At some point in the future, the Solar System's in for a roasting. And then some. About 6 or 7 billion years from now, the Sun will exhaust its hydrogen supply and swell to become a red giant. Its luminosity will balloon enormously, along with its radius. Mercury and Venus, the innermost two planets, might become completely engulfed. This image shows the Sun as it might appear from Earth. Even from there, the swollen star still fills the sky of the planet, whose atmosphere has been totally stripped away. See also Meltdown.