Do Pluto's moons pose risks for NASA spacecraft? (+video)

One strategy the researchers suggest is pointing New Horizons' dish antenna forward, "to act as a meteorite shield to protect the spacecraft from impacts," Stern said. "This technique is not new — the Cassini probe used that when crossing Saturn's ring plane as well." [Pluto's 5 Moons Explained: How They Measure Up (Infographic)]

The researchers are now also making plans to avoid these hazards if New Horizons needs to. "We are now exploring nine other options, 'bail-out trajectories,'" Stern said.

New Horizon's current plan would take it about halfway between Pluto and the orbit of its largest moon, Charon. Four of the bail-out trajectories would still take the spacecraft between Pluto and Charon's orbit.

"They would get maybe up to about 15 closer to Charon's orbit, but that can make a large difference in terms of safety," Stern explained. "These zones would get scoured of debris by Texas-sized Charon.

Safe passage to Pluto

The other alternatives would take New Horizons much further away from Pluto, past the orbits of its known moons.

"If you fly twice as far away, your camera does half as well; if it's 10 times as far, it does one-tenth as well," Stern said. "While placing New Horizons farther out would still accomplish the primary objectives we have for it, it would not exceed them. On our current path, we'd get imaging resolutions down to about a tenth of a kilometer (330 feet) for some places on Pluto, but if we fly substantially far away, we'd meet the 1-kilometer (3,300 feet) objective we had."

"Still, half a loaf is better than no loaf," Stern said. "Sending New Horizons on a suicide mission does no one any good. We're very much of the mind to accomplish as much as we can, and not losing it all recklessly. Better to turn an A+ to an A- than get an F by overreaching."

It remains uncertain what levels of risk might prompt the researchers to change New Horizons' course — say, a 25 percent chance of hitting a millimeter-sized grain, or a 10 percent chance of hitting a centimeter-sized pebble.

"We're working on making recommendations to NASA regarding that later this year, and then with NASA the project team will make that decision if the time comes," Stern said.

The latest the research team can alter the spacecraft's trajectory is about 10 days before it gets to Pluto. "After that, there's not enough fuel to make a change," Stern explained. "We don't often get into situations in spaceflight where we have to make last-minute decisions. We're going to learn as much as possible before our final approach in 2015."

The scientists detailed their research today (Oct. 16) at the annual meeting of the American Astronomical Society's Division for Planetary Sciences in Reno, Nevada.

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