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A Mirror For The Moon by Michael Gross
21 June 2007
Cosmologists have long argued that a Moon-based
telescope with a parabolic mirror made of a rotating liquid would
be ideally suited to studying very distant (and thus very old) structures
of the universe in unprecedented detail. Researchers using a chemical
approach have now succeeded in creating a liquid based system that
comes very close to the requirements for such a project.
Ermanno Borra at the University
of Laval, in Quebec, together with colleagues elsewhere in Canada,
the US and Northern Ireland, tested the properties of several
different types of liquids and identified a commercially available
ionic liquid, 1-ethyl-3-methylimidazolium ethylsulphate, as the
most promising candidate. They spray-coated the surface of this
liquid with silver, and found a much-improved reflectivity in
the relevant infrared wavelength range compared to silver-coatings
on other types of liquid, such as polyethylene glycol.
Borra and colleagues analysed the
surface of the silver-coated ionic liquid and found colloidal
particles in the size range of a few tens of nanometres. Hypothesizing
that this was the reason why the reflectivity wasn't quite as
good as in pure metallic silver, they changed their recipe to
include a layer of chromium before applying the silver. The resulting
double-coated liquid proved such a success, concluded the researchers,
that only technological fine-tuning remains.
"A giant rotating dish of highly
reflective liquid could prove ideal"
- Paul Halpern
Similarly, the melting point of the commercial ionic liquid used
as a base isn't quite low enough to ensure the material stays
liquid at the ambient temperatures of the moon. The researchers,
among them Pete Worden, director of Nasa Ames Research Center,
express confidence that they will identify the optimal level for
the lunar telescope among the millions of possible combinations
of ions,.
But is this the future of astronomy
or just pure lunacy? Paul Halpern, professor of physics at the
University of the Sciences in Philadelphia, US, welcomed the proposal
enthusiastically. 'It may indeed become economically feasible
to establish a lunar telescope,' Halpern told Chemistry World.
'A giant rotating dish of highly reflective liquid could prove
ideal,' he said. 'A reflector 100 metres in diameter could collect
thousands of times more light than the Hubble Space Telescope
and potentially image the primordial stars believed to have formed
in the very early Universe.'
