University of Maryland undergraduates have impressed professional astronomers by finding a rare pair of asteroids that orbit and regularly eclipse one another.

The students in an undergraduate astronomy class confirmed that a previously unstudied asteroid, dubbed 3905 Doppler, is in fact two asteroids gravitationally tied to each other, the university reported Tuesday.

Fewer than 100 asteroids of this type have been identified in the main asteroid belt between Mars and Jupiter, said Melissa Hayes-Gehrke, who teaches the hands-on class for non-astronomy majors in which eight students made the find in the fall semester 2013.

Discovered in 1984, 3905 Doppler in subsequent decades attracted little attention until the students observed it for four nights in October.

Puzzling changes in the observed light from the object -- known as its light curve -- were finally determined to be a result of one of the asteroid pair eclipsing the other.

The two asteroids -- the smaller one is about three-quarters the length of the larger one -- are probably roughly potato-shaped and pocked with impact craters made by strikes from other space debris, Hayes-Gehrke said.

Her students picked 3905 Doppler and two other asteroids from an astronomy journal's list of asteroids worth observing because they were well positioned in the autumn sky and were scientific enigmas.

"This is a fantastic discovery," UM astronomy Professor Drake Deming, who was not involved with the class, said. "A binary asteroid with such an unusual light curve is pretty rare. It provides an unprecedented opportunity to learn about the physical properties and orbital evolution of these objects."