Pluto-Bound Spacecraft Crosses Orbit of Neptune

NASA’s New Horizons spacecraft, which is en route to explore Pluto and its planetary system in 2015, crossed the orbit of Neptune on 25 August, 25 years to the day after NASA’s Voyager 2 flew by Neptune.

The timing is “a cosmic coincidence that connects one of NASA’s iconic past outer solar system explorers with our next outer solar system explorer,” according to Jim Green, director of NASA’s Planetary Science Division, who participated in a 25 August briefing about this milestone.

At the briefing, New Horizons principal investigator Alan Stern said the mission “is going to be a bonanza for science” in terms of learning about the Plutonian system. “Everything we know about the Pluto system today could probably fit on one piece of paper,” said Stern, who is with the Southwest Research Institute, Boulder, Colo. He rattled off some things that are known about Pluto: The dwarf planet is 70% rock by mass, has an atmosphere made up primarily of nitrogen, and has winds, polar caps, a surface changing with time, and at least five satellites.

“This is just mouthwatering. It is a science wonderland that we look forward to exploring,” Stern continued. “We don’t know a thing now, and a year from now, we are going to write the textbook.”

Stern said that the piano-sized spacecraft “carries the most sophisticated suite of reconnaissance instruments ever brought to bear on a first reconnaissance flyby in the history of mankind.” Those instruments include high-resolution cameras that can take 70-meter-per-pixel images of the Plutonian system, spectrometers, and in situ plasma and dust instruments that will map Pluto and its satellites, examine Pluto’s atmospheric composition and escape rate, and search to see whether the dwarf planet has more than the five currently known moons.

The target timing for New Horizons to fly by Pluto and its moons is July 2015.

Exploring Part of the Kuiper Belt Region

Stern also emphasized the significance of the mission in exploring part of the Kuiper Belt region at the outer part of the solar system. “What New Horizons is doing is flying to the biggest, the brightest, the first discovered, and—from what we know—the richest, most complex of these dwarf planets in the Kuiper Belt: to the Pluto system.”

There is a possibility of an extended mission for New Horizons to explore other Kuiper Belt objects once it leaves the region around Pluto. Stern said that a search earlier this year by the Hubble Space Telescope for Kuiper Belt objects found some potential candidates to explore. However, scientists do not yet know whether any of the candidates are within the spacecraft’s fuel reach.

Also at the briefing was Ed Stone, Voyager project scientist with the California Institute of Technology, Pasadena, who focused on the discoveries from that earlier mission’s exploration of the outer heliosphere. Stone said, for instance, that Neptune’s moon Triton has a polar cap in the southern region that is frozen nitrogen, geysers erupting in ice, and “an active, alive surface on this cold little moon.” Stone said that Triton is about the same size as Pluto and has about the same composition. He speculated, “It is certainly possible that the surface of Pluto will show some remarkable changes associated with a very active geological life. Time will tell.”

Stern said the New Horizons team stands on the shoulders of Stone and others who have been pioneers in exploring the deep outer solar system. “When I was growing up, we had the privilege of seeing the first orbiter at Mars and the first lander, and the first missions to Jupiter, to Saturn, and Uranus and Neptune, and they were enthralling,” he noted. “This is the first opportunity in a generation to really explore a new planetary system for the first time.”

For more information, see http://www.nasa.gov/newhorizons.

—Randy Showstack, Staff Writer