NASA's New Horizons spacecraft - now just two years away from Pluto - is on a riskier mission than previously realized, thanks to the threat posed bty the planet's moons and possible rings.
Launched over nine years ago, the spacecraft is due to make a close approach to the planet in July 2014.
But, as it's neared its goal, its science team has become increasingly aware of the possibility that dangerous debris may be orbiting in the Pluto system.
"We've found more and more moons orbiting near Pluto — the count is now up to five," says Dr Alan Stern, principal investigator of the New Horizons mission.
"And we've come to appreciate that those moons, as well as others not yet discovered, act as debris generators populating the Pluto system with shards from collisions between those moons and small Kuiper Belt objects."
Because the ship is traveling so fast — more than 30,000 miles per hour — even a millimeter-sized grain could cripple or destroy it. The team's already trying to prepare, by using sophisticated computer simulations of the stability of debris, giant ground-based telescopes, stellar occultation probes of the Pluto system and the Hubble Space Telescope to search for debris in orbit.
As a back-up plan, they're also plotting alternative, more distant courses through the Pluto system that would preserve most of the science mission but avoid deadly collisions.
"We're worried that Pluto and its system of moons, the object of our scientific affection, may actually be a bit of a black widow," says Stern.
"We may not know whether to fire our engines on New Horizons and bail out to safer distances until just 10 days before reaching Pluto, so this may be a bit of a cliff-hanger. Stay tuned."