Red Giant

vaisvil

Earth’s fate
Main article: Future of the Earth (from Wikipedia)
Above is an artist’s depiction of the Sun entering its red giant phase viewed from Earth. All life on Earth is extinct at this phase.

During the Sun’s life in the main sequence, the Sun is becoming more luminous (about 10% every 1 billion years, at the present time). The surface temperature of the Sun is almost constant. The increase of luminosity is essentially due to a slow increase in the solar radius. The increase in solar luminosity is such that in about another billion years Earth’s water will evaporate and escape into space, rendering it inhospitable to all known terrestrial life. Earth is not expected to survive the Sun’s transition into a red giant. At its largest, the Sun will have a maximum radius beyond Earth’s current orbit, 1 AU (1.5×1011 m), 250 times the present radius of the Sun. By the time the Sun has entered the asymptotic red giant branch, the orbits of the planets will have drifted outwards due to a loss of roughly 30% of the Sun’s present mass. Most of this mass will be lost as the solar wind increases. Also, tidal acceleration will help boost Earth to a higher orbit (similar to what Earth does to the Moon). If it were only for this, Earth would probably remain outside the Sun. However, current research suggests that after the Sun becomes a red giant, Earth will be pulled in owing to tidal deceleration.