New Horizons makes Its Pluto Flyby

New Horizons Makes Its Pluto Flyby
NASA scientists won’t know if flyby is successful until later when data reaches Earth

Members of the New Horizons science team at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., react to seeing the spacecraft's last image of Pluto before closest approach later Tuesday.

NASA scientists juggled jubilation and anxiety Tuesday as a U.S. spacecraft reached the climax of its epic encounter with Pluto, culminating a nine-year voyage across 3 billion miles to reach the unexplored dwarf planet.

Traveling at about 30,000 miles an hour, the New Horizons spacecraft was scheduled to fly within 7,800 miles of Pluto at 7:49 a.m. EDT Tuesday.

During the 22 hours of its closest approach, however, mission managers at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., which designed, built, and operates the $720 million mission, didn't know if their spacecraft and its irreplaceable trove of data was intact or had been destroyed by orbital debris.

Since late Monday, the probe has been incommunicado and flying on autopilot because it can’t make its preprogrammed observations and transmit to Earth at the same time. NASA and its mission managers won't know if all went as planned until a brief spacecraft signal reaches them at 9 p.m. EDT or so Tuesday. As a fail-safe measure, they retrieved all the information gathered by the probe’s instruments in recent days before the radio blackout began, including a detailed color image of Pluto taken about 16 hours before the probe’s closest approach.

“We will breathe the final sigh of relief at 9 p.m. and that is when we can call it a successful flyby,” said mission principle investigator Alan Stern at the Southwest Research Institute office in Boulder, Colo.

Even so, they felt they had much to celebrate when the mission countdown clock reached the official moment of the closest encounter.

“Today, we have now visited every single planet in our solar system,” said NASA Administrator Charles Bolden. “It is an achievement in national pride and national spirit.”

Preliminary images and instrument readings have revealed an icy red orb much larger than scientists had expected—about two-thirds the size of Earth’s moon. By the most recent measurements, Pluto is 2,370 kilometers across, making it easily the biggest known object beyond the orbit of Neptune.

Its surface is marked by chasms and craters set off by an enigmatic heart-shaped region. The dwarf planet has a polar ice cap composed of frozen methane and nitrogen.

NASA officials expect to release the first images taken during the flyby on Wednesday.