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)

This incredible panoramic photographs are distorted to create miniature worlds and terrifying tunnels. (Photo by Caters News)

A US Marine leads two Viet Cong suspects in restraints during the Tet Offensive on February 20, 1967. (Photo by Bettmann Archive/Getty Images)

Image of the Clouds taken in August 2014 by astronauts on board the International Space Station (ISS). A year from space photographs of hurricanes, typhoons and meteorite craters show an astronauts-eye view of our planet from hundreds of miles above the earth. The illuminating images were taken by astronauts onboard the International Space Station (ISS) over the course of 2014. (Photo by NASA/SPL/Barcroft Media)

A group of 1000 customers receive a facial massage at a sports centre in Jinan, Shandong province, China, May 4, 2015. A group of 1000 women were given a 30 minutes facial beauty treatment together on Monday that achieved a Guinness record for the largest group of people having beauty treatment in the same location, according to local media. (Photo by Reuters/Stringer)

A woman wears a mask while carrying a dog in the street on January 22, 2020 in Wuhan, Hubei province, China. A new infectious coronavirus known as “2019-nCoV” was discovered in Wuhan as the number of cases rose to over 400 in mainland China. Health officials stepped up efforts to contain the spread of the pneumonia-like disease which medicals experts confirmed can be passed from human to human. The death toll has reached 17 people as the Wuhan government issued regulations today that residents must wear masks in public places. Cases have been reported in other countries including the United States, Thailand, Japan, Taiwan, and South Korea. (Photo by Getty Images/China Stringer Network)

A tourist pauses for photos with her mask on at Sensoji Temple Thursday, January 30, 2020, in Tokyo. The country began evacuating Japanese citizens on Wednesday from the Chinese city Wuhan hardest-hit by the virus. (Photo by Jae C. Hong/AP Photo)

Race fans watch from the grandstands as Air Force One circles the Daytona International Speedway as President Donald Trump makes his arrival to attend the NASCAR Daytona 500 auto race at Daytona International Speedway, Sunday, February 16, 2020, in Daytona Beach, Fla. (Photo by Jim Topper/AP Photo)