The sun-shaded crater at the moon's south pole might be frigid, but the argument over whether to build an observatory there someday remains on the torrid side. A newly developed liquid might shift the debate's balance by allowing construction of giant telescope mirrors that dwarf the resolving power of the best space telescopes in the works.
Astronomers have been debating the merits of lunar observatories for decades. One faction says Earth's natural satellite offers many of the advantages of space-based astronomy--freedom from atmospheric distortions and much longer uninterrupted observing periods--and can house larger telescopes (ScienceNOW, 19 February). The other camp argues that advances in space telescope technology have precluded the need for moon-based astronomy, particularly given the complexity and cost of lunar construction. One way around those difficulties, moon advocates say, is to build telescopes up to 100 meters in diameter using mirrors with a thin but highly reflective liquid coating. The liquid rides atop a spinning base that keeps it spread out and perfectly shaped, and it would be easier to ship to the moon than a solid mirror. The resulting instrument could observe objects with up to 1000 times higher resolution than NASA's James Webb Space Telescope, which is scheduled for launch in 2013. Such facilities have been tested on Earth. Canada's Large Zenith Telescope, for example, features a 6-meter liquid mirror, and researchers have been looking for liquids that can withstand the harsh cold and cosmic radiation on the lunar surface.
Now Canadian and U.S. researchers have discovered a material that just might work. Expanding on previous laboratory experiments, they managed to add a silver coating to a commercially available material called an ionic liquid. The result was "pure magic," says lead author Ermanno Borra of Université Laval in Quebec. As the researchers report in tomorrow's issue of Nature, the material provides an extremely smooth and stable surface that stays liquid at temperatures well below 0°C and does not evaporate in a vacuum. Borra says the next step is to improve the liquid's reflectivity and its ability to withstand temperatures below –150°C. That should be feasible, he says, because ionic liquids exist in trillions of variations.
Planetary geologist Jeffrey Taylor of the University of Hawaii, Manoa, says mirrors based on the new liquid should be tested by astronauts during the next round of lunar missions, with an eye to full-scale development. Taylor, who has participated in NASA's lunar astronomy plans, says testing liquid mirrors would provide important lessons in materials science and manufacturing techniques for future moon installations. "You can't lose trying this," he says.