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Kepler helps astronomers discover a new class of planet: the “Mega-Earth”

Kepler 10-c is a newly discovered exoplanet 17 times more massive than the Earth. Image Credit: David Aguilar/CfA

With the help of the Kepler Space Telescope, astronomers have discovered a new type of planet. A team from the Harvard-Smithsonian Center for Astrophysics (CfA) announced the find during a press conference at a meeting of the American Astronomical Society (AAS). This new variety of extrasolar planet (exoplanet) was originally thought to be impossible. The rocky world, which has been dubbed Kepler 10-c, has a mass 17 times that of Earth, classifying it as a “mega-Earth”.

Kepler space telescope shortly after the assembly tho the third stage of its Delta II 7925. Photo Credit: Troy Cryder/NASA

Kepler space telescope shortly after the assembly tho the third stage of its Delta II 7925. Photo Credit: Troy Cryder/NASA

Scientists thought a world that size would stockpile Hydrogen gas as it grew, eventually becoming a Jupiter-like gas giant instead of a rocky planet. However, Kepler 10-c, a terrestrial alien world approximately 560 light-years from Earth in the constellation Draco, has been dubbed the “Godzilla of Earths” as it is vastly larger than any previously discovered “super-Earths“.

Kepler 10-c was originally spotted by the Kepler Space Telescope, which scans the cosmos and locates exoplanets using the transit method. It observes stars and watches for any dimming that might be indicative of a planet passing in front of it. Astronomers then measure the amount of dimming and are able to calculate how massive the planet is. Kepler can only determine exoplanet size and cannot determine an exoplanet’s composition, however.

This new “mega-Earth” orbits a Sun-like star once every 45 days. It spans 18,000 miles in diameter (about 2.3 times as large as Earth), which should place it in the mini-Neptune category; however, Kepler 10-c lacks a thick, gaseous envelope. With the help of the HARPS-North instrument on the Telescopio Nazionale Galileo (TNG) located in the Canary Islands, the team was able to determine the mass of Kepler 10-c. The results were shocking; with a mass 17 times that of Earth, Kepler 10-c must be composed of rocks and other solid materials.

“Kepler-10c didn’t lose its atmosphere over time. It’s massive enough to have held onto one if it ever had it,” explains Xavier Dumusque of CfA. “It must have formed the way we see it now.”

Current theories have a difficult time explaining how such a planet would form, but new observation data indicates there may be more mega-Earths out there. Astronomer Lars A. Buchhave discovered a correlation between the size at which a planet evolves from rocky to gaseous and that planet’s oribital period. As more planet hunters study longer-orbital periods, more mega-Earths may be discovered.

An image of the Kepler field of view in the Milky Way Galaxy. Image Credit: NASA

An image of the Kepler field of view in the Milky Way Galaxy. Image Credit: NASA

Identifying Kepler 10-c as a mega-Earth has major implications for the possibility of life and the history of our universe. The Kepler 10-c system is approximately 11 billion years old, forming around three billion years after the Big Bang. In the early universe, only Hydrogen and Helium were present. The heavier elements, like Iron and Silica, required to form rocky planets were not around as they were produced by the first generation of stars.When that first generation of stars died in massive stellar explosions (supernovae), they ejected the necessary ingredients into space, which were then used to form future stellar generations as well as planets. This process of seeding the cosmos, occurred over billions of years; however, Kepler 10-c is proof the universe was able to produce rocky planets despite limited resources.

“Finding Kepler-10c tells us that rocky planets could form much earlier than we thought. And if you can make rocks, you can make life,” says Dimitar Sasselov, director of the Harvard Origins of Life Initiative.

The Harvard-Smithsonian Center for Astrophysics (CfA), is headquartered in Cambridge, Mass. and is a joint venture between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists aim to study the origin, evolution and ultimate fate of our universe.


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