Discovery of a very special moon – 1789
When Sir William Herschel first spotted Saturn's moon Enceladus, he didn't know it was special. It just looked like a little speck of light circling the magnificently ringed planet.
But we now know better. We have a spacecraft way out there near Saturn, Cassini, and it has been circling around the planet, taking measurements and photos, for the past six years. And what it shows about Enceladus is that half of the moon is cratered (like most planets and moons in the solar system) but the other half is smoooooth. Even more interesting, there are “tiger stripes,” which are four depressions or cracks, on one portion of the smooth half (shown here with false color), and water geysers periodically go off through cracks. The water instantly turns into ice, of course, and it is the apparently the snow made from these geysers that fills in and covers the craters and makes that part of the moon smooth.
That's pretty surprising, and nobody knows why the cracks and geysers are only on one part of the moon instead of scattered pretty evenly over the moon.
Stay tuned for more about Enceladus in the future!