Observing Jupiter from Mauna Kea Observatory, Hawaii

Mount Hualalai viewed from the
MKO dormitories. Credit: Steve Miller.

I have been visiting Hawaii to use the telescopes of the Mauna Kea Observatory for 20 years. But I still get a thrill every time I come up here. The Big Island of Hawaii is like nowhere else on Earth.

The Hawaiian chain is made up of some of the most isolated places in the world, set in the middle of the Pacific Ocean. Once you get to the West Coast of the United States - and that involves an 11-hour flight from London where I live most of the time - it is still another 5 to 6 hours of flying over the ocean. Hilo, on the eastern shore of Hawaii, is at longitude 155 West and latitude 20 North, with an 11-hour time lag to London in the summer.

Mauna Kea viewed from across
Hilo Bay. Credit: Steve Miller.

Hilo is my favourite place in Hawaii: it is where my wife grew up and still has her family home; a place to take a few days rest after the long flight over and before heading up the mountain.

The prevailing westward-blowing Trade Winds (usually) bring rain to the eastern side of Hawaii. (This year, there has only been 50cm of rain so far, very dry by Hilo standards.) That makes for tropical rain forest. But the 50 kilometre drive up to the observatory dormitories takes you up 3,000 metres in altitude, and the vegetation changes from lush "jungle", through Ohia forest, to scrub, to not very much at all except a few bushes and plants that the Brits have christened "triffids" for their odd, slightly menacing look.

A pukiawe bush on the slopes of Mauna
Kea, an example of the mountain's
unique plant life. Credit: Steve Miller

Looking westwards from the dormitories over the lava fields and cinder cones down towards the Kona side of the island, you are looking out over what becomes desert. The two giant mountains - Mauna Kea and Mauna Loa - that dominate the centre of the Big Island ensure that almost all of the rainfall happens on the eastern side of the island: Kona is pretty much in a total rain shadow.

Henrik and Steve outside the
NASA IRTF. Credit: Steve Miller

Tonight is our acclimatisation night. Although we will go up to the summit to watch the sunset, and get a bit of 4,200-metre altitude exposure, Henrik Melin (my co-observer) and I will spend most of the night at the 3,000-metre level where the dormitories are. We will use the time preparing, logged on to the interface of the NASA Infrared Telescope Facility (IRTF), setting up for our four six-hour shifts observing Jupiter.

The mountain top of Haleakala on the
neighbouring island of Maui viewed
above the cloud tops. Credit: S Miller.

Our goal is to map the emission from a molecule (strictly speaking a molecular ion) called H3+, the third form of Hydrogen, after the H atom and the H2 molecule. This ion is formed high up in Jupiter's atmosphere, where the pressure is less than one millionth of a bar, and temperatures soar to well over 1,000 K. It traces high levels of energy inputs: around the poles of Jupiter, it shows where high energy particles smash into the top of the atmosphere causing bright aurorae, like our Northern and Southern Lights on Earth; at lower latitudes, it is formed ultraviolet radiation from the Sun.

There's a free drink on Steve at the Rome
EPSC for the first person to email him
 with the correct identification of this!

We will use spectroscopy, breaking up the (infrared) light from Jupiter into individual fingerprint lines from H3+, clearly identifying the molecule as if we were forensic scientists. But better - spectroscopy not only tells us who left the tell-tale fingerprints, but we can also say how hot their "hand" was at the time.

The domes of the twin Keck 10-metre
telescopes viewed against the
setting Sun. Credit: Steve Miller

IRTF is definitely not the biggest telescope in the suite available on Mauna Kea: with a mirror that comes in at just under 3 metres in diameter, it is dwarfed by the twin 10-metre Keck telescopes, and Gemini and Subaru, both at 8 metres in diameter. But it is one of the older generation. It opened in 1979 alongside the United Kingdom's Infrared Telescope (UKIRT) and the Canada-France-Hawaii Telescope (CHFT).

And in many ways it is my favourite. It was the first telescope I used here in 1990. It devotes 50% of its time to solar system science. And it still welcomes observers at the summit to do time-critical hands-on observations.