Space is mostly just what it says on the tin: empty space. The solar system is no exception; it’s a massive volume occupied by little more than the Sun’s mass — the mass of all the planets, moons, comets, asteroids, space dust, and stray electrons are just a bit more than a rounding error. But oh what mass it is when you get up close to it.
The NASA space probe Cassini, on its seven-year journey to Saturn, cozied up to Jupiter in December 2000 and captured a succession of images of Io and Europa passing over the Great Red Spot during the moons’ orbit of the gas giant planet. Kevin Gill turned those images into the incredible video embedded above. That we have such crisp, smooth video of two small moons orbiting a planet some 444 million miles away from Earth is something of a miracle — it looks totally rendered. Also in the video is footage of Titan orbiting Saturn — that horizontal line bisecting the frame is Saturn’s rings, edge-on.
On one of its final passes of Saturn, the Cassini probe captured this image of a wave structure in Saturn’s rings known as the Janus 2:1 spiral density wave. The waves are generated by the motion of Janus, one of Saturn’s smaller moons.
This wave is remarkable because Janus, the moon that generates it, is in a strange orbital configuration. Janus and Epimetheus (see “Cruising Past Janus”) share practically the same orbit and trade places every four years. Every time one of those orbit swaps takes place, the ring at this location responds, spawning a new crest in the wave. The distance between any pair of crests corresponds to four years’ worth of the wave propagating downstream from the resonance, which means the wave seen here encodes many decades’ worth of the orbital history of Janus and Epimetheus. According to this interpretation, the part of the wave at the very upper-left of this image corresponds to the positions of Janus and Epimetheus around the time of the Voyager flybys in 1980 and 1981, which is the time at which Janus and Epimetheus were first proven to be two distinct objects (they were first observed in 1966).
The photograph is also an optical illusion of sorts. The rings appear to be getting farther away in the upper lefthand corner but the plane of the photograph is actually parallel to the plane of the rings…it’s just that the wavelength of the density wave gets shorter from right to left.
Update: Here are those density waves converted into sound waves. The first set sounds like an accelerating F1 car.
The Cassini spacecraft took a photo of two moons of Saturn, Tethys and Enceladus, beautifully aligned with each other. The cosmic ballet goes on. (via slate)
The Cassini probe, launched from Earth in 1997 (six months before I started publishing kottke.org), has been taking photos of Saturn and its moons for 11 years now. The Wall Street Journal has a great feature that shows exactly what the probe has been looking at all that time. (Note: the video above features flashing images, so beware if that sort of thing is harmful to you.)
Discovering life was not on the agenda when Cassini was designed and launched two decades ago. Its instruments can’t capture microbes or detect life, but in a couple of dozen passes through the plumes of Enceladus, it has detected various molecules associated with life: water vapor, carbon dioxide, methane, molecular nitrogen, propane, acetylene, formaldehyde and traces of ammonia.
Wednesday’s dive will be the deepest Cassini will make through the plumes, only 30 miles above the icy surface. Scientists are especially interested in measuring the amount of hydrogen gas in the plume, which would tell them how much energy and heat are being generated by chemical reactions in hydrothermal vents at the bottom of the moon’s ocean.
That’s pretty crazy…it sounds like science fiction. NASA is doing a wonderful job producing great science with the lean budgets they are given.
Over at The Planetary Society, Emily Lakdawalla highlighted an image taken by the Cassini spacecraft of Saturn separate from its rings.
This enormous mosaic showing the flattened globe of Saturn floating amongst the complete disk of its rings must surely be counted among the great images of the Cassini mission. From Earth, we never see Saturn separate from its rings. Here, we can see the whole thing, a gas giant like Jupiter, separated at last from the rings that encircle it.
Taking this idea one step further, I removed the rings completely, along with the “ringlight” lighting up the night hemisphere, creating a more-or-less pure look of what Saturn would look like without its rings.
Stay Connected