NASA's New Horizons spacecraft is about to make history, with its close flyby of Pluto on Tuesday morning, July 14, 2015. The latest data to come in has shown that Pluto is somewhat larger than previous estimates, confirming that the dwarf planet is the largest known object beyond the orbit of Neptune. NASA will offer a live webcast (below) of the flyby, starting at 7:30am ET/4:30am PT. Further updates at Space.com.