LAUREL, Md. — Almost there.

After nine and a half years and three billion miles, NASA’s New Horizons spacecraft was on course to take the first close-up look at Pluto on Tuesday morning.

“Fasten your seatbelts,” S. Alan Stern, the mission’s principal investigator, said Monday at a news conference here at the Johns Hopkins Applied Physics Laboratory, which is operating the mission. “New Horizons is arriving at the Pluto system.”

Among the science findings so far: a precise measurement of Pluto’s diameter; greater than expected amounts of nitrogen leaking from the atmosphere into space; confirmation of nitrogen and methane ices at the polar region; and images that show strange, and different, landscapes on Pluto and Charon, its largest moon.

“Pluto has not disappointed,” Dr. Stern said. He described the data so far as “mouthwatering,” but said it was still too early to answer some of the mysteries, like the strange features of Pluto and Charon.