Chajnantor Plateau

Chajnantor Plateau
Name	Chajnantor Plateau
Settlement type	Plateau
Subdivision type	Country
Subdivision name	Chile
Subdivision type1	Region
Subdivision name1	Antofagasta Region
Elevation m	5000

Chajnantor Plateau The Chajnantor Plateau is a high, arid plateau situated in the Andes of northern Chile notable for hosting major millimeter and submillimeter astronomical facilities. Its extreme elevation, dry atmosphere, and relative radio darkness have attracted international collaborations such as the Atacama Large Millimeter Array, the APEX project, and other observatories operated by institutions including the European Southern Observatory, the National Radio Astronomy Observatory, and the National Astronomical Observatory of Japan. The site plays a central role in contemporary observational campaigns linked to cosmology, star formation, and planetary science.

Geography and location

The plateau lies within the Antofagasta Region of Chile, near the Salar de Atacama and east of the Atacama Desert, at elevations around 5,000 metres above sea level on the western flank of the Altiplano. Chajnantor is bounded by volcanic complexes such as the Licancabur, Lascar, and Láscar volcanoes and is positioned within the drainage basin of the Loa River. Administratively it is accessed from the city of San Pedro de Atacama and is proximate to transport routes connecting to the regional capital Antofagasta and international corridors toward Bolivia and Argentina.

Climate and environment

The plateau experiences a hyperarid climate typical of the Atacama Desert, with precipitable water vapour among the lowest on Earth, frequent thermal inversions associated with the Humboldt Current, and large diurnal temperature swings influenced by high solar insolation and thin atmosphere at altitude. These conditions create excellent transparency for millimetre and submillimetre windows used by instruments associated with projects like ALMA and APEX. The local ecology includes high-elevation puna habitats connected to Andean condor ranges and vicuña populations, with environmental oversight involving agencies such as the Chilean Ministry of Environment and conservation groups engaged with the nearby Los Flamencos National Reserve.

Astronomical observatories and instruments

The plateau hosts a concentration of radio, millimetre, and submillimetre facilities including the Atacama Large Millimeter Array (a partnership among ESO, the National Science Foundation, and the National Institutes of Natural Sciences (Japan)), the Atacama Pathfinder Experiment operated by Onsala Space Observatory and Max Planck Institute for Radio Astronomy partners, and site-testing instruments associated with projects like the Cosmic Background Imager, the Atacama Cosmology Telescope, and prototype elements of the Square Kilometre Array pathfinders. Individual instruments located on or near the plateau include high-precision interferometers, single-dish radiotelescopes, and atmospheric monitoring equipment developed by institutions such as the California Institute of Technology, Harvard–Smithsonian Center for Astrophysics, and the Kavli Institute for Cosmological Physics. The site has been used for receiver development by groups from the Jet Propulsion Laboratory and instrument consortia from the Max Planck Society and National Astronomical Observatory of Japan.

History and development

Interest in the plateau grew during late 20th-century site surveys conducted by organizations like the European Southern Observatory and the National Radio Astronomy Observatory, following earlier astronomical initiatives in the Atacama Desert region involving Cerro Tololo Inter-American Observatory and La Silla Observatory. The selection of the plateau for the ALMA project resulted from comparative studies involving sites such as Mauna Kea and Pico de Orizaba, culminating in multinational agreements among partners from North America, Europe, and East Asia. Infrastructure development has been shaped by agreements with the Chilean government, coordination with indigenous communities including Atacameño people stakeholders, and environmental assessments overseen by national and international institutions.

Scientific research and discoveries

Research conducted on the plateau has driven advances across fields: high-resolution imaging of protoplanetary disks and star-forming regions by consortia including ALMA Partnership teams has revealed ringed disk structures and kinematic signatures linked to planet formation; studies by collaborations involving the Planck Collaboration and Atacama Cosmology Telescope teams have constrained cosmological parameters and foreground contamination; molecular line surveys executed with instruments associated with the Max Planck Institute for Astronomy and the Harvard–Smithsonian Center for Astrophysics have mapped cold molecular gas in the interstellar medium of the Milky Way and external galaxies such as NGC 253 and M82. Observations from the plateau have contributed to detections of complex organic molecules, imaging of black hole environments in coordination with the Event Horizon Telescope network, and measurements of the Sunyaev–Zel'dovich effect in galaxy cluster surveys conducted by collaborations like the South Pole Telescope and Atacama Cosmology Telescope consortia.

Access and infrastructure

Access to the plateau is via paved and unpaved roads from San Pedro de Atacama and regional highways connecting to Antofagasta; logistical support is provided by operations centers maintained by ESO, AUI, and other partner organizations. On-site infrastructure includes array pads, power generation, data transmission facilities linked to fiber networks, high-altitude operations camps, and specialized medical and emergency services coordinated with institutions such as the Chilean Air Force and regional health authorities. Environmental and cultural impact mitigation is managed through protocols involving the Chilean Ministry of Culture, international funding agencies, and institutional environmental offices to balance scientific activity with regional conservation and community interests.

Category:Plateaus of Chile Category:Atacama Desert Category:Astronomical observatories in Chile