There’s never been a better time to be a planetary scientist:
For almost all of [the field’s] history, it could study only the eight planets that make up the local solar system. But the boom in exoplanet research over the past decade or so has furnished the field with a wealth of data from elsewhere in the galaxy. Much of this has come from a specially designed space telescope called Kepler, some of the discoveries of which are illustrated in the artist’s impression above, along with objects from the local solar system, for comparison. Kepler’s discoveries, and others, have done plenty of exciting violence to old theories of what planets are and how they form. Several papers discussing what is happening were presented at the meeting of the American Astronomical Society which took place this week in Washington, DC.
Astronomers are particularly interested in planets intermediate in size between rocky Earth and gassy Neptune, which along with Uranus is one of the solar system’s two “ice giants,” and which has a radius 3.8 times that of Earth and is around 17 times as massive. Planets of this intermediate size are common, but because the local solar system does not host one, they are also mysterious. Are they scaled-up Earths, scaled-down Neptunes or a mixture of the two? And, if they are a mixture, where is the boundary between the rocky ones, known as super-Earths, and the gaseous ones, known as mini-Neptunes?
(The Kepler telescope has identified 238 planets and 3,538 “planet candidates” in this section of the Milky Way. Photo: Carter Roberts.)