Chajnantor

Chajnantor is a high-altitude plateau in the Atacama Desert of northern Chile, located in the Antofagasta Region near San Pedro de Atacama. Rising at about 5,000 meters above sea level, the Llano de Chajnantor hosts one of the world’s premier facilities for millimeter and submillimeter astronomy. Its extremely dry and stable atmosphere, with very low precipitable water vapor, provides favorable observing conditions for high-frequency radio waves.

The principal facility on Chajnantor is the Atacama Large Millimeter/submillimeter Array (ALMA), a multinational collaboration that uses a large ensemble of radio dishes to achieve high-resolution images of cold cosmic objects. The ALMA complex also includes the Atacama Compact Array, comprising smaller antennas to recover broader emission, and dedicated short-wavelength capabilities. In addition to ALMA, the Llano de Chajnantor hosts other submillimeter facilities such as the APEX telescope.

History and operations: Site testing began in the 1990s to identify a suitable location for millimeter astronomy in northern Chile. In 2003, ALMA was formed as a partnership among North American, European, and East Asian institutions to build a greatly enhanced array on the plateau. Construction proceeded through the 2000s, with first light of ALMA in 2011 and a gradual transition to full operations by the mid-2010s.

Impact: Chajnantor has become a central site for studies of star and planet formation, molecular clouds, and galaxy evolution, enabling advances in our understanding of the cold universe and the processes at work in its earliest stages.