The Pierre Auger Observatory in Argentina has spent almost ten years looking for the source of ultra-high-energy cosmic rays but to no avail. Now the observatory faces an uncertain future.

01 October 2014

Argentina, famed for its beef and wine, is also home to the Pierre Auger Observatory, which uses water-filled plastic tanks spaced across the plains of Pampa Amarilla at the foot of the Andes to search for the origin of ultra-high-energy cosmic rays.

Katia Moskvitch

Each canister is filled with 12,000 litres of purified water, which produces a faint but detectable streak of blue-ish light when a charged particle passes through. Most lie on land owned by local farmers. This tank has been on Anselmo Francisco Jake's land for about two decades.

Katia Moskvitch

In addition to the tanks, the observatory has 27 fluorescence telescopes grouped at four sites around the edges of the array. These telescopes scan the skies for the faint ultraviolet light produced when the high-energy particles rip through the atmosphere.

Katia Moskvitch

The cosmic rays never reach the ground. Instead, they hit an air molecule high in the atmosphere, blasting loose billions of secondary particles in an 'air shower' that continues to cascade downwards along the cosmic ray's original path. These air-shower particles are the ones generally detected by Augers 1,600 tanks, shown as yellow dots superimposed over their actual location near the town of Malarge.

Cosmus: Randy Landsberg, Dinoj Surendran and Mark SubbaRao (Univ. Chicago/Adler Planetarium)/AIRES: Sergio Sciutto/PAO (CC BY-SA)

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Astronomy: To catch a cosmic ray