Ethan Siegel reports that for a long time, he thought the Solar System was the template for the planets to be found in the Universe. Inner, rocky worlds dominate the hottest part of the Solar System, with large, gaseous planets orbiting much farther out. The largest rocky planet was Earth. The smallest gas giant was Uranus. The mass difference between the two was a factor of 17, with Uranus having four times Earth radius. So it was quite a surprise when exoplanet discoveries started rolling in. Not only can planets of various sizes and masses appear anywhere in a solar system orbit, but of all the mass-and-size combinations out there, the most common type of planet is one we do not have at all, a Super-Earth.
Categorized as being between two and 10 times the mass of Earth (and with an appropriately scaled-up radius), Super-Earths outnumber any other class of planet, including the Neptune-like worlds, the Jupiter-like worlds, Earth-like worlds (and smaller) and anything else that have been detected to date. A large number of possibilities abounded at this discovery, but even more questions ensued. Such as ...
1. Are these worlds more like Earth, with rocky surfaces and thin atmospheres, or are they more like Uranus, with thick envelopes of gas?
2. Do they hang onto large amounts of hydrogen and helium, or are these elements light enough to escape their planet gravitational pull?
3. Are they potentially habitable to life like ours, or are the conditions there completely inhospitable?
Recent reports would have you believe that the answer to that last question is yes, and that these worlds might be home to the realizations of our expectations. But a cold, hard look at the scientific facts, and at the physics behind planetary science, casts doubts on that in no uncertain terms. good graphics.
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