Observatory equipped with antenna

The first of many antennas has been handed over to the Atacama Large Millimeter/submillimeter Array (ALMA) project.

It will operate at wavelengths of 0.3 to 9.6 mm. At these wavelengths, a high, dry site is needed for the telescope to be able to see through the Earth's atmosphere. This is why it is being built on the 5000 m high plateau of Chajnantor in the Atacama region of Chile.

It will initially comprise 66 high-precision antennas, with the option to expand in the future. There will be an array of fifty 12 m antennas, acting together as a single giant telescope, and a compact array composed of 7 and 12 m diameter antennas.

The 12 m antennas will have reconfigurable baselines ranging from 15 m to 16 km. Resolutions as fine as 0.005 arcseconds will be achieved at the shortest wavelengths.

The first 12 m diameter antenna, built by Mitsubishi Electric Corporation for the National Astronomical Observatory of Japan, one of the ALMA partners, has been handed over to the observatory. It will shortly be joined by North American and European antennas.

"Our Japanese colleagues have produced this state-of-the-art antenna to exacting specifications. We are very excited about the handover because now we can fully equip this antenna for scientific observations," said Thijs de Graauw, ALMA Director.

Antennas arriving at the ALMA site undergo a series of tests to ensure that they meet the strict requirements of the telescope. The antennas have surfaces accurate to less than the thickness of a human hair, and can be pointed precisely enough to pick out a golf ball at a distance of 15 km.

With ALMA, astronomers will study the cool universe — the molecular gas and tiny dust grains from which stars, planetary systems, galaxies and even life are formed.

This antenna handover means the observatory team can now proceed with integrating the rest of the components, including the sensitive receivers that will collect the faint cosmic signals from space.

The antennas are tested at the Operations Support Facility, at an altitude of 2900 m, before being moved to the plateau of Chajnantor. The Operations Support Facility will also be the observatory's control centre.

"The ALMA antennas must withstand the harsh conditions at Chajnantor with strong winds, cold temperatures and a thin atmosphere with half as much oxygen as at sea level. This forbidding environment also poses challenges for the workers building ALMA," said de Graauw.

The antennas, which each weigh about 100 tonnes, can be moved to different positions in order to reconfigure the ALMA telescope. This will be carried out by two custom-designed transporters, each of which is 10 m wide, 20 m long and has 28 wheels (ESO 32/07).

The ALMA project is a partnership between the scientific communities of East Asia, Europe and North America with Chile.