An artist's conception of the tiny new planet Kepler-37b, which is slightly larger than Earth's moon and orbits its host star every 13 days. It likely has a surface temperature of in excess of 400C (700F). Astronomers don't think the tiny planet has an atmosphere or could support life as we know it, but the moon-size world is almost certainly rocky in composition. (Photo by Reuters/NASA/Ames/JPL-Caltech)
