Of all the ways that professional and amateur astronomers work together, arguably their most successful collaborations involve planetary observations. Amateurs routinely alert their professional counterparts to rapid changes on Mars and Jupiter — and most recently Saturn.With Saturn now well placed high in the evening sky, it's been getting a lot of scrutiny from high-end observers around the world. On March 13th, Philippine observer Christopher Go recorded a localized brightening in the planet's South Tropical Zone, and soon others were posting images on the website of the Association of Lunar and Planetary Observers.
One of them was Anthony Wesley, the Australian made famous last year when he noticed the black smudge caused by an impact on Jupiter. After recording the outbreak on March 22nd, Wesley notified scientists coordinating observations of NASA's Cassini spacecraft. By March 25th the spacecraft's Composite Infrared Spectrometer (CIRS), which already had observations planned near the spot's latitude, had homed in on it.
Early results from Cassini's quick look, announced today in a press release, reveal that the spot contains traces of phosphine (PH3) and slightly cooler temperatures than its surroundings. This implies that the storm cell had dredged up gas from deeper down; after reaching higher altitudes, ammonia in the plume condensed into highly reflective ice crystals.
Disturbances like this one seem to be concentrated in this latitude band of Saturn's southern hemisphere — so much so that observers refer to it as "Storm Alley." It was there that Cassini's cameras recorded a series of lightning flashes last November.