September 11, 2013
Near-Earth Object, Long Believed To Be An Asteroid, Is Actually A Comet
redOrbit Staff & Wire Reports - Your Universe Online
When is a near-Earth asteroid not a near-Earth asteroid? When an international team of researchers discover that the object has been misidentified by the scientific community for the past three decades, and is actually a comet.The bombshell discovery was the result of an ongoing project headed up by experts from Northern Arizona University (NAU), and was presented this week at the European Planetary Science Congress 2013 in London. Using the Spitzer Space Telescope, they discovered evidence of cometary activity in 3552 Don Quixote - the third largest near-Earth object - which had evaded astronomers for some 30 years.
“Don Quixote has always been recognized as an oddball,” explained Joshua Emery, a member of the research team and an assistant professor of earth and planetary sciences at the University of Tennessee, Knoxville. “Its orbit brings it close to Earth, but also takes it way out past Jupiter. Such a vast orbit is similar to a comet's, not an asteroid's, which tend to be more circular—so people thought it was one that had shed all its ice deposits.”
Michael Mommert, a post-doctoral researcher at NAU and a Ph.D. student at the German Aerospace Center (DLR) in Berlin at the time the work was carried out, said that Don Quixote’s orbit resembled that of a comet, leading experts to assume that it was a comet that had shed the carbon dioxide and water that comprise its tail.
However, after reexamining images of Don Quixote from August 2009 – when it was in the part of the orbit closest to the sun – the researchers discovered that the object possesses a coma and a faint tail. They also re-examined images from five-years earlier, when the comet was farthest away from the sun, and found that the surface was composed of silicate dust (which is similar in nature to comet dust).
“The power of the Spitzer telescope allowed us to spot the coma and tail, which was not possible using optical telescopes on the ground,” said Emery. “We now think this body contains a lot of ice, including carbon dioxide and/or carbon monoxide ice, rather than just being rocky.”
According to Mommert, the discovery suggests that CO2 and water ice could also be present on other near-Earth objects. The research also confirmed the size of Don Quixote, as well as the low, comet-like reflectivity of its surface. Furthermore, the study could have implications for the origins of water here on Earth, as comets could be the original source of some of it and the amount on this object represents approximately 100 billion tons of water.