Astronaut Candidate

The existence of ample amounts of hydrogen in the subsurface ocean of Enceladus indicates that microbes--if any exist there--could use it to obtain energy by mixing with carbon dioxide dissolved in water. This particular chemical reaction, termed methanogenesis, because it manufactures methane as a byproduct, may have been of critical importance in the emergence of life on our planet. 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. Cassini's successful mission of exploration to the Saturn system is over, but planetary scientists are left with a cornucopia filled with important new information that Cassini/Huygens sent back to Earth before its mission ended. A collaborative NASA/European Space Agency/Italian Space Agency mission, the robotic spacecraft was made up of two components. The first was the European Space Agency's (ESA's) Huygens Probe, that had been named in honor of the Dutch mathematician and astronomer Christiaan Huygens (1629-1695), who discovered Titan. The Huygens Probe also closely observed Saturn's lovely system of gossamer rings. The second component, the NASA-designed Cassini Orbiter, was named after the Italian-French astronomer Giovanni Dominico Cassini (1625-1712), who discovered four of Saturn's other intriguing, numerous, and icy moons.