ÐÓ°ÉÔ­´´

‘Great God! This is an awful place.’ Reading these words emblazoned
over the bar at the Amundsen-Scott South Pole Station, you cannot but wonder
if Antarctica really has changed since Robert Falcon Scott stood here in
1912. Yes, the American base bearing his name and that of his Norwegian
rival Roald Amundsen is a warm, though spartan haven which is now easily
reached by plane. But walk a few hundred metres beyond what passes for civilisation
and the featureless ice-scape of the polar plateau appears much as it did
79 years ago.

This near pristine environment is a magnet for scientists in fields
as diverse as aeronomy and glaciology. But more and more researchers are
now looking beyond the shimmering aurora australis, and the troubling ozone
hole, to study the Sun, the stars, and how the Universe has evolved. Today,
the geodesic dome at the American base is surrounded with instruments monitoring
the Universe at visible, radio, and gamma-ray wavelengths.

The potential of the South Pole as an astronomical site was first officially
recognised in 1970 in a report by the American National Academy of Sciences.
ÐÓ°ÉÔ­´´s – astronomers working on meteorological and geophysical projects
– who were then working at the Antarctic base gave an optimistic assessment
of the South Pole as a site for observing the Sun and stars. Unfortunately
these findings were ignored.

Nevertheless, Martin Pomerantz, a physicist who studied cosmic rays
and was then director of the Bartol Institute at the University of Delaware,
decided to pursue the idea of establishing an Antarctic observatory. He
had recognised the potential of a Polar site after travelling to Antarctica
during the International Geophysical Year in the late 1950s. At first Pomerantz
was not successful, but eventually, he enlisted leading researchers in different
areas of astronomy to help him to produce a research proposal for observing
at the South Pole.

One of Pomerantz’s first collaborators was Ulf Kusoffsky of the Royal
Swedish Academy of Sciences. In January 1979 they took a small refracting
telescope to the South Pole to assess the advantages of a Polar environment
for observing the Sun. One important plus was that the Sun could be observed
24 hours a day during the Antarctic summer. More significant than the researchers’
120 hours of continuous observations was their discovery that the view was
much steadier than they had expected from records of the climate.

Pomerantz returned the following year accompanied by Eric Fossat and
Gerard Grec of the University of Nice. Using the telescope erected the previous
year, they studied the interior of the Sun by detecting oscillations of
the Sun’s surface. These oscillations provide a way to probe the Sun’s structure
just as seismic waves help geologists to understand the interior of the
Earth. Identifying clearly the different modes of vibration requires very
long runs of continuous observations. Unfortunately, the day-night cycle
precludes carrying out long runs anywhere on Earth except in the polar regions.
The solar research programme at the South Pole has been so successful that
solar physicists have worked there virtually every year since.

Pomerantz’s promotion of Antarctic astronomy was not confined to solar
physics. In 1984 and 1985 he returned to the South Pole with another group
of French astronomers to study emissions from space in the little-known
submillimetre band of wavelengths – sandwiched between long-wave infrared
and short-wave radio waves. The radiotelescope they used, with its 45-centimetre
aperture, had previously operated at what is probably the finest astronomical
site on Earth – the summit of Mauna Kea, which reaches 4200 metres, on the
island of Hawaii. The researchers found that the Antarctic skies are only
one-tenth as ‘noisy’ as those over Hawaii.

Looking for footprints in the sky

One of the prime scientific reasons for studying the submillimetre and
adjacent millimetre spectral regions is to probe the cosmic background radiation
that has lingered from the big bang – the primordial explosion that started
our Universe. In particular, cosmologists want to know if this emission
has the same temperature and intensity in all directions. If astronomers
discover subtle variations in the intensity, for example, it will have important
consequences for theories of how matter first clumped together to form galaxies
in the Universe just after the big bang. The first ‘protogalaxies’ should
have left ‘footprints’ on the cosmic background radiation, in the form of
subtle variations in intensity in different directions. But finding variations
is no simple task. It involves measuring minute differences in temperature,
of a few millionths of a kelvin through an atmosphere at 300 K. Balloon
flights or satellites, such as NASA’s Cosmic Background Explorer (COBE),
can raise the equipment above the atmosphere, but they can carry only relatively
small telescopes. In addition, it takes years to prepare such flights and
they are far more expensive and inconvenient to use. A high, dry plateau
such as Antarctica provides an ideal site for a large millimetre-wave telescope
to study the cosmic background radiation.

In 1986, the first team to attempt such observations at the South Pole
was organised by Pomerantz and a research group from AT&T Bell Laboratories.
Although the observations were unsuccessful, they collected enough promising
data to encourage them to return two years later. When they did, they were
not alone. During the Antarctic summer of 1988 to 1989, AT&T and teams
from Princeton and the University of California, Santa Barbara, operated
five cosmic background experiments at a specially constructed site, about
1 kilometre from the South Pole. They returned two years later to make further
observations. In the following summer, researchers from the University of
California at Berkeley and the University of Milan erected five different
telescopes at the same site. This American-Italian collaboration was interested
in the radio spectrum between 4 and 36 centimetres. At these long wavelengths,
the researchers hoped to see distortions in the spectrum of the cosmic background
characteristic of a massive energy release in the early Universe.

The results obtained so far are sufficiently encouraging for countries
other than the US to make observations from the South Pole. This year a
team from Jodrell Bank in Britain will erect a cosmic background experiment
at Halley Bay, the base of the British Antarctic Survey. Researchers from
the University of Rome also plan to repeat their pioneering observations
made in 1987 and 1988 at millimetre wavelengths from the Italian Antarctic
base at Terra Nova Bay.

Another, more venerable, scientific problem is also being tackled at
the Amundsen-Scott Station. In the same year as Amundsen reached the South
Pole, the Austrian physicist Victor Hess began a series of balloon flights
that led to a new science – that of cosmic-ray physics. Today, researchers
know that cosmic rays are, in fact, atomic nuclei (mostly hydrogen) stripped
of their orbiting electrons. Some unknown process in the depths of space
accelerates these particles to energies far exceeding those obtained in
the most powerful accelerator laboratories. Indeed, the most potent cosmic
rays can attain the energy of a strongly served tennis ball. When one of
these particles, called a primary, ploughs into Earth’s upper atmosphere,
it triggers a so-called air shower of lower-energy particles which can be
detected at ground level.

Since Hess’s day researchers have sought the origin of cosmic rays.
Unfortunately, the primaries are electrically charged and so their paths
are bent by the galactic magnetic field. The direction from which a primary
cosmic ray arrives at the Earth is therefore no indication of where it came
from. Many theorists believe that processes generating high-energy cosmic
rays also cause the emission of gamma rays. One particularly promising theory
suggests that the intense magnetic fields of neutron stars in certain binary
star systems act as natural particle accelerators. Gamma rays are not deflected
by electromagnetic fields in space, and those of sufficiently high energy
can produce air showers of secondary particles. By searching for the objects
that emit gamma rays, researchers hope also to pinpoint the elusive sources
of cosmic rays.

In 1983 cosmic-ray researchers Wilhelm Stamm and Manfred Samorski at
the University of Kiel in Germany discovered mysterious radiation, with
incredibly high energies exceeding 1015 electronvolts. The radiation was
presumably electrically neutral and came from the direction of a binary
star called Cygnus X-3. This radiation was almost certainly gamma rays.
If Cygnus X-3 is such a powerful source of high-energy gamma rays, then
only a few such objects are needed to account for all the cosmic rays in
our Galaxy.

Michael Hillas of the University of Leeds set out to track down other
similar sources. His group operated an elaborate detector for air showers
at Haverah Park near Leeds, but its location was not good for this task.
Objects such as Cygnus X-3 are found mainly in the plane of our Galaxy and
near its core. These are regions best observed from the southern hemisphere.
In addition, the type of detector that Hillas was using is most sensitive
to those parts of the sky which are 40 o or more above the horizon. Simple
geometry left him no choice but to move to the South Pole.

With no Antarctic experience, the research group at Leeds approached
Pomerantz and suggested they should collaborate. Pomerantz says: ‘I was
thrilled, because I’d been in this field for 50 years and finally I’d be
involved in an experiment trying to detect the sources of cosmic rays.’

The South Pole Air Shower Experiment got off to a flying start. The
team saved time by making a scaled-down copy of the array at Haverah Park,
and detected their first cosmic rays only four weeks after arriving at the
South Pole in 1987. Their timing could not have been better. Part of the
way through the planning stage, Supernova 1987A exploded. It became one
of their candidate sources.

Superficially the array looks like 24 ‘beehives’ arranged in a series
of interconnecting hexagons around a central hut. The beehives are light-proof
boxes, each containing a scintillator that emits a flash of light when a
high-energy particle travels through it. The light pulses are sensed by
photomultipliers and recorded on magnetic tape. It is a very reliable and
prolific instrument. During its first winter of operation it was active
for 95 per cent of the available time and recorded more than 20 million
air showers. Indeed, the researchers have been almost drowned in a flood
of data. They still have not fully analysed it. The South Pole turned out
to be such a good site for gamma-ray observations that the researchers achieved
in weeks as many observations as they would have recorded in years at a
site basin in middle latitudes.

One result was clear after only a few weeks of observing. Supernova
1987A was not a detectable source of ultra-high-energy gamma rays. The supernova
1987A had, however, attracted another breed of gamma-ray astronomers to
the South Pole. Gamma rays with energies between 1011 and 1015 electronvolts
do not create secondary particles with sufficient energy to reach Earth’s
surface. However, these secondaries generate characteristic pulses of so-called
Ceerenkov light, a ‘photic-boom’ emitted when particles pass through the
atmosphere with speeds greater than light going through the air in the atmosphere,
which can be detected with a simple telescope with a photomultiplier tube
at its focus.

Trevor Weekes of the Smithsonian Astrophysical Observatory, who deployed
such a system in 1989, is now cooperating with Bob Morse of the University
of Wisconsin, Jim Gaidos of Purdue University and others in the construction
of a more elaborate telescope to detect this radiation. The first stage
of this project, which will continue for several years, was conducted last
year. It is an array of 10 reflectors, 90 centimetres wide, mounted so that
a promising candidate source called Centaurus X-5 passes through its field
of view each day. The team switched on the array on 24 April and it ran
through the Antarctic winter of 1990. The main problems that the researchers
encountered included interference from moonlight and strong auroral displays.

A major polar observatory

During the past Antarctic summer, Weekes and colleagues are upgrading
a prototype system by constructing a tracking mount, or ‘carousel’ on which
they are mounting twin 90-centimetre reflectors and a television camera
to monitor sky conditions. Next summer, Morse and his colleagues plan to
install the existing 10-telescope array on the carousel. They will also
begin constructing a single large telescope consisting of 48 tessellated
mirrors each 60 centimetres in diameter.

Astronomers hope to build on the current success of the South Pole as
an observing site. They are backed by John Lynch, the US National Science
Foundation’s programme manager for polar astronomy and aeronomy. Lynch declares:
‘One of my goals is to turn the pole station into a major astronomical observatory.’
Many of the astronomical projects performed so far have lasted just one
season. Observers have had to erect their equipment, test it, make their
observations, and then dismantle it again in a single summer.

If the South Pole is to become a major observatory where observations
can be performed on a routine basis, then permanent facilities are needed.
Perhaps the best evidence that major facilities are on their way is the
recent award of a multi-million dollar contract by the US National Science
Foundation to a consortium of astronomers based at the Yorkes Observatory
of the University of Chicago, to establish the Center for Astrophysical
Research in Antarctica (CARA). In the next few years, CARA scientists will
deploy advanced cosmic background submillimetre and infrared telescopes
at the South Pole (This Week, 16 March 1991).

Two other projects that are now in the planning stage may have a profound
influence on polar astronomy. First, the current South Pole Station has
exceeded its designed lifetime and its replacement is imminent. If astronomers
have their way the new station will be designed as an astronomical observatory
from the outset. Secondly, all existing Antarctic facilities are run by
individual nation states. What could be more in keeping with the spirit
of the Antarctic Treaty, asks Lynch, than the creation of one or more international
bases?

One possibility is to establish an observatory some 800 kilometres from
the South Pole at the crest of the East Antarctic ice cap. Here the altitude
is more than 4000 metres, with an atmospheric pressure equivalent to that
found 5000 metres above sea level. This rarefied atmosphere combined with
only a few centimetres of snow per year and mid-winter temperatures as low
as -90 °C make it potentially a better observing site than the South
Pole.

The scientific potential of such an observatory is not its only selling
point. Its ability to promote international cooperation and strengthen the
Antarctic Treaty are major advantages. Moreover, it would help in preparing
for human exploration of the Solar System: conditions at such a facility
would resemble those at a lunar or Martian outpost rather than an Antarctic
base. This plan received a boost at the recent meeting of the Scientific
Committee for Antarctic Research in Sao Paulo, Brazil. The committee is
the world coordinating body for Antarctic research, and it issued a statement
urging all its member nations to support this project.

Since the days of the first explorers, humans have always seen the reflection
of their own hopes and desires in Antarctica’s ice. As the treaty governing
the last undeveloped continent enters its fourth decade, it is clear to
many that the narrow dreams of national glory, territorial expansion and
economic exploitation which motivate much activity in Antarctica are not
true expressions of the human spirit. Perhaps astronomers are showing us
that this ‘last place on Earth’ is nothing less than a stepping stone to
the wider Universe.

David Smith is on leave from his position as technical editor of Sky
& Telescope as a Knight Science Journalism Fellow at MIT.

* * *

Astronomers take advantage of Antartica’s clear weather

Antarctica is often described as the highest, coldest, driest, and least
populated continent. Each of these extremes attracts astronomers. The South
Pole lies at 2835 metres above sea level and the pressure altitude is even
higher. Such an elevation puts a telescope above the turbulent lower atmosphere
that causes the blurring astronomers call ‘seeing’.

Antarctica is one of the driest of deserts with only a few centimetres
of precipitation annually. At the South Pole, summer temperatures rarely
rise above -20 °C and winter temperatures plummet to -70 °C and
colder. Thus what little water vapour there is falls to the ground as tiny
ice crystals. This exceptional low humidity is particularly appealing to
those studying infrared and radio wavelengths that are strongly absorbed
by atmospheric water vapour. Radio astronomers also benefit from the lack
of radio interference caused by major centres of population.

Antarctica’s weather offers astronomers another advantage. The presence
of a near-permanent high-pressure system over the South Pole promotes relatively
stable, clear weather. This, combined with 24 hours of daylight in summer
and 24 hours of darkness in winter, allows for near-continuous observations
of the Sun and stars for periods of many days. Strong winds are rare at
the South Pole. Antarctica’s famous blizzards are mainly a coastal phenomenon
caused when existing snow is whipped up by cold, dense air cascading off
the interior plateau.