Never before has a space probe come so close to the pint-sized moon embedded in Saturn’s rings — and when NASA’s Cassini buzzed Pan, the spacecraft revealed what a strange moon it really is.
This is Pan, a 22 mile-wide moon that scoots through Saturn’s rings, orbiting the gas giant once every 13.8 hours. And it’s weird.
Resembling a giant ravioli or some kind of “flying saucer” from a classic alien invasion sci-fi comic, Pan is known as a “shepherd moon” occupying the so-called Encke Gap inside Saturn’s A Ring. This gap is largely free of particles and it has become Pan’s job to hoover up any stray material — the moon’s slight gravity pulls particles onto its surface and scatters others back out into the ring system. This gravitational disturbance creates waves that ripple through the ring material, propagating for hundreds of miles.
On March 7, NASA’s Cassini mission came within 15,268 miles of Pan, revealing incredible detail in the moon’s strange surface. It’s thought that its characteristic equatorial ridge (a trait it shares with another Saturn moon Atlas) is caused by the gradual accumulation of ring material throughout the moon’s formation and with these new observations, scientists will be able to better understand how Pan came to be.
As Cassini rapidly approaches the end of its mission, eventually orbiting through Saturn’s ring plane as a part of its “Grand Finale,” we can expect more of these striking views from orbit before the veteran probe is steered into Saturn’s atmosphere in September, bringing its historic mission to an end.
I do admit, I’m terrible with names, but I never forget a face. In this case, the face I didn’t forget was a little moon orbiting Saturn (it’s the one that looks like the Death Star from Star Wars). However, after seeing this photo, I doubt I’ll ever forget Tethys’ name again.
In a photo snapped by the awesome Cassini Equinox mission back in November, the little moon with characteristic impact crater carved into its crust can be seen to be drifting behind Titan. Tethys only disappears for 18 minutes behind Titan’s thick atmosphere, but it was enough to ignite my interest in the icy world.
It’s strange how a simple photograph and perfect timing can ignite the imagination, as I doubt “just another moon shot” would have the same effect. No, this is a moon drifting in front of another moon as seen by a veteran spaceship orbiting the second largest planet in the solar system millions of miles away. Sometimes words are insufficient to describe the enormity of what we are doing in space.
So, sod the words and look at this, you won’t be disappointed:
As Saturn approaches its August 11th equinox (during which the Sun will be directly above the gas giant’s equator at noon for 27 months), the Cassini Equinox Mission can do some moonlet spotting. During this time, sunlight will cast long shadows of any object protruding from the 10 metre-thick rings.
In this case, hidden inside Saturn’s B-ring, a moonlet with a diameter of approximately 400 metres becomes obvious when sunlight hits the rings edge-on. The result is a very obvious 25 mile-long shadow. This discovery wouldn’t have been possible during any other time, as Cassini can only see the small rock because of its shadow. If the Sun was above or below the rings, no shadow would be cast, and therefore no moonlet would be visible.
Saturn experiences an equinox twice every Saturnian year (once every 15 terrestrial years), and NASA planned the Cassini mission to coincide with this interesting period to economise on the position of the Sun, spotting small objects like this little satellite…
In October 2008, Cassini flew very close to the surface of Saturn’s icy moon Enceladus. From a distance of only 50 km from the moon, the spacecraft was able to collect samples of a plume of ice. In an earlier “skeet shot”, Cassini captured detailed images of the cracked surface, revealing the source of geysers blasting the water into space. At the time, scientist were able to detect that it was in fact water ice, but little else would be known until the molecular weight of chemicals in the plume could be measured and analysed.
At the European Geophysical Union meeting in Vienna this week, new results from the October Enceladus flyby were presented. Frank Postberg and colleagues from the Max Planck Institute for Nuclear Physics have discovered traces of sodium salts and sodium bicarbonate in the plume for the first time.
It would appear that these chemicals originated in the rocky core of the moon and were leached from the core via liquid water. The water was then transported to the surface where it was ejected, under pressure, into space. Although scientists are aware that the chemical composition in the plume may have originated from an ancient, now frozen, sub-surface ocean, the freezing process would have isolated the salt far from the surface, preventing it from being released.
“It is easier to imagine that the salts are present in a liquid ocean below the surface,” said Julie Castillo of NASA’s Jet Propulsion Laboratory in Pasadena, California. “That’s why this detection, if confirmed, is very important.”
This is the best evidence yet that Enceladus does have a liquid ocean, bound to cause a stir amongst planetary scientists and re-ignite excitement for the search for life living in a salty sub-surface ocean.
The mystery of Saturn’s hexagonal shape embedded in its violent north polar cyclone just became more intriguing.
NASA’s Cassini probe has been orbiting the ringed gas giant for four years and has just returned some of the most detailed images of the planet’s stormy atmosphere to date. The south pole has been mapped and the north polar region has been imaged in near-infrared wavelengths. The north pole is currently facing away from the Sun, so by observing the atmosphere in these wavelengths, Cassini scientists can see Saturn’s cloud formations silhouette against the background glow of the gas giant’s internal heat. This provides the perfect opportunity to see the hexagon in unprecedented detail.
In a previous Astroengine article, I explored the possibility that the variation in radioactive decay rates may be synchronised with Earth’s orbital variations in distance from the Sun. Naturally, this would be a huge discovery, possibly questioning the fundamental law that nuclear decay rates are constant, no matter where the material is in the Universe. One of the conclusions in the original decay rate research suggested that we should attach a sample of a radioisotope onto an interplanetary mission far beyond the orbit of Earth. By doing this, the relationship between decay rates and distance from the Sun should become obvious, and terrestrial decay rate variations can be tested.