Probe crashes into Moon's surface - BBC

http://news.bbc.co.uk/2/hi/science/nature/5309656.stm

Scientists hope to view the rock beneath the moon's surface Mission update

Europe's lunar satellite, the Smart 1 probe, has ended its mission by crashing onto the Moon's surface in a controlled collision.

It was a spectacular end for the robotic probe, which has spent the last 16 months testing innovative and miniaturised space technologies.

Smart 1 has also produced detailed maps of the Moon's chemical make-up, to help refine theories about its birth.

At 0542 GMT (0642 BST), the probe thumped into a volcanic plain.

With an impact speed of about 7,200km/h (4,500mph), even at a glancing blow of just one degree to the surface, the probe met a sufficiently violent end for telescopes to observe the event from Earth.

Smart 1 was returning pictures as it plunged towards the Moon's Lake of Excellence. Controllers and scientists at the European Space Agency's (Esa) operations centre in Darmstadt, Germany, clapped and cheered after the spacecraft smacked into the surface.

Astronomers in Hawaii observed a flash as Smart 1 crashed

"As planned, Smart 1 has landed," said Professor Bernard Foing, the mission's project scientist from Esa.

The Canada France Hawaii Telescope on Mauna Kea, in Hawaii, captured an infrared picture of a bright flash as Smart 1 hit its target.

"I was really surprised as the flash was very impressive. I was betting on not seeing much," said Gerhard Schwehm, mission manager for Smart 1.

The hope now is that the impact will have kicked up a big enough plume of fresh lunar "soil" for scientists to study its composition using ground telescopes.

The impact was expected to leave a 3m by 10m (10ft by 30ft) crater on the Moon, spreading debris over 80 sq km (30 sq miles).

"We know a lot about the Moon, but there are things we need to know more precisely if we are to embark on ambitious projects like those the US has planned," Dr Schwehm told the BBC News website.

A fleet of spacecraft - both orbiters and landers - are now expected to visit the Moon in the next few years.

GIANT IMPACT THEORIES Suggest Mars-sized object crashed into early Earth Debris thrown into space aggregated into the Moon Evidence in similar composition of Earth and Moon rocks Smart will tell how much Earth is in the Moon and vice versa

This train of robotic explorers will culminate in US astronauts returning to the lunar surface for the first time since the Apollo missions, probably in 2020.

Smart 1 was launched on an Ariane 5 rocket in September 2003 as a technology demonstrator.

It became Europe's first space science mission to use an ion engine instead of chemical combustion to reach its destination.

The system drew power through the probe's solar wings and then used this energy to propel the spacecraft forward by expelling charged particles of xenon. It was highly efficient, covering 100 million km in a series of looping orbits and using just 60 litres of "fuel".

Professor Manuel Grande has been principal investigator on one of Smart's miniaturised instruments: the compact X-ray spectrometer known as D-CIXS.

SMART'S SPACE GAINS Mini-instruments, navigation and operational software to go on future Solar System probes Smart-like solar-electric engines to become the dominant propulsion system Data improves Moon knowledge - history of impacts and volcanism; good landing sites

It has made mineral maps of the Moon's composition, looking at the distribution of calcium, magnesium, aluminium, silicon and iron.

Knowing the absolute abundances of these elements will help to refine theories for the Moon's formation. These describe the satellite emerging from the debris thrown out from a mighty collision between Earth and a Mars-sized body billions of years ago.

"It will take a long time for to work through the detail; the devil is in the detail with the X-ray instruments," said the University of Wales, Aberystwyth, researcher.

"But when we finally put the picture together what we will get is maps of what the Moon is made of."

On Saturday, mission controllers had to raise Smart 1's orbit by 600m (2,000ft) to avoid hitting a crater rim on final approach. Had the orbit not been raised, the craft would have crashed one orbit too soon - making the impact difficult or impossible to observe.

"Smart 1 will now rest in peace on the Moon," said Professor Foing.

"We are now collaborating with the international community, preparing the way for the future exploration of the Moon - the next fleet of orbiters, landers; leading to robotic villages and human bases."

HOW SMART 1'S ION ENGINE WORKS 1. Xenon gas atoms are pumped into a cylindrical chamber, where they collide with electrons from the cathode. The electrons - which are negatively charged - knock electrons off the xenon atoms, creating xenon ions - which are positively charged. 2. Coils outside the chamber create a magnetic field, which causes electrons from the cathode to spiral and become trapped at the mouth of the chamber. 3. The build-up of negatively charged electrons at the mouth of the chamber attracts the positively charged ions, accelerating them out of the chamber. 4. The stream of accelerated ions leaving the chamber thrusts the spacecraft forward. Although the force is small, over time it creates great speed in the frictionless environment of space.