COROT-Exo-7b: a 1.7 Earth radius planet

[chris]

A new press release from ESA reports that COROT has detected the transit of an extrasolar planet with a radius on 1.7 times Earth's. This is the smallest radius measured for any exoplanet found to date (though the pulsar planets are almost certainly smaller.)

http://www.esa.int/SPECIALS/COROT/SEM7G6XPXPF_0.html

This post at oklo.org suggests that the discoverers have yet been able to gather enough radial velocity data to pin down the mass:

http://oklo.org/?p=315

--Chris

[t00fri]

A new press release from ESA reports that COROT has detected the transit of an extrasolar planet with a radius on 1.7 times Earth's. This is the smallest radius measured for any exoplanet found to date (though the pulsar planets are almost certainly smaller.)

http://www.esa.int/SPECIALS/COROT/SEM7G6XPXPF_0.html

This post at oklo.org suggests that the discoverers have yet been able to gather enough radial velocity data to pin down the mass:

http://oklo.org/?p=315

--Chris

Wow!

Fridger

[iniaes]

Something for those who are interested in the search for extra solar planets (last time i checked there are over 200)

The Kepler space telescope will be launched later this year, and is currently at NASA getting prepped for launch http://mediaarchive.ksc.nasa.gov/search.cfm?cat=194 or http://kepler.nasa.gov/

The Kepler telescope is a "photometer" with enough sensitivity to detect Earth size planets from the dimming effect they have as they pass between their parent star and us. It will survey 100,000 stars over 3 years.

[ajtribick]

There is a second planet in this system, a super-Earth with about 8.4 Earth masses. Unfortunately CoRoT-7c does not appear to transit. The mass of the transiting planet CoRoT-7b is determined to be about 4.8 Earth masses, which implies an Earth-like density. CoRoT-7 is thus the third known multi-planet system with a transiting planet, the second being HAT-P-13.

[Fenerit]

CoRoT-7b

0.87 Sun radii, 20h orbital period, the minimum orbital velocity might not be < 53 Km/s (approx.).

[Hungry4info]

CoRoT-7 is thus the third known multi-planet system with a transiting planet, the second being HAT-P-13.

What was the first?

[ajtribick]

CoRoT-7 is thus the third known multi-planet system with a transiting planet, the second being HAT-P-13.

What was the first?

Mercury and Venus transit the Sun from time to time...

[AVBursch]

There are a number of things that can be inferred from what we know about COROT-7b.

The density of COROT-7b (from mass and diameter) comes to 5.60 g/cm^3. This is practically identical to Earth, Venus, and Mercury. However, their compositions are different. Mercury has an extremely high iron content. Earth has a much lower iron content than Mercury but still has a higher density than Mercury due to gravitational compression. COROT-7b, with a mass 4.8 times that of Earth, would have even stronger gravitational compression. Extrapolationg, one can infer that COROT-7b has a lower iron content, and higher silicate content, than Earth.

Earth's uncompressed density, that is, what Earth's density would be if gravitational compression was not present, is 4.4 g/cm^3, but gravitational compression makes the Earth 26% denser, to 5.54 g/cm^3. COROT-7b would have a great deal more gravitational compression than Earth does. COROT-7b's uncompressed density is 3.23 g/cm^3, but the planet's gravity is strong enough to compress the material, almost doubling the planet's density. In fact, the planet's composition would be a lot like Mars (high silicate content, relatively low iron content).

The difference in composition can be explained from the perspective of planet formation. Mercury had most of its mantle blown away by collisions because its gravity is relatively weak, leaving behind a planet with a high iron content. Earth had part of its mantle blown away by a massive collision, but was still able to hang onto more of its mantle. COROT-7b, however, has much stronger gravity than Earth. This allowed COROT-7b to retain virtually all of its primordial material even in the event of a massive collision. COROT-7b has an escape velocity of 18.9 km/s and a surface gravity of 16.64 m/s^2.

Only time will tell, but the planet is likely to have an atmosphere of silicon vapor and iron vapor, as well as oceans of lava on its surface. In spite of the extreme temperature, the planet would still be able to hold onto an atmosphere of silicon vapor and iron vapor because of its relatively high escape velocity. Because the planet transits, astronomers should be able to employ the same tricks that were used to get the spectrum of the hot jupiter world HD 209458b to get a spectrum of COROT-7b's atmosphere. Unfortunately, COROT-7b is much smaller than HD 209458b, so doing this will require better equipment.