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The exoplanet known as Corot-7 b is unusual in many respects. It is one of the smallest planets known, and orbits its parent star very close (less than 2% of the Earth-Sun distance, or $0.0172\pm0.00029$ astronomical units (AU)), and consequently has a very short orbital period of less than 1 Earth day (0.853585 Earth days). This in itself is not unsual, but it is not a gas giant hot Jupiter. Rather, it has a radius of only 1.65 times that of Earth, and it is thought to be a rocky, terrestrial planet.
The mass of Corot-7 b has been hotly debated, with different researchers coming up with different answers, in the range of 2 to 9 Earth masses. Its density and composition are therefore also uncertain. Even with this uncertainty in mass, Corot-7 b is consistently an outlier (by a long shot) on a diagram of orbital period versus mass period for confirmed exoplanets. Models that attempt to explain the period versus mass data always have to make an exception for Corot-7 b because they are unable to account for it. Historically speaking, outliers such as Corot-7 b are the objects that will eventually force the development of a correct theory. Any model that cannot account for Corot-7 b must be regarded as incomplete or wrong. The host star for Corot-7 b has a mass similar to our Sun and a radius that is about 87% of that of our Sun. The system is about 489 light years from Earth.
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Reference for the latest mass estimate of Corot-7 b (in August 2012): Hatzes et al. 2012.
Just one example of a paper that attempts to interpret the diagram of orbital period versus mass period for confirmed exoplanets: Benitez-Llambay, Masset, and Beauge (2011).
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File under: Corot-7 b; Rocky, terrestrial planet that is an outlier in the mass-orbital period plane.