Super-dense objects could be a new class of planet

Nature : The Kepler mission to find extrasolar planets has located several unusual objects that have no similar representative in our solar system. These unusual bodies have radii similar to Earth’s but are denser. None of the accepted theories of planet formation explain how they exist. One alternative theory is that the bodies are the heavy cores of much lartger planets that moved too close to their parent star, which burned away the lighter elements in the atmosphere and surface layers. An international team of researchers created computer simulations to model that planetary behavior and found that such planets could have been formed. The simulations showed that the process must have been quick: If the burning of the outer layers was slow, the decreasing internal pressures would allow the planet’s core to expand and become less dense. A quicker burning away would result in a fast cooling of the dense core, which would lock it into the smaller size. The researchers admit that there are a lot of uncertainties about the simulation because of the lack of information about planetary temperatures and pressures. And other theories may explain the planets as well, though they have not been tested yet.