This image compares the first Earth-size exoplanets found around a Sun-like star to planets in our own solar system, Earth and Venus. NASA's Kepler mission discovered the newfound planets, called Kepler-20e and Kepler-20f. Kepler-20e is slightly smaller than Venus with a radius .87 times that of Earth. Kepler-20f is a bit larger than Earth at 1.03 times the radius of Earth. The paper presenting the discovery was led by Francois Fressin of Harvard University.
One of the greatest scientific questions is whether or not there exist habitable worlds other than our own. This question has been posed for millennia, yet, remarkably, the time is at hand in which we can aspire to answer this age-old question. The study of exoplanets has proceeded at a breakneck pace from the detection 20 years ago of the first planets outside the Solar system to the recent discovery of the first Earth-sized worlds orbiting a Sun-like star. A major milestone was reached in 2012, when the Kepler Mission announced 2,324 exoplanet candidates, most of which are intermediate in size between Earth and Neptune.
The recent progress motivates several profound scientific questions: Can we develop the technology required both to determine the masses and hence densities of these Earth-sized worlds, and to undertake a survey of the nearby stars to find our neighboring exo-Earths? Can we understand the physical structures and atmospheres of these worlds, and by inference their formation history and the likelihood that they possess water oceans? Can we anticipate the chemical signature of life that might be observable remotely?
The Harvard-Smithsonian Center for Astrophysics is leading many exciting developments at the forefront of exoplanet research. In addition to active leadership of many activities of the Kepler Mission, CfA scientists are developing new tools and observatories devoted to discovering and characterizing Earth-like worlds; these facilities include the MEarth Observatory, the newly commissioned HARPS spectrograph, and the GCLEF instrument for the Giant Magellan Telescope. The exoplanet group at the CfA consists of 40 individuals with an emphasis on the mentorship of the next generation of leaders on the rapidly developing field.