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A veritable array: ALMA's 64 antennas will allow the first direct observations of planet formation. Credit: ESO

Astronomers have finally got the official go-ahead to build the world's most powerful radio telescope, in the Chilean Andes.

The $650-million Atacama Large Millimeter Array (ALMA) is expected to help researchers explore processes such as the formation of galaxies, stars and planets, the intricacies of which are obscured from the most powerful optical telescopes by dust clouds.

But millimetre-range wavelength radiation will pass through these clouds and be detected by ALMA. The telescope will use 64 portable dishes spread over an area 14 km across to observe it with a spatial resolution up to 50 times higher than the most powerful current instruments, such as the IRAM array at Plateau de Bure in the French Alps.

“It's going to be revolutionary,” predicts Peter Shaver, an astronomer with the European Southern Observatory (ESO), based in Garching, Germany. “Even our largest optical telescopes cannot see through the dust, so ALMA will allow direct observations of planet, star and galaxy formation for the first time.”

ALMA will analyse higher radio frequencies than the existing Very Large Array, a radio telescope array in New Mexico, which observes cosmic events such as black holes. It will also pick up signals in a different part of the electromagnetic spectrum from the planned James Webb Space Telescope (JWST), which will observe infrared radiation (see page 3).

And unlike the JWST, ALMA's completion is fully assured: at a meeting in Washington DC on 25 February, representatives of the ESO and the US National Science Foundation signed the official agreement to build it. Both had already said that they would reach the agreement, “but it's still a relief to have it signed and sealed”, says Richard Kurz, who is European project manager for ALMA and is also based at the ESO's Garching headquarters. Construction will now begin later this year, with the first scientific results due by the end of 2007.

One signature missing is that of Japan. Although Japanese astronomers had hoped to participate in the project from the outset (see Nature 401, 627–628; 199910.1038/44215), their government has not yet committed any funding. If this situation changes, the current 'baseline' plans for ALMA could be upgraded, Kurz says. “Extra Japanese funding would allow us to add on some additional features,” he explains.

ALMA will also help Chile to continue to develop local astronomy expertise: its scientists will receive 10% of the available viewing time on the telescope, and the project partners say that they will pay student fellowships to allow young Chilean researchers to work with the new facility.

Ultimately, the team hopes that the ALMA array will be able to monitor radiation with wavelengths of 0.33–10 mm, divided into 10 convenient bands. For now, instruments operating in just four of these bands are planned, but Kurz says that others can be added later.