More than three-quarters of the planet candidates discovered by NASA’s Kepler spacecraft have sizes ranging from that of Earth to that of Neptune, which is nearly four times as big as Earth. Such planets dominate the galactic census but are not represented in our own solar system. Astronomers don’t know how they form or if they are made of rock, water or gas.
The Kepler team on January 6 reported on four years of ground-based follow-up observations targeting Kepler’s exoplanet systems at the American Astronomical Society meeting in Washington. These observations confirm the numerous Kepler discoveries are indeed planets and yield mass measurements of these enigmatic worlds that vary between Earth and Neptune in size.
Using one of the world’s largest ground-based telescopes at the W.M. Keck Observatory in Hawaii, scientists confirmed 41 of the exoplanets discovered by Kepler (shown above in an artist’s conception) and determined the masses of 16. With the mass and diameter in hand, scientists could immediately determine the density of the planets, characterizing them as rocky or gaseous, or mixtures of the two.
Ji-Wei Xie of the University of Toronto validated 15 pairs of Kepler planets ranging from Earth-sized to a little larger than Neptune. Xie measured masses of the 30 planets, thereby adding to the compendium of planetary characteristics for this new class of planets.
“We now face daunting questions about how these enigmas formed and why our solar system is devoid of the most populous residents in the galaxy,” said Geoff Marcy, a professor of astronomy at the University of California, Berkeley.