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 child plays with a plastic badminton racket in the old quarters of Delhi, India, March 3, 2016. (Photo by Anindito Mukherjee/Reuters)

A fisherman carries a sailfish on his head to the fish market in Hamarweyne near the port of Mogadishu on April, 4, 2016. (Photo by Mohamed Abdiwahab/AFP Photo)

Employees prepare spacesuits at the Russian-leased Baikonur cosmodrome in Kazakhstan on August 19, 2015. Members of the main crew of the 45/46 expedition to the International Space Station ISS, Kazakhstan's cosmonaut Aydyn Aimbetov, Russian cosmonaut Sergei Volkov and Denmark's astronaut Andreas Mogensen from the European Space Agency, are scheduled to blast off to the International Space Station (ISS) on September 2, 2015. (Photo by AFP Photo)

Hot air balloons take to the skies as they participate in the mass assent at sunrise on the second day of the Bristol International Balloon Fiesta on August 11, 2017 in Bristol, England. More than 130 balloons have gathered for the four day event, now in its 39th year and now one of Europe's largest annual hot air balloon events, being hosted in the city that is seen by many as the home of modern ballooning. (Photo by Matt Cardy/Getty Images)

A dog dressed as Oscar the Grouch takes part in the annual halloween dog parade at Manhattan's Tompkins Square Park in New York, NY, U.S. on October 21, 2017. (Photo by Lucas Jackson/Reuters)

A horse named Quinn, with a skeleton painted on it to help educate officers, is pictured during a visit by Britain's Queen Elizabeth II (unseen) and Britain's Prince Charles, Prince of Wales (unseen) to the Household Cavalry Mounted Regiment at the Hyde Park Barracks in west London on October 24, 2017. (Photo by Chris Jackson/AFP Photo)

Journalists interview a girl, member of the Cryophile amateurs winter swimmers club, after bathing in the ice waters of the Yenisei River, during the celebrations for the upcoming Christmas and New Year, in Krasnoyarsk, Russia, December 23, 2017. (Photo by Ilya Naymushin/Reuters)