Planets in Process

People who study how humans grow up have it easy -- they can watch children and see how their bodies and minds develop over time. Scientists who study planets and stars, on the other hand, just don't live long enough to watch the evolution of objects that exist for millions of years. Instead they tend to spot a young star in one direction of the sky, an older one somewhere else, and develop theories on how one kind of star can grow into the other. But sometimes, nearby, there are processes that space scientists actually can watch.

The wakes made  in Saturn's ring,
by gravity from the moon Prometheus.

Current theories say our early solar system was one big disk of dust and debris.  Over time, the material coalesced into all the planets, moons and asteroids we see today.  NASA’s Cassini spacecraft has been watching almost the exact same process happen in Saturn's beautiful rings, where the icy particles collect into giant snowballs every time the moon Prometheus swings by.

The gravitational pull of the moon sloshes ring material around, creating wakes like a speed boat cutting through the water. As the wake of debris pushes out, it triggers the formation of icy objects as large as 12 miles in diameter. Such a snowball is so big that it would cover the entire island of Manhattan and extend well east and west. But what's most exciting is that this is the first time scientists have been able to actively watch any kind of planetary object form, says Carl Murray, a Cassini team member based at Queen Mary, University of London.

Let's face it -- sometimes it's hard to believe that, as big as our Earth is, it was formed from nothing but a whole lot of space dust. But watching how dust can cling together to build something 12 miles long can help explain just how it's done. And if it can grow to that size, it can keep growing bigger. . . and bigger. . . and bigger. . . to the size of moons and planets.