What is Mercury's fate? Experts believe that our sun will eventually expand and become a red giant in about 7.6 billion years. In doing so, the sun will absorb Mercury, Venus and probably Earth. Or perhaps the planet will be destroyed another way. Here an artist depicts a planet the size of Mercury colliding with a satellite the size of our moon. NASA has found evidence that a collision like this occurred about 100 light-years away on a planet near the HD 172555 star.