Thursday, October 09, 2008

Star-Gazing with Liquid Mirrors

For years, scientists have wanted to put a telescope on the moon. Its lack of atmosphere makes for a clear, cloudless view of the universe.

However, the feasibility of lugging up tremendously heavy equipment into space and the economic cost of doing so are obstacles that have always accompanied the idea, until now.

An international team of researchers may have found a way to build a large lunar observatory on the Moon, using liquid mirror telescopes made of ionic liquids, a special class of organic compounds.

Traditionally, liquid mirror telescopes on Earth have used mercury for its ability to remain molten at room temperature and reflect a high percentage of light. Despite its good qualities, mercury is extremely dense or heavy, making it difficult to launch. Once on the moon, it would evaporate very quickly. Not to mention the price-mercury is very expensive.

Ionic liquids have properties that solve these issues. Scientists often describe ionic liquids as "molten salts". This catch-all phrase basically means a salt that has been heated to such extreme temperatures (thousands of degrees Fahrenheit) that it melts into a stable liquid, flowing much like water and only slightly denser. The team is currently trying to synthesize ionic liquids that will remain molten even at liquid-nitrogen temperatures, between -346 and -320 degrees Fahrenheit.

Ionic liquids aren't very reflective, but this can be remedied by coating a spinning mirror of the stuff with an ultrathin layer of silver-so thin that it solidifies on top of the liquid. This protects it from tarnishing or evaporating. Naturally, tilting a liquid mirror would ruin the telescope-the fluid would pour out of the container.

To get past this, optics experts are currently toying around with methods to "tilt" the view of a telescope, without actually doing any tilting. These include electromechanically warping secondary mirrors suspended above a liquid mirror, or even warping the liquid mirror itself.

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