The Exoplanet That Should Have Been A Gas Giant

By Jana Louise Smit on Wednesday, October 7, 2015
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“Space can be mapped and crossed and occupied without definable limit; but it can never be conquered.” —Arthur C. Clarke, “We’ll Never Conquer Space”

In A Nutshell

A recently discovered planet fooled astronomers into believing that it was a gas giant. But when the final numbers were all added up, Kepler-10c proved to be the first planet of its kind: a solid rocky world soundly challenging everything astronomers knew about planet formation. Planets this size were previously thought to be incapable of being anything other than a gas giant. Not only should Kepler-10c not exist (according to science), but it’s rewriting space history. It was thought that the early universe wasn’t capable of forming rocky worlds due to the scarcity of heavy elements, but this uber-prehistoric planet proves it was very possible.

The Whole Bushel

Thought to be a gas giant, astronomers expected Kepler-10c to be a lightweight similar to Saturn. But unlike the ringed planet, which is so light it would float in water, Kepler-10c clocked in with a mass heavier than Earth. Seventeen times heavier, in fact. That’s when its strangeness began to challenge many accepted theories about planets and the early universe.

The planet was first discovered by NASA’s Kepler spacecraft in a system 560 light-years from Earth in the Draco constellation. Because of its 45-day-long year, the goliath world orbits its sun too closely to support any life that would be familiar to Earthlings. The only other body keeping the oddity company in its system is a world that is equally hot, a lava world known as Kepler-10b.

While Kepler-10c’s size (bigger than two Earths) was known for some time, every assumption about this globe and the history of the universe was turned on its head when scientists realized that it was more of a floating boulder than an airy gas ball. The formation of such a planet wasn’t even considered possible since it was previously believed that the super-gravitation exerted by such a colossus would absorb hydrogen and helium until it inevitably bloated it into a gas giant. Yet, there it was. An impossible rocky world sitting in plain view, delighting the astronomers and sending planet formation theorists back to their drawing boards.

The appearance of this “mega-Earth” has ramifications related to its rockiness stretching back into the earliest times of the universe. The system in which Kepler-10c orbits dates at around 11 billion years old, an age researchers say means that it took shape around three billion years after the big bang. During those times, the universe consisted more of gases such as helium and hydrogen than heavy elements like silicon and iron, the very things a solid world would need in order to be born. Their scarcity was due to the time it took for the first stars after the big bang to die off and explode, sending their rare silicon and iron bits back into space to be collected by forming bodies and newer stars. This violent cycle would then be repeated over and over, requiring billions of years and the growing availability of heavy elements to make the birth of rocky worlds even possible.

This points to the possibility that the necessary elements were far more abundant during an age when they were thought to be too rare to form anything remotely like Kepler-10c. Because of this new discovery, astronomers can now include older star systems when they search for new Earth-like planets. Previously overlooked, their inclusion in man’s never-ending space-combing will increase the possibility of finding life elsewhere in the universe.

Show Me The Proof

Featured photo credit: NASA
NASA: Astronomers Confounded By Massive Rocky World
Harvard-Smithsonian Center for Astrophysics: Astronomers Find a New Type of Planet: The “Mega-Earth”