Credit: NASA/JPL-Caltech

Asteroids can differ in the degree of porosity, or the amount of empty space that makes up their structures. At one end of the spectrum is a single solid rock and, at the other end, is a pile of rubble held together by gravity. Observations from NASA's Spitzer Space Telescope, taken in infrared light, have helped to reveal that a small asteroid called 2011 MD is made-up of two-thirds empty space, which means it has essentially the same density as water.

Provider: Spitzer Space Telescope

Image Source: http://www.spitzer.caltech.edu/images/5895-sig14-018-Solid-as-a-Rock-Porosity-of-Asteroids

Curator: Spitzer Space Telescope, Pasadena, CA, USA

Image Use Policy: http://www.spitzer.caltech.edu/info/18-Image-Use-Policy