How Planet Hunting Works

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.

Between 2005 and 2008, researchers discovered five super-Earths, each boasting masses between five and 10 times that of the Earth.

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.

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.

What discoveries were made in 2010 and 2011?