To planetary scientists, astronomers and astrophysicists, Earth is but one of several known worlds that host a substantial atmosphere and corresponding climate. By comparing these worlds, researchers can gain insights to their atmospheric compositions, current climatic states, and possible evolutionary histories. Through these comparisons, we have learned that warming by greenhouse gases can play a key role in determining a planet or moon’s average temperature at its surface.
Over the past 50 years, robotic probes have visited every terrestrial planet, the largest asteroids, Jupiter, Saturn, Uranus, Neptune, and now Pluto – one of several dwarf planets, or “Plutoids” that inhabit the Kuiper Belt of icy objects. For New Horizons, this has been a 9 year 3 billion mile journey. Next for the grand-piano-size spacecraft are other objects in the Kuiper Belt and beyond.
Water has been identified in the most uncanny of places – as vapors in the nebulae that roam our Milky Way Galaxy, as ices in the protoplanetary disks that surround many protostars, and as liquids below the icy crusts of the Jovian moons Europa, Ganymede, and Callisto. In 2005, the Cassini spacecraft imaged geysers of liquid water erupting from the surface of Saturn’s moon Enceladus. The liquid form of water is especially important to biotic processes, as it provides an essential solvent for making the sundry hookups and energy transfers that are necessary to life.