Pluto (R) and its moon Charon are pictured from about 6 million kilometers in this July 8, 2015 NASA handout photo from the New Horizons Long Range Reconnaissance Imager (LORRI). [Photo/Agencies]

"The Pluto system is enchanting in its strangeness, its alien beauty," said Stern, a planetary scientist at Southwest Research Institute in Boulder, Colorado.

With the encounter finally at hand, it all seems surreal for the New Horizons team gathered at Johns Hopkins University's Applied Physics Laboratory. The energy there was described as electric.

Project manager Glen Fountain said New Horizons, at long last, is like a freight train barreling down the track, "and you're seeing this light coming at you and you know it's not going to stop, you can't slow it down."

"Of course, the light is Pluto, and we're all excited," Fountain said.

Three new discoveries were revealed Monday, a tantalizing sneak preview as the countdown to closest approach reached the 21-hour mark.

Besides the revised size of Pluto - still a solar system runt, not even one-fifth the size of Earth - scientists have confirmed that Pluto's north pole is indeed icy as had been suspected. It's packed with methane and nitrogen ice.

And traces of Pluto's nitrogen-rich atmosphere have been found farther from the dwarf planet than anticipated. New Horizons detected lost nitrogen nearly a week ago.