Japanese scientists believe another planet, up to two-thirds the size of Earth, is orbiting in the far reaches of the Solar System... "Because of the very cold temperature, its surface would be covered with ice, icy ammonia and methane," said lead researcher Tadashi Mukai. The study by Mukai and co-worker Patryk Lykawka will be published in the April issue of the Astronomical Journal. "The possibility is high that a yet unknown, planet-class celestial body, measuring 30 per cent to 70 per cent of the Earth's mass, exists in the outer edges of the Solar System," says a statement released by...