Near-Earth Asteroid Isn't an Asteroid at All -- It's a Comet

An asteroid scientists have had their eye on for some 30 years isn't an asteroid at all, according to new observations by a team from Northern Arizona University. Based on the study, presented at the European Planetary Space Conference in London this week, the space rock is actually a comet.

According to Michael Mommert, a post-doctoral researcher at NAU who was studying as a PhD student at the German Aerospace Center at the time of the study, the assumption was that the object, known as 3552 Don Quixote, represented a dead comet, or one that had shed the carbon dioxide and water that produce tails.

"Its orbit resembled that of a comet, so people assumed it was a comet that had gotten rid of all its ice deposits," he explained in a statement.

Using NASA's Spitzer Space Telescope, however, the researchers prove this is not the case for the third-largest near-Earth asteroid.

According to David Trilling, NAU associate professor, 3552 Don Quixote is "sopping wet" with an estimated 100 billion tons of water.

The discovery was made after Mommert and Trilling, using Spitzer, found that the object was far brighter than they expected.

However, Trilling explains, "The images were not as clean as we would like, so we set them aside."

Later, Mommert and colleagues at the Harvard-Smithsonian Center for Astrophysics took a closer look, comparing infrared images of the object, which revealed a visible atmosphere, also known as a coma, and a faint tail.

The findings were later corroborated by measurements of the comet's size and low reflectivity.

The discovery's implications have little to do with any potential impact with Earth -- the odds of which are extremely low. Rather, Mommert explains, the study opens the door to the possibility that other near-Earth objects could also contain carbon dioxide and water ice.