Looking through liquids

Chemists at Queen’s University Belfast are working with NASA and scientists in Canada and the United States to design a telescope that can be stationed on the Moon.



The instrument will have a mirror consisting of a liquid with a thin metal film on its surface that rotates to form a bowl shape, known as a parabola. When the liquid spins in a perfect parabola, it will be able to reflect infrared light from distant stars and galaxies that cannot be picked up by telescopes on Earth because of atmospheric interference and light pollution.



Telescopes with parabolic liquid mirrors are said to be much cheaper and easier to make and maintain than conventional telescopes with glass mirrors. Liquid mirror telescopes employed in observatories on Earth traditionally use mercury as the reflective liquid. However, mercury cannot be used for a lunar liquid mirror telescope as the high-vacuum conditions on the Moon would cause the mercury to boil.



The Queen’s team has been investigating the possibility of preparing a reflective liquid for the telescope consisting of an ionic liquid that can be coated on its surface with a thin layer of a reflective metal.



Ionic liquids generally have negligible vapour pressures which mean that they do not boil, even under vacuum. Many ionic liquids do not freeze at the sub-zero temperatures found on the Moon. They have the added advantage that they are much lighter than mercury – a key consideration for transporting a telescope to the Moon.



In a report in the June 21 issue of the science journal Nature, the Belfast, Canadian, and US scientists showed that a commercially-available ionic liquid can be coated with silver and that the coated fluid is stable over several months.



‘The discovery that an ionic liquid can be coated with a very thin metal layer is a major breakthrough,’ said chemistry professor, Ken Seddon, who is one of the authors of the report and Director of Queen’s University Ionic Liquids Laboratories (QUILL).



‘We now plan to design and prepare ionic liquids with melting points of around 100K that can be coated with a reflective metal for the lunar telescope,’ said Assistant Director of QUILL, Maggel Deetlefs.