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)

An Afghan policeman frisks a man while a burqa-cald woman sits in the trunk of a car on a roadside in Herat, Afghanistan, 05 July 2015. At least 18 police, two civilians and 30 rebels were killed in central Afghanistan during three days of fierce fighting, police said on 04 July. The clashes ended 04 July after security forces retook control of nine police checkpoints that had fallen to the rebels. (Photo by Jalil Rezayee/EPA)

Mud-covered tourists pretend to be trapped inside a mud prison at the Daecheon Beach Mud Plaza in the city of Boryeong on South Korea's west coast, July 17, as they take part in the Boryeong Mud Festival, which opened that day and runs through July 26. Boryeong mud is rich in natural mineral component and is considered to prevent skin aging. (Photo by EPA/Yonhap)

Bottlenose dolphins swim over visitors in water tank at the Hakkeijima Sea Paradise aquarium-amusement park complex in Yokohama, southwest of Tokyo, Tuesday, July 21, 2015. Temperatures in Tokyo's metropolitan area neared around 96 degree Fahrenheit, or 35 degree Celsius, on Tuesday. (Photo by Shuji Kajiyama/AP Photo)

Cosplayer Monzerath Gutierrez, who portrays Dragon Ball Z character Trunks, female version, poses for a portrait during the 4th edition of the MiniCon Anime convention, at the School of Dance, in Managua, Nicaragua, Sunday, July, 26, 2015. (Photo by Esteban Felix/AP Photo)

Beautician Alex Smith, 26, does the nails of Jules Aspen, 40, at the Madame Beauty salon in Chirton, North Tyneside, UK on July 13, 2020. Nail bars, beauty salons, tattoo and massage studios, physical therapy businesses, spas and piercing services are able to reopen in the latest lifting of restrictions in England. (Photo by Owen Humphreys/PA Images via Getty Images)

Border guard officers, wearing masks against COVID-19 infection adjust their outfits before a distinguished service awards ceremony for employees of the interior ministry in Bucharest, Romania, Thursday, July 16, 2020. Romania has registered on Thursday the highest number of COVID-19 infection cases since the pandemic reached the country in February, 777 in a 24 hours interval, as many fail to observe the mandatory protection measures, like the use of a face mask indoors or maintaining social distancing. (Photo by Andreea Alexandru/AP Photo)

A woman carries an inflatable float with the sahpe of a portion of pizza in a Barcelona, on July 18, 2020. Four million residents of Barcelona have been urged to stay at home as virus cases rise, while EU leaders were set to meet again in Brussels, seeking to rescue Europe's economy from the ravages of the pandemic. (Photo by Josep Lago/AFP Photo)