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In-Between Planets

March 4, 2014

Over the past five years, the Kepler space telescope has discovered thousands of possible planets in other star systems. Some are small, like Earth. Others are big and fluffy, like Jupiter, the giant of our solar system. For veteran planet hunter Geoff Marcy, though, the big surprise is what’s in between.

MARCY: Perhaps the most remarkable discovery by Kepler are these planets between the size of Earth and four times the size of Earth. This is a size range that dominates the planet inventory from Kepler.... These are planets we never expected based on our own solar system. [:19]

Kepler discovered the planets as they passed in front of their parent stars. These “transits” revealed how big the planets are. Astronomers then used ground-based telescopes to measure the gravitational pull of some of these planets, which revealed how massive they are. The combination revealed how dense the planets are, which provided a rough idea of what they’re made of.

MARCY: Those smaller than twice the size of the Earth have mostly a rocky core, maybe small amounts of water and gas. But those that are two to four times the size of the Earth are clearly that large because of their low densities, indicating that they have gas on top of a rocky core. [:20]

The rocky planets are known as super-Earths, while the gas planets have been dubbed “mini-Neptunes” for their resemblance to another solar system planet. So far, though, scientists don’t really know how these worlds formed or why they’re so common — two new mysteries from a planet-hunting space telescope.

More about Kepler tomorrow.


Script by Damond Benningfield, Copyright 2014

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