European spacecraft Smart 1 is at the Moon's gateway, the region beyond which the probe is tugged more strongly by lunar gravity than by the Earth's. Dr Bernard Foing, chief scientist at the European Space Agency said the landmark was of symbolic importance.

Smart 1 will shed light on Earth's only natural satellite

On the night of Monday 15 November, Smart 1 will begin delicate manouevres to bring it into orbit around the Moon.

Once captured by the Moon's gravity, it begins to spiral closer to the lunar surface until reaching its final orbit.

The £70m probe will begin braking on Monday when it reaches a distance of about 50,000km. The ion engine will then fire continuously for four days as the spacecraft begins its inexorable spiral towards the Moon.

Eventually it will reach a stable elliptical orbit where it will range between 3,000km and 300km from the moon's surface.

Smart 1 will test a highly efficient solar-electric propulsion system as one of its key mission objectives.

The engine works by expelling a beam of charged xenon atoms - ions - from the back of the probe.

This produces thrust in the opposite direction, pushing the spacecraft forward.
The energy to feed the system comes from the solar panels, hence the term "solar-electric".

When it begins its scientific investigations in January 2005, Sm carries an X-ray spectrometer called D-CIXS which will comprehensively map chemical elements on the Moon's surface. This will help scientists test theories of its birth and evolution.

"We believe that the Moon is the daughter of the Earth and it was created [4.5 billion years ago] when a planetary embryo the size of Mars impacted the Earth," Dr Foing explained.

Suggests Mars-sized object crashed into early Earth Debris thrown into space aggregated into the Moon Supported by similar composition of Earth and Moon rocks

"This sent some mantle of the Earth into orbit and the debris re-condensed to form the Moon."

Conversely, studying the Moon's origins and evolution could also shed light on the composition of the early Earth.

One target for D-CIXS is the biggest impact crater in the Solar System - a massive hole in the Moon more than 2,000 miles across on its far side.

By looking down the hole, it should be possible to analyse the composition of rocks deep within the Moon's interior.

Perpetual light

Smart 1 will also survey a flat region known as the Peak of Eternal Light near the south pole which is thought to be bathed in perpetual sunlight and also appears to be flat.

This could render it a particularly suitable spot for future manned lunar bases.

"We will look at types of future landing activities for robotic and human bases," said Dr Foing.

"Smart-1 can be used as a precursor for long-term exploration of the planets."

The temperature in this region is stable at -20C; much more acceptable than the equator where the temperature varies from 120C to -170C.

Smart 1 will also look for water ice in very deep craters nearby which some scientists think could be used both to drink and to create oxygen for moonbase dwellers.

It will also search for possible building materials for a future moonbase.

"Another thing you need is building blocks. You need to find bits of the moon that are good for turning into concrete for building your lunar base," said Professor Manuel Grande, lead scientist for D-CIXS from the Rutherford-Appleton Laboratory in Didcot.

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