Second rocky world makes Kepler-10 a multi-planet system

May 26, 2011 by Leslie Mullen,
NASA’s Kepler has identified more than 1,200 candidates for extrasolar planets thus far. Credit: NASA

The Kepler Telescope team has announced a second planet orbiting the star Kepler-10. The existence of this planet was suspected previously, but new analytical techniques were needed to confirm its existence.

The Kepler Telescope team has found a new , one they describe as a “scorched, molten Earth.”

The planet is about 2 times the size of Earth, and is very close to the Sun-like star Kepler-10, completing an orbit in only 45 days. Being so close to its sun, the blazing-hot new planet is not expected to have any liquid water or life as we know it.

The star Kepler-10 is located 564 light-years away, in the Draco constellation (although it is not bright enough to be seen with the naked eye).

Named Kepler-10c, the new planet’s existence was suspected when the Kepler team announced earlier this year that they’d found Kepler-10 b, a terrestrial planet orbiting the same star. However, the data was not conclusive enough for scientists to feel certain that what they were seeing was due to a planet.

A new technique was required to rule out other possibilities. The Kepler telescope looks at dips in starlight when a planet passes in front of a star from our point of view -- an event called a planetary transit. But other objects, such as stars, can also pass in front of the observed star and block the light.

To be sure the transit was not caused by eclipsing stars, the Kepler team combined a new computer simulation technique called “Blender” with infrared data from NASA’s Spitzer Space Telescope.

Blender is light-curve fitting software that allows the scientists to rule out other possible causes of the dip in starlight. When astronomers are observing a star, the total light emitted by the star over time can be represented as a relatively flat line. A short-lived dip in this line, called a light curve, indicates some of the light has been blocked briefly.

“We try to exhaustively look at all the things that could cause a light curve,” said Francois Fressin of the Harvard-Smithsonian Center for Astrophysics and a member of the Kepler team.

Blender results show that only a very small fraction of other objects can reproduce the exact same kind of light-curve as a planet. This helps give the scientists confidence that the light curve they are witnessing is due to the new planet Kepler-10c rather than something else.

Fressin said that the Blender method can be used to help the Kepler team figure out if any of the 1,235 candidates they have found so far are rocky like the Earth.

Bill Borucki, Kepler’s principal investigator, said hundreds more planet candidates are expected to be found before the end of the three-year mission. However, he noted that the Kepler team won’t release more data sets until June 2012 because they need more time to observe the stars and rule out other explanations for the changes in starlight.

’s main goal is to discover how common are Earths in habitable zones around Sun-like . Whether they are rare or common, once such worlds are located, astronomers can try to study them in order to learn whether they have alien life.

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1 / 5 (5) May 26, 2011
Ironically, the techniques they are using have almost no chance of finding an Earth-like planet in an Earth-like orbit, even if it does exist, and even if it is on the correct orbital plane, and even if they are looking directly at it.

The the planet would only transit the star about once per year give or take a month or two, and would only be "visible" (by dimming the star) for a few hours at most.

Gliese is much closer than the Kepler objects, and most of the planets are larger and orbit closer since it is a red dwarf, so that made it easier to find gravitational perturbations.

While the transit method is probably one of the best possible methods for finding an earth-like planet on a sun-like star, it takes years and years.
1 / 5 (4) May 26, 2011
I'm not sure how exactly they are detecting the "dimming" of the transiting planet blocking the star, but intuitively it might actually be easier to look for "red shift," caused by changes in emission spectra and heat radiation from the planetary atmosphere (not to be confused with the gravitational, doppler, or cosmic red shift,) as opposed to a "mere dimming" of the star light.

Any planet with a stable atmosphere should produce infrared light which will be, on average, equal to the Star's luminous flux at the planet's own position divided by 4, per unit area: surface of a sphere vs surface of the cross sectional disk. This will be with the spectral lines of the material of the planets middle and upper atmosphere.

I doubt we have anything sensitive enough to detect this directly, but an earth-like planet in a Sun-like solar system should emit around 340 watts per meter squared of primarily infrared and visible radiation, with primarily nitrogen and oxygen spectra.
5 / 5 (5) May 26, 2011
You can tell the astronomers love their telescope when they are naming stars after it :).

@spectator - our range of detecting earthlike planets (in the right orbit for water) is limited, but not impossible. It also becomes much easier to see them when we look at smaller, cooler stars.

They have already found one that may be capable of holding liquid water. As we are near the edge of being able to detect what we're looking for, this experience will help us fine tune our tactics for when something a little more powerful comes along.

Who says we only want to look for earthlike planets orbiting middle aged yellow stars?
1 / 5 (2) May 26, 2011
Well, I was going to suggest that it actually makes more sense to look for planets orbiting red dwarfs, rather than solar mass stars, since the stable orbits would be smaller on average, and therefore both the gravitational perturbation methods and the transit methods would work better.

Unfortunately, the planet at Gliese is too cold.

I think they said it would need over 10 atmospheres pressure worth of CO2 in order to be stable. Given it's estimated mass and estimated temperature, that would make it a terrestrial-gas giant hybrid; totally unlike anything in our solar system.

It wouldn't be habitable to humans except in pressurized vehicles, even if you could somehow deal with the extra gravity at 1.5 to 2 g-forces, which we can't do that either. Ten atmospheres is 145psi, which is well above the typical operating pressure of a nail gun, or equivalent to around 270 feet below the sea surface on Earth.

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