BY DR EMILY BALDWIN
Posted: 23 January, 2009
The UK-built C1XS instrument flying aboard the Chandrayaan-1 orbiter has successfully detected its first X-ray signature from the Moon.
C1XS is an X-ray spectrometer, which works by detecting X-rays from the Sun which have been absorbed by atoms in the lunar soil, then re-emitted in such a way as to reveal the chemistry of the surface in that location, since each element has its own signature in X-rays. The sensitivity of the instrument is related to the activity of the Sun, for example, under ‘normal’ conditions, C1XS will be able to detect magnesium, aluminium and silicon X-rays. But during a solar flare, it may also be able to ‘see’ higher energy elements such as iron, titanium and calcium, thus enabling scientists to create an inventory of the Moon's chemical makeup.
The red curve shows the combined signal from all 24 C1XS X-ray detectors during the solar flare at 02:35-02:38 UT on 12 December 2008. The black dashed line shows the normal background signal detected by C1XS. The three “fingers” sticking up between 1 and 2 keV are due to the presence of the elements magnesium, aluminium and silicon (left to right) on the Moon.
This first detection was extremely significant for the mission since the solar flare was approximately 20 times weaker than the minimum C1XS was designed to detect. “We were pleasantly surprised that we managed to detect such a weak flare,” C1XS Science Principal Investigator Barry Kellet tells Astronomy Now. “In fact, the surprise was in reverse, we looked at the data first and saw that we had seen something and then were quite stunned to see the size of the flare that was occurring at the time.”
C1XS collected three minutes of data from a solar flare that was unleashed on 12 December 2008. The signal reveals the X-ray fingerprint of part of the lunar surface that corresponds to a region close to several of the Apollo landing sites, and near to an impact crater called Boscovich. The measurement also proves that C1XS suffered very little damage in the transition from the Earth, through the radiation belts, to the Moon. “Our performance at the Moon is significantly better than we could have ever hoped for,” says Kellet.
Chandrayaan-1 was flying over the nearside of the Moon in a region of lunar highlands when the flare went off.
The team will be praying that the Sun comes out of its quiet phase soon, entering into its expected period of greater activity. “The measurements depend on the Sun,” explains Kellet. “We have every expectation that the Sun will get more active. In that case, we expect to get global coverage of the Moon towards the middle or end of the third year of operations.”
The X-rays produced by the Sun are measured by a separate detector system, the X-ray Solar Monitor (XSM), supplied by the University of Helsinki, in order to accurately calibrate the X-rays detected at the Moon’s surface. Once the science team have processed the data from this first significant flare, and subsequent flares, they will begin to build up a detailed picture of the ingredients that make up the Moon. Ultimately, the results will yield vital clues to the origin of the Earth-Moon system, and what happened to the Moon since it formed and subsequently cooled.
“This sophisticated instrument will not only help us better understand the origin of the Earth-Moon system but will ensure that the UK plays an important role in this international activity,” adds Professor Richard Holdaway, Director of STFC’s Space Science and Technology Department.
C1XS is a toaster-sized instrument that was built by engineers and scientists at the Rutherford Appleton Laboratory in Didcot.
Chandrayaan-1 is India’s first mission to the Moon, and was launched from the Satish Dhawan Space Centre at Sriharikota in India on 22 October.
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