An artist's conception shows Voyager 1 encountering a stagnation region. To the left is interstellar space. NASA/JPL-Caltech hide caption

itoggle caption NASA/JPL-Caltech

Artist's concept of NASA's Voyager spacecraft. For 35 years, the probes have been beaming images and information back to Earth via a 23-watt transmitter. NASA/JPL-Caltech hide caption

itoggle caption NASA/JPL-Caltech

This artist's conception illustrates Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star. It is the first planet that NASA's Kepler mission has confirmed to orbit in a star's habitable zone — the region around a star where liquid water, a requirement for life on Earth, could persist. NASA/Ames/JPL-Caltech hide caption

itoggle caption NASA/Ames/JPL-Caltech

The compact car-sized Mars Science Laboratory is due to land on the red planet on Aug. 6, 2012. It is equipped with a suite of instruments to study rocks and soils, and take other measurements. NASA/JPL-Caltech hide caption

itoggle caption NASA/JPL-Caltech