On the fringes of Saturn’s rings—careening through a chaos of colliding chunks of ice and captured by a powerful camera aboard the Cassini spacecraft—is a clump of debris that could become the gas giant’s newest moon.
Astronomers first spotted the smudge on an image beamed back from Cassini last year, and they spent the next 12 months vetting their data and snapping more shots of the disturbance in Saturn’s great rings. The results, published yesterday, are unlike anything scientists have ever seen.
“We have not seen anything like this before,” Carl Murray, an astronomer at Queen Mary University in London, said in a statement. “We may be looking at the act of birth, where this object is just leaving the rings and heading off to be a moon in its own right.”
They didn’t see the proto-moon directly—at about half a mile in diameter, it’s still too small for that. Rather, they noticed the effect of the clump’s gravity on the surrounding ice chunks. The entire debris cloud is only six miles in diameter and about 740 miles long.
Once astronomers had zeroed in on the cloud’s position, they calculated where else it would should appear in other images taken by Cassini.
Phil Plait, writing at Bad Astronomy:
They found the clump in more than 100 such pictures! But in most cases it’s so faint and difficult to see that it was completely overlooked before. It appears brighter at certain viewing angles, which is why it was so obvious in the discovery image. The earliest it was seen was in May 2012, but before then Cassini was not in a good orbit to detect the clump, so there’s no way to really know how old it is.
Discoveries like these excite astronomers and planetary scientists because they catch the process of formation in the act. We weren’t around to witness the birth of the Earth or the moon or Saturn itself, but by studying events like these, we can get a better idea of how, exactly, planetary bodies take shape.
Will the icy cloud stick around long enough to turn into a full-fledged moon? Only time will tell.