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 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.
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.
However, mega-Earths formed, the discovery of another type of rocky
world bodes well in the search for life beyond Earth, Sasselov
added.
"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.
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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.
(Editing by Eric Walsh)
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