From South Pole to Dome C: Antarctic astronomy 10 years on
The rear door of the Hercules lifted, a shaft of bright light illuminated the dark interior of the transport plane, and the first bite of the polar air gripped me. I'd arrived at the South Pole at last. It was January 1994, nearly four years on from when a small group of idealists had dared to dream that Australians could do astronomy in Antarctica. With the encouragement of colleagues from the recently formed US Center for Astrophysical Research in Antarctica, we'd put together two experiments to test our speculations about the conditions we'd encounter. There were two questions we hoped to answer that coming winter. Would the infrared sky be 100 times darker than in Australia, and was there 'super-seeing' of the stars?
Jamie Lloyd, who'd just finished his honours year at the University of New South Wales (UNSW), was the advance party, and I was the following infantry division. He'd arrived a week before me, hand-carrying what looked, to anyone else, like a golden dust-bin with him on the plane. It was the IRPS, or Infrared Photometer Spectrometer, the subject of his honours thesis. Ten years previously it had been a state-of-the-art instrument on the Anglo Australian Telescope, used by David Allen to pioneer the fledgling field of infrared astronomy. Now it was about to become Australia's first experiment at the South Pole, and our first step on the road which we hope will lead to the building of the world's largest telescopes on the summits of the Antarctic plateau, able to look back in time to the formation of planets, stars and galaxies.
I was bringing with me a second experiment, put together by Rodney Marks, a young graduate student who in the last year had taught himself French, headed off to the Université de Nice on the French Riviera to learn the science of micro-thermal turbulence from its master, Jean Vernin, and returned to UNSW to build his own experiment to measure the turbulence above the South Pole.
The IRPS had been 'winterised' over the previous six months by Jamie, working under the supervision of my colleague Michael Ashley, both doing their best to anticipate how it would perform when left outside, at up to minus 75 degrees for six months, while needing to be filled each day with liquid nitrogen (100 degrees colder still), in the winter dark, by winterer John Briggs. Jamie had laboured heroically in the week before I arrived putting the IRPS together, working in a laboratory still under construction, confined to the corner of a desk, with two other telescopes also going up around him. However the IRPS was still in bits when I got there, and we had all of a one hour change-over, for Jamie was to depart on the plane I'd just arrived on!
Jamie tried to brief me on where he'd got up to, while I sat mutely in the galley, trying to take it in while gasping for breath, as all new arrivals to Pole do, unaccustomed to the thin, dry air at a pressure altitude of over 3,000 m. Then Jamie shot off, and I was left with John Briggs to get the IRPS and the micro-thermal experiments together in this alien environment.
Somehow we did it and, a week later, when I saw the Moon pass through the beam of the 5mm diameter 'telescope' that the IRPS effectively was, shining brightly in the infrared 'L-band' of 3.8 microns, it was perhaps the most exciting moment of my professional life as an astronomer.
That winter the IRPS confirmed for us that the infrared sky was indeed as dark as we'd anticipated (see Figure 1, and photograph previous page). However, we also found that the boundary layer generated considerable turbulence that disturbs the smooth wave-front arriving from an astronomical source in its last few metres before it would reach a telescope, creating the appearance of an excessive twinkling of the stars.
The infrared observations led us, four years later in 1998, to our first 'real' astronomical experiment, when we worked with our US colleagues on the 60cm SPIREX telescope, to image star forming regions in our Galaxy in the thermal infrared wavebands, from 2-4 microns. We were able to view extensive clouds of complex organic molecules enshrouding protostars, still embedded within great clouds of dust, the natal cocoons from which they were being born (see infrared image previous page).
The micro-thermal turbulence measurements, on the other hand, caused something of a puzzle to us as we sought to understand the implications they posed. They led to a series of further experiments over the coming years as we fully characterised the turbulence. Yet, while the measurements caused some dismay at first, they may be leading us to a remarkable, if somewhat abstruse, conclusion, now that we have managed to take them from Dome C.
Dome C is one of the summits of the Antarctic plateau, in the middle of the Australian Antarctic Territory, and the site of the French-Italian Concordia Station. Our measurements suggest that it may be the best site in the world for the next generation of optical/infrared telescopes with diameters of up to 100m. The extremely narrow boundary layer in which all the turbulence is generated greatly simplifies the requirements for adaptive optics correction, an essential element in recovering the diffraction limit of a telescope from distortions caused by the atmosphere, thereby allowing the telescope to image sources with a clarity almost equivalent to being in space.
This January marks for us a decade of astronomy on the Antarctic plateau. The early site testing experiments were soon followed by a more sophisticated approach, that of the 'automated astrophysical site testing observatory' or AASTO (see image on previous page), and involving scientists from the ANU. Driven by the enthusiasm and vision of John Storey, leader of the UNSW group, a series of increasingly sophisticated experiments were built for the AASTO: sky monitors to measure the sky at optical, infrared and sub-millimetre wavebands, and instruments to characterise the turbulence profiles at all heights through the atmosphere.
Working with the AASTO has been an eventful experience, for the trials of winterising and automating experiments are not trivial ones! The greatest challenges have been caused not by the experiments, but by the need to provide reliable power to run them in a warm but autonomous environment. Perhaps reminiscent of the challenge faced by Mawson's men in 1911 trying to get their 'air tractor' working to haul their equipment, the problem of reliable power generation almost proved our nemesis.
Perseverance paid off, and the AASTO produced a string of results. The site testing program at the South Pole is now virtually over; we expect measurements there to finish after this coming winter. Our work at the Pole is not over, however. One of the experiments is already being adapted to a new use, the search for exoplanets, orbiting around other stars! That story will have to wait for another day.
We have now reached the next stage of the journey to an Antarctic observatory, Dome C. With the rapid development of Concordia station by the French and Italians, a new frontier is opening here for Antarctic science. Extreme cold, dryness, absence of katabatic winds, and high elevation hold the promise of providing the best Earth-based site for observing the distant Cosmos.
Jon Lawrence, a postdoctoral fellow in our group, redesigned the AASTO into the AASTINO (automated astrophysical site testing international observatory), complete with a new, improved power generator, a Whispergen engine (see image above). Originally designed for ocean yachting but now transformed for Antarctica, and working on the principle of a Stirling thermodynamic engine, it has proved far more reliable than the propane-fuelled thermoelectric generator used on the AASTO. This last winter the AASTINO operated, completely autonomously, for over 100 'days' at Dome C. While we communicated with it via Iridium telephone, it was sited over 1,000 km away from the nearest human being. See for yourself the amazing results from the webcam at http://www.phys.unsw.edu.au/southpolediaries/– hardly a day of cloud was seen during the entire period!
The first scientists will be wintering at Concordia Station in two seasons' time. The initial results from the first full season of winter measurements there exceeded expectations, and interest in the site as the possible location for an 'extremely large telescope' (ELT) is growing rapidly, especially in Europe. A few parameters for the site still need to be ascertained before such a decision would be made, in particular the characteristics of high-altitude turbulence. We are building an instrument, a 'multi-aperture scintillation sensor', or MASS, in conjunction with NASA's Jet Propulsion Laboratory, in order to make the necessary measurements this coming winter. If the results turn out as we anticipate, there may be only one logical place to build the ELT – a prospect that has one salivating!
Visit the South Pole Diaries website at http://www.phys.unsw.edu.au/southpolediaries/ for further information, including our daily diaries from 1994, picture galleries and web cameras of the South Pole and Dome C, and a full bibliography of Antarctic astronomy publications.
Michael Burton, School of Physics, University of New South Wales