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)

World medieval jousting champion Rod Walker poses before next month’s St Ives Medieval Faire, the only solid wood lance joust tournament in the southern hemisphere in Sydney, Australia on August 26, 2016. (Photo by Dan Himbrechts/AAP)

People in costume take photos during a Halloween event on October 31, 2015 in Lan Kwai Fong, Central District, Hong Kong. Halloween, a named taken from 'All Hallows' Even' falls on the day before All Saints' Day on November 1, a holiday when Christians remember their deceased loved ones. (Photo by Jerome Favre/Getty Images)

People carrying red umbrellas march through downtown Skopje, Macedonia, marking the International Day to End Violence against s*x Workers, Thursday, December 17, 2015. A group of s*x workers, supported by members of non-government organizations, rallied Thursday demanding rights for the s*x workers and destigmatization of their profession. The banner reads: The Stigma Kills. (Photo by Boris Grdanoski/AP Photo)

After their wedding ceremony, groom and bride, Nathan Mauger, Connie Young with family and friends, toast to the solar eclipse from the Rose Garden in Manito Park, Monday, August 21, 2017, in Spokane, Wash. (Photo by Colin Mulvany/The Spokesman-Review via AP Photo)

Doutzen Kroes and Candice Swanpoel arrive at the Mert Alas x Marcus Piggot book launch party at Public Hotelon September 7, 2017 in New York City. (Photo by Pierre Suu/GC Images)

In this September 16, 2017 photo, a music fan poses for the photo against an angel wings' mural at the Rock in Rio music festival in Rio de Janeiro, Brazil. (Photo by Leo Correa/AP Photo)

A woman walks with her baby past a PM militarized police soldier in position and aiming his rifle in Rocinha favela in Rio de Janeiro, Brazil on September 23, 2017. Although shooting was reported in the early hours of Saturday in Rocinha – for the seventh day running – officials said that Friday's deployment of 950 soldiers to reinforce police had brought the crisis under control. (Photo by Carl De Souza/AFP Photo)