Milky Way A group of scientists from the Ohio State University said some terrestrial planets in our galaxy could contain up to 50 percent diamond, the Space.com portal reported.\"It\'s possible for planets that are as big as fifteen times the mass of the Earth to be half made of diamond,\" said Cayman Unterborn, a graduate student at Ohio State UniversityThe theory stems from a longtime suspicion that that Earth\'s lower mantle may contain a diamond-rich layer just above its core.The scientists simulated temperatures and pressure in the lower mantle to find out how diamonds are formed and used the data they received to make a computer simulation of planet formation process in carbon-rich systems.The study revealed that alien planets containing more carbon than Earth could have more diamonds in its mantle, up to 50%.\"Our results are striking, in that they suggest carbon-rich planets can form with a core and a mantle, just as Earth did,\" the project\'s chief scientist Wendy Panero said. \"However, the cores would likely be very carbon-rich - much like steel - and the mantle would also be dominated by carbon, much in the form of diamond.\"However, those giant earthlike planets dubbed \"carbon super-Earths\" are most likely incapable of supporting life. Such planets would have no geothermal energy and tectonic plate shifts, as well atmosphere and magnetic field.\"We think a diamond planet must be a very cold, dark place,\" Panero said.