World’s Largest Space Array Opens Wednesday

ALMA, the world’s largest space array, opened on Wednesday.

Atacama Large Millimeter-submillimeter Array (ALMA) is not just the largest space array but the largest ground-based astronomical observatory of any kind. To allow for the best sky viewing possible from planet earth, it was constructed in the driest habitat on earth — Chilé’s Atacama Desert, where it essentially doesn’t rain. Because of the lack of rainfall, the region has become a world center for astronomy, and ALMA was sparked by a partnership with North American, European, Taiwanese, and Japanese groups.

Some areas of the Atacama Desert have not seen a drop of rain in 400 years, and the average annual rainfall is 0.004 inches of rain per year. The ALMA space array was built on the Altiplano de Chajnantor, a plateau in high, dry mountains at an altitude of 5,000 meters above sea level. ALMA officials said that the average rainfall at this location is less than 100 millimeters.

The ALMA space array was designed to capture radio waves from outer space that are just millimeters in wavelength. In a wet climate, some radio waves would be absorbed or scattered before reaching the array.

The original Very Large Array consisting of 27 antennas is near Socorro, New Mexico, also in a dry climate. In addition to its many astronomical discoveries, that site played a role in the 1997 movie Contact.

With 66 antennas, ALMA is far larger and is expected to be capable of even more ground-breaking — or should that be sky-shattering? — observations.

The large space arrays could be considered as a kind of hack. By creating the separate large but manageable moveable parts, astronomers can construct the equivalent of a much larger radio telescope. It would take a single telescope 14,000 meters in diameter to perform the same job as the 66 smaller telescopes in ALMA.

Thijs de Graaw, ALMA’s director, said that the large space array will look at how planets and stars were formed, but it will also go far beyond that to study the origins of the universe at the time of the Big Bang.

Here’s a look at the last pieces of the world’s largest space array being moved into place, courtesy of C. Padilla and ALMA (ESO/NAOJ/NRAO).

ALMA large array

[Credit for top photo of construction work: ALMA (ESO / NAOJ / NRAO), W. Garnier
Acknowledgement: General Dynamics C4 Systems]