First rocky exoplanet found
The European Space Agency has announced the discovery of the first clearly terrestrial-type exoplanet ever found. The newly discovered world, COROT-Exo-7b, has a diameter smaller than twice that of Earth and orbits a star not unlike our Sun. The new world is unlikely to harbor life. The COROT-Exo-7b “year” is only 20 hours long, meaning that it orbits so close to its primary that sunward surface temperatures are likely between 1000 and 1500°C. If the world resembles Mercury in composition – being mostly composed of silicates and metals – the sunward face is probably a magma ocean.
Barring unforeseen orbital strangeness COROT-Exo-7b is almost certainly tide-locked, meaning one side permanently faces its star. If so, the planet might not only have a magma ocean on one side, it would have a frigid, permanently dark surface on the other. If the planet rotates such that its “day” is longer or shorter than its “year”, however, things get even stranger. COROT-Exo-7b’s crust would be constantly melting and solidifying as the world turned relative to its sun, meaning that the surface magma ocean would constantly rotate around the planet’s surface. The same rocks would remelt over and over again with each pass. In metallurgy this process is called zone refining, and is used to purify steel of impurities. Melt one section of a steel bar inside a form-fitting hole, then move the heat source down the long axis of the bar. The liquid zone moves, with steel refreezing behind the moving heat focus. As the melt zone moves it picks up all the strange elements that don’t easily fit into the crystal structure of the steel grains… refining the steel by concentrating rare elements into the melt zone. COROT-Exo-7b’s magma ocean might be an igneous petrologist’s dream, chock full of every weird heavy metal on the periodic table.
That scenario might be true even if the world is tide-locked, because interior convective processes likely would keep the crust and outer mantle moving by convection. Even on a world with a surface temperature of over 1500°C, the interior could be a lot hotter…. especially on a metal-rich planet with a far greater mass of heat-generating U-238 and K-40 than Earth.
The ESA announcement discusses water on the planet, but that’s unlikely. With half the planet’s surface a seething cauldron of lava it’s very unlikely that even water vapor would survive in the atmosphere over geologic time. That close to its star, H2O molecules would readily undergo photolytic decomposition to H2 gas and O radicals, which would be swept away on the streaming solar wind. No, COROT-Exo-7b is probably bone dry. But in compensation it might rain molten steel, and snow copper, silver and gold.
~ by Planetologist on February 3, 2009.