Science News

NASA discovers ‘Mega-Earth’

Thu, 5th Jun 2014

A massive planet twice the size and 17 times the mass of Earth has been announced by scientists at NASA.

The distant exoplanet TrES-2b, shown here in an artist's conception, is darker than the blackest coal.Kepler-10c is a planet discovered by Kepler, a space telescope launched by NASA, as part of its mission to discover new worlds similar to Earth.

It is around twice the size of the Earth, but new research published this week in Arxiv has shown it is heavier than anyone thought possible.

Weighing in at around 17 times heavier than the earth, Kepler-10c is composed of dense, solid material.

Planets of this magnitude usually have such intense gravitational pulls that a cloud of gas develops around them during formation, causing them to reach great sizes.

This is common to all the giants in our own solar system, such as Neptune or Saturn. Kepler-10c weighs the same as Neptune, but is about half the diameter, but it does not have this same gassy envelope.

Previously it was unheard of for a planet of this size to be composed entirely of rocky material.

Kepler-10c is located over 500 light-years away, in the Draco constellation.

Astronomers were able to get an idea of its size through observing the dimming of the star it orbits when the planet passes in front. Scientists have now been able to establish the mass of the planet using an approach called the radial velocity technique.

Dr Nikku Madhusudhan, a lecturer at the Institute of Astronomy at the University of Cambridge, who was not involved in the study, explains:

“They were basically looking at the “wobble” of the host star that is caused by the gravitational tug from the planets in the system; so by looking at the wobble of star itself one can figure out the masses of the various planets in the system”.

Kepler-10c is remarkable not only for its size, but its age. The star it orbits is 11 billion years old, meaning it formed just a few billion years after the Big Bang. This puts the dense giant at over double the Earth’s age, another record breaker for a rocky planet. This could impact our search for extra terrestrial life, as Madhusudhan continues:

“This tells us that rocky terrestrial planets out there could be really old, much older than the earth. This puts a limit, if there was life at some point in the Universe, on how far back this life could have begun on planets like this.”

Kepler-10c itself isn’t a candidate for alien inhabitants, likely being too large and too hot to sustain life, but it reveals that life out there could have begun long before the Earth even formed.

Kepler-10c Giant Earth Interview - Madhu Madhusudhan


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With an orbit of 0.24 AU, that puts Kepler-10c inside of Mercury's orbit.  Perhaps the close interaction with the host star strips the planet's atmosphere, especially for a  relatively old planet.

However, there are  a number of planets considered "hot jupiters" which are even closer to their stars.

Kepler-10c is relatively small, about 1/20th the mass of Jupiter. 

A planet's temperature would be related to the distance from the sun, and thus the atmospheric density would also be related to the distance from the sun.  The lower atmosphere density would mean the upper atmosphere would be further from the planet, and thus experience less gravity, potentially allowing the lighter elements (hydrogen/helium) to be lost. CliffordK, Thu, 5th Jun 2014

Planets this close to their parent star are likely to be tidally locked.

This means that one side is searing hot, and gas at this temperature is likely to be rapidly lost to space, or carried away by stellar winds.

It also means that the other side is exposed to space, and incredibly cold, and gas at this temperature is likely to be frozen - or at least liquid near the day/night boundary.

Heat from the planet's interior, or conducted through the planet from the sunny side would continually boil off gasses from the cold side, where they are heated on the hot side, and lost. This mechanism could degas a gassy world, leaving only a rocky core.
evan_au, Sun, 8th Jun 2014

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