A couple of weeks ago, amateur astronomers discovered a new storm erupting on Saturn. The accomplished astrophotographer Anthony Wesley got pictures of it, and I wondered to myself when Cassini would snap some shots. Turns out, I didn't have to wait long! The spacecraft took images of the planet on December 24th, returning -- as usual -- jaw-dropping pictures of Saturn showing the storm:
This image, taken with a blue filter, shows the storm clearly. The main spot is huge, about 6,000 km (3600 miles) across -- half the size of Earth! Including the tail streaming off to the right, the whole system is over 60,000 km (36,000 miles) long.
Curious, I checked out the archive of raw Cassini images, and sure enough pictures were also taken in infrared filters which pick out the gas methane, abundant in Saturn's atmosphere:
A lot more detail can be seen here! I'm not sure how to interpret this, but it's interesting to me that in the main oval there's a spot with less methane on the left, and a bright spot on the right with a faint ring of clouds circling it. The banding on the planet can be spotted more easily in this image as well.
There's an added bonus in these images: the shadow of the rings on the planet's clouds is obvious, but the rings are nearly invisible! You can just make out the rings as a thin line going horizontally across Saturn in the first image. These pictures were snapped when Cassini was almost directly above the rings, which are so thin they vanish when seen edge-on. Actually, that works out well as otherwise they might interfere with the view of the storm in these shots.
As I said above, the storm is so big it was actually discovered by amateurs here on Earth, so if you happen to have a good 'scope you might be able to spot it yourself; Saturn is up in the middle of the night right now, so if you get up a couple of hours before dawn it's well placed for viewing. Saturn's about as far from Earth as it can be right now, unfortunately, at a distance of 1.4 billion kilometers, so its disk is pretty small, and the storm even smaller. So this is challenging, but possible.
Incidentally, I'll add that with the raw images in different filters available in the archives, it's possible to grab them and put them together to make pseudo-true-color images. Guillermo Abramson is an Argentinian physicist who contacted me and let me know about his efforts, one of which is displayed here. It's not exactly true color because it's difficult to compensate for the different filter properties, different exposure times, and so on, but his pictures are interesting. Playing with images in this way sometimes reveals details you might not see in grayscale versions... and with thousands of eyes able to look at the pictures things might be spotted which would otherwise be missed.
And I'll just bet we'll be seeing lots more images of this vast storm as time goes on. It'll be very interesting to see how it evolves over time, and I'm sure there are lots of scientists across the planet (our planet, that is) who feel the same way.
Images credit: NASA/JPL/Space Science Institute