Atacama Cosmology Telescope Patches

The Atacama Desert () is a desert plateau located on the Pacific coast of South America, in the north of Chile. Stretching over a strip of land west of the Andes Mountains, it covers an area of , which increases to if the barren lower slopes of the Andes are included.

The Atacama Desert is the driest nonpolar desert in the world, and the second driest overall, behind some specific spots within the McMurdo Dry Valleys. It is the only true desert to receive less precipitation than polar deserts, and the largest fog desert in the world. The area has been used as an experimentation site for Mars expedition simulations due to its similarities to the Martian environment.

The constant temperature inversion caused by the cool north-flowing Humboldt ocean current and the strong Pacific anticyclone contribute to the extreme aridity of the desert. The most arid region of the Atacama Desert is situated between two mountain chains, the Andes and the Chilean Coast Range, which are high enough to prevent moisture advection from either the Pacific or the Atlantic Ocean, creating a two-sided rain shadow effect.

Setting

According to the World Wide Fund for Nature, the Atacama Desert ecoregion occupies a continuous strip for nearly along the narrow coast of the northern third of Chile, from near Arica (18°24′S) southward to near La Serena (29°55′S). The National Geographic Society considers the coastal area of southern Peru to be part of the Atacama Desert and includes the deserts south of the Ica Region in Peru. However, other sources consider that the part of the desert in Peru is a different ecosystem, and should properly be named as Pampas de la Joya desert.

Peru borders it on the north and the Chilean Matorral ecoregion borders it on the south.To the east lies the less arid Central Andean dry Puna ecoregion. The drier portion of this ecoregion is located south of the Loa River between the parallel Sierra Vicuña Mackenna and the Cordillera Domeyko. To the north of the Loa lies the Pampa del Tamarugal.

The Coastal Cliff of northern Chile west of the Chilean Coast Range is the main topographical feature of the coast. The geomorphology of the Atacama Desert has been characterized as a low-relief bench "similar to a giant uplifted terrace" by Armijo and co-workers. The intermediate depression (or Central Valley) forms a series of endorheic basins in much of the Atacama Desert south of latitude 19°30'S. North of this latitude, the intermediate depression drains into the Pacific Ocean.

In December 2023, scientists, for the first time, reported on a recently discovered area in the territory of Puna de Atacama, which may have similarities to Earth during the Archean eon and thus to the environment of the first life forms on Earth. It could as well be similar to conceivably-hospitable conditions on the planet Mars during earlier Martian times.

Climate

The Atacama has a cold desert climate (in the Köppen climate classification, ''BWk'') with generally mild temperatures year-round and only slight temperature differences across seasons. Rather than the intense heat of many other deserts around the world, the almost total lack of precipitation is the most prominent characteristic of the Atacama Desert.

Aridity

The Atacama Desert is commonly known as the driest place in the world, especially the surroundings of the abandoned Yungay mining town, where the University of Antofagasta Desert Research Station is located, in Antofagasta Region, Chile. The average rainfall is about per year, although some locations receive only in a year. Moreover, some weather stations in the Atacama have never received rain. Periods up to four years have been registered with no rainfall in the central sector, delimited by the cities of Antofagasta, Calama, and Copiapó, in Chile. (Excerpt) Evidence suggests that the Atacama may not have had any significant rainfall from 1570 to 1971.

The Atacama Desert may be the oldest desert on earth, and has experienced hyper aridity since at least the Middle Miocene, since the establishment of a proto-Humboldt current in conjunction with the opening of the Tasmania-Antarctic passage ca. 33  Ma. The opening of the Tasmania-Antarctic passage allowed for cold currents to move along the west coast of South America, which influenced the availability of warm humid air to travel from the Amazon Basin to the Atacama. Though there was a general lack of humid air after 33 Ma, there were punctuated intervals of increased humidity, such as between around 10.86 and 6.4 Ma, when the Tiliviche Palaeolake existed before turning into a salar sometime before the Middle Pliocene. The long history of aridity raises the possibility that supergene mineralisation, under the appropriate conditions, can form in arid environments, instead of requiring humid conditions. The presence of evaporite formations suggests that in some sections of the Atacama Desert, arid conditions have persisted for the last 200 million years (since the Triassic).

Aridity in Atacama Desert predates the rise of the Central Andes, yet hyper-aridity is generally thought to have resulted from the rise of the Andes. As such it is hypothesised it had climatic conditions akin to the Namib Desert prior to the rise of the mountains.

The Atacama is so arid that many mountains higher than are completely free of glaciers. Only the highest peaks (such as Ojos del Salado, Monte Pissis, and – debatably – Llullaillaco) have some permanent snow coverage.

The southern part of the desert, between 25° and 27°S, may have been glacier-free throughout the Quaternary (including during glaciations), though permafrost extends down to an altitude of and is continuous above . Studies by a group of British scientists have suggested that some river beds have been dry for 120,000 years. However, some locations in the Atacama receive a marine fog known locally as the ''camanchaca'', providing sufficient moisture for hypolithic algae, lichens, and even some cacti—the genus ''Copiapoa'' is notable among these.

Geographically, the aridity of the Atacama is explained by its being situated between two mountain chains (the Andes and the Chilean Coast Range) of sufficient height to prevent moisture advection from either the Pacific or the Atlantic Oceans, a two-sided rain shadow.

Despite modern views of the Atacama Desert as fully devoid of vegetation, in pre-Columbian and colonial times a large flatland area there known as Pampa del Tamarugal was a woodland, but demand for firewood associated with silver and saltpeter mining in the 18th and 19th centuries resulted in widespread deforestation.

Comparison to Mars

In a region about south of Antofagasta, which averages in elevation, the soil has been compared to that of Mars. Owing to its otherworldly appearance, the Atacama has been used as a location for filming Mars scenes, most notably in the 2004 television series '' Space Odyssey: Voyage to the Planets''.

In 2003, a team of researchers published a report in which they duplicated the tests used by the ''Viking 1 ''and'' Viking 2'' Mars landers to detect life and were unable to detect any signs in Atacama Desert soil in the region of Yungay. The region may be unique on Earth in this regard and is being used by NASA to test instruments for future Mars missions. The team duplicated the Viking tests in Mars-like Earth environments and found that they missed present signs of life in soil samples from Antarctic dry valleys, the Atacama Desert of Chile and Peru, and other locales.
However, in 2014, a new hyperarid site was reported, María Elena South, which was much drier than Yungay and, thus, a better Mars-like environment.

In 2008, the ''Phoenix Mars Lander'' detected perchlorates on the surface of Mars at the same site where water was first discovered. Perchlorates are also found in the Atacama and associated nitrate deposits have contained organics, leading to speculation that signs of life on Mars are not incompatible with perchlorates. The Atacama is also a testing site for the NASA-funded ''Earth–Mars Cave Detection Program''.

On 21 February 2023, scientists reported the findings of a "dark microbiome" of unfamiliar microorganisms in the Atacama Desert.

Extreme weather events

In June 1991, Antofagasta and Taltal and inland regions as far as Calama received unusual rainfall leading to formation of a series of mudflows that killed 91 people.

In 2012, the altiplano winter brought floods to San Pedro de Atacama.

On 25 March 2015, heavy rainfall affected the southern part of the Atacama Desert. Resulting floods triggered mudflows that affected the cities of Copiapo, Tierra Amarilla, Chanaral, and Diego de Almagro, causing the deaths of more than 100 people.

Flora

In spite of the geographic and climatic conditions of the desert, a rich variety of flora has evolved there. Over 500 species have been gathered within the border of this desert. These species are characterized by their extraordinary ability to adapt to this extreme environment. The most common species are herbs and flowers such as thyme, llareta, and saltgrass (''Distichlis spicata''), and where humidity is sufficient, trees such as the chañar (''Geoffroea decorticans''), the pimiento tree and the leafy algarrobo (''Prosopis chilensis'').

The llareta is one of the highest-growing wood species in the world. It is found at altitudes between . Its dense form is similar to a pillow some thick. It concentrates and retains the heat from the day to cope with low evening temperatures. The growth rate of the llareta has been recently estimated at , making many llaretas over 3,000 years old. It produces a much-prized resin, which the mining industry once harvested indiscriminately as fuel, making this plant endangered.

The desert is also home to cacti, succulents, and other plants that thrive in a dry climate. Cactus species here include the candelabro (''Browningia candelaris'') and cardon (''Echinopsis atacamensis''), which can reach a height of and a diameter of .

The Atacama Desert flowering (') can be seen from September to November in years with sufficient precipitation, as happened in 2015.

Fauna

The climate of the Atacama Desert limits the number of animals living permanently in this extreme ecosystem. Some parts of the desert are so arid, no plant or animal life can survive. Outside of these extreme areas, sand-colored grasshoppers blend with pebbles on the desert floor, and beetles and their larvae provide a valuable food source in the ''lomas'' (hills). Desert wasps and butterflies can be found during the warm and humid season, especially on the lomas. Red scorpions also live in the desert.

A unique environment is provided by some ''lomas'', where the fog from the ocean provides enough moisture for seasonal plants and a few animal species. Surprisingly few reptile species inhabit the desert and even fewer amphibian species. '' Chaunus atacamensis'', the Vallenar toad or Atacama toad, lives on the ''lomas'', where it lays eggs in permanent ponds or streams. Iguanians and lava lizards inhabit parts of the desert, while salt flat lizards, ''Liolaemus'', live in the dry areas bordering the ocean. One species, ''Liolaemus fabiani'', is endemic to the Salar de Atacama, the Atacama salt flat.

Birds are one of the most diverse animal groups in the Atacama. Humboldt penguins live year-round along the coast, nesting in desert cliffs overlooking the ocean. Inland, high-altitude salt flats are inhabited by Andean flamingos, while Chilean flamingos can be seen along the coast. Other birds (including species of hummingbirds and rufous-collared sparrow) visit the ''lomas'' seasonally to feed on insects, nectar, seeds, and flowers. The ''lomas'' help sustain several threatened species, such as the endangered Chilean woodstar.

Because of the desert's extreme aridity, only a few specially adapted mammal species live in the Atacama, such as Darwin's leaf-eared mouse. The less arid parts of the desert are inhabited by the South American gray fox and the viscacha (a relative of the chinchilla). Larger animals, such as guanacos and vicuñas, graze in areas where grass grows, mainly because it is seasonally irrigated by melted snow. Vicuñas need to remain near a steady water supply, while guanacos can roam into more arid areas and survive longer without fresh water. South American fur seals and South American sea lions often gather along the coast.

Human presence

View of Caspana, a village and Likan Antai settlement in the interior Atacama Desert">Likan_Antai.html" ;"title="Caspana, a village and Likan Antai">Caspana, a village and Likan Antai settlement in the interior Atacama Desert

The Atacama is sparsely populated, with most towns located along the Pacific coast. In interior areas, oases and some valleys have been populated for millennia and were the location of the most advanced pre-Columbian societies found in Chile.

Chinchorro culture

The Chinchorro culture developed in the Atacama Desert area from 7000 BCE to 1500 BCE. These peoples were sedentary fishermen inhabiting mostly coastal areas. Their presence is found from today's towns of Ilo Province">Ilo