Tuesday, 5 February 2013

Second Night: Io's Volcanoes and Saturn's Beacon

View of the IRTF as the sun was setting.
After a brief hike up a cinder cone near to Hale Pohaku, it was time for dinner and the drive up to the IRTF for my second night on the summit.  John Lacy took me out to show me the TEXES instrument, and as he's leaving in the morning it's now my job to help Tommy Greathouse with the liquid-N2 and liquid-He fills to keep the instrument cold.

Jupiter and Volcanic Io

Things were a little windy at first, but we started with 3 hours of Jupiter time between 6pm and 9pm, running Glenn Orton's program to map a set of meteorological variables in the deep atmosphere.  This involved spectra sensitive to tropospheric temperatures, ammonia, phosphine and cloud opacity, all done in medium resolution scan mode, which means we can take spectra with the slit aligned north south and stepped from east to west across the whole planet.  Lots of rifting could be seen on the southern edge of Jupiter's NEB (north equatorial belt), but none of Jupiter's giant vortices were present (the GRS was just rising at the end of this 3-hour section).  But we did spot something really unusual in the southern hemisphere, in the latitude normally occupied by lots of white ovals.  There was a large cold feature, seemingly surrounded by a ring of elevated ammonia, suggestive of some dynamical circulation modulating the ammonia and aerosol fields....  [Correction:  Here's a great example of how O2-deprivation messes with your mind.  Oval BA is currently to the east the GRS, so would rise first.  The GRS transited at 08:35UT, so it makes sense that this rather dramatic southern hemisphere feature was just Oval BA, transiting the central meridian at 07:00UT at a longitude of 210W].

Inside the IRTF dome, showing the full
telescope at zenith.
Next we spent three hours on Con Tsangs and John Spencer's Io observing program.  We were trying to measure the abundance of SO2 in Io's atmosphere to distinguish between sources from SO2 frost or active volcanism on this moon of Jupiter.  More details of these Io observations, which will continue over the next few nights, can be found here.

From midnight until 2.30 am we spent our time looking at starburst regions in galaxies, again trying to measure the gas flows.  We were all getting a little philosophical at this time of night, and on viewing galaxy NGC4194, 129 million light years away from Earth, we notes that the light we're measuring from IRTF right now was emitted from that galaxy during the Cretaceous period, when dinosaurs still walked the Earth.  Pretty profound stuff! But I took this opportunity to head outside to do some long exposure photography of Orion, Ursa Major and the faint Milky Way....

Saturn's Beacon

When I was doing modelling and preparing for this run last month, I used a Cassini observation to predict the location of Saturn's giant stratospheric vortex, nicknamed the beacon, and it should have been right in view between 13:30-14:30 UT (i.e., by about 4am in Hawaii).  So the last three hours of the run were devoted to Saturn and mapping the stratospheric perturbations from the beacon.  We started measuring the powerful ethane emission as the beacon rotated on (spectacular manifolds of emission lines), then moved to methane for an age to try to measure stratospheric temperature, then back to ethane as the beacon was right on the central meridian (right on schedule, too!), before finishing with scans for acetylene and ethylene as the beacon was setting.  All these hydrocarbons are expected to be perturbed by the unusual chemistry within the vortex, to varying degrees, so we'll have to model these spectra to see what's really going on.
Watching the Saturn beacon data roll in....

One of the nice things about the ethane lines, apart from being fast, is that they show Saturn's rapid rotation too.  As we have the pixels aligned north-to-south, but move them east to west, we see the lines Doppler shifted towards us on the western limb and away from us on the eastern limb, as Saturn rotates west to east, just like on Earth.  You can actually see the lines moving in the spectra because Saturn is spinning!

Our last job of the night was a refill of the liquid helium and liquid nitrogen.... I've never played with liquid so cold before, and it took about an hour for us to transfer it into the dewar that surrounds TEXES, so the sun was well above the horizon by the time we headed down for breakfast.

View towards the west, showing the Keck domes after sunset.

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