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)

Pedestrians stop to look at and photograph a DeLorean Motor Company DMC-12 customized to look identical to the car used in the film "Back to the Future Part II" and that will be part of a Lyft promotion in New York, October 21, 2015. In the 1989 movie, main character Marty McFly traveled to the future to October 21, 2015. (Photo by Lucas Jackson/Reuters)

Kanphitcha Sungsuk, 21, (C), lines up with young men to speak to officers during an army draft held at a school in Klong Toey, the dockside slum area in Bangkok, Thailand, April 6, 2017. Thailand is widely seen as a paradise for gay and transgender people, but many complain of being treated as second-class citizens and the obligation to respond to the draft can be a nightmare when they turn 21. (Photo by Athit Perawongmetha/Reuters)

A young woman flashes the victory sign in front of a bonfire as Turkish Kurds gather during Newroz celebrations for the new year in Diyarbakir, southeastern Turkey, on March 21, 2018. Newroz (also known as Nawroz or Nowruz) is an ancient Persian festival, which is also celebrated by Kurdish people, marking the first day of spring, which falls on March 21. (Photo by Ilyas Akengin/AFP Photo)

A honor guard soldier stands at attention during a memorial religious service for those killed in the 1989 anti-communist uprising in University Square, in Bucharest, Romania, Wednesday, December 21, 2022. Participants and relatives of those killed marked the 33rd anniversary of the anti-communist uprising which started in Bucharest on Dec. 21, 1989 and left more than one thousand people dead and ended the rule of dictator Nicolae Ceausescu. (Photo by Andreea Alexandru/AP Photo)

Switzerland's forward #19 Eseosa Aigbogun (L) fights for the ball with Philippines' defender #16 Sofia Harrison (R) and Philippines' forward #21 Katrina Guillou during the Australia and New Zealand 2023 Women's World Cup Group A football match between the Philippines and Switzerland at Dunedin Stadium in Dunedin on July 21, 2023. (Photo by Sanka Vidanagama/AFP Photo)

A fan dressed as “Loki” poses before the European premiere of “Avengers: Age of Ultron” at Westfield shopping centre in Shepherds Bush, London April 21, 2015. (Photo by Stefan Wermuth/Reuters)