A soldier from the South Korean army special forces breaks stone plates with her head during a martial arts demonstration for Memorial Day at Korea War Memorial Museum in Seoul, South Korea, Monday, June 6, 2016.(Photo by Ahn Young-joon/AP Photo)

A kid wearing rollerblades hitches a ride via motorbike, in Port-au-Prince, Haiti, Sunday, October 25, 2015. The country held the first-round presidential vote Sunday. Haitians chose between 54 presidential hopefuls and a slew of legislative and municipal candidates. (Photo by Ricardo Arduengo/AP Photo)

Soldiers of China's People's Liberation Army (PLA) jump as part of their winter training in temperature of negative 26 degrees Celsius at China's border with Russia in Heihe, Heilongjiang province, December 14, 2015. (Photo by Reuters/Stringer)

Paramilitary policemen take part in a training in Chaohu, Anhui province, China December 28, 2015. (Photo by Reuters/China Daily)

Fire over Vieira de Leiria, Portugal, on October 16, 2017 as a series of deadly wildfires broke out across Spain and Portugal as the approach of Hurricane Ophelia whipped up strong winds that fanned the flames. (Photo by Helio Madeiras/News Pictures)

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)

A man strikes a pose in front of a giant torta, or sandwich, during a press conference to promote the 13th annual Torta Festival, in Mexico City, Wednesday, July 20, 2016. The five day festival presents a variety of the Mexican street food made from the most exotic ingredients that include ostrich or stingray, to the classic ham, grilled steak or slow cooked pork. The festival's purpose is to maintain the tradition of eating tortas, and promote the vendors of the Mexican sandwich. (Photo by Marco Ugarte/AP Photo)

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)