The newly discovered 'mega-Earth' Kepler-10c dominates the
foreground in this artist's conception. Its sibling, the
lava world Kepler-10b, is in the background and both orbit
a sunlike star. REUTERS/David A. Aguilar/Center for
Astronomers have discovered a new type of rocky planet
beyond the solar system that weighs more than 17 times as much
as Earth while being just over twice the size, scientists say.
The so-called "mega-Earth" circles a very old star called
Kepler-10, which is located about 560 light-years away from
Earth in the constellation Draco.
The discovery, announced at the American Astronomical Society
meeting in Boston, was a surprise since planets that big were
believed to be mostly gas, not solid rocky bodies like Earth
or Mars, said physicist Dimitar Sasselov, director of the
Harvard Origins of Life Initiative.
Scientists do not yet understand how the planet, known as
Kepler-10c, formed. It has a diameter of about 18,000 miles
(29,000 km), 2.3 times greater than Earth's.
"A mega-Earth is a lot of solids concentrated in the same
place without any gas. That is a problem because our
understanding for how planets form requires the solids to get
together in an environment where almost 99 percent of the
mass ... is hydrogen and helium," Sasselov told reporters at
a press conference.
He also used the phrase, "the Godzilla of Earths!", BBC
Smaller solid bodies, like Earth or Mars, which are believed
to form from leftover materials, take less time to pull
themselves together. With a longer incubation time, large
planets should gather up massive amounts of gas in the
process - or so scientists thought.
How ever mega-Earths formed, the discovery of another type of
rocky world bodes well in the search for life beyond Earth,
"As far as we know - and we know very little about origins of
life - we think the emergence of life from geochemistry,"
occurs on solid planets, Sasselov said.
Related research shows that about 75 percent of the planets
found with NASA's Kepler space telescope are less than four
times Earth's diameter.
In the solar system, there is nothing between the size of
Earth, the largest rocky planet, and Neptune, the smallest
gas giant with a diameter nearly four times Earth's.
"We really want to know about these planets," astronomer Lars
Buchhave, with the Harvard-Smithsonian Center for
Astrophysics, told reporters.
"Are they rocky planets with a thin, compact atmosphere like
the Earth, or are they rocky cores with some sort of extended
hydrogen-helium envelope and where there is really no
surface?" he said.