Nickname: Godzilla of Earths
Weight: About 17 times as much as Earth
Size: 29,000km across (Earth is 13,000km across)
Texture: Rocky and hard
Class: Mega-Earth, an alien world that dwarfs the other rocky planets known to exist outside the solar system, as described by The Guardian. Kepler 10c has the distinction of being the first in the category.
Location: About 560 light-years from Earth in the constellation Draco
First glimpse: 2011, but at the time, only its size was known
Sibling: Kepler 10b, discovered in 2011
Host/parent star: Kepler-10, a sunlike star which Kepler 10c circles once every 45 days.
Discoverer: Mr Xavier Dumusque, a researcher at the Harvard Smithsonian Center for Astrophysics (CfA). He said, "This is a planet that doesn't fit the usual models of planetary formation."
Head-scratcher attributes: Astronomers are surprised at the discovery as they conventionally work on the premise that any planet this size would pull so much hydrogen as it forms and become a gas giant - Neptune, Saturn and Jupiter are examples - but it didn't.
Equally mysterious are Kepler-10c's age and abundant iron and silicon composition. Apparently, host star Kepler-10 is about 11 billion years, which means that it formed only about three billion years after the Big Bang. Silicon and iron - heavy elements need to make rocky planets like Kepler-10c - were rare then. So Kepler-10c's discovery suggests that "rocky planets could form much earlier than we thought. And if you can make rocks, you can make life," says CfA researcher and Harvard Origins of Life Initiative director Dimitar Sasselov. He added that Kepler-10c has positive implications for life.
Life-sustaining characteristics - or maybe not: In a statement, Mr Sasselov said that Kepler-10c has positive implications for life. The Guardian's science correspondent Ian Sample wrote: "Researchers cannot say whether the planet is hospitable to life, but if it has an atmosphere and clouds, the surface could be cool enough for life to survive."
Mr Jack Lissauer, a planet-formation theorist at the NASA Ames Research Center, who wasn't involved in the study, said in an interview with Time that Kepler-10c "is definitely not an Earth twin". The Time article reported that the planet's general Earthiness did not mean it could sustain life. With an orbit of a mere 45 days, it's too close to its star for water to remain liquid on its surface. The planet's composition is also not quite the same as Earth's, with 10 per cent of its mass consisting of volatile substances like oxygen and water. Earth only has 1 per cent of them.