Kepler-10c: The planet that shouldn't exist


June 2, 2014

Kepler-10c is 17 times more massive than the Earth (Image: NASA/Harvard-Smithsonian Center for Astrophysics/David Aguilar)

Kepler-10c is 17 times more massive than the Earth (Image: NASA/Harvard-Smithsonian Center for Astrophysics/David Aguilar)

Despite being currently offline, the Kepler space telescope is still turning up surprises. One of them is an Earth-like planet that’s so large that astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) call it a “mega-Earth.” Revealed in a press conference at a meeting of the American Astronomical Society (AAS), planet Kepler-10c is 17 times heavier than the Earth, and may require scientists to rethink their ideas on planet formation and the likelihood of life in our galaxy.

Kepler-10c lies 560 light-years from Earth in the constellation Draco, where it orbits Kepler-10 with a year of 45 days. This makes it so close to its star that it’s too hot to sustain life. It shares the star system with Kepler-10b, which is a “lava world” three times the size of Earth and has a year only 20 hours long.

When first discovered by the Kepler space probe, Kepler-10c’s diameter was measured at 2.3 times that of Earth (about 18,000 mi / 29,000 km), which led scientist to think that it was a “mini-Neptune” with a structure similar to that of the gas giants of the Solar System. But the true "mega" nature of the planet has since been uncovered by a CfA team led by astronomer Xavier Dumusque. Using the Kepler data as a starting point, the team looked at Kepler-10c with the HARPS-North instrument on the Telescopio Nazionale Galileo in the Canary Islands. While Kepler was only able to determine the size of Kepler-10c, the telescopic analysis by CfA combined with the Kepler data allowed the team to deduce the mass as well.

Astronomers now believe that Kepler-10c is 17 times heavier than the Earth, which, with its diameter, is significant. Despite their great size, gas giants are actually not very dense because of they’re made up of vast atmospheres of hydrogen and helium around a small rocky core. The planet Saturn, for example, is so light that it would float in water – if you could find a large enough bathtub. Kepler-10c, on the other hand, is solid, which is unheard of for a planet that size.

According to current theory, such a planet shouldn't exist. The CfA team says that any planet that size would have enough gravity to collect a massive atmosphere around it, turning it into a gas giant the size of Jupiter or larger. This one appears to be a giant ball of rock. If this so, then it raises questions about how planets form.

"Kepler-10c didn't lose its atmosphere over time," says Dumusque. "It's massive enough to have held onto one if it ever had it. It must have formed the way we see it now."

In addition, the Kepler-10 star system is 11 billion years old. This means it formed only 3 billion years after the Big Bang. The presence Kepler-10c with its rocky structure indicates that the heavy elements needed to make such a planet were available earlier than thought. If this is the case, then the CfA team says that there may be habitable planets that may be very old, which increases the chances of life being found elsewhere in the universe.

Source: NASA, CfA

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past. All articles by David Szondy

Wouldn't the high surface temperature and closeness to its star have stripped the atmosphere off the planet preventing it from having a dense atmosphere. Seems almost obvious to me, but the math would need to be done on this hypothesis to confirm that these conditions would strip off the atmosphere.


"This makes it so close to its star that it’s too hot to sustain life." I would rephrase that as "life as we know it". I mean there are all kinds of life-forms that exist on this planet in environments we could not exist in, so to automatically dismiss this planet as a life-sustaining because we do not understand it is pretty arrogant. What if the life breeds in a high radiation, super-thermal environment?

Jeffrey Hamlin

One thing that I have not heard about is the question of Moons, do these super earths have moons? Can we detect moons at all, and what size would these moons be? Does Kepler-10 have moons, and if it does ; how many?

Kristianna Thomas

"According to current theory, such a planet shouldn't exist." And so we stumble along, tripping over perceived certainty along the way to understanding where/what we are.

Bruce H. Anderson

maybe some heavier elements decaying within the perhaps its thicker 'mantle'

Alan Etherington

Good news! I'm glad to find evidence that sentient life could have evolved earlier than thought, making it more likely we will find it sooner. I would love to experience contact. I don't know why but this has been a dream of mine since 1952. I have no desire to land on an uninhabited planet, but conversing with an ET is mind blowing.

Jeff: When we say "life" it should be taken for granted we mean "as we know it". How could we speak about "life as we don't know it"?

Don Duncan

"...and may require scientists to rethink their ideas on planet formation..." You know, it's weird that scientists believe that rocky planets, like the Earth started when pieces of floating rock collided with one another, and created heat, eventually creating an active core of heated content which has been sustained for billions of years. -When have they been able to reproduce this on a smaller scale? - never.

To me, it make more sense that the Core was the original component of the planet, as even Gaseous planets supposedly have cores of some sort. Now, imagine that the core is an electrical phenomena with gravitation fields which allow it to attract material which passes by or happens to be surrounding it. If heavier, more magnet elements are closer, then they get pulled in closer to each other forming a shell around the core. When other gaseous materials get close enough to the magnetic/gravitational field(which leaks through the outer shell), then that material forms loosely around this field creating an atmosphere. In the case of Gas Giants, there is little rocky material around for it to attract, but has more gaseous material nearby. The cores themselves could have been tiny black holes or stars to begin with.

Daniel Gregory
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