On January 14, 2000 (December 8, 1999 lunar calendar), the US probe "MESSENGER" passed by Mercury. NASA's "MESSENGER" probe took pictures of Mercury's surface. Human exploration of Mercury took a new step. NASA's probe "MESSENGER" passed by Mercury on the 14th and began a two-day photo and data collection work. It is expected that 1,300 photos will be sent back to Earth. The last close-up exploration of Mercury was in 1974. More than 30 years later, NASA personnel are expecting major discoveries. NASA's "Mariner 10" flew by Mercury three times in the 1970s, but covered less than half of the planet. Scientists hope that "MESSENGER" will give them a glimpse of the remaining 55% of Mercury that has yet to be explored. " MESSENGER set out in 2004, flying at a speed of 26,000 kilometers per hour. On the 14th, it took pictures and collected other data at a distance of 200 kilometers from the surface of Mercury, and came closest to Mercury at 3:4 am Beijing time this morning. MESSENGER will be behind Mercury 50 minutes before its closest approach, and NASA personnel will have to wait for MESSENGER to appear before receiving data. "MESSENGER" has a video camera and can store more than 700MB of data. "MESSENGER" will then pass Mercury twice more, gradually slowing down, and will not enter the orbit until three years later.