This image of asteroid 2011 MD was taken by NASA's Spitzer Space Telescope in February 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 was taken by Spitzer's Infrared Array Camera at a wavelength of 4.5 microns.
Image credit: NASA/JPL-Caltech/Northern Arizona University/SAO
Note: For more information, see Spitzer Spies an Odd, Tiny Asteroid. For more information on NASA's Asteroid Redirect Mission, see NASA Update on Asteroid Redirect Mission and NASA Announces Latest Progress in Hunt for Asteroids.