Key exotic molecule found in space
Interstellar space harbours an exotic form of hydrogen believed to play a key role in cosmic chemistry, astronomers have confirmed. Dr Thomas R. Geballe of the Joint Astronomy Center in Hilo, Hawaii, and Professor Takeshi Oka of the University of Chicago achieved a scientific breakthrough when they detected hydrogen-three-plus (H3+) in two interstellar clouds. Taking advantage of an instrument upgrade on the UK Infrared Telescope (UKIRT), located at the Mauna Kea this year, after previous searches had failed. Their discovery is announced in a Letter to the scientific journal Nature, published on 28 November 1996.
Astro-chemists have long believed that many of the larger, complex molecules found in interstellar clouds could not form without H3+, but until now there was no direct evidence that it existed in space.
Chemistry in the unfamiliar conditions of outer space cannot be checked easily in Earth-based laboratories, but this new discovery suggests that current theories about how chemistry in interstellar space works are broadly correct.
Ordinary hydrogen molecules are made up of two hydrogen atoms, each atom consisting of a single proton as nucleus, together with one electron - making a total of two protons and two electrons in the molecule. H3+ consists of three protons and two electrons, so it has an overall positive electric charge - hence the 'plus' part of its name. Technically it is described as a 'molecular ion' - an electrically charged molecule. H3+ is structurally stable, but reacts very easily with other atoms and molecules. It is thought that in space, H3+ initiates chains of chemical reactions, which produce many of the dozens of larger molecules detected by astronomers since the 1970s, although the H3+ itself is destroyed in the process.
Although it is not naturally present in the Earth's atmosphere, H3+ can be made relatively easily in the laboratory. In 1980, Professor Oka was the first to measure its infrared spectrum in a laboratory. Since then, he and Dr Geballe, as well as other groups of researchers, have been looking for its signature in the infrared radiation from interstellar clouds. Theory predicts that H3+ is made in these clouds when cosmic ray particles strike ordinary molecules of hydrogen, the most common substance in the universe.
The amount of H3+ that Dr Geballe and Professor Oka have found in two interstellar clouds (known to astronomers as AFGL2136 and W33A) matches predictions that take into account creation by the action of cosmic rays and the rate of destruction in chemical reactions.
Now the search is on for H3+ in more interstellar clouds. A detailed comparison of the amount of H3+ against other key molecules, will make it possible to discover the exact role it plays in the processes of cosmic chemistry.
Dr Jacqueline Mitton, RAS Public Relations Officer
Phone: Cambridge ((0)1223) 564914
FAX: Cambridge ((0)1223) 572892