, 2020, reveals the disintegration of the comet’s hard core. Hubble images identify up to 30 separate fragments. The comet was about 91 million miles from Earth when the image was taken. The comet may be a truncated chunk of a larger comet that was swept away by the sun 5,000 years ago. Comets have been artificially colored in this perspective to increase detail for analysis. Credits: Science: NASA, ESA, Quanzhi Ye (UMD); Image processing: Alyssa Pagan (STScI)
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Comet Atlas may be a blast from the past
When our early ancestors colonized the Nile Valley, 5,000 years ago at the dawn of civilization, a bright comet likely appeared in the sky before dawn. There is no direct evidence of this visitor because the beginning of recorded history is still several centuries away.
The belief is that the comet has at least split in half, and that it will not return to the Sun via the same orbital path until after 5,000 years. This forensic evidence can be attributed to the Great Comet of 1844 which is roughly the same as the brightest star to the naked eye, Sirius. The second segment, called Comet Atlas, appears towards the beginning of 2020.
Unlike its sibling who survived a trip around the sun in 1844, Atlas faced sudden death while still 100 million miles from the sun. It collapsed as described earlier
This pair (see above for more images) of Hubble Space Telescope images of Comet C/2019 Y4 (ATLAS), taken on April 20 and April 23, 2020, reveals the disintegration of the comet’s dense core. Credits: Science: NASA, ESA, Quanzhi Ye (UMD); Image processing: Alyssa Pagan (STScI)
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It is thought that about 5,000 years ago a comet swept 23 million miles from the sun, closer than the planet Mercury. The comet may have been a fascinating spectacle for civilizations across Eurasia and North Africa at the end of the Stone Age.
However, visitors to this anonymous space are not recorded in any known historical record. So how do astronomers know the existence of such interplanetary intruders?
Enter comet ATLAS (C/2019 Y4), which first appeared by early 2020.
Comet Atlas, first detected by the Earth-Shocking Last Warning System (ATLAS), operated by the University of Hawaii, quickly met its sudden death in the mid-2020s when it broke apart into a series of tiny ice shards.
In a new study using observations from
This guilty family is common. The most dramatic example seen was in 1994 when the cursed comet Shoemaker-Levy 9 (SL9) was pulled into pieces by
But Comet Atlas was just “weird,” said Ye, who noted with Hubble the timing of its collapse. Unlike real comets, Atlas disintegrates when it is farther from the Sun than Earth, at a distance of more than 100 million miles. This was far beyond his father’s distance across the sun. “That confirms the oddity,” Ye said.
“If it’s so far apart from the sun, how did it last its last circumnavigation of the sun 5,000 years ago? That’s a big question,” Ye said. “It’s very unusual because we didn’t expect it. This is the first time a member of the comet family in a long time has been seen exploding before passing near the sun.”
Observing the shattered fragments provides clues as to how the original comet was put together. Conventional wisdom is that comets are fragile lumps of dust and ice. Maybe thick, like raisin pudding.
In a new paper at Astronomy JournalAfter a year of analysis, Yi and co-investigators reported that one segment of ATLAS disintegrated within days, while another segment persisted for weeks. “This tells us that one part of the core is stronger than the other,” he said.
One possibility is that the tip of the ejecta may have spun the comet so fast that centrifugal forces ripped it apart. An alternative explanation is that it contains so-called super fly snow that blows the pieces away like fireworks bursting in the atmosphere. “It’s complicated because we’re starting to look at this hierarchy and the evolution of comet fragmentation. The behavior of Comet Atlas is interesting but difficult to explain.”
Comet Atlas’s surviving sibling will not return until the fiftieth century.
Reference: “Disintegrated Comet C/2019 Y4 (ATLAS). 1. Hubble Space Telescope Observations” By Quanzhi Ye, David Jewett, Man Tu Hui, Qisheng Zhang, Jessica Agarwal, Michael SB Kelly, Yun Young Kim, Jing Li, Tim Lister, Max Machler, and Harold A. Weaver, 21 July 2021 and Astronomy Journal.
DOI: 10.3847 / 1538-3881 / abfec3
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