Astronomers have detected hydrogen peroxide (H2O2) in the atmosphere of Mars for the first time. This is the first time that a chemical catalyst of this sort has been found in a planetary atmosphere other than the Earth's. Catalysts control the reactions of the most important chemical cycles in the Earth's atmosphere. The result shows that scientists' knowledge of the Earth's atmosphere can be used to explain the chemistry of atmospheres on other planets, and vice versa.

The work is announced in the March issue of the journal "Icarus". The observations were made at the James Clerk Maxwell Telescope (JCMT), situated near the 14,000-ft summit of Mauna Kea in Hawaii.

Image of Mars made with the Hubble Space Telescope during the 2003 opposition. The James Clerk Maxwell Telescope spectral observations of hydrogen peroxide were made during the same period. Credit: J. Bell (Cornell U.), M. Wolff (SSI), NASA, ESA

Dr Todd Clancy, at the Space Science Institute (SSI) in Boulder, Colorado, led the research team. He says "Mars is one of three observable terrestrial atmospheres. Unlike Venus, Mars is hospitable enough to be considered a possible human habitat in the future. And unlike the Earth, Mars is not extensively explored and so presents an opportunity to discover new and exciting phenomena."

Dr Brad Sandor, also at SSI, explains "We took advantage of the excellent 2003 opposition of Mars, when the Earth and Mars passed close by each other in their orbits around the sun, to measure Martian atmospheric H2O2 for the first time."

The Earth's atmosphere has been studied much more than that of Mars. Scientists have had to rely on their terrestrial experience to guess how the Martian atmosphere reacts to solar radiation, and how its overall photochemical balance is controlled.

Models predicted that hydrogen peroxide was the key catalytic chemical that controls Mars atmospheric chemistry. Until now, scientists were unable to detect the predicted amount of H2O2, so some researchers argued that the models were wrong.

However, the new measurements of hydrogen peroxide made with the JCMT agree with the predictions of standard photochemistry. Dr Clancy continues "We have largely confirmed that the chemical balance of the Mars atmosphere is determined by the products of the photolysis of water vapor, without the need for special or unknown changes to current theory."

The James Clerk Maxwell Telescope, atop Mauna Kea on the Big Island of Hawaii. Credit: Nik Szymanek

Dr Gerald Moriarty-Schieven of the National Research Council of Canada worked on the project with Dr Clancy and Dr Sandor, and is based at the Joint Astronomy Centre in Hawaii, which operates the JCMT. He explains more about the JCMT observations: "The 2003 opposition was especially favorable since it occurred when Mars was closest to the sun in its orbit, and hence unusually close to us as we passed by. Mars was at its warmest, when the most H2O2 is available to observe, and the JCMT can make especially sensitive H2O2 measurements."

What impact does this result have for the search for life on Mars? Dr Clancy says "Hydrogen peroxide is actually used as an antiseptic here on Earth, and so it would tend to retard any biological activity on the surface on Mars. For this reason, as well as the ultraviolet radiation and lack of water, bacteria-like organisms are not expected to be viable on the surface. Most arguments for finding life on Mars now center on subsurface regions."

The James Clerk Maxwell Telescope (JCMT)
The JCMT is the world's largest single-dish submillimetre-wave telescope. It collects faint submillimetre-wavelength signals with its 15 metre diameter dish. It is situated near the summit of Mauna Kea on the Big Island of Hawaii, at an altitude of approximately 4000 metres (14000 feet) above sea level. It is operated by the Joint Astronomy Centre, on behalf of the UK Particle Physics and Astronomy Research Council, the Canadian National Research Council, and the Netherlands Organisation for Scientific Research.