Inside the Afar Triangle in Ethiopia’s Danakil desert, camel caravans are used to carry salt. For centuries, the essential mineral has been mined by the Afar people, known for their ability to withstand extremes. The terrain is rugged, travelers are scarce and so are motor vehicles, where the average annual temperature is the highest in the world, and can rise to 122 degrees Fahrenheit, 50 degrees Celsius. (Photo by Ziv Koren/Polaris)

NASA says it could be another 20 years before humans touch down on Mars, but in a sense, the Mars Society has been exploring the red planet for more than a decade – in Utah. Photo: Csilla Orgel, a geologist of Crew 125 EuroMoonMars B mission, makes her way back to the Mars Desert Research Station (MDRS) in the Utah desert March 3, 2013. The MDRS aims to investigate the feasibility of a human exploration of Mars and uses the Utah desert's Mars-like terrain to simulate working conditions on the red planet. Scientists, students and enthusiasts work together developing field tactics and studying the terrain. All outdoor exploration is done wearing simulated spacesuits and carrying air supply packs and crews live together in a small communication base with limited amounts of electricity, food, oxygen and water. Everything needed to survive must be produced, fixed and replaced on site. (Photo by Jim Urquhart/Reuters)

Gold medallists of China perform Synchronised Swimming Free Combination routine at the Munhak Park Tae-hwan Aquatics Center during the 17th Asian Games in Incheon September 23, 2014. (Photo by Tim Wimborne/Reuters)

Shoko Ota of Japan celebrates winning the Women's Standing 10km Individual Cross Country during day one of the Winter Games NZ at Snow Farm on August 13, 2011 in Wanaka, New Zealand. (Photo by Camilla Stoddart/Getty Images)

In this November 26, 2018 photo, men run during 100 meters athletics competition of the second edition of the Panamanian indigenous games in Piriati, Panama. These games were held in the Embera town of Piriati, some 55 miles (90 kilometers) east of Panama City. (Photo by Arnulfo Franco/AP Photo)

Young cheetahs eat meat at The Cheetah Conservation Fund (CCF) center in Otjiwarongo, Namibia, on August 13, 2013. The CCF started breeding Anatolian livestock dogs to promote cheetah-friendly farming after some 10,000 big cats – the current total worldwide population – were killed or moved off farms in the 1980s. Up to 1,000 cheetahs were being killed a year, mostly by farmers who saw them as livestock killers. But the use of dogs has slashed losses for sheep and goat farmers and led to less retaliation against the vulnerable cheetah. (Photo by Jennifer Bruce/AFP Photo)

Men carry others, so they do not soil their shoes and clothes, through a mudslide caused by Tropical Storm Erika in Carries, Haiti, August 29, 2015. Erika, a tropical storm that killed 20 people on the Caribbean island of Dominica and at least one person in Haiti, fell apart on Saturday over eastern Cuba, the U.S. National Hurricane Center said. (Photo by Andres Martinez Casares/Reuters)