June 22, 2007	Friday	Jamadi-us-Sani 06, 1428

PARIS: Desolate, airless and with no people around for hundreds of thousands of kilometers, the Moon is a great place – for astronomers, that is. Skywatchers have an enduring hope of one day building a lunar observatory, where gleamings from the earliest stars can be snared without the curse of man-made light pollution and Earth’s atmospheric distortion.

But making telescopic mirrors – dozens are needed in a giant complex – is eye-wateringly expensive, for it requires grinding and polishing glass to an accuracy of a few tens of billionths of a metre. And, after making a mirror, there’s the risk of breaking it when you haul it to the Moon.

Enter an idea that has been kicked around for more than a century and a half – the liquid mirror telescope.

Under this, mercury is gently spun on a round table, so that centrifugal force combined with gravity forces the quicksilver to spread out, with its edges thicker than its centre.

The parabolic shape is exactly what is needed to focus the reflected light on a detector, and supporters say the optical qualities are as good as with glass.

So far, several pilot schemes using liquid mirror telescopes (LMTs) up to six metres across have been launched on Earth, and backers say their cost is just one or two percent of large conventional scopes.

According to their calculations, an LMT on the Moon, with an aperture of 20 to 100 metres, would be able to observe objects 100 to 1,000 times fainter than the US James Webb Space Telescope, a $3.5-billion next-generation orbiting telescope scheduled for launch in 2013.

Now a team of US pioneers believe they have made strides towards resolving the big challenge facing a lunar LMT – finding a substitute for mercury, which would freeze on an unlit surface of the Moon.

A team led by Ermanno Borra, a physicist at the Universite Laval in Quebec, Canada, used vacuum vaporisation to apply liquid chromium to a water-repelling, commercially available solvent called ECOENG 212.

They then applied liquid silver on top of the chromium, delivering a result with ‘excellent’ optical quality and which remained stable throughout the study.

The outcome is not the Holy Grail, because the reflectivity is still not up to scratch and the solvent freezes at -98 C (-144 F), which is still too high for lunar temperatures as low as -130 C (-202 F).

The good news, though, is that ECOENG 212 is part of a vast category of chemicals called ionic compounds, which are environmentally-friendly crystalline solids that melt into liquids at low temperatures.

“As there are at least a million simple ionic liquids and a trillion ternary [triple-ingredient] ionic liquid systems, there is a phenomenally wide choice for optimising the properties of the liquid sub-state, to minimise [freezing] point and volatility, while maintaining optimal infrared reflectivity,” Borra’s group report on tomorrow in Nature.—AFP