The NASA/ESA Hubble Space Telescope has captured one of the most detailed observations of a comet breaking apart.
This image captured by Hubble’s Wide Field Camera 3 shows a dust-bathed cluster of fragments receding from the main nucleus of Comet 332P/Ikeya-Murakami at speeds in the range of 0.06 – 3.5 m/s. The nucleus of the comet is the bright object at lower left. This observation was made on January 27, 2016. Image credit: NASA / ESA / D. Jewitt, University of California at Los Angeles.
The comet in question is called 332P/Ikeya-Murakami. It was discovered independently on November 3, 2010 by two Japanese astronomers, Kaoru Ikeya and Shigeki Murakami.
This comet originates from the Kuiper Belt, the outer boundary of our Solar System.
It is approximately 4.5 billion years old, measures 1,600 feet (488 m) in diameter and orbits the Sun in 5.42 years.
In a series of images taken over a three-day span in January 2016, Hubble revealed 25 building-size blocks that are drifting away from 332P/Ikeya-Murakami at a leisurely pace.
The observations suggest that the comet may be spinning so fast that material is ejected from its surface. The resulting debris is now scattered along a 3,000-mile (4,830 km) long trail.
The results of these observations were published in a paper that appeared in the Sept. 15, 2016, issue of the Astrophysical Journal Letters (arXiv.org preprint).
“We know that comets sometimes disintegrate, but we don’t know much about why or how they come apart,” said lead author Dr. David Jewitt, from the University of California at Los Angeles.
“The trouble is that it happens quickly and without warning, and so we don’t have much chance to get useful data.”
“With Hubble’s fantastic resolution, not only do we see really tiny, faint bits of the comet, but we can watch them change from day to day. And that has allowed us to make the best measurements ever obtained on such an object.”
The Hubble observations reveal that 332P/Ikeya-Murakami shards brighten and dim as icy patches on their surfaces rotate into and out of sunlight. Their shapes change, too, as they break apart.
The icy relics comprise about 4% (two million tons) of the parent comet and range in size from roughly 65 to 200 feet (20-61 m) wide. They are moving away from each other at a few miles per hour.
Dr. Jewitt and his colleagues calculated that the comet probably shed material over several months, between October and December 2015.
They suggest that even some of the ejected pieces have themselves fallen to bits in a kind of cascading fragmentation.
“Our analysis shows that the smaller fragments are not as abundant as one might expect based on the number of bigger chunks. This is suggestive that they’re being depleted even in the few months since they were launched from the primary body. We think these little guys have a short lifetime,” Dr. Jewitt said.
The Hubble images show that the parent comet also changes brightness cyclically, completing a rotation every two to four hours.
Based on the Hubble data, the researchers suggests that sunlight heated up the comet, causing jets of gas and dust to erupt from its surface. Because the nucleus is small, these jets act like rocket engines, spinning up the comet’s rotation.
“In the past, astronomers thought that comets die when they are warmed by sunlight, causing their ices to simply vaporize away,” Dr. Jewitt said.
“Either nothing would be left over or there would be a dead hulk of material where an active comet used to be. But it’s starting to look like fragmentation may be more important. In 332P/Ikeya-Murakami we may be seeing a comet fragmenting itself into oblivion.”
The team estimates that 332P/Ikeya-Murakami contains enough mass to endure another 25 outbursts.
“If the comet has an episode every six years, the equivalent of one orbit around the Sun, then it will be gone in 150 years,” Dr. Jewitt said.
Fragmenting comets such as 332P/Ikeya-Murakami have long been objects of fascination for astronomers worldwide. Famously, Comet Shoemaker-Levy 9 disintegrated in 1992, crashing into the atmosphere of Jupiter at nearly 200,000 km per hour, creating scars on it almost half the size of Earth.
Hubble will continue to observe 332P/Ikeya-Murakami and comets like it, unraveling the nature of these mysterious objects.
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David Jewitt et al. 2016. Fragmentation Kinematics in Comet 332P/Ikeya-Murakami. ApJ 829, L8; doi: 10.3847/2041-8205/829/1/L8
This article is based on a press-release issued by NASA.
