ÐÓ°ÉÔ­´´

We know it is 4.6 billion years old. We know its surface is made of
oxygen, silicon and aluminium. We have sent spacecraft to analyse it. We
have 400 kilograms of it stashed in laboratories on Earth. We have even
left footprints on it. But scientists are keen to do more. They would like
to map it, measure it, build on it and observe from it. Eventually, they
might even live on it. Although it is 25 years since we first landed on
the Moon, lunar exploration has only just begun.

Future exploration is likely to have an international flavour. At the
first International Lunar Workshop in Switzerland earlier this year, the
European Space Agency (ESA) suggested collaborating with international space
agencies including those of US, Russia and Japan and with scientists from
other countries on a project that could culminate in a permanent Moon base.
The ESA wants the International Moon Programme to begin in 2002 with a
£300 million mission to test lunar landing techniques. If this and
further missions are successful, astronauts might land on the Moon once
again by 2020.

Last month, a Japanese think-tank, the Lunar and Planetary Society,
proposed building a lunar base by 2024 at a cost of $30 billion – a tenth
of previous estimates. To save money, it says that the construction work
could be carried out entirely by robots using the Moon’s natural resources.
The robots and other equipment would be ferried there by the Japanese H-II
rocket which had its maiden flight in February.

Much work needs to be done before these plans can go ahead. Some has
already begun. Earlier this year, the American spacecraft Clementine photographed
the entire surface for the first time using 11 different wavelengths of
light. One of the first findings from the analysis of the 200-metre resolution
digital images was a giant 300-kilometre depression on the surface near
the South Pole. ÐÓ°ÉÔ­´´s hope the data will reveal whether ice exists
in this permanently shadowed region – perhaps as remnants of comet impacts.
Obviously, such a natural resource would be useful for human habitation.

As the results from Clementine are being examined, scientists at ESA
are designing the next generation of lunar explorers. One of the scientific
missions being considered is the Moon Orbiting Observatory which will be
placed in polar orbit 100 kilometres above the surface. MORO will carry
a stereo camera which will give three-dimensional images showing the shape
of the landscape to a resolution of less than 10 metres. It will measure
the height of surface features to an accuracy of a few metres with a radar
altimeter and produce images of the entire surface using a camera sensitive
to 250 separate wavelengths of light. Because minerals reflect light at
specific wavelengths, these pictures will provide a detailed map of the
type and abundance of minerals on the surface, thereby helping scientists
to understand the geological processes that shaped it.

MORO will also carry a gamma-ray detector to pick up the high-energy
radiation produced by atoms on the surface as they are excited by solar
radiation and cosmic rays, and by radioactive elements. Because the energy
of the gamma-rays depends on the element that produced them, measurements
of the energies will show the type of elements present on the surface. So
MORO can make an accurate inventory of the amounts of oxygen, silicon, magnesium,
iron and calcium as well as potassium, uranium and thorium.

ESA’s scientists also plan to measure the Moon’s gravitational field
by the way in which it influences the spacecraft’s orbit. Variations in
MORO’s orbit can be detected by Earth-based tracking stations but only when
the spacecraft is visible – the far side of the Moon cannot be mapped this
way. To deal with this, MORO will release a second, small satellite into
a different orbit which it will track to produce the first gravity map of
the farside.

ON THE FAR SIDE

Planetary scientists know that the far side is very different from
the near side. The crust is thought to be 40 kilometres thicker, for instance,
and the large craters lack the basalt rock filling of their counterparts
on the near side. Since the Moon’s gravitational field is determined by
the density and amount of rock in the crust and below, a comprehensive gravity
map will help scientists to refine their ideas about how the crust formed
and whether it was influenced by the Earth’s gravitational pull.

The Japanese Institute of Space and Astronautical Science is independently
planning a lunar flyby in 1997. As it passes, the spacecraft will fire three
probes equipped with seismic sensors at different parts of the surface.
Although there is little seismic activity, moonquakes occur when meteors
hit the surface sending shock waves through the body of the Moon. The arrival
times of these waves and their strength at different sites on the surface
depend on the type of materials they pass through and the route they take.
Such measurements should reveal the internal structure of the Moon.

Planetary scientists are not the only ones interested in the Moon. Because
it lacks an atmosphere, astronomers say it would be an ideal observatory
(in fact, the Moon does have an atmosphere, though it is a very thin one
that contains no more gas than the air in a three-bedroom house on Earth).
The Moon turns once every 27.3 days, allowing long uninterrupted viewing.
And in the permanently shadowed craters near the poles, the temperature
remains constant at about -200 degree C: ideal conditions for infrared telescopes.
In particular, astronomers are interested in placing telescopes on the far
side of the Moon because it is permanently shielded from electromagnetic
pollution from the Earth such as radio and TV broadcasts. Jocelyn Bell-Burnell,
president of the Royal Astronomical Society and an expert on radio astronomy,
says it is becoming harder to find quiet radio sites. She says, ‘used thoughtfully,
the Moon could be a very exciting observatory’.

Using a technique known as very long baseline interferometry, astronomers
could combine the observations from a radio telescope on the Moon with those
from Earth-based dishes. The set-up would be equivalent to a dish some 384
000 kilometres across. Its resolution would be 10 000 times greater than
existing radio telescopes, providing astronomers with details such as solar
flares on stars 100 light years away.

A much more ambitious project proposed by Bernard Burke at the Massachusetts
Institute of Technology would involve the construction of an array of 27
optical telescopes stretching 10 kilometres across the lunar surface. These
could be constructed from raw materials such as aluminium found on the Moon.
Glass could also be manufactured from lunar silicon dioxide and giant, high-quality
mirrors would be easier to cast in low-gravity conditions than on Earth.
Instead of seeing stars as points of light as we do on Earth, such an array
could resolve details such as sunspots on stars up to 300 light years away.

UNDERGROUND ACTIVITY

The Moon may also become a stepping stone for exploring the rest of
the Solar System. It is easier to launch spacecraft from the Moon because
of its lower gravity, but engineers would have to build the main bulk of
each rocket there first from lunar raw materials. Eventually, the oxygen
needed to fuel such craft could be taken from the lunar soil by electrolysis
or by heating it in solar-powered furnaces.

The Moon could also be used to study life, with a controlled artificial
environment yielding important information about how plants and humans cope
with low-gravity conditions. It would also be an ideal place to investigate
the effects of radiation on life and its molecular building blocks – possibly
showing how life began on Earth and whether it is likely to exist elsewhere.

If all this research is to take place at all, the scientists will need
permanent lunar bases. These bases, built using lunar reserves of iron,
aluminium and glass, would have to be underground to protect them from solar
radiation and from the temperature variations of up to 250 degree C throughout
the lunar day. Friedrich Horz, of the Johnson Space Center in Houston says
that such bases could be constructed in hollow lava tubes between 50 and
100 metres across that stretch under the surface of fields of volcanic rock.

Although ESA is keen to explore the Moon, it is quick to point out that
the lunar environment must be preserved. Each Apollo mission released gas
equivalent to the whole of the existing lunar atmosphere. For example,
at the site of the third manned mission to land on the surface, Apollo 14,
it will be years before the atmospheric pressure returns to normal as the
gas escapes into space. Frequent visits could create a permanent atmosphere
of rocket exhaust in some places. Human activity will require radio communications
– destroying the very conditions scientists want to exploit. Even bases
and the scientists themselves will generate infrared (heat) radiation which
could ruin the results of infrared telescopes. Bell-Burnell believes it
may be necessary to operate astronomical instruments remotely, visiting
the sites only to carry out maintenance and essential repairs. Bases should
have rigidly controlled and self-contained life support systems. The recycling
of all wastes, particularly liquids and gases which could pollute the atmosphere,
would be essential to preserve the lunar environment.

The Moon is a potential wealth of resources and a natural laboratory
and observatory that could yield rich scientific bounty. But it would be
easy to damage the thing we want to study. At the moment, scientists are
discussing how to prevent the damage they could cause. Whether humans will
preserve the lunar environment when they return remains to be seen.

Julie Cave is a planetary scientist at University College London. She
is also a member of the MORO science team.