Magnetic view

Leicester University has beaten off more than 80 competitors for NASA funding to develop an X-ray telescope that could be used on the Moon.

In collaboration with scientists from the US and the Czech Republic, the team will use the grant for a technical feasibility study for the Magnetosheath Explorer in X-rays (MagEX) telescope.

This will be used to investigate the magnetosheath, the magnetic shield that protects the Earth from solar wind, a stream of electrically charged particles emitted by the Sun that can harm humans because of its radioactivity.

When the particles strike the magnetosheath — a mixture of neutral particles and ionised plasmas — it glows in X-rays that would be invisible to the naked eye, but would be detectable by the lunar telescope.

'MagEX will be unique in that it will be able to view our Earth's entire magnetosheath for the first time,' said Dr Steven Sembay, Leicester's lead scientist. 'We will be able to look at the whole dynamic picture of how the solar wind is interacting with our magnetosheath.'

Existing methods of studying the magnetosheath only give a partial picture because instruments are put out into space for in situ point measurement, which means measurements of the particle radiation from the Sun are taken only as they pass the instrument.

At less than 1m high and with a weight of 20kg-40kg, the telescope would be compact enough for an astronaut to unpack and install on to the Moon, said Sembay. To enable the telescope to see X-rays, technology such as micropore optics and sensors such as charged coupled devices (CCDs) are being investigated.

'You image X-rays by designing something that allows them to deflect off a small angle,' said Sembay. 'This telescope uses what is called a micropore optic, a similar structure to what crustaceans such as lobsters use to image things.

'The X-rays come along, they bounce off the side of the wall of the optic and are brought into focus, and this can be made quite compact and the mirror can be made out glass, but it is not a lens in the conventional sense. The actual focusing is done through the holes in the micropore plate, not through the lens, like you do in optical imaging. We will probably also use CCDs for the detector, which are sensitive to X-rays.'

Like a digital camera, the telescope will take an image, which gets downloaded to the Earth frame by frame. Each image is encoded with information about the strength of each X-ray's energy.

Sembay suggested two possible power sources for the telescope. 'In the Apollo programme they used radiothermal isotope generators, a lump of radioactive material which through its heat was used to generate electrical power. We might use something like that or we might have to use solar cells and battery power,' he said.

The Moon was chosen as the platform for the telescope because of its stability (it maintains the same face to the Earth as it orbits), it is the right distance from the magnetosheath to allow a full view, and because of the lunar temperature.

'Most of the interesting measurements will be done in the lunar nights, which means the temperatures are very cold. That helps because the instruments we use are best operating at very cold temperatures. For example, the best range for CCDs is about -100ºC to about -120ºC.

'We still have to work out what we can do in the lunar day, but we get a minimum of 14 days of lunar night a month, and that's very high and very good,' said Sembay.

According to Sembay, not much is known about the physics of the magnetosheath, which is a non-static structure that becomes compressed and distorted under the pressure of the solar wind. A visual depiction of the magnetosheath would show the area surrounding the side of the Earth facing the Sun being compressed by the solar wind, and the rest of the magnetosheath being pushed in the opposite direction.

'The solar wind pressure can vary quite remarkably and the whole magnetic structure will contract and expand on short time- scales of a few hours or much less. If it wasn't for the solar wind, the magnetic structure would be almost symmetrical,' said Sembay.