Future Missions
Kepler's findings will support two planned missions -- the Space Interferometry Mission (SIM) and the Terrestrial Planet Finder (TPF) -- by determining which types of nearby stars are likely to possess planets. This information will tell SIM and TPF where to point their instruments.
Both missions will use a technique called nulling interferometry to cancel out glare from a target star and reveal orbiting planets. Two telescopes look at the same star, but the light from one telescope is put a half step out of phase with light from the other before they are combined, causing them to cancel each other out. Conversely, the light from the planet is combined in a way that strengthens its signal.
TPF combines its interferometric observations with data from a coronagraph, which cancels glare by blocking the star's direct light with a physical object so that only the corona of the star is visible, like a pilot blocking the sun with his or her thumb. With the bulk of the glare reduced, orbiting planets become more visible.
Planet Hunting Milestones: From Handfuls to Hundreds
Before Kepler came along, the stable of distant planets located by astronomers numbered in the tens and hundreds, not thousands. Nevertheless, this was an extraordinary number considering the limitations faced by scientists using available instruments -- particularly ground-based telescopes, which require researchers to compensate for atmospheric distortions.
For example, in 2009, astronomers reported the first exoplanet ever found through astrometry, adding it to the list of 350 planets previously found by the Doppler shift method. Had it been confirmed, VB 10b would have tipped the scales at six times more massive than Jupiter. However, subsequent Doppler spectroscopy observations failed to detect the expected radial velocity shifts in its parent star, VB 10, and the claim was refuted [source: Bean].
That same year, using six months of observations from ground-based amateur-style telescopes, scientists announced GJ 1214b, a planet 6.5 times more massive than Earth and 2.7 times wider. Researchers believe that the planet might be made mostly of water. GJ 1214b orbits a red dwarf star more than 40 light-years from Earth at a distance equivalent to one-fortieth the space between Mercury and our sun.
In 2008, astronomers, using the Hubble Space Telescope's Near Infrared Camera and Multi-Object Spectrometer, detected carbon dioxide on an exoplanet for the first time. The method involved subtracting the parent star's spectroscopic data from the combined data of star and planet. Unfortunately, the Jupiter-sized exoplanet HD 189733 b orbits too close to its star to be habitable, but the technique could provide valuable information if applied to other habitable candidates. Scientists are interested in carbon dioxide because it, like methane, can point to biological processes.
From 2005 to 2008, researchers discovered five super-Earths, each boasting masses between five and ten times that of the Earth.
Fifteen years earlier, in the early 1990s, astronomers identified the first three exoplanets ever found: three planets circling a pulsar (a rapidly spinning neutron star) called PSR B1257+12. By 1995, they had located a massive planet orbiting the star 51 Pegasi. Dubbed 51 Pegasi b, it was the first planet found revolving around a sun-like star.
Although scientists had theorized the existence of exoplanets for many years, it was only in the early 1990s that they finally discovered their first one. From that day forward, the hunt has only grown in intensity and rate of discovery. Who knows what exciting discoveries future decades will bring?
