• Question: Will Earth survive the Sun's red giant phase?

    Asked by anonymous to Steve, Emma, Christian, Bose, Alice on 9 Mar 2016.
    • Photo: Alice Harpole

      Alice Harpole answered on 9 Mar 2016:

      Certainly not in the state we know it today! As the sun evolves, its surface will become hotter. Over the next billion or so years before it even reaches the red giant phase, the energy received by the Earth will increase by about 10%, causing the oceans to boil. The extra water vapour in the atmosphere will produce a very extreme greenhouse effect, increasing the temperature even more (this is similar to what happens currently on Venus, which has a much higher surface temperature than Mercury despite being further from the Sun due to the greenhouse effect of its atmosphere).

      When it does reach the red giant phase in about 5 billion years, its outer layers will expand. The gravitational pull on the planets will decrease (as it will have lost lots of its mass), so the planets will drift outwards. The Earth will end up somewhere near where Mars orbits now. We’re not entirely sure how large the Sun will end up being, but it could end up engulfing the Earth entirely.