Manuel Grande wants to run a few more rings around the moon. At the end of this exercise, with luck, he and his colleagues will know why the moon is there and where it came from. He may even have pinpointed the perfect place for a future manned lunar base, and all with a little instrument on a European spacecraft called Smart-1.
Thirty years ago this week the Apollo astronauts confirmed that the moon was not made of green cheese - and brought back the rocks to prove it - but from the point of view of solar system science, they all went to the wrong place.
This they had to do in order to get home again. They landed on the moon's "seas" at the equator, on the side facing the earth: Apollo 11 actually touched down in the Sea of Tranquillity. But the rocks they gathered told a story of violence, and melting, and lava flows over the aeons. These said nothing about the original fabric - the quantities and varieties of silicon and magnesium and aluminium - of the earth's mysterious waltz partner, and nothing about the cataclysm about 4.4 billion years ago, by which the moon was made.
"The best theory is that a Mars-sized object hit a proto-earth. Somehow the cores combined and a great wodge of mantle type stuff was sprayed around and part of that recondensed into the moon. But when you look at the elemental compositions and the isotopic half-lives from Apollo data there are quite a lot of discrepancies," Dr Grande says. "This theory is the best there is, but the devil is in the details and the details are on the moon."
Dr Grande is a member of the planets and space plasma group at the Rutherford Appleton laboratory in Oxfordshire, and the chief investigator for a new x-ray instrument aboard Smart-1, or small mission for advanced research technology. This will be built by the Swedes and launched by the European Space Agency in 2002, which in turn will be 30 years since the last Apollo astronaut picked up the last rock from the moon.
The kind of terrain safe for Apollo to land and take off represented only a tenth of the moon's surface. There are secrets to be wrested from the ancient highlands, and from impact craters so vast and deep - one is 2,500 km across and 12 km deep - as to have torn open the crust, and exposed the mantle.
The moon is a strange place, and strangely asymmetric. Its day is 28 earth days, or one orbit of the planet earth, from where only one side is visible. The surface facing the sun warms to 100¡C; in contrast the dark side drops to -200¡C. The Apollo teams visited a tiny fraction of the surface. A small military satellite called Clementine circled for just two lunar days before moving on; a satellite called Prospector which identified billions of tons of frozen water in polar craters last year is still circling and is about to crash on its surface. But Smart-1 will map it for a year, reading the signals from the ground below to provide a finely-detailed account of the elements in its rocks. This, says Dr Grande, could be enough for a history lesson in the making of both a planet and its moon.
"One of the very sensitive tests of this theory are the ratios of iron and magnesium: they can show you how the rocks crystallised out and that can show you if the moon came from the same place as earth. We don't have the measurements for the whole moon but when we do it will tie down what is possible," he says. "It might be that these numbers say, well, the earth and the moon couldn't have come from the same place; or it might say yes they could, and this and this must have happened."
Ten years ago President Bush talked of a return to the moon, but never set aside the money for the programme. The Japanese - who have their own mission, Selene, a year after Smart-1 - see commercial and scientific possibilities. It would be a chic place for very exclusive holidays; its low gravity would make it an easy place to jump off from into deep space; its dead surface (there are no earthquakes) would make it a stable place for telescopes. The problem has been where to put a lunar base that would survive a 300¡ C shift in temperature every lunar day, and how to keep it supplied with electricity, air and water.
But there is oxygen in the lunar rocks, and possibly billions of tons in craters at the poles where the sun never penetrates. There is at least a chance that there will be surface spots at the poles where the sun shines all the time. Solar power means electricity. With electric power, you could get oxygen from the rocks, and helium for fusion machines, and you could split the hydrogen from water for fuel, provided you had water. But do such places exist? That's why Smart-1 needs a year in orbit.
"You have the big craters at the pole which never see the light of the sun, and equally, between them you can have areas which see the light of the sun all the time. That would, obviously, be a great place for a lunar base: you could get power off the sun that's shining all the time, but equally you are neither fried nor frozen and you can crawl down into the craters and take the water out. If you only see these things in one season, the summer or winter, you don't know exactly which bits are always illuminated and which are never illuminated," says Dr Grande.
He can remember the original moon landings: he stayed up all night. But it didn't change his life, he says. He already knew, as a boy, that he wanted to be a space scientist. His interest started with that strange thing, space weather - what happens when electrically-charged bits from the sun slam into a planet's magnetic field - and was first fascinated by the planet Mercury.
"You have a planet with a magnetic field, so it has a magnetosphere, so it has auroras and so on. It has no atmosphere, so all that stuff hits the planetary surface. Mercury is an awful place: when these things hit the surface you get strong x-ray fluxes. I started off thinking what sort of instrument would I like to fly at Mercury? And it came back to: oh well, here's the chance to fly it at the moon. And I suddenly discovered that the Moon was great fun too."
