Earth's solid surface and moderate climate may be due, in part, to a massive star in the birth environment of the Sun, according to new computer simulations of planet formation. Without the star's radioactive elements injected into the early solar system, our home planet could be a hostile ocean world covered in global ice sheets."The results of our simulations suggest that there are two qualitatively different types of planetary systems," said Tim Lichtenberg of the National Centre of Competence in Research PlanetS in Switzerland. "There are those similar to our solar system, whose planets have little water, and those in...