The NASA Extreme Environment Mission Operations (NEEMO) 21 mission began on July 21 as an international crew of aquanauts splashed down to the undersea Aquarius Reef Base, located 62 feet below the surface of the Atlantic Ocean in the Florida Keys National Marine Sanctuary. The NEEMO 21 crew will perform research both inside and outside the habitat during a 16-day simulated space mission. During simulated spacewalks carried out underwater, they will evaluate tools and mission operation techniques that could be used in future space missions, including journeys to Mars. (Photo by Karl Shreeves/NASA)

Ukrainian state emblem is seen on a gun's holster as soldiers guard naval base in the village of Novoozernoye, some 91 km west of Crimean capital Simferopol, Ukraine, on Monday, March 3, 2014. Ukraine says Russian forces controlling the strategic region of Crimea are demanding that the crew of two Ukrainian warships in Sevastopol's harbor must surrender. (Photo by Ivan Sekretarev/AP Photo)

Residents move the wreckage of cars that were swept away by flood in Bekasi, West Java, Indonesia, Friday, January 3, 2020. Severe flooding in greater Jakarta has killed scores of people and displaced tens of thousands others, the country's disaster management agency said. (Photo by Achmad Ibrahim/AP Photo)

Factory waste including dyes from the many textile factories in the region drain into a tributary of the Citarum river on August 27, 2018 outside Bandung, Java, Indonesia. (Photo by Ed Wray/Getty Images)

The oldest car to wear the Porsche badge goes on view at Sotheby's on May 21, 2019 in London, England. The only surviving 1939 Porsche Type 64 Berlin-Rome, No. 3, this rare piece of motoring history was the personal car of Ferdinand and Ferry Porsche, predating the first production Porsche, the 356. The car is on view at Sotheby's in London from 21st -24th May prior to being offered for sale by RM Sotheby's in Monterey, California, 15-17th August 2019, with an estimate in excess of $20 million. (Photo by Tristan Fewings/Getty Images for Sotheby's)

A vendor sleeps at his vegetables shop at a main market in Colombo, Sri Lanka May 31, 2016. (Photo by Dinuka Liyanawatte/Reuters)

A fishmonger carries a shark on his motorcycle in Padang, West Sumatra, Indonesia August 25, 2016. (Photo by Iggoy el Fitra/Reuters/Antara Foto)

A girl carries on her head a pile of dried shrubs she gathered for cooking and heating, in Kabul, Afghanistan November 18, 2015. (Photo by Omar Sobhani/Reuters)