Water is essential for the existence of carbon-based lifeforms, so when scientists hunt for extraterrestrial life, they look for it whenever probes are sent to other planets or when they peer through space-based telescopes into the cosmos. Though H2O is much more difficult to detect from instruments on the Earth, new water-detecting receivers fitted to the ALMA radio telescope in Chile have been designed to take advantage of the scope's high, arid, location, and give scientists a new ground-based capability for investigating the possibility of life elsewhere in the universe.

Building on the results of testing of Band 5 receivers on the Atacama Pathfinder Experiment (APEX) telescope last year, ALMA (the Atacama Large Millimeter/submillimeter Array) has been equipped with new receivers in the wavelengths 1.42 mm to 1.83 mm (211 GHz to 163 Ghz) at the low-energy end of the electromagnetic spectrum. ALMA is generally limited to frequencies from 30 GHz to 960 GHz (9.9 mm to 0.31 mm wavelengths) in ten separate frequency bands, so the addition of the new Band 5 receivers has vastly increased its radio-frequency view of the sky.

"The new receivers will make it much easier to detect water, a prerequisite for life as we know it, in our Solar System and in more distant regions of our galaxy and beyond," said ALMA Program Scientist, Leonardo Testi. "They will also allow ALMA to search for ionised carbon in the primordial Universe."

In normal circumstances, the use of such receivers to detect water in space was very difficult because the water molecules in our own atmosphere interfere with the readings. However, as ALMA is located some 5,000 m (16,400 ft) above the Atacama desert of northern Chile on the desolate Chajnantor plateau where the air is virtually moisture-free, the sensitivity of the new receivers can be fully utilized in a fashion largely impossible in many other places on Earth.

Band 5 receivers operate at the vibrational frequencies of a range of molecules, including H2O (water), CS (Carbon Monosulfide), HNC (hydrogen isocyanide), and SiO (silicon monoxide), all of which are important elements in astrochemical studies surrounding interstellar gas formation and transition. In this vein, initial testing of the new receivers involved detailed H2O, CS, and HNC observations of a giant star formation of colliding galaxies known as Arp 220 located near the middle of the Milky Way; spectral studies of the red supergiant star (Sgr B2 (N)) in Saggitarius; and the detection of SiO and H2O when studying one of the largest of all known stars, VY Canis Majoris.

"It's very exciting to see these first results from ALMA Band 5 using a limited set of antennas," Said European Southern Observatory (ESO) team member Robert Laing. "In the future, the high sensitivity and angular resolution of the full ALMA array will allow us to make detailed studies of water in a wide range of objects including forming and evolved stars, the interstellar medium and regions close to supermassive black holes."

Technical experts and astronomers from ESO and the European ALMA Regional Centre (ARC) network have since assessed and processed the data from the initial Band 5 tests, and their results have been published on the ALMA website.

According to ESO, the new receivers are now being installed and prepared for use on the ALMA instrument for active duty in the very near future.

Source: ESO

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