Nine planets circle around the sun. Since the sun's temperature is so important to life on Earth, you might think that other planets lying close to the sun could also have life on them. Unfortunately, the heat from the sun burned up the atmospheres of Mercury and Venus that could have sustained life on those planets. Mars might have had some type of life in the past, but Jupiter'sgravity would crush any life on this huge planet made of gas. The only hope for finding any type of life might be in an ocean on one of Jupiter's moons.