Astronomers have announced the discovery of a new type of planet 鈥� a dense, rocky world they鈥檝e dubbed a 鈥渕ega-Earth.鈥�
The planet that weighs 17 times as much as Earth and, despite theories that such a world could not exist without becoming a gaseous giant, it is made of rock and other solid materials.
The discovery was announced Monday during a meeting of the American Astronomical Society.
"We were very surprised when we realized what we had found," said astronomer Xavier Dumusque, of the Harvard-Smithsonian Center for Astrophysics (CfA), in a statement.
The mega-Earth -- also known as Kepler-10c -- is located 560 light years from the Earth in the constellation Draco. It has a diameter of 29,000 kilometres, which is 2.3 times larger than that of Earth.
It is also one of the first planets to be larger than a 鈥渟uper-Earth,鈥� a planetary body that is at least 10 times the weight of our world.
The planet was originally spotted by NASA鈥檚 Kepler spacecraft, which tracks planets using their transit method. It measures the distance between stars that dim as planets pass in front of them to determine the physical size of a world.
But the Kepler spacecraft can鈥檛 tell whether a planet is gaseous or rocky. So the research team then used an instrument on the Telescopio Nazionale Galileo, in the Canary Islands, to measure Kepler-10c鈥檚 mass.
They said the result was shocking.
"This is the Godzilla of Earths,鈥� said CfA researcher Dimitar Sasselov. "But unlike the movie monster, Kepler-10c has positive implications for life."
The Kepler-10 system is about 11 billion years old and was formed less than three billion years after the Big Bang. This means that the planet in question -- the 10c, or mega-Earth -- was created close to a time when it was assumed the universe contained only hydrogen and helium.
Denser materials and heavier elements needed to make rocky planets, like silicon and iron, were introduced after the first generation of stars exploded. This was supposed to have taken billions of years.
"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," added Sasselov.
The mega-Earth follows a string of new planetary discoveries made over the last few years. In 2012, NASA鈥檚 Hubble Space Telescope confirmed a 鈥渨aterworld,鈥� a planet whose atmosphere is made primarily of water and water vapour. High pressures and temperatures can transform the water into different states, resulting in hot ice or superfluid water. The planet responsible for the discovery, named GJ1214b, is located 40 light-years from Earth and is 2.7 times heavier.
By contrast, one of Kepler-10c鈥檚 neighbours has been labelled a 鈥渓ava world.鈥� Researchers say that its orbit is so close to its sun-like host star that the surface is likely an enormous ocean of lava. The planet鈥檚 temperature is several thousand degrees and its core is probably made of rock and iron. A year on this lava world only takes 8.5 hours due to its rapid orbit.
Diamond planets are also a recent discovery. A 2012 paper argued that 55 Cancri e, a planetary body within the Cancer constellation, is so rich in carbon that it holds at least three times our planet鈥檚 weight in diamonds. These diamonds are covered in layers of graphite beneath an extremely hot atmosphere. A 2014 study conducted by Yale astronomy professors found that these carbon-rich planets may be more common than previously thought, and that this carbon-rich environment could be indicative of life.
As for the mega-Earths, further observational studies have shown that astronomers are likely to find more of them in their exploration of longer-orbiting systems.
