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A Rapidly Disintegrating Comet

Comet 332P/Ikeya-Murakami has had a short but colorful history in our observations. First detected in 2010 by two amateur astronomers in Japan, the comet has been spinning off debris at least since 2015 and probably earlier. A large fragment, as big as Comet 332P itself, may have broken off in 2012. Still close to the comet, its discovery prompted a team led by David Jewitt (UCLA) to request time on the Hubble Space Telescope to study what was happening.

Among a long page of posted quotations on Jewitt’s UCLA website is this by Erwin Schrodinger: “The task is, not so much to see what no one has yet seen; but to think what nobody has yet thought, about that which everybody sees.” In this case, what everybody now sees is our most in-depth look at a comet’s disintegration ever. The trick is what to make of what we see.

The Hubble observations, taken in early 2016, show us 25 separate fragments, mixtures of dust and ice that are slowly separating from the comet at no more than the pace I make on my morning walk. The fragments make up about four percent of the parent comet, ranging in size from 20 meters to 60 meters. Comet 332P completes a rotation every two to four hours, and it’s thought that the fragments may be thrown from the surface by this spin, leaving them to fan out along a trail fully 4800 kilometers long.

Another quote Jewitt references on his web page comes from Heraclitus: “If you do not expect the unexpected, you will not find it; for it is hard to be sought out, and difficult.” A comet’s gradual death as it approaches the Sun would not be considered unexpected, but in this case what has to be sought out is the process. It turns out to be far from gentle. Says Jewitt:

“In the past, astronomers thought that comets die when they are warmed by sunlight, causing their ices to simply vaporize away. But it’s starting to look like fragmentation may be more important. In comet 332P we may be seeing a comet fragmenting itself into oblivion.”

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Image: This NASA Hubble Space Telescope image reveals the ancient comet 332P/Ikeya-Murakami disintegrating as it approaches the sun. The observations represent one of the sharpest views of an icy comet breaking apart. The comet debris consists of a cluster of building-size chunks near the center of the image. They form a 4800-kilometer-long trail, larger than the width of the continental U.S. The fragments are drifting away from the comet, dubbed comet 332P, at a leisurely pace, roughly the walking speed of an adult.. Credit: NASA, ESA, David Jewitt/UCLA.

This is a short period comet that when discovered was 1.6 AU out, its detection taking place one month after perihelion in October of 2010. It has evidently survived a roughly 10 million year journey to the inner system, and Jewitt and colleagues estimate that it contains enough mass for about 25 more outbursts. With an orbital period of less than six years, we may be looking at a very short-lived spectacle, in astronomical terms. As Jewitt says:

“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. It’s just the blink of an eye, astronomically speaking. The trip to the inner solar system has doomed it.”

The Hubble images captured 332P/Ikeya-Murakami breaking up almost 110 million kilometers from Earth, as comet and its debris orbit the Sun at approximately 80,000 kilometers per hour. The comet turns out to be smaller than originally thought, measuring about 500 meters across. Its fast rotation is probably the result of sunlight heating the surface, causing it to expel jets of dust and gas. The material we see in the image was probably shed between October and December of 2015.

The paper is Jewitt et al., “Fragmentation Kinematics in Comet 332P/Ikeya-Murakami,” published online by Astrophysical Journal Letters 15 September 2016 (abstract / preprint). David Jewitt’s entertaining selection of quotes can be found here. I can’t resist adding one last quote because it’s a personal favorite from Yogi Berra: “In theory there is no difference between theory and practice. In practice there is.”

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Comments on this entry are closed.

  • Alex Tolley September 20, 2016, 16:00

    I thought comets accumulate a layer of dust that insulates them and prevents further evaporation. Is that a false idea or does it only apply to some comets?

  • ljk October 5, 2016, 8:54

    Comet may have struck Earth just 10 million years after dinosaur extinction

    By Paul Voosen

    Sep. 28, 2016 , 2:15 PM

    DENVER—Some 56 million years ago, carbon surged into Earth’s atmosphere, raising temperatures by 5°C to 8°C and causing huge wildlife migrations—a scenario that might mirror the world’s future, thanks to global warming. But what triggered this so-called Paleocene-Eocene thermal maximum (PETM) has remained a mystery.

    Now, in new work presented on 27 September here at the annual meeting of the Geological Society of America, a group of scientists bolsters its claim that a small comet impact kicked off the PETM, stirring up the carbon just 10 million years after a similar event decimated the dinosaurs. The group announced the discovery of glassy, dark beads, set in eight sediment cores tied to the PETM’s start—spheres that are often associated with extraterrestrial strikes.

    The critical evidence was hardly the result of a targeted campaign, according to Morgan Schaller, a geochemist at the Rensselaer Polytechnic Institute in Troy, New York, who presented the team’s work. The spheres were hiding in plain sight—in sediments off the coast of New Jersey.

    Full article here:

    http://www.sciencemag.org/news/2016/09/comet-may-have-struck-earth-just-10-million-years-after-dinosaur-extinction

    To quote:

    The story may appear to be all wrapped up, but the group’s interpretation is misguided, says Jerry Dickens, an oceanographer at Rice University in Houston, Texas, who attended the talks. “They have completely misinterpreted the data and missed the correct, and more cool, story.” Dickens does not doubt that the spheres originated in an impact, or that the charcoal stemmed from forest fires. But both the spheres and charcoal were likely present throughout the PETM-associated clays, not just in small layers at the start. As the PETM got going, and erosion rates sped up in the warming world, sediments rich in carbon and oxygen accrued at faster rates at the New Jersey sites. This abundance of oxygen and carbon would have fueled microbes to degrade the charcoal and spheres, eliminating evidence for them higher up in a way that they couldn’t at the core’s base. This vanished evidence, he said, results “in a strange thing where they imagine a boundary horizon where it looks very important, but it’s not.”

    Others at the session were more convinced. “It is a really amazing discovery,” says Birger Schmitz, a geologist at Lund University in Sweden who also attended the talks. “The data look sound.” He says the evidence points to a small impact event of an asteroid or comet, maybe a body a couple kilometers across. However, similar objects hit Earth without triggering a global disturbance, he notes. “I have no idea of how a small asteroid could have triggered all the things that happened during the PETM.” To spark such a large carbon influx, the strike must have hit an unusual carbon-filled place like an oil reservoir, he says.