View Full Version : Liquid Mirrors!

06-25-2007, 11:49 AM

June 21, 2007 — The first big telescope on the moon could be poured out of a barrel if Quebec astronomer Ermanno Borra has anything to do with it.

Borra and his colleagues have managed to float a thin layer of silver on a non-evaporating "ionic liquid" — sort of a room-temperature, molten salt — to make a liquid mirror that could be used on the moon as a gigantic, super-powerful telescope.

Ionic liquids are up to the task because they stay fluid down to about -145 degrees Fahrenheit (-98 degrees Centigrade) and don’t evaporate in a vacuum. The fluid could be poured out into a giant dish and gently spun — causing some of the liquid to move to the edges and form a naturally smooth and perfect curved surface to reflect and concentrate starlight.

"The liquid wants to stay parabolic," Borra told Discovery News. Micrometeorites or other minor disturbances on the moon would be fleeting and the liquid surface would return to its perfectly smooth curve again. "Whereas with a glass mirror, Nature conspires to wreck it."

Other than the unusual liquid mirror, the telescope would work just like glass-mirrored telescopes called Newtonian reflectors, named for their inventor, Sir Isaac Newton. A report on the ionic fluid telescope appears in the June 21 issue of the journal Nature.

"You could have a one-kilometer (wide) liquid mirror telescope," said Borra. Shipping a massive traditional glass mirror of even a small fraction of that size is completely impractical.

Conversely, such a gargantuan liquid telescope wouldn’t work well on Earth because weather and the quaking ground would create too many disturbances. The only successful liquid telescopes made on Earth are several meters wide and made with mercury.

Nor would a very large liquid telescope work well in orbit, since there needs to be a force pulling down on the liquid as well as the centrifugal effect of the spinning to produce the curved liquid surface.

A liquid space telescope is possible, said Borra, but only if it’s constantly accelerating, perhaps with the help of a solar sail, to mimic the effect of gravity.

Among the benefits of a large lunar telescope would be its ability to see objects 100 to 1,000 times fainter than even the next generation of space telescopes. It could also see distant objects which shine in the same wavelengths of infrared in which Earth is blindingly bright, Borra explained.

"Further improvements to the ionic liquid will be necessary before it can be used in a space telescope," observed chemist Robin Rogers of the University of Alabama. "Nevertheless, this report surpasses most descriptions of these liquids because the application depends completely on the physical and chemical properties of the ionic liquid — in fact, it seems that only an ionic liquid will do."

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06-25-2007, 11:51 AM

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