In Pictures: 10 of Earth's Most Alien Landscapes

Ethiopia’s Danakil Depression is the definition of inhospitable. The sunken volcanic landscape is rife with acidic hot springs, bubbling lavas, salty sands and toxic vapours. However, microorganisms thrive among the region’s sulphuric pools and mineral chimneys. Scientists say this hell on Earth is an excellent Mars analogue.

Roughly 300 metres (1,000 feet) beneath Earth’s surface, gargantuan selenite crystals stud a hot, humid, normally pitch-black cave in Mexico’s Naica mine. Some of the beams are more than 10 metres (30 feet) long; the widest spans 4 metres (13 feet). Though the 'Cave of Crystals' was only found in 2000, scientists searching for life in unlikely places quickly put it on their radar. In 2017, NASA’s Penelope Boston announced the discovery of microbes in the crystals, some of which may have been trapped for 50,000 years.

With its rugged sandstone cliffs and vermillion hue, Jordan’s Wadi Rum is one of the planet’s most unearthly landscapes. The desert, whose name means 'Valley of the Moon' in Arabic, has masqueraded as Mars in several Hollywood blockbusters, including the 2015 science-fiction film 'The Martian'. Space agencies use other deserts nearby, such as Israel’s Negev, as Mars analogues for training exercises.

Salar de Uyuni, tucked into the Bolivian Andes, is the largest salt flat on Earth. It’s so bright white that it’s visible from space—and sometimes, a thin layer of water covers its salt crust, turning the surface into a giant mirror. Salt-loving microorganisms flourish in its extremely briny environment.

If humans ever inhabit the moon or Mars, moving into a lava tube wouldn’t be a terrible idea. The subsurface structures offer a natural refuge from hazardous radiation, dust storms, micrometeorites and extreme temperatures, and they could be large enough to hold entire towns. In fact, on Earth, astronauts are already training for missions in lava tubes.

Antarctica is a popular destination for scientists investigating alien oceans. The thick ice layers that cover and surround the continent conceal a freezing sea, rich with life—a configuration that closely mirrors the structure of the outer solar system’s icy moons, including Europa and Enceladus. To look for life in those extraterrestrial seas means accessing those buried oceans, so scientists are developing robotic submersibles and testing them in Antarctic waters.

California's Mono Lake is an earthly stand-in for the Mars of four billion years ago, when the planet was starting to lose its surface water. As the lake's waters slowly evaporate and recede, they reveal tufas, strangely shaped towers of calcium carbonate. Scientists use the lake to test hardware bound for Mars, and they study microbes that live in its salty, alkaline waters.

Since 2003, scientists have used Svalbard, a Norwegian archipelago near the Arctic circle, as a testing ground for technology destined for Mars. With its cold temperatures, rocky outcrops, permafrost and volcanic geology, Svalbard closely mirrors several Martian environments, such as the red planet’s poles and equatorial craters. The Arctic environment also helps scientists identify and detect life’s chemical signatures.

Borup Fiord Pass, a glacier-carved valley on Canada’s Ellesmere Island, is home to a stinky yellow patch of ice that resembles the surface of Jupiter’s moon Europa. The glacier’s alien, Europa-like environment is work of salty springs that spew sulphur onto the icy crust. Scientists studying the glacier have found diverse microbial communities and use it to practise detecting life from a distance.

Chile’s Atacama desert is frequently used as a simulant of Mars: it’s one of the driest places on Earth, with annual rainfall averaging less than one inch, and its terrains offer many distinct test beds for Mars-bound rovers. Despite its extremes, life has gained a foothold in the Atacama’s soils and in the summit lakes atop nearby mountains.