Here I am trying to write up my Top Ten Pictures of 2008, when I get an email from Carolyn Porco. Dreading what I'll see, I open it. Sure enough, incredible new images from Cassini, just when I've finalized my Top Ten list! Arg! I peruse them anyway, and then find this:
That's Enceladus, a tiny water-ice moon orbiting Saturn. The ridges and cracks are ice floes, not too different from what you see on the Earth's north pole. Note that there's no solid land under our terrestrial arctic region, and for the same reason we think that Enceladus is actually a global ocean covered with floating ice. The lack of craters is because there are few old features on the moon. The shifting floes erase anything that isn't young.
This image is spectacular (and a much higher-res version is at the Cassini CICLOPS site). It was taken as Cassini flew past Enceladus, creating a mosaic of incredible resolution. It's composed of 28 separate images using seven different camera positions on the surface (called footprints), with four different filters used at each footprint. Cassini ranged from 30,000 - 48,000 km (19,000 - 30,000 miles) from the moon's surface while the images were taken.
Near the bottom you can see the Tiger Stripes, cracks in the surface (called sulci) which are the sources of water geysers detected previously by Cassini. The cause of the geysers is still under debate, but it's known that the geysers are noticeably warmer than the rest of the Enceladan surface. The material spewed out contains organic materials, too.
Yeah, water and organic materials, and a known mechanism (tidal heating) to keep the water liquid, and to help mix it. Provocative, isn't it?
Someday, we'll have to plumb the depths of this little moon. Until then, though, we have the Cassini mission still making its rounds of Saturn, and still patrolling its army of moons, returning gorgeous images and even more surprising science.
And as far as my Top Ten list goes... I will very reluctantly leave this one off, because I don't want you to wait to see it. Think of this as "Number -1", a taste of what's to come.
Image credit NASA/JPL/Space Science Institute