ALMA's drivers carry oxygen to move 115-tonne telescopes around a Chilean plateau
High in Chile's Atacama Desert, two giant 28-wheeled trucks lift radio dishes weighing 115 tonnes and set them down on concrete pads with precision. The air at 5,000 metres is so thin that the driver's seat was designed to hold an oxygen tank. Shuffling the dishes lets the array zoom in or out.
The Atacama Large Millimeter/submillimeter Array links 66 antennas on the Chajnantor plateau, chosen because its altitude and dryness let faint millimetre-wavelength signals through with little interference from the atmosphere. Spreading the dishes as far as 16 kilometres apart sharpens detail, while clustering them within 150 metres captures broader structures. More pads were poured than there are antennas, so the layout can change. The German-built transporters, 20 metres long and weighing 130 tonnes, haul dishes up from a support base at 2,900 metres.
Politics shaped the hardware. The project merged an American plan and a European one in 1997, and Japan later joined, contributing a compact array of sixteen smaller dishes for wide-field views. Rather than one standard design, each region had its own companies build antennas: General Dynamics supplied twenty-five 12-metre dishes, Thales Alenia Space another twenty-five in Europe's largest industrial contract for ground-based astronomy, and Mitsubishi Electric assembled Japan's share. The name was fixed in 1999; alma means soul in Spanish. At roughly $1.4 billion, it is the costliest ground-based telescope operating.
Its first public images, released in October 2011, showed the Antennae Galaxies, a colliding pair, revealing cold, dense gas where new stars form, invisible in ordinary light. In 2014 ALMA photographed the disc around the infant star HL Tauri and found bright concentric rings separated by gaps, a sign that planets were already forming in a system perhaps no more than a million years old, younger than most theories allowed.
ALMA was also one of the dishes in the Event Horizon Telescope network, whose 2019 picture of a black hole was the first ever made directly. It took part in the disputed detection of phosphine in Venus's atmosphere, a gas that on Earth is linked to living things; later reanalyses have argued both for and against the finding.
Source: Atacama Large Millimeter Array
