Located 5000 meters above sea level on the Chajnantor plain in the Chilean Andes, ALMA (Spanish for "soul") will be Earth's highest continuously operated observatory. It will consist of 64 12-meter dishes, observing the universe at millimeter and submillimeter wavelengths. This relatively unexplored part of the electromagnetic spectrum, between infrared and radio waves, opens a window into some of the coolest and dustiest objects in the universe, such as the clouds of dust and gas that form planetary systems, as well as into the farthest reaches of space and time. ALMA will have a collecting area of some 7000 square meters, larger than a football field and far surpassing any existing millimeter-wave telescope. And its high, dry location is largely free of atmospheric water vapor, which absorbs millimeter waves (Science, 19 March, p. 1836).
"It will take us back to the era where we see galaxies form," says Bob Dickman, coordinator of the Radio Astronomy Unit at the U.S. National Science Foundation (NSF). "No matter how distant the first galaxies are, ALMA will detect them," adds Ewine van Dishoeck of Leiden University in the Netherlands. By combining signals from multiple dishes--a technique called interferometry--the array will create images of these distant objects as sharp as a single imaginary dish spanning the 10-kilometer width of the array. Interferometry is a household word in radio astronomy, but it requires great finesse at the shorter millimeter and submillimeter wavelengths that ALMA will observe.
Major partners in the agreement are the U.S. National Radio Astronomy Observatory and the European Southern Observatory, an intergovernmental organization with eight member states. Research institutes in France, Germany, the Netherlands, and the United Kingdom will also take part, while Japan is expected to join later. Europe will chip in $16 million and the United States $26 million for the first phase of design and development; in 2001 the partners will make a final decision about whether to proceed. The observatory's total cost is expected to exceed $400 million.