Antarctica may be the bottom of the world but – as the coldest, driest, highest continent on Earth – it’s proving ideal for observing the universe.
“Wrap up warm” has long been a mantra among astronomers everywhere, given that so much observation of the cosmos necessarily has to take place out in the open, at night! However, if you’ve ever grumbled about surviving a few hours outside during even a cold British winter night, just remember it could be worse – you could be in Antarctica, or even at the South Pole.
“I still remember the first time I flew down there,” says Kael Hanson, Director of the Wisconsin IceCube Particle Astrophysics Centre at the University of Wisconsin-Madison. “It was early November, which was just when the station opens for most people, and it was about –45˚C. It was quite a shock just to get off the aeroplane, and be out in that cold.
“It’s blinding bright too; unbelievably bright, because you have all this snow and everything is reflecting in your face. It’s also at altitude. The first couple of days you find yourself catching your breath – sometimes you wake up sort of gasping for air, just because of the altitude. It’s a pretty extreme environment.”
Extreme it might be, but that’s actually what makes Antarctica in general – and the South Pole in particular – such an ideal spot to locate your telescope. According to theoretical physicist Francis Halzen, also of the University of Wisconsin-Madison, the South Pole now ranks with the grand research laboratories such as Fermilab and CERN.
Astronomers ideally want somewhere cold, dark, remote and dry; Antarctica, and the South Pole in particular, fit the bill very well, which is why some of the world’s leading telescopes are now located less than a mile from the South Pole. Indeed, if you’re interested in millimetre-wavelength observations that are generally absorbed by atmospheric moisture, then the only place arguably better than Antarctica for your telescope is in space – which, of course, is a tad more inconvenient to reach later should you ever wish to upgrade your equipment. The South Pole is therefore an ideal location for astronomers, as the growing number of observational platforms established in the last few decades clearly shows.
It helps that, while the land at the South Pole is estimated to be around 100 metres (328 feet) above sea level, the ice sheet on top of it adds a further 2,700 meters (9,000 feet)! Given that the air we breath is enough of a distorting barrier to interfere with many astronomical observations – it’s why we see the stars twinkle, after all – telescopes located near the South Pole have significantly less atmosphere to look through.
The air’s also very cold and dry, reducing the atmospheric emission of infrared light which can interfere with observations. Plus, during the constant darkness experienced in Antarctica during the winter months (our summer), the relative lack of daily temperature extremes reduces the strength of any distorting air currents in the aurora-filled skies.
Such extreme conditions, nevertheless, can push both astronomers and their instruments to their physical limits. The Amundsen-Scott Station near the South Pole is only accessible for about three months each year, when it’s warm enough to fly aircraft in and out; this creates necessarily tight windows of opportunity for any telescopes to be assembled, calibrated and started up. Most of the teams involved with these projects will then leave, leaving only a few “winter-overs” to maintain things during the long “night” when the sun doesn’t rise above the horizon.
FLEXING THEIR BICEPS
Arguably, Antarctica-based astronomy really hit the headlines in March 2014 when a team working at the BICEP2 and Keck Array Experiments – led by John Kovac, of the Harvard-Smithsonian Center for Astrophysics – announced that they had successfully detected the much-sought “B-mode” polarisation in the cosmic microwave background (CMB) – some of the earliest light in the universe. This, they believed, was direct evidence of the gravitational waves generated during the theorised “cosmic inflation” which occurred in the earliest moments of the universe.
However, subsequent interpretation of their findings, allied with new data from the European Space Agency’s Planck satellite, suggested that this wasn’t the case – that the detected polarisation was, in fact, more likely due to the presence of greater than assumed levels of dust in our own galaxy. Nevertheless, the global interest in the findings proved that the work being carried out at “the bottom of the world” is – and remains – on the cutting edge of science.
BICEP (Background Imaging of Cosmic Extragalactic Polarisation), and the subsequent neighbouring Keck Array were (and are) designed specifically to detect the “B-mode” signature in the CMB. BICEP1 operated from the Dark Sector Lab at Amundsen-Scott South Pole Station – one of three permanent research stations in Antarctica, funded by the USA’s National Science Foundation – between January 2006 and December 2008. A second-generation instrument, BICEP2, featured a significantly greater number of detectors and operated from January 2010 until December 2012. By that time, the neighbouring Keck Array – a suite of five telescopes, each duplicating the BICEP2 detector – was fully operational.
BICEP2 has since been replaced by BICEP3 which, while retaining the same 2,460 detectors as the Keck Array, will cover much more of the sky. BICEP3 also has been designed without the need for the expensive liquid helium cooling system used by its predecessors to keep its detectors sufficiently cool.
As John Kovak has pointed out, one irony of Antarctic astronomy is that, sometimes, the South Pole just isn’t cold enough by itself!
WHAT’S IN A NAME?
Another telescope located at the South Pole to take advantage of its clear skies is the aptly – if not particularly imaginatively – named South Pole Telescope (SPT). Originally constructed in 2006 by a team led by several postdoctoral scientists from the University of Chicago, the 10 metre (30 feet) diameter telescope remains physically the largest ever deployed in Antarctica.
This scale was necessary for two reasons: to ensure the SPT’s observations at millimetre and sub-millimetre wave-lengths were – given the distance of the observed objects – both as sharp and as bright as possible.
The SPT’s initial project, began in March 2007 was a wide survey searching for distant clusters of galaxies based on their distortion of the CMB. When this data was combined with existing information on the galaxies estimated masses and the speed at which they were moving away from us (as measured by the red-shift of the light), the results have provided useful clues as to the nature of dark energy, the mysterious theoretical form of energy which is helping push everything in the universe apart.
Following the success of this first objective, the new SPTpol camera was installed in 2012. While providing even greater sensitivity, the more significant feature was – as the name suggests – the new sensor’s capability of measuring the polarisation of the incoming light. This means that the SPT, alongside the neighbouring BICEP instruments and Keck Array, is now being used chiefly to search for “B-mode” component in the polarisation of the CMB.
In July 2013, the SPT team announced they had done so, although this particular polarisation was the result of gravitational lensing of more conventional “E-mode” CMB polarisation. Nevertheless, according to the SPT project, this was a significant development in their cosmological work. “Successfully detecting this tiny B-mode signal represents a major milestone along the way to using the CMB to learn about the earliest moments of the universe.”
UP, UP AND AWAY
Even at the South Pole, atmospheric interference is still a problem for some astronomers, which is why – despite a reputation for having some of the fiercest weather on the planet – Antarctica is a global hot spot for scientific ballooning, including NASA’s own Ultra Long Duration Balloon Project. Balloons may strike you as old-tech, but there’s plenty of cutting edge technology involved in what remains a remarkably inexpensive way – at least in comparison with launching a satellite – of getting scientific instruments above 99.5% of the Earth’s atmosphere.
These 21st century balloons – designed to offer long-duration flights at stable altitudes – are often massive structures: NASA’s new heavy-lift Super Pressure Balloon (SPB), for example, is made from some 22 acres of toughened polyethylene film and is big enough, when fully inflated, to contain an entire football stadium. Plus, it’s capable of staying in position for weeks or even months.
Antartica is particularly good for scientific ballooning for two reasons: the circumpolar wind is a strong steady wind high in the stratosphere that carries balloons steadily and predictably around the globe; while the nightless Antarctic summers minimise the daily heating and cooling by the sun that causes balloons to lose altitude over time.
Notable balloon-carried projects include: ATIC (Advanced Thin Ionization Calorimeter), an international collaboration to measure the energy and composition of cosmic rays, first launched in 2000; BESS (Balloon-born Experiment with Superconducting Spectrometer), a joint US-Japan experiment to detect anti-matter particles in cosmic radiation at high altitudes; and NASA-funded ANITA (Antarctic Impulsive Transient Antenna), which is studying ultra-high energy (UHE) cosmic neutrinos (electrically neutral sub-atomic particles) by detecting the radio pulses emitted by their interactions with the Antarctic ice sheet. Three generations of ANITA have so far been launched (the most recent in December 2014), each dependent on the circumpolar winds to propel it around the continent for approximately a month before landing and recovery.
UNDER ICE
The IceCube Neutrino Observatory (aka IceCube) consists of an array of 5,000 highly sensitive optical sensors, buried sufficiently deep in the ice – from 1,450 metres (4,757 feet) to 2,450 metres (8,038 feet) – to hopefully detect the tiny cascade of electro-magnetic particles, including Chenenkof radiation, which occurs when neutrinos interact with the ice.
“The idea of a detector goes way back to 1960 with Russian Moisey Markov, who had the idea of using a big volume of water, but by the 1980s some people had the idea to use ice – if it was clear enough,” explains Kael Hanson, Director of the Wisconsin IceCube Particle Astrophysics Centre at the University of Wisconsin-Madison. “Because the optical properties of the ice at the South Pole are so favourable, light travels 100 metres — maybe up to 200m — in the deep ice without getting absorbed, so we can place our sensors relatively far apart and, in that manner, effectively instrument one square kilometre of target relatively cheaply,” says Hanson.
“Ice is even more transparent to radio waves,” he adds, “so we started a new line of detectors down there which use radio emission from neutrinos that interact with the ice. We think we can actually get much larger volumes using radio waves.
As early as April 2012, IceCube detected two neutrinos with energy signatures from outside the solar system, which the team nicknamed Bert and Ernie. “After we found Bert and Ernie we had the signal we knew we were looking for, and so we could go back and do a follow-up analysis of the data,” Hanson says. “From the first two years’ data, we found 26 more events that we think were coming from the same general phenomena, being accelerated in supernova remnants. The neutrinos are now really beginning to come out all over the place, now that we know what we’re looking for.”
DEEP DOWN
There’s more than you might think – and presumably much more than we currently know – underneath the Antarctica ice, not least an estimated 400 sub-glacial lakes. The largest and best known of these is Lake Vostok, named after the Russian research station that sits above its southern tip, itself famed for, in 1983, the coldest recorded temperature on Earth – -89°C (-129°F).
Approximately 250km (160 miles) long, and 50km (30 miles) at its widest point, Lake Vostok – at 12,500 square kilometres (4,830 square miles) it’s roughly eight times the size of London – has been isolated by about four kilometres (2.5 miles) of ice for an estimated 15 millions years.
Almost from when Lake Vostok’s existence was first confirmed in the early 1990s, astro-biologists have been speculating about what extreme alien eco-system the lake could contain, given that evolution has had 15 million years to do its own thing in the dark. More importantly, there are potential parallels with the sub-surface ocean which many believe exists on Jupiter’s moon Europa. If life is found in Lake Vostok, then why not on Europa?
Despite criticisms and pleas from the likes of the United States National Research Council and the Antarctic and Southern Ocean Coalition, Russian scientists have in the last few decades instigated several attempts to drill down to the lake. Relying largely on techniques which use Freon and kerosene to lubricate the borehole, there have been fears any recovered samples – and the lake itself – could be irretrievably contaminated.
The first core of freshly frozen lake ice was obtained on 10 January 2013, which Russian scientists say included DNA unlike any known bacteria. A second borehole was completed in January 2015; whatever the results of its analysis, it’s clear than a wide variety of technical, procedural and ethical issues will still be hotly discussed for years to come – and are likely to shape any future exploration of locations such as Europa.
THE OLDEST FORM OF ASTRONOMY
Astronomy in Antartica didn’t start with building the first telescopes or drilling the first boreholes. It began on 5 December 1912, when Francis Howard Bickerton, a member of Sir Douglas Mawson’s Australasian Antarctic Expedition, happened to pick up part of a meteorite, soon termed the Adelie Land Meteorite (ALM)
At least that’s the view of Michael Burton, a lecturer in astronomy and physics at the University of New South Wales. Weighing about 1 kilogram (2.2 pounds), the ALM – eventually classified as an “ordinary” chondrite – would be just the first of many thousands of discoveries.
Antarctica is now the richest source of meteorites in the world. Firstly, while meteorites fall randomly all around the planet, it’s easier to spot them against a plain background and a minimal accumulation of indigenous sediments; the East Antarctic ice sheet is perfect hunting ground for any meteorite hunter – go to the right place, and any rock you see must have plummeted from the sky.
Secondly, as the East Antarctic icesheet flows toward the edge of the continent, it’s occasionally blocked by mountains or subsurface obstructions, which help push meteorites trapped in old deep ice to particular areas of the surface where the elements blow away the snow and ice while preserving the meteorites.
In recent years, with human attention turning once again to the Moon and Mars, it’s useful to remember that a lot of what we have learned about our nearest astronomical neighbours wasn’t achieved by going there but by examining fragments which had been blasted off them, come crashing down in Antarctica and then been seen and picked up by people searching the freezing Antartica landscape.
Possibly the largest such programme is the US Antarctic Search for Meteorites (ANSMET) which, by 2012 had collected more than 20,000 meteorites. Parallel programmes have been run by Japan, China, and other nations over the years, providing much much of the extraterrestrial materials now available for scientific study around the world.
LAKE VOSTOK
Frozen Surface
The ice covering Lake Vostok is measured around 4km (2.5 miles) thick; that compares with estimates of up to 30km (19 miles) protecting Europa’s oceans.
Into the Deep
Measurements of Lake Vostok suggest an average depth of 432 metres (1,417 feet); Europa’s oceans are estimated at 100km (60 miles) – containing more than twice the volume of Earth’s oceans.
Water World
Lake Vostok remains liquid at -3˚C (27˚F) thanks to geothermal heat and high pressure. The heater for Europa’s oceans are tidal forces experienced during its speedy orbit round Jupiter.
WHERE DO COSMIC RAYS COME FROM?
Cosmic rays can tell us much about the universe, but how do we detect them?
Explosive Birth
Cosmic rays are high energy particles released primarily by massive supernova explosions. They include both electrically charged particles (protons, electrons) and non-electrically charged neutrinos.
Journey Into Space
Travelling through space, the electrically-charged cosmic rays will be deflected by the magnetic fields of nearby stars and galaxies; neutrinos, however, will head on unaffected.
Down to Earth
About 100 trillion neutrinos pass through your body every second, but you’d have to wait about 100 years for one to interact with one of your atoms!
Blocking out the Noise
IceCube is buried up to 2,500 metres (8,200 feet), using the Earth itself as a filter to block out more-locally produced cosmic rays while letting neutrinos in.
Into the Detector
IceCube consists of an array of 86 “strings” of digital optical modules (DOMs) set 125 metres (410 feet) apart. Each string has 60 DOMs some 17 metres (55 feet) apart.
Flash Photography
When neutrinos interact with the ice, they break up into electrically charged particles that emit Cherenkov light; this is what is recorded by the DOMs, and sent to the surface IceCube laboratory.
IceTop
IceTop, built as a “veto” and calibration detector for IceCube, also measures the cosmic-ray arrival directions in the Southern Hemisphere, as well as their flux and composition.
Gathering the Data
About 100 GB of timestamped, collected data is sent every day from the IceCube Laboratory on the surface to a data warehouse at the University of Wisconsin-Madison.
SPACE LAB AT THE SOUTH POLE
Antarctica is where a lot of space science is happening.
South Pole Telescope
The SPT team have recently installed a bigger, more sensitive camera on the telescope.
“In the next several years, we should be able to get to the sensitivity level where we can measure the number of neutrinos and derive their mass, which will tell us how they contribute to the overall density of the universe. This measurement will also enable even more sensitive constraints on inflation and has the potential to measure the energy scale of the associated physics that caused it.”
– Bradford Benson, Associate Scientist at Fermilab and Assistant Professor, University of Chicago.
IceCube
“We embedded more than 5,000 photosensors in the ice, more than a mile below the surface, to watch for faint flashes of light produced when subatomic particles called neutrinos happen to interact with atoms in the ice. I don’t know whether neutrinos will ever be useful – perhaps for communications, or geological exploration, or because what we learn from them provide new theories that allow us to better control matter and energy. But I’m willing to bet that the greatest invention of 2115, whatever it is, will connect back in some way to fundamental research being carried out now by someone who has no idea what it may ever be good for.”
– Tyce DeYoung, Associate Professor, College of Natural Science, Michigan State University.
BICEP2
“”South Pole Station is only accessible for about three months out of each year. The temperatures are only warm enough to fly planes in and out for that period of time. When we take one of these telescopes like BICEP1 or BICEP2 to the South Pole, we come in with a team and we work furiously for three months to try to get everything to work, to put it all together, to calibrate it, to tune it up, get it in pristine condition. Then all of us get on an aeroplane and leave – except for one guy. He watches the plane go and knows there isn’t going to be another one for about nine months.”
– John Kovac, Associate Professor of Astronomy and Physics, Harvard University
ANITA (BALLOON LAUNCH)
“To launch a balloon the surface winds have to be below about 8 knots, which is about 9 miles an hour. You also have to have low winds up to about 800 feet. The team use a small weather balloon, called a pi-ball (pilot balloon) to check those. Sometimes those winds will be stiff even if it is calm on the ground. You’ll see the pi-ball go up and then all of a sudden it will take off sideways. When these big stratospheric balloons are launched but not yet fully inflated, they are about 600 feet long. So if they go up and hit wind shear, they can be torn apart.”
– W Robert Binns, PhD, research professor of physics at Washington University.
METEORITE HUNTING
“During the systematic searches and sweeps we used only our eyes to scan the blue ice, sometimes with the aid of binoculars. Forming a line either on snowmobile or on foot we worked by moving in parallel transects spaced apart according to the terrain and concentration of meteorites. The fun began when someone waved his or her arms to signal the rest of the team to converge at the find. A snowmobile with a GPS receiver parked next to the meteorite to record about five minutes of location data and a collection bag was brought out.”
– Linda M V Martel, Hawaii Institute of Geophysics and Planetology.
HOW TO LAUNCH A SPACE BALLOON
Balloons are right on the cutting edge of space technology.
Launch Day Morning
The day begins with an evaluation of weather conditions; if this proves unfavourable, the launch will be postponed until either later the same day, or the next day.
Take Positions
The launch team take up their positions, while final tests are made. Auxiliary balloons used to hold the gondola during the release phase are filled with helium.
Bringing things together
The avionic gondola is brought to the launch area, and integrated with the remaining elements of the balloon for final testing and checking.
The Scientific Gondola
The scientific gondola, weighing up to 1,100kg (2,425 pounds), is assembled under the auxiliary balloons, as communication links between it and mission control are tested.
Main Balloon
The main balloon in carefully unfolded on a long protective mat, with operators donning gloves to protect the fragile material.
Inflation
The balloon is inflated with helium by two operators, a process which can take between 15 and 45 minutes.
Release
The main balloon is released and rises into the sky, ascent and flight path monitored by mission control. The auxiliary balloons are released from the gondola.
Rising to the Ceiling
The ballon reaches its given ceiling for the flight, which can be up to an altitude of 42km (26 miles). The collection of scientific data commences at this point.
Mission Completed
After a suitable landing site is identified, and recovery crews informed and mobilised, the flight chain is separated from the balloon. Both fall back to the ground.
Return to Earth
The deflated balloon falls to earth at about 20 metres (66 feet) a second; it is recovered, folded up and returned to the launch site.
Safe and Sound
Thanks to deployed parachutes, the scientific equipment lands gently within approximately 10km (6.2 miles) of the balloon. The recovery team secure the area.
Repatriation
A helicopter is used to lift the scientific equipment and any other relevant ballon components onto a lorry, for safe transit back to base.
Article published in All About Space #28.
