Astronomers Discover Earth-Sized Exoplanet

Using the HARPS spectrograph attached to the 3.6-m European Southern Observatory telescope at La Silla, Chile, a team of Swiss, French, and Portuguese astronomers have discovered the most Earth-like exoplanet to date.

The planet, known as "e" in the Gliese 581 planetary system, is only about twice the mass of Earth. Planet Gliese 581e orbits its host star in just 3.15 days. Because its mass is equivalent to about 1.9 Earth-masses, it is very likely to be a rocky planet, according to the researchers. However, its proximity to its host star makes it unlikely that the planet is habitable. Thanks to these new observations, the researchers have concluded that another planet in the system, Gliese 581d (discovered in 2007) is in the habitable zone, where liquid water could exist. Gliese 581d is about 7 Earth-masses in size.

The gentle pull of an exoplanet as it orbits its host star introduces a tiny wobble in the star's motion that can be detected on Earth through the use of spectroscopy. HARPS (High Accuracy Radial Velocity for Planetary Searcher) is believed to be the most precise spectrograph in the world, and is one of the most successful instruments for detecting exoplanets.