Terrestrial snow at Chabot on December 16, 2008
Photo by Craig CoryellDriving to work today, I was amused to notice that the raindrops falling on my windshield were a bit grainy–and getting more so the higher up the hill I drove. I starting to think, is it starting to sleet? By the time I reached Chabot–at 1500 feet elevation–the precipitation had turned to bona fide snow!

This is quite unusual for the Oakland Hills, of course. In the ten years I've worked here, this is the second, maybe third, dusting I've witnessed. I recall the great freeze of '74, when it actually snowed in Oakland close to sea level—that's the year all the eucalyptus in the hills froze and died.

My mind wandered—pretty far out in space (an occupational hazard at Chabot). I started thinking about all the recent news and discoveries from around the Solar System, my thoughts guided by the fat white flakes drifting down all around the observatory domes.

Last September, NASA's Mars Phoenix Lander detected snow falling high in the atmosphere–about 4 kilometers high. This Martian snow, however, quickly evaporated in Mars' thin, dry air, never reaching the ground. Phoenix used a laser probe to make the detection–so we don't actually have picture to look at!

Snows of the Solar System may also fall out of the plumes of "cryovolcanoes"–the frigid outer Solar System's version of volcanism (may it live long and prosper). On moons such as Saturn's Enceladus and Neptune's Triton, plumes of material have been detected spouting from fissures and cracks–probably fueled by heat generated by tidal forces from their parent planets.

On Enceladus, the geyser plumes contain water vapor and ice crystals, and are believed to come from subsurface lakes of "warm" water (32 degrees Fahrenheit–in other words, ice water… but that's a veritable hot spring, or magma chamber, on a cold moon like Enceladus!).

The ice crystals in the geysers' plumes mostly fall back to Enceladus–maybe in a diffuse fall of "snow" across the globe? I'm waiting for those pictures…

Saturn's large moon Titan is speculated to possibly have a form of cryvolcanism, though no direct detection has yet been made. Still, any water vapor that might erupt from a Titanian cryovolcano might be expected to fall in a form of snow….

Triton, much farther from the Sun than Saturn, is even colder than Enceladus. In fact, it's been called the coldest measured surface in the Solar System, at -391 degrees Fahrenheit. Here, nitrogen freezes solid. Triton cryovolcanoes, or geysers, may be partially solar-heated, but tidal heating within Triton is probably dominant. Triton's geysers spout nitrogen gas and dark material, which falls across the landscape in dark streaks and lighter deposits of frozen nitrogen–a form of extreme cryo-snow, to my imagination!

Now, are you as cold as I am just thinking about it? Time for a cup of cocoa…

Artist concept of a geyser erupting on Enceladus.
Credit: David Seal.Back when I was young…okay, a previous generation might have ended that sentence with, "…I’d walk forty miles through the snow to get to school…" But I'm not exaggerating when I say, when I was young we knew next to nothing about faraway places in the Solar System…such as the moons of Saturn.

A layer of the veil around Saturn’s moons was removed when Pioneer 11 and Voyagers 1 and 2 made flybys of Saturn in the '70s and '80s. The Saturnian moons, it appeared, were not the lumps of rock and dust that Earth's own Moon is made of, but objects containing no small amount of water ice. Not terribly surprising, considering the low temperatures of the outer solar system where ice-rich comets roam.

Visions of frozen alien landscapes, replete with icicles and ice cliffs and ice fields and ice ice ice! were conjured in my imagination, and in artist depictions of majestic ringed Saturn seen from moons like Rhea or Dione or Enceladus.

Four years ago, Saturn’s first permanent visitor from Earth–the Cassini spacecraft–arrived there, and since has been making extreme closeup examinations of Saturn, its rings, and its increasingly wondrous and beautiful moons. Cassini is almost literally ripping apart veil after veil of our ignorance of these little worlds.

Far from a contingent of enormous but simple snow cone balls, Cassini has shown us that some of Saturn’s moons are apparently alive with liquid motion. First, there were the surface “lakes” and “seas” on Titan, probably made of extremely cold liquid hydrocarbons like methane and ethane–the stuff that spouts out of the gas range in your kitchen. Lakes and seas and rolling waves of liquid natural gas are fine and dandy for an imagined shoreline scene–but take a dip in those "waters" and an actual water-based creature like you would freeze solid in seconds. Scenic, but not inviting for a swim…

But recent observations by Cassini have shown that Titan's frigid unearthly lakes and Enceladus' snowball exterior may just be additional veils that are now being lifted.

In March, Cassini flew within 30 miles of the surface of Enceladus and right through a plume of material venting into space from the moon’s interior—an enormous "geyser." Earlier observations had sensed the presence of water in the plume, giving rise to speculation that liquid water in some form might exist beneath Enceladus' surface—perhaps chambers of liquid heated by tidal stressing of the interior.

When Cassini flew through the plume, its chemical sensors "sniffed" more than just water in the stream, but a good deal of organic molecules as well…not unlike material found in comets, stuff left over from the formation of the Solar System that may have been the building blocks of life on Earth.

The other "water find" was that of a possible liquid ocean under the crust of Titan–similar perhaps to the deep liquid water ocean believed to exist under the surface of Jupiter's moon Europa. Unexpected "drift" in the locations of landmarks on Titan's surface is what suggests a liquid ocean–water with perhaps some ammonia–that the frozen crust may be floating on.

With all the liquid water and organic chemistry being revealed in the Saturn system (and elsewhere in the outer solar system), our imaginations can shift from the older standards of envisioning otherworldly landscapes of sculpted ice or even seascapes of liquid hydrocarbon lapping on shores of water ice sand, to something a little more, shall we say, "lively…"?

Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.