Friday, 15 April 2011

Yet more frustration

Following on from Henrik Melin's and Tom Stallard's blogs, it's a shame to have to report that the weather on Maunakea is still playing with us unfairly. Tom and I are currently using the Keck II telescope. This is one of the William Keck Observatory's two 10-meter telescopes on the summit. Our target is Saturn; our purpose to support observations being made by the Cassini spacecraft orbiting the Ringed Planet.

Except ... just when the sky is clear, the air immediately around the telescope has decided to get rather too moist for observing. The danger is that drops of water, or even ice crystals, will start to form either on the primary, light-gathering, mirror, or on the secondary mirrors, that focusses the light back down into the instruments. So, after a few short observations to show that we really could get the spectra of Saturn that we wanted, the weather has decided that we can't! And it looks as if by the time we can open the telescope again, Saturn will have dropped below our horizon.

It's at times like this when you realise that astronomy really is real-time. Saturn will never be quite the same again, and if it had been doing something really, really interesting, well - we missed it. Never mind, we have another shot at it in two days time - weather permitting.

So our plan had been to try to measure the spectrum coming from Saturn's upper atmosphere at a very high spectral and spatial resolution. The upper atmospheres of giant planets are composed mainly of molecular and atomic hydrogen, into which a bit of helium has been mixed. Sunlight and the impact of high-energy electrons, hurled at the planet from its magnetosphere and the solar wind, create a third form of hydrogen called H3+ (H-three-plus) that consists of three hydrogen atoms joined together and then ionised by the loss of a negative electron to form a positively charged, molecular ion.

H3+ is a signature molecule; it shows up where energy is being deposited into Saturn and energetic processes are occurring. Tracing where it is to be found, how much, and how hot, helps us to understand just how the saturnian magnetosphere - that region of space controlled by Saturn's magnetic field - couples into the planet itself. And we are hoping that will then help us to understand some other key questions - like why is the upper atmosphere of Saturn (and Jupiter, Uranus and Neptune) much hotter than it should be, based on the amount of sunlight the planet receives.

Tonight, Tom and I are not actually on the summit of Mauna Kea (4,200 meters above sea level) but at the much more comfortable 800-ish meter altitude level of Waimea. For the Keck observatory, working astronomers are kept pretty well oxygenated at the main HQ itself, communicating by video conference with the telescope operator, who is at the summit controlling things. It works pretty well, although I still prefer the hands-on feel of being at the summit and sitting next to the telescope operator.

PS we just got open again and onto Saturn - for one minute. Hey-ho!

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