Earth and Mars may become tidally locked with the expanding subgiant Sun. The Earth and Moon are very likely destroyed by falling into the Sun, just before the Sun reaches the tip of its red giant phase and its maximum radius of 256 times the present-day value. Before the final collision, the Moon possibly spirals below Earth's Roche limit, breaking into a ring of debris, most of which falls to the Earth's surface. During this time, most of the Earth's atmosphere will be lost to space and it's surface will consist of a lava ocean with flouting continents of metals and metal oxides as well as icebergs of refractory materials, with an average temperature of over 2,400 K (2,130 °C; 3,860 °F). During this era, Saturn's moon Titan may reach surface temperatures necessary to support life. The Sun reaches the tip of the red-giant branch of the Hertzsprung–Russell diagram, achieving its maximum radius of 256 times the present-day value. In the process, Mercury, Venus, very likely Earth, and possibly Mars are destroyed.