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.
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.
Amateur telescopes can reveal thousands of other galaxies in those sections of the sky that are sufficiently far from the Milky Way’s congested disk. The digital images of elliptical, spiral, irregular, and interacting galaxies that these “citizen scientists” can now obtain surpass the best images obtained professionally just 25 years ago.