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.

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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…

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