National Geographic Daily News
An illustration of mega-Earth

The newly discovered mega-Earth, Kepler-10c (foreground), discovered by NASA's Kepler Space Telescope, is depicted orbiting its sun in this artist's conception. In the background is its companion planet, Kepler-10b, the first confirmed rocky planet found outside our solar system.

ILLUSTRATION BY DAVID A. AGUILAR, CfA

Marcus Woo

for National Geographic

Published June 3, 2014

Astronomers have discovered the heaviest planet yet that's predominantly rocky, a hefty body 17 times more massive than Earth. Called Kepler-10c, the planet orbits a star that is similar to the sun, though nearly twice as old, and located about 560 light-years away in the constellation Draco.

The exoplanet, which has been dubbed a "mega-Earth," could be the first of a new class of massive rocky planets found at more distant orbits from their stars, said the astronomers who announced their discovery this week at the American Astronomical Society meeting in Boston.

Kepler-10c weighs as much as Neptune. But while Neptune has a radius about 3.9 times wider than Earth's, Kepler-10c has a radius only 2.3 times bigger. For a planet to be so compact and heavy, it must be primarily made of rock, the scientists reason.

Astronomers assume that rocky planets are necessary for habitability, since any life would likely need to have evolved near a solid surface. The discovery of a massive rocky planet like Kepler-10c "increases the number of planets out there which could be potentially habitable," explained one member of the research team, Dimitar Sasselov of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

Almost All Rock

Finding a rocky planet of such a massive size was not the biggest surprise, though, said Xavier Dumusque of Harvard-Smithsonian, who led the research. "The surprise is that there is no gas around it."

Planets are born from the disk of gas and dust that surrounds an embryonic star. A body as massive as Kepler-10c has so much gravity that it should have collected enough hydrogen and helium to turn into a giant gas planet like Jupiter.

"It's very difficult to put together a large solid planet like this without accreting even a small amount of hydrogen and helium, which is there in the disk," Sasselov explained.

The Kepler Space Telescope detected the planet in 2011, along with its companion, Kepler-10b, which was the first confirmed rocky planet found outside the solar system. Astronomers could use data from Kepler to measure the planets' radii, but they could only get a rough estimate of the planets' masses.

To better determine how heavy the planets are, Dumusque, Sasselov, and their colleagues used the Galileo National Telescope in the Canary Islands to measure how fast the planets were orbiting their star. From the speeds, the researchers deduced what the masses were and that the planets must be made of rock.

The Diversity of Planets

Kepler-10c is certainly interesting and appears to be an outlier for now, but it may not be that bizarre.

"Something on the order of the mass of Neptune and [that] is rocky with metallic material and perhaps a thin veneer of a hydrogen and helium atmosphere—that doesn't seem outside the realm of reasonable possibility," said Gregory Laughlin of the University of California, Santa Cruz, who was not involved in the finding.

There are a number of conceivable ways to create a planet like Kepler-10c, said Jack Lissauer of the NASA Ames Research Center in Moffett Field, California, who also wasn't a part of the team. The planet could have resulted from the collision of two smaller bodies that didn't have much gas to begin with. Or all of the gas in the embryonic star's disk may have somehow dissipated quickly, before the planet had time to accumulate any.

But calling Kepler-10c "rocky"—or even a "mega-Earth"—is a little misleading, since it's nothing like Earth, Lissauer noted. "I would call it a rock-rich world," he said. Although the planet is made nearly entirely of rock, there may be enough surrounding gas to create extreme pressures at the planet's surface, he explained.

"This is an important discovery," Lissauer said, because it "shows how diverse planets can be."

24 comments
Charlie Zogby
Charlie Zogby

Just did a quick calculation - the gravity on the surface of this planet would be 3.2 times the gravity on the surface of the Earth.  That would definitely be uncomfortable and make it difficult to get back off the planet, but it's nowhere near as bad as I imagined at first when I read that it's 17 times as massive.

Arup Ghosh
Arup Ghosh

It is very difficult to say that  Kepler-10c planet have any chance for life. But if it possible because of rocky condition of whole planet that will be unexpectable.


Nikolay Stamenkov
Nikolay Stamenkov

I am very happy with that Dimitar Sasselov is Bulgarian, and that he was the discoverer of the planet. Congratulations!

Marcos Toledo
Marcos Toledo

Could this be superman home world oops that planet exploded in 1938 ACE just a thought.

Stephen Davis
Stephen Davis

you all can go and live on ur mega-earth but me not living mother earth.

D Varley
D Varley

Some of these planets or moons will intime show their full potential but we as as a generation or even existence may never see the progress of this (planet). Our distant generations in the future may. We can't dream of these cold rocks with no atmosphere, we were probably the same millions of years ago. You never know we were stalked by dinosaurs until when ever perhaps the comet came to earth and created such forces (including diamonds and the like not to mention certain elements and exact chemical fusion if I can call it that!that may or not have some influence on us as a human race as in spawning us! There are loads of planets out there with life of some sort. ( don't forget we all started as an amoeba ( I think it goes like that) I'm not a scientist by any means I'm a realist if that's the right word. The main thing is to be able to bend space ( worm hole)( ??) somebody once said if you can imagine it it probably (can)be done . We need

to travel space not in light years but in a numerical time of our earth or we won't be interested we're getting right bored for eight months going to our great red planet it'll end up like aliens;(somebody or every body will kill each other with boredom) forget mars we need to travel fast!!!

Michael Wheater
Michael Wheater

Just how much has this search for exoplanets cost so far? Wouldn't these funds be better directed at saving life here, on Earth; in the developing world, for instance?

J. Griffin
J. Griffin

There are so many bigger planets than Earth. Maybe it is time to start calling Earth a "dwarf planet". 

David Castelli
David Castelli

Good, keep the caveman English here and let the educated folks move on.

Dwayne LaGrou
Dwayne LaGrou

The cost is not an issue really. The Space telescopes and Earth bound telescopes have been in use for years, So the cost has already been paid. Now is the important part. With the information gleaned from these telescopes mankind has discovered an immense amount of information. I'm sure that you have a microwave oven, Which was invented due to scientists discovering that certain wavelengths of radio energy had the power to make water molecules vibrate so fast that they heated up to boiling very fast. There are so many things we use today that were invented due to information learned from our exploration of space. Sooner or later the human species are going to be living on other planets, Weather they are in our solar system or another. But we won't know where to go unless we look for planets that are compatible with humans. Just think how many items from Star Trek that were actually invented and are in use today. Science is vital to our health. Our life spans have more that doubled due to science.

So I think the cost of these things is very little when compared to the information we receive.

Beam me up Scottie !!!

dfksdf dksd
dfksdf dksd

@Michael Wheater Sure. We could also reallocate all funds for scientific research to such undertakings - and that would be a thoroughly disastrous decision. You obviously don't think much of the value of scientific research. You should remember though that it is thanks to the "useless" elucubrations of past scientists that you are able to post such opinions to an electronic forum like this one.

David Castelli
David Castelli

So you're saying let's cut off all funding of science until every is living in a utopia and everyone has a perfect standard of living? ... Do you realize all the improvements to society science has brought forth??

David Castelli
David Castelli

No he probably doesn't plan on going soon but what does that have to with mankind's search for knowledge?

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