The landscape appeared more Martian than terrestrial—barren for the most part, with a reddish hue, and dotted with salt-splashed mountain ridges. We passed a few wild donkeys among the desert shrubs and a field of cacti along the way. Ahead of the final ascent by bus, we heard dire warnings about the risks associated with altitude sickness, ultraviolet exposure, and dehydration. A paramedic checked my heart rate, blood pressure, and oxygen-saturation level, and clipped a pulse oximeter on my finger—all part of the requisite ritual before visiting the Atacama Large Millimeter Array (ALMA), an elaborate grid of radio dishes erected on a high plateau in northern Chile.
At 16,500 feet, there is half as much oxygen in the air as at sea level. Walking, let alone working long hours, at such altitude often results in nosebleed, vomiting, and fatigue. In rare cases, fluid accumulation in the lungs or the brain could be fatal. Some people in our group needed to use oxygen canisters, even though our visit only lasted a couple of hours. The extreme conditions on the Chajnantor plateau that strain the human body are the very reasons that astronomers have built the world’s most expensive ground-based telescope there, at a cost of nearly $1.5 billion. At the high and dry site, where the annual rainfall averages about four inches, the air contains very little moisture, which would otherwise absorb the millimeter-wave emissions that come beaming down from the heavens above. Living up to astronomers’ lofty expectations, ALMA has spotted planets forming around nearby young stars and dusty galaxies in the far reaches of the universe, and a whole lot else in between.