NASA Souvenirs



Water in its life-sustaining liquid phase exists beyond our own planet, both in our Solar System--and elsewhere. With oceans of water sloshing around on 71% of our own planet's surface, Earth still remains the only planet known to have stable bodies of liquid water. Liquid water is essential for all known life forms on Earth. The existence of water on the surface of Earth is the outcome of its atmospheric pressure and a stable orbit in our Sun;s circumstellar habitable zone. The habitable zone is that Goldilocks region, surrounding a star, where the temperature is not too hot, not too cold, but just right for life sustaining water to exist in its liquid phase. However, the origin of Earth's water still remains unknown. Most of the moons of our Sun's family circle the quartet of large gaseous planets located in our Solar System's outer limits: Jupiter, Saturn, Uranus and Neptune. The four solid inner planets--Mercury, Venus, Earth and Mars--are almost entirely moonless. Earth is the only inner planet that hosts a large Moon, while Mars sports only a pathetic duo of misshapen little Moons (Phobos and Deimos), that are either captured asteroids that escaped from the Main Asteroid Belt between Mars and Jupiter, or are instead the outcome of a primordial collision between Mars and a large protoplanet. I have talked to MIT and Harvard grads who still think that if a rocket whizzes by you in space it makes a whooshing sound much like a jet craft does in the atmosphere. Someone forgot to tell them there is no sound where there is no air. So what, you say?