More on the recent Keck Observations of Io

On Friday, I posted a note about Franck Marchis' observations of Io using the Keck Telescope's adaptive optics system on June 28, 2010.  These observations allow us to sneak a peek at the ongoing volcanic activity on Io's anti-Jovian hemisphere.  Their images revealed hot lava at several volcanoes like Pillan Patera (the most intense hotspot seen on that date), Isum Patera, Marduk, Prometheus, and Volund (not Zamama as previously suspected).  These hotspots were seen in both 3.8 μm and 4.7 μm wavelength images, in the near infrared.  Hotspots were seen in only the 4.7 μm wavelength image, indicative of more cooled lava, at Rata Patera, Culann Patera, near Kurdalagon Patera, Tupan Patera, near a patera at 42.5 South Latitude, 172.5 West Longitude, and at a patera located at 6 degrees South, 190 degrees West.  All but the last of these hotspots was seen before by either Galileo or New Horizons as active volcanoes.  None of these hotspots were seen in the 2.1 μm image, suggesting that none of these volcanoes were vigorously active on June 28.  The 2.1 μm instead showed Io's surface in reflected sunlight.  Silicate materials show up as dark in the 2.1 μm image, while sulfurous materials show up as bright.

Now as Franck pointed out, this isn't the most exciting set of results.  Save one new hotspot, all the others were seen as active before and none are currently in an outburst phase.  But regardless, it is important to observe Io more often to understand what is typical in terms of volcanic activity on the satellite.  How often do outbursts occur?  You are not going to know that if some observing days reveal none.  Exciting, okay, maybe not, but VERY useful.

Anyways, I was a bit curious about the one exception to this "boring" fest, the new hotspot at 6 degrees South, 190 degrees West.  The patera this hotspot seems to be associated with is 60 kilometers by 45 kilometers in size.  The image at left shows various views taken by Galileo during its mission between November 1996 and October 1999.  As you can see, no changes were observed at this volcano during the Galileo mission, nor did the volcano look any different in New Horizons images taken in February 2007. While the 2.1 μm image from Keck has a very low resolution (150 km or so), there does seem to be dark spot associated with this volcano that would indicate the emplacement of dark lava, whereas before, the floor of the patera was covered with sulfurous materials.

Very intriguing stuff that at least one volcano on Io seems to have reawakened.

Link: Keck AO Observations: Io Volcanism - “Mornes plaines” [www.cosmicdiary.org]