Mankind will return to the Moon this month. A European rocket – with less power than a puff of breath – is set to enter lunar orbit after taking a year to travel there from Earth.
The Smart-1 robot probe, launched by the European Space Agency, will spend 2005 using an X-ray detector to map the composition of the Moon’s surface. Results will then be used to solve one of astronomy’s greatest mysteries: the origin of the Moon.
Most scientists believe the Earth and the Moon were created when an ancient planet and our own world collided four billion years ago. Moon rock studies have provided some supporting, but not conclusive, evidence for this idea.
‘Apollo astronauts brought back a third of a tonne of lunar rocks but from only a few localised sites,’ said Professor Manuel Grande of Britain’s Rutherford-Appleton laboratory.
Smart was originally designed to test the feasibility of ‘ion engines’ which operate by shooting out streams of electrically-charged xenon. This generates a tiny thrust equivalent to a postcard resting on a person’s hand. But unlike standard chemical rockets, which can fire only in bursts before exhausting their fuel, an ion engine can burn continuously for years. This has allowed Smart slowly to expand its orbit round Earth since its launch in September 2003. Now the interplanetary tortoise is scheduled to enter the Moon’s gravitation field on 15 November.
Once in lunar orbit, Smart will continue to fire its engines so that it ends up sweeping low over the Moon. It will then use its British-built detectors to scan the surface.
The sun emits X-rays and these are reflected back into space by atoms on the Moon’s surface. A magnesium atom will reflect an X-ray in a different way from an iron atom, and Grande’s detector can detect these differences.
Flying over the lunar poles, so that it covers the entire Moon as it revolves below, Smart will create strip maps of the surface – and eventually a global map of its composition.
‘We have a good idea what the lunar plains – the dark grey areas we can see at the equator – are made of,’ Grande said. ‘The Apollo astronauts landed and collected their samples there. The higher, mountainous areas – the lighter areas we can see from Earth – are formed of older rocks. We want to know what they are made of, as well.’
Smart’s map should provide that data and show if scientists are right in believing that the Moon coalesced from a vast ring of debris generated when an ancient planet the size of Mars destroyed itself after crashing into Earth. Understanding the origins of the Moon will therefore give insights into the nature of our planet.
‘The mission has been a total success,’ said Octavio Camino, operations manager for Smart. ‘We have shown that even a small ion engine like Smart’s can get us across space. Now we are planning to build space telescopes and robot probes to planets such as Mercury, using bigger and more powerful ion engines. These will take years off space-travel times. Instead of decades-long missions, we will take only a couple of years to cross space for future projects.’
But a major problem remains. Ion engines need electricity and only solar panels can provide enough at present. So ion engine missions will be restricted to planets and moons near the Sun. The solution to this problem will be to build a new type of electricity generator, say engineers.
Such a project is now being tackled by Nasa, It has recently begun designing a nuclear power plant that could supply enough electricity to run ion engines on deep-space missions. The first such mission would seek out life on Europa, the ice-covered moon of Jupiter.
Scientists believe nuclear-powered ion-drives are their only real hope of exploring deep space, and vigorously support their development. Not surprisingly, anti-nuclear protesters, like the Global Network Against Weapons and Nuclear Power in Space, have pledged opposition. Robin McKie, Guardian Unlimited