Of all the planets of the Solar System, our Earth is unique. It is the only planet known to harbour life of a wide variety – from the simplest one-celled organisms to the most complex ones like human beings. All the planets of the Solar System have now been explored by spacecraft and we know that nowhere else does liquid water, which is essential for life, exist. Nowhere else can one enjoy the scenic beauty that we see on this planet. There are mountains and volcanoes on other planets, but they do not evoke the joy and awe as they do on Earth. What makes our planet so different from the others? At the root of all this is a singular combination of factors not found in case of any other planet. Our Earth happens to be at just the right distance from the Sun; it is neither too close nor too far away. Had it been a little closer to the Sun it would have been too hot for life.