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.

5 Responses to “First rocky exoplanet found”

  1. Forget paper. Tell me what it would be like and I’ll stick it in a book.

  2. I can’t get this idea out of my head now. An advanced species using this rotating molten sea to harvest rare metals.

    • Such a thing would be quite a sight. Even if the magma ocean didn’t creep around the planet, it would be constantly churning and convecting due to thermal differentials between the surface and bottom layer. Deeper into the mantle the thermal anomaly of one tide-locked side facing the star would probably generate vertical and lateral convective currents in the rock, meaning that even areas on the dark side would experience enhanced volcanism from solar input affecting the light-side mantle. I can’t easily imagine the kinds of complex mineralogy, igneous sedimentology and overall geologic weirdness that planetary setup would produce…. hmmm, interesting topic for a paper.

  3. Hey now, a lot of sci fi stories from the 30’s taught me that if you stand exactly at the edge between the day and night sides, you’re fine!

    Or is that the sci fi version of jumping up in the air just before the plane crashes?

    • No, that would work… not for Mercury, because of its weird non-unit orbital harmonic, but it would work for any tide-locked world. You’d ideally site your mining op on the dark side, near the terminator, so you can deal with life support without having to duck and cover for solar flares… but if you’re close to the terminator, you could use replaceable PV satellites for power indefinitely. So says the sci-fi geek.

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