Rare, Eclipsing Binary Asteroids Discovered by Undergraduate Astronomy Class

A team of undergraduate students taking an astronomy lab course unwittingly made a valuable scientific observation when they chose to study the asteroid 3905 Doppler, discovering that the space rock is actually space rocks - a pair of rare, eclipsing binary asteroids.

The binary asteroid pair is among hundreds of thousands of pieces of cosmic debris in our solar system's main asteroid belt between Mars and Jupiter. But 3905 Doppler is remarkable because the asteroids are in a regularly eclipsing orbit. Fewer than 100 of this type of asteroid have been discovered in the asteroid belt.

"This is a fantastic discovery," said Drake Deming, a University of Maryland astronomy professor who was not involved with the astronomy class that made the discovery. "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. When the astronomy lab was in session across four nights in September 2013, their objective was to measure changes in intensity in an asteroid's reflected light and then graph a lightcurve.

Melissa Hayes-Gehrke, who teaches the hands-on class for non-astronomy majors at University of Maryland, said that it was not readily apparent that the student's asteroid observations were significant.

"When we looked at the images we didn't realize we had anything special, because the brightness difference is not something you can see with your eyes," Hayes-Gehrke said. But when the two teams of four students assigned to 3905 Doppler used a piece of software to chart the asteroid's lightcurve, they observed the object's light occasionally fading to nothing, essentially just going dark.

"It was incredibly frustrating," said Alec Bartek, a senior physics major from Brookeville, MD. "For some reason our light curve didn't look right."

It turned out the dark spots on the lightcurve were occurring when one of the asteroids in the pair passed in front of the telescope's view of the companion asteroid, an asteroid eclipse that would explain the sharp dip in the lightcurve.

The team was able to compare their data with concurrent observations of 3905 Doppler made by amateur Italian astronomer Lorenzo Franco, which enabled them to confirm that the system was indeed an eclipsing binary, with an unusually long orbit time of 51 hours.

Sophomore economics major Brady Bent of Arbutus, MD, said he didn't' realize how special his team's discovery was at first. "I thought it just meant we would have to do more work," he said. "As we continued to analyze our data, other professors in the astronomy department came over to view our work. At this point I understood just how rare our find was."

The students' discovery that 3905 Doppler is an eclipsing binary asteroid will be presented in a poster session Tuesday (Jan. 7) at the 223rd meeting of the American Astronomical Society in National Harbor, MD., and published in April in the Minor Planet Bulletin.