From its perch up in space, Spitzer can use its heat-sensitive infrared vision to spy asteroids and get better estimates of their sizes.

This is what the author of a study that appeared in Astrophysical Journal Letters on June 19 said in a NASA press release about the space telescope. The Spitzer was used by a group of astronomers that authored the paper to study the dimensions and other physical properties of an asteroid named 2011 MD. They’ve found it to be suitable for NASA’s purpose, i.e. to bring a near-Earth object (NEO) into an orbit around the moon and study it – all by the 2020s. This elevation to suitability also makes 2011 MD the third such candidate NASA will consider as it ramps up the mission, dubbed the Asteroid Redirect Mission (ARM).

This image of asteroid 2011 MD was taken by NASA's Spitzer Space Telescope in Feb. 2014, over a period of 20 hours. The long observation, taken in infrared light, was needed to pick up the faint signature of the small asteroid (center of frame). The Spitzer observations helped narrow down the size of the space rock to roughly 20 feet (6 meters), making it one of a few candidates for NASA's proposed Asteroid Redirect Mission for which sizes are approximately known.
This image of asteroid 2011 MD was taken by NASA’s Spitzer Space Telescope in Feb. 2014, over a period of 20 hours. The long observation, taken in infrared light, was needed to pick up the faint signature of the small asteroid (center of frame). The Spitzer observations helped narrow down the size of the space rock to roughly 20 feet (6 meters), making it one of a few candidates for NASA’s proposed Asteroid Redirect Mission for which sizes are approximately known. Image: NASA/JPL-Caltech/Northern Arizona University/SAO

Why was Spitzer used? From the release:

Prior to the Spitzer study, the size of 2011 MD was only very roughly known. It had been observed in visible light, but an asteroid’s size cannot be determined solely from visible-light measurements. In visible light alone, for example, a white snowball in space could look just as bright as a dark mountain of cosmic rock. The objects may differ in size but reflect the same amount of sunlight, appearing equally bright.

The advantage that infrared light presents, on the other hand, is that it reveals the body’s temperature, mass and density. Subsequently, the study’s authors were able to conclude that 2011 MD is lighter than asteroids usually are, and is possible two-thirds hollow. This, they think, could be because it is actually a collection of rocks or is one rock surrounded by debris. One more thing about this new candidate for ARM is its odd, oblong shape.

The team says the small asteroids probably formed as a result of collisions between larger asteroids, but they do not understand how their unusual structures could have come about. They plan to use Spitzer in the future to study more of the tiny asteroids, both as possible targets for asteroid space missions, and for a better understanding of the many asteroid denizens making up our solar system.

Knowing the size of the NEO to bring closer is important because it will help NASA plan the “how” of the mission. In another press release yesterday, the space agency said it was awarding $4.9 million to 18 proposals each of which described a method to execute the ARM, over a period of six months. NASA started accepting these proposals in March this year and reportedly received 108. Two names quickly jump out from among the proposals:

  • Deep Space Industries, which announced in January 2013 that it plans to scout for a near-Earth object, mine a small sample from it, and return that to Earth by 2016. The press release states that, through the ARM, DSI wants to “examine public-private partnership approaches”.
  • Planetary Society, which wants to put bacteria on the asteroid retrieval vehicle to “transport extremophiles through deep space and return them to Earth to test panspermia and astrobiology.”

The 2011 MD press release is available here, and the one about the proposals, here.