JPL: Comet Found Hiding in Plain Sight

[bystander]

Comet Found Hiding in Plain Sight
NASA | JPL-Caltech | Spitzer Space Telescope | 2013 Sep 10

[url=http://www.spitzer.caltech.edu/images/5659-sig13-010][b][i]Spitzer Spies a Comet Coma and Tail[/i][/b][/url] - [b][i]Credit: NASA/JPL-Caltech/DLR/NAU[/i][/b]

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Click to view full size image 1 or image 2

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For 30 years, a large near-Earth asteroid wandered its lone, intrepid path, passing before the scrutinizing eyes of scientists armed with telescopes while keeping something to itself. The object, known as Don Quixote, whose journey stretches to the orbit of Jupiter, now appears to be a comet.

The discovery resulted from an ongoing project coordinated by researchers at Northern Arizona University, Flagstaff, Ariz., using NASA's Spitzer Space Telescope. Through a lot of focused attention and a little luck, they found evidence of comet activity, which had evaded detection for three decades.

The results show that Don Quixote is not, in fact, a dead comet, as previously believed, but it has a faint coma and tail. In fact, this object, the third-biggest near-Earth asteroid known, skirts Earth with an erratic, extended orbit and is "sopping wet," said David Trilling of Northern Arizona University, with large deposits of carbon dioxide and presumably water ice. Don Quixote is about 11 miles (18 kilometers) long.

"This discovery of carbon dioxide emission from Don Quixote required the sensitivity and infrared wavelengths of the Spitzer telescope and would not have been possible using telescopes on the ground," said Michael Mommert, who conducted the research at the German Aerospace Center, Berlin, before moving to Northern Arizona University. This discovery implies that carbon dioxide and water ice might be present on other near-Earth asteroids, as well.

The implications have less to do with a potential impact, which is extremely unlikely in this case, and more with "the origins of water on Earth," Trilling said. Impacts with comets like Don Quixote over geological time may be the source of at least some of it, and the amount on Don Quixote represents about 100 billion tons of water -- roughly the same amount that can be found in Lake Tahoe, Calif.

NAU-led team discovers comet hiding in plain sight
Northern Arizona University | 2013 Sep 10

Near-Earth Asteroid Is Really a Comet
University of Tennessee, Knoxville | 2013 Sep 10

“Oddball” Asteroid is Really a Comet
Universe Today | Jason Major | 2013 Sep 10

[bystander]

Don Quixote: An Asteroid that is a Living Comet
Smithsonian Astrophysical Observatory
Weekly Science Update | 2013 Oct 11

[i]An infrared image of the Near-Earth Object and comet, Don Quixote, showing its newly discovered tail. The very bright core of the comet has been masked out (although leaving a bright stripe, as is normal in these cases) to reveal the tail in the upper part of the image. Background stars can also been seen, along with a fiducial dimension marker indicating about 50,000 kilometers at the distance of the comet. [b](Credit: NASA-Spitzer and CfA)[/b][/i]

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Near Earth Objects (NEOs) are asteroids or comets whose orbits sometimes bring them close to the earth's orbit. An NEO could therefore someday collide with the Earth -- giving them considerably more parochial interest than most objects in astronomy. The 1908 Tunguska event, for example, that flattened over 2000 square kilometers in Russia was by some basic estimates caused by an asteroid only 60 meters in diameter. The asteroid that struck Siberia last spring (the Chelyabinsk meteor) was only about 40 meters in diameter. While it is relatively easy to detect an NEO in visible light by watching its movement across the sky from night to night, determining its size is more difficult. This is because the optical brightness of an NEO is the result of two factors, its size and its reflectivity. CfA astronomers have for several years been using the IRAC infrared camera on Spitzer to measure the infrared light emitted from NEOs, and modeling the flux to determine the reflectivity and thus the sizes of NEOs.

NEOs are thought to originate from collisional fragments of objects in the asteroid belt beyond the orbit of Mars, and over 10,000 NEOs are known today. Short-period comets can also be NEOs, Unlike the asteroids, these comets most likely originated in the Kuiper belt, a reservoir of icy bodies outside the orbit of Neptune. Their orbits are disturbed as a result of gravitational perturbations with the giant planets, and some end up as NEOs. As they get closer to the Sun these comets become active and produce comae and tails, as expected for comets, but the activity is significantly briefer than their orbital lifetimes near the Earth which are estimated to last tens of millions of years. As a result, it is very likely that the NEO population being studied includes a significant number of extinct comets. So far 160 of them have been identified.

The NEO asteroid Don Quixote was discovered in 1983, and infrared and optical measurements indicate that it is big: about 18.7 kilometers in size, making it the third largest known NEO. Its reflectivity, and its particular orbit, suggested to astronomers that it was actually an extinct comet. CfA astronomers Joe Hora and Howard Smith, together with a team of colleagues, used Spitzer to study it. Although it is so large and bright that it had already been measured in the infrared, the scientists wondered if the more sensitive Spitzer measurements could discern something about its putative cometary nature. After careful processing of the comet's image, which was so bright in the infrared that it virtually blinded the camera, the team discovered a tail to this comet extending about 100,000 kilometers. From the infrared color of the tail, the team also concluded that the infrared light is largely produced by carbon dioxide gas being emitted from the comet's surface at a rate of about 7000 liters per second. The result, besides highlighting the advantages of more sensitive observations of known bright asteroids, suggests that carbon dioxide ice can remain frozen in near-Earth space over a very long time.

The Discovery of Cometary Activity in Near-Earth Asteroid (3552) Don Quixote - Michael Mommert et al, ApJ 2013 (in press)

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[neufer]

[size=200]Don Quixote is '[i]sopping wet[/i]'[/size]

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Comet Found Hiding in Plain Sight
NASA | JPL-Caltech | Spitzer Space Telescope | 2013 Sep 10

Don Quixote is not, in fact, a dead comet, as previously believed, but it has a faint coma and tail. In fact, this object, the third-biggest near-Earth asteroid known, skirts Earth with an erratic, extended orbit and is "sopping wet," said David Trilling of Northern Arizona University, with large deposits of carbon dioxide and presumably water ice. Don Quixote is about 18 kilometers long.

"This discovery of carbon dioxide emission from Don Quixote required the sensitivity and infrared wavelengths of the Spitzer telescope and would not have been possible using telescopes on the ground," said Michael Mommert. This discovery implies that carbon dioxide and water ice might be present on other near-Earth asteroids, as well.

The implications have less to do with a potential impact, which is extremely unlikely in this case, and more with "the origins of water on Earth," Trilling said. Impacts with comets like Don Quixote over geological time may be the source of at least some of it, and the amount on Don Quixote represents about 100 billion tons of water -- roughly the same amount that can be found in Lake Tahoe, Calif.

[Beyond]

Don "Sponge Bob" Quixote