 The Sun will evolve to become a red giant in about 5 Ga . Models predict that the Sun will expand to roughly 1 AU ( 150 @,@ 000 @,@ 000 km ) , which is about 250 times its present radius . Earth 's fate is less clear . As a red giant , the Sun will lose roughly 30 % of its mass , so , without tidal effects , Earth will move to an orbit 1 @.@ 7 AU ( 250 @,@ 000 @,@ 000 km ) from the Sun when it reaches its maximum radius . Earth was , therefore , once expected to escape envelopment by the expanded Sun 's outer atmosphere , though most , if not all , remaining life would have been destroyed by the Sun 's increased luminosity ( peaking at about 5 @,@ 000 times its present level ) . A 2008 simulation indicates that Earth 's orbit will decay due to tidal effects and drag , causing it to enter the red giant Sun 's atmosphere and be vaporized . 
