An electronic signal travels from NASA's Jet Propulsion Lab in Pasadena, California, to a robotic rover clinging to the underside of foot-thick ice on an Alaskan lake. The rover's spotlight begins to glow. "It worked!" exclaims John Leichty, a young JPL engineer huddled in a tent on the lake ice nearby. It may not sound like a technological tour de force, but this could be the first small step toward the exploration of a distant moon...
Photo: Scientists at NASA's Jet Propulsion Laboratory (JPL) inspect a probe like one that might someday travel beneath the ice of Jupiter's moon Europa.
Of the 1,780 confirmed planets beyond our solar system, as many as 16 are located in their star’s habitable zone, where conditions are neither too hot nor too cold to support life. Size also matters: A planet that’s too small can’t maintain an atmosphere; one that’s too large will have a crushing atmosphere. A recently detected planet 493 light-years from Earth, Kepler-186f, is close to Earth's size and is located in its solar system's habitable zone.
Image: This artist's depiction shows Kepler-186f, an Earth-size world in the "habitable zone" of a red dwarf star.
ILLUSTRATION BY NASA/JPL-Caltech/T. PYLE