SIM PlanetQuest (formerly called the Space Interferometry Mission), currently under development, will determine the positions and distances of stars several hundred times more accurately than any previous program. This accuracy will allow SIM to determine the distances to stars throughout the Galaxy and to probe nearby stars for Earth-sized planets.
This breakthrough in capabilities is possible because SIM will use optical interferometry. Pioneered by Albert Michelson, who won the Nobel Prize in Physics in 1907, optical interferometry can fulfill its full potential only outside the distorting effects of Earth's atmosphere. There, it can combine light from two or more telescopes as if they were pieces of a single, gigantic telescope mirror. Developed for use in space with SIM, this technique will eventually lead to the development of telescopes powerful enough to take images of Earth-like planets orbiting distant stars and to determine whether these planets sustain life as we know it.
SIM will combine the light from two sets of four 30-centimeter (1-foot) diameter telescopes arrayed across a 10-meter (33-foot) boom to achieve a resolution approaching that of a 10-meter diameter mirror. This will allow it to perform extremely sensitive astrometry so that it will be able to detect very small wobbles in the movement of a star due to unseen companions. Objects of Earth mass could be inferred around a star up to 30 light-years (9 parsecs) away. Through a process known as synthesis imaging, SIM will also be generate images of objects such as dust disks around stars and look for gaps or clearings in the debris that might indicate the presence of unseen worlds. SIM will conduct its 7-year mission from a heliocentric, Earth-trailing orbit.
SIM is being developed by the Jet Propulsion Laboratory under contract with NASA and in close collaboration with industry partner Northrop Grumman in Redondo Beach, California. As of May 1, 2007, the project was in its preliminary design phase. Launch of SIM has been deferred indefinitely by NASA headquarters.