As the Sun provides us with energy, it is also being reflected back into space. Because this give and take is in balance, our planet stays at pretty much the same total temperature, which is a very good thing. If Earth reflected back more energy than it received, the planet would cool, eventually becoming an ice ball. If the opposite happened, as some scientists fear could be occurring with global warming, the planet would heat up. Interestingly, some planets, including Jupiter and Neptune, radiate much more heat than they receive, which has led to speculation that there is a heat source within these planets. Some astronomers consider Jupiter a kind of failed star; if it had been more massive, it could have become a second Sun, and Earth would be part of a binary star system.