Artist's rendering of NASA's Wind probe, which launched in 1994 to investigate the solar wind.
An artist's concept of NASA's Advanced Composition Explorer spacecraft (ACE), which launched in 1997 to study space weather.
An artist's impression of the SOHO spacecraft (short for Solar and Heliospheric Observatory).
Artist's concept of the STEREO spacecraft observing a coronal mass ejection. When there's no CME to be found, STEREO still gathers images of the background stars.
An artist's conception shows NASA's MESSENGER spacecraft in orbit around Mercury.
An artist's interpretation of the European Space Agency's Venus Express spacecraft orbiting the second planet in our solar system.
Japan's Venus Climate Orbiter "Akatsuki" was designed to study both the atmosphere and surface of Venus.
An artist's concept of NASA's twin ARTEMIS spacecraft, which moved from Earth orbit to lunar orbit in 2011.
Artist’s rendition of NASA’s Lunar Reconnaissance Orbiter over the lunar surface.
Artist's view of NASA's Spitzer Space Telescope against the infrared sky.
Artist impression of the infrared Herschel spacecraft, which is helping scientists better understand the universe's early days.
Artist's impression of the European Space Agency's Planck spacecraft. Planck's main goal is to study the Cosmic Microwave Background — the relic radiation left over from the Big Bang.
This graphic from the China Lunar Exploration Program shows the progress of China's Chang'e 2 moon probe from its lunar orbit out to the L2 Lagrange point 1.5 million km from Earth.
NASA's Deep Impact probe gave scientists their first close-up look at the interior of a comet when it hit. Here, an artist illustrates the 2005 encounter.
An artist's conception of the European Space Agency's Mars Express craft.
NASA's Mars Odyssey spacecraft passes above Mars' south pole in this artist's concept illustration. The spacecraft has been orbiting Mars since October 24, 2001. The spacecraft serves as a vital relay for NASA's Mars rover Curiosity. [Related: Mars Rover Curiosity Landing Coverage]
NASA's Mars Reconnaissance Orbiter passes over the Red Planet's south polar region in this artist's concept illustration.
During its 84th and 85th days (sols) on Mars in late 2012, NASA's huge Mars rover Curiosity snapped this newest mosaic self-portrait.
NASA's Opportunity Mars rover used its front hazard-avoidance camera to take this picture showing the rover's arm extended toward a light-toned rock named Tisdale 2 on Aug. 23, 2011.
NASA's Dawn spacecraft arrived at the giant asteroid Vesta in July 2011 and departed in September 2012 for the dwarf planet Ceres.
An artist's illustration of Rosetta's Philae lander on the surface of Comet 67P/Churyumov-Gerasimenko. Rosetta is due to arrive at the comet in mid-2014.
The Juno spacecraft passes in front of Jupiter in this artist's depiction. Juno is slated to arrive at the solar system's largest planet in 2016.
This artist's concept shows a flyby of Saturn's moon Enceladus by NASA's Cassini spacecraft.
This artist’s concept shows NASA's New Horizons spacecraft during its 2015 encounter with Pluto and its largest moon, Charon.
Artist's concept of Voyager 1 and Voyager 2 at the edge of the solar system.