The Mars Express spacecraft captured this view of the Martian moon Phobos during a January 2011 flyby. Phobos is the larger of Mars' two moons, measuring 26.6 kilometers (16.5 miles) at its widest point and possessing a heavily cratered surface. Observations of the moon’s position over the past century suggest that tidal forces from Mars are slowly pulling Phobos towards it. If so, the moon may collide with Mars in the very distant future. This image is an anaglyph. Viewing of 3-D anaglyphs requires red-blue 3-D glasses.