An experimenter of Dark Matter Experiment "PandaX", which means Particle and Astrophysical Xenon Detector, checks facilities in the Jinping Underground Laboratory, located at 2,400 meters under the surface of Jinping Hydropower Station, in southwest China's Sichuan Province, June 28, 2016. PandaX is designed to build and operate a ton-scale liquid xenon experiment to detect the dark matter, invisible material that scientists say makes up most of the universe's mass. The PandaX program, headed by China's Shanghai Jiao Tong University, was conducted in the Jinping lab, one of the world's deepest underground labs opened in December 2010. The Jinping lab provides a "clean" space for scientists to pursue the dark matter. Researchers said the extreme depth helps block most cosmic rays that mess with the observation. (Photo/Xinhua)
