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)

A view of the spectacular colour of clouds at sunset on January 17, 2005 in Beijing, China. (Photo by China Photos/Getty Images)

A swimmer competes in Le Defi Monte-Cristo (Monte Cristo Challenge) swimming event at the Chateau d'If, off the coast of Marseille, southern France, on June 21, 2019. Created in 1999 and inspired by Alexandre Dumas' character of Edmond Dantes, the Monte Cristo Challenge will take place from June 21 to 23, 2019. (Photo by Boris Horvat/AFP Photo)

Hideki Tokoro, president of whaling company Kyodo Senpaku, boards Japan's new whaling mothership, the Kangei Maru, following the ship's launch ceremony at a port in Shimonoseki city, Yamaguchi prefecture on May 21, 2024. The nearly 9,300-tonne ship set sail on its maiden hunting voyage on May 21, heralding a new era for the controversial practice defended by the government as an integral part of national culture. (Photo by Yuichi Yamazaki/AFP Photo)

Chase Elliott (9) makes a pit stop during the NASCAR Xfinity series auto race at Chicagoland Speedway, Sunday, June 21, 2015, in Joliet, Ill. (AP Photo/Nam Y. Huh)

People row their canoes on a flooded street at a village in Kawlin township, Sagaing division, Myanmar, July 21, 2015. Heavy rains caused flooding over 20,000 acres of rice field and in about a hundred villages, killing at least eight people, according to local media. (Photo by Soe Zeya Tun/Reuters)

Milena Pino, 15, puts on makeup prior to taking part in a speed competition with horses at the International Livestock Fair Show in Havana March 21, 2015. (Photo by Alexandre Meneghini/Reuters)

Soviet Army soldiers sit on their tanks in front of the Czechoslovak Radio station building in central Prague during the first day of Soviet-led invasion to then Czechoslovakia on August 21, 1968. (Photo by Libor Hajsky/Reuters)