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Baltimore
USA
3700 San Martin Drive
21218
MD
outreach@stsci.edu
410-338-4444
http://hubblesite.org
AU
1.105
1.064
Hubble
2021-31
Good
WFC3
2021-08-10
1.2
16111
https://archive.stsci.edu/proposal_search.php?mission=hst&id=16111
STScI
stsci
https://hubblesite.org/contents/news-releases/2021/news-2021-31
STScI-H-p2031a-f-2504x736.png
https://stsci-opo.org/STScI-01FCRMPQKH2BGH2WHX2RR9G6RH.png
ICRS
TAN
2000.0
Full
Optical
LP
350
Blue
A.2.2.1
Observation
Space Telescope Science Institute Office of Public Outreach
About 5,000 years ago a comet swept within 23 million miles of the sun, closer than the innermost planet Mercury. The comet must have been a spectacular sight to those young civilizations across Eurasia and North Africa that were arising at the end of the Stone Age.
However, this nameless space visitor is not recorded in any known historical account. So how do astronomers know that there was such an interplanetary intruder?
Enter comet ATLAS (C/2019 Y4), which first appeared near the beginning of 2020.
ATLAS quickly met an untimely death in mid-2020 when it disintegrated into a cascade of small icy pieces. Such a comet’s self-destruction happens once or twice a decade.
Astronomer Quanzhi Ye of the University of Maryland reports that ATLAS is a broken-off piece of that ancient visitor from 5,000 years ago. Why? Because ATLAS follows the same orbital “railroad track” as that of a comet seen in 1844. This means the two comets are siblings from the parent comet that broke apart very long ago. The link between the two comets was first noted by amateur astronomer Maik Meyer.
Such comet families are common. The most dramatic visual example was in 1994 when the doomed comet Shoemaker-Levy 9 (SL9) was pulled into a string of pieces by Jupiter’s gravitational pull. This “comet train” 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 about the time of the breakup. Unlike its hypothesized parent comet, ATLAS disintegrated while it was farther from the Sun than Earth, at a distance of over 100 million miles. This was much farther than the distance where its parent passed the Sun. “This emphasizes its strangeness,” said Ye.
“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,” said Ye. “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 closest to the sun.”
Observing the breakup of the fragments offers clues to how the parent comet was put together. The conventional wisdom is that comets are fragile agglomerations of dust and ice. And, they may be lumpy, like raisin pudding.
In a new paper to be published in the July 21 Astronomical Journal after one year of analysis, Ye and co-investigators report that one fragment of ATLAS disintegrated in a matter of days, while another piece lasted for weeks. “This tells us that part of the nucleus was stronger than the other part,” he said.
Two possibilities are that because of the action of jets, the short-lived piece may have spun up so fast that centrifugal forces tore it apart. An alternative explanation is that it has so-called super-volatile ices that just blew the piece apart like an exploding aerial firework. “It is complicated because we start to see these hierarchies and evolution of comet fragmentation. Comet ATLAS’s behavior is interesting but hard to explain.”
Comet ATLAS’ surviving sibling won’t return until the 50th century.
image/png
C/2019 Y4 Atlas
Comet ATLAS
65535
0231
2504
736
3
NASA, ESA, STScI, D. Jewitt (UCLA)
2021-08-19
COMET ATLAS WAS A BLAST FROM THE PAST
STScI
8
8
8
736
2504
1
2
2
3
720000/10000
720000/10000
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