Wednesday, 21 March 2012

Cooking the planets if CoRoT-7.

The CoRoT-7 stellar system was discovered in 2009 by the European Space Agency's COROT space probe. The system is roughly 489 light years away in the constellation of Monoceros, and comprises of a G-type star (CoRoT-7A)with 91% of the Sun's mass surrounded by at least two planets. The first of these, CoRoT-7b, orbits at a distance of 0.017 AU (i.e. 1.7% of the distance between the Earth and the Sun) every 20.5 hours and has a mass of about 7.4 times that of the Earth. The second planet, CoRoT-7c, orbits CoRoT-7A at a distance of 0.046 AU (4.6% of Earth's orbital distance) every 3.7 days and has a mass about 15 times that of the Earth. A possible third planet, CoRoT-7d, may orbit at 0.08 AU, and have a mass over 16 times that of the Earth's.

An artist's impression of CoRoT-7b. Catalano Fabien.

In a paper published on 19 March 2012 on the online arXiv database at Cornell University Library and accepted for publication in the journal Astronomy and Astrophysics, a team of scientists lead by Katja Poppenhaeger of the Hamburger Sternwarte, carry out an examination of the effects of being this close to the star on the planets of the CoRoT-7 system, based upon new observations by the European Space Agency's XMM Newton X-ray space telescope.

Poppenhaeger et al. calculate that CoRoT-7b is slowly being evaporated by the heat of it's star, losing 130 000 tonnes of mass every second. The CoRoT-7 system is thought to be about 1.5 billion years old, so if CoRoT-7b has not moved radically within the system during this time, and its composition has not changed greatly either, then it is likely to have lost between four and ten times the mass of the Earth during its history.

They also estimated that CoRoT-7c would be losing mass due to evaporation as well, but at roughly 10% of the rate for CoRoT-7B (i.e. about 13 000 tonnes of mass per second). However unlike CoRoT-7b, CoRoT-7c does transit the star, so that its radius and density cannot be calculated, making calculations on its makeup, and therefore how it will react to irradiation, highly speculative.

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