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Moon and Jupiter
Jupiter, the largest planet in the solar system, is attended by the largest family of known moons — almost 70. The four biggest are worlds in their own right. Io is the most volcanically active body in the solar system. Europa is considered a possible home for life, with a deep ocean of liquid water beneath a thin crust of ice. And Ganymede is the biggest moon in the solar system.
The fourth big moon, Callisto, has its own distinction. It’s probably the most in-active moon around. During its four-and-a-half-billion-year history, it’s been pounded by countless space rocks, so its surface is the most heavily cratered of any known moon or planet. But nothing much else has happened. There’s no evidence of volcanoes, earthquakes, or any other process to reshape the surface.
Callisto is almost as big as the planet Mercury. It orbits Jupiter at a distance of more than a million miles. There’s evidence of an ocean far below its surface, but it’s not considered a good home for life.
Photographs reveal thousands of impact craters of all ages and sizes. That means that nothing has happened to erase the craters except more impacts. So this big moon sits quietly on the edge of the Jovian system — waiting for the next collision with a space rock.
And Jupiter stands close to our own moon tonight. It looks like a bright star to the lower left of the Moon as they climb into good view by about 10 p.m. Callisto and Jupiter’s other big moons are visible through binoculars.
Script by Damond Benningfield, Copyright 2015