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Western Slope Skies - Solar System Moons

Jovian family portrait.jpg
Galilean Satellites composite, Europa second from the left

A world encased in ice, in some places 15 miles thick. Surface temperatures that, at most, reach -215 degrees Fahrenheit. And, below the icy depths, a global ocean. Are you picturing Hoth, from Empire Strikes Back? Think a little closer to home – this icy planet is no planet at all. Meet Europa, one of Jupiter’s 79 moons (and counting!).

A moon is not so different from a planet, except these natural satellites orbit a planet or asteroid instead of a star. Moons come in all shapes, sizes, and materials. Our capital-M Moon is Earth’s only, but other planets have dozens, or none at all. Planetary scientists studying our solar system keep discovering more moons, each with their own unique features and potential.

Galileo Galilei first discovered moons other than our own in 1610. At the time, most people believed that everything orbited around Earth, the center of the universe. But Galileo witnessed 4 large moons orbiting Jupiter. Galileo’s observations of these moons, now called the Galilean satellites, helped change our understanding of the universe. Europa is one of these four.

Much has changed since 1610, yet Europa is still high on the list for scientific study. Planetary scientists believe Europa may hold the key to life outside of Earth. Europa’s icy shell is mostly water ice and may hide a global, potentially habitable, ocean below. Liquid water, along with a source of energy and the right chemical building blocks, are the components for life as we know it. This ocean could support life forms like those found near underwater volcanoes and other extreme locations on Earth. In humanity’s constant search for companionship, the idea that similar lifeforms could live near to us (astronomically speaking) is tantalizing.

Europa is just one of over 200 moons we’ve discovered in our solar system. It isn’t even the only one with potential for life. Public attention has shifted to places far, far away thanks to the James Webb Telescope, but scientific discoveries continually remind us of how little we know about our own space neighborhood.

Take a moment to look for Jupiter tonight, rising in the east in the late evening. Imagine Europa and the seventy-some other moons orbiting that distant planet. Now imagine hundreds more fantastical worlds, each with their own potential, in a galaxy not so far away.


Western Slope Skies is produced by the Black Canyon Astronomical Society and KVNF Community Radio. This feature was written and voiced by Austin Tumas, lead interpretation ranger at Hovenweep National Monument.