Rare Eclipsing Binary Asteroid Discovered by Astronomy Students

Students in a University of Maryland undergraduate astronomy class have made a startling discovery. A previously unstudied asteroid isn't just one object, but is instead made up of a pair of asteroids that orbit and regularly eclipse each other. The rare discovery may help researchers investigate these sorts of asteroids in the future.

So far, fewer than 100 eclipsing binary asteroids have been identified in the main asteroid belt between Mars and Jupiter. This latest discovery, known as 3905 Doppler, is therefore unusual. It was first detected in 1984, but over the next few decades, it attracted scant attention. Then in September 2013, the students chose to study it due to its position in the autumn sky.

"This is a fantastic discovery," said Drake Deming, a professor involved with the class, in a news release. "A binary asteroid with such an unusual lightcurve is pretty rare. It provides an unprecedented opportunity to learn about the physical properties and orbital evolution of these objects."

A lightcurve is a graph of a celestial object's brightness over time. Variations in brightness are often due to the object's shape, with spherical objects like planets yielding lightcurves that do not vary, and asymmetrical objects like asteroids producing peaks and valleys as the amount of reflected light varies. By measuring the time between maximum light intensities, the students could tell how fast an asteroid was rotating.

By examining the images that they took, the students eventually found that the two asteroids are probably potato-shaped and pocked with impact craters made by strikes from other space debris. The smaller one is about three-quarters the length of the larger one, and they orbit each other end to end. Each orbit takes 51 hours, which an unusually long time.

Currently, scientist plan to further look at this pair of asteroids in order to learn more about it. More specifically, they hope to find out a bit more about the rotational speed and why it's so slow.

The findings were presented at the 223^rd meeting of the American Astronomical Society in National Harbor, Maryland on January 7^th.