by Michael Mommert
Post-doctoral Researcher
Department of Physics and Astronomy

We could study an asteroid up close by sending astronauts to one somewhere out in space—or we could simply bring one to the astronauts.

That’s basically the idea behind NASA’s announced Asteroid Robotic Retrieval Mission, which aims to catch a near-Earth asteroid and redirect it in an orbit around the moon. There, the asteroid could be visited and scrutinized by astronauts.

Surprisingly, the biggest problem with this idea is not its technical feasibility but finding a suitable target asteroid. The perfect candidate should have an orbit that closely resembles that of the Earth in order to minimize the amount of fuel needed to change its orbit. For the same reason, it cannot be too big and heavy.

The perfect size for this mission is from 20 to 30 feet in diameter. Despite the fact that presumably millions of asteroids of this size exist, only a few of them are on Earth-like orbits and even fewer have been found.

One promising candidate asteroid, named 2009 BD, was observed in October last year by an international team led by myself and NAU associate professor David Trilling using the Spitzer Space Telescope. Although we did not detect the asteroid, a combination of models allowed us to determine its size and other physical properties.

Unfortunately for NASA, we found that 2009 BD has a diameter of approximately 12 feet—too small for the planned mission.

Scientifically, however, 2009 BD provides unique information on the properties of such small asteroids. Our observations point toward two possible scenarios for the nature of 2009 BD: The object is either made from pure rock that is covered by a thin layer of snow-white dust, or it is a collection of bare rock slabs that are somehow held together.

Either scenario is significantly different from what has been observed in larger asteroids.

So the search for a candidate target asteroid for the Retrieval Mission goes on. The next candidate on the list, 2011 MD, will be observed by our team using Spitzer in a few weeks. Let’s hope for NASA that this object better fits its needs. From a scientist’s point of view, we are looking forward to see what surprises 2011 MD can offer us.