Pluto's small moons may pose a serious threat to NASA's New Horizon spacecraft once it reaches the planet in 2015.

The discovery of several moons around Pluto makes the region more hazardous and may pose a threat during the probe's flyby, according to New Horizon's principal investigator Alan Stern of the Southwest Research Institute in San Antonio, Texas.

These small moons are under constant bombardment from nearby space rocks called Kuiper Belt objects. The moons' low gravity prevents them from holding on to the debris that fly into the air, and instead, these rocks are caught in the orbit around Pluto.

"The most likely problem we would encounter is to be hit by something that is large enough to instantly destroy the spacecraft," Stern said.

Pluto now has four moons but scientists believe that there are likely more that are hidden. The three moons were discovered in the last five years. Further studying the system with the Hubble Space Telescope, as well as several ground-based telescopes, could help reveal other hidden moons and their orbits well before New Horizons arrives, scientists said.

As an alternative, scientists have determined the need for a good "safe haven bailout trajectory," or SHBOT - an orbit that New Horizons could shift into that would keep it away from the most likely danger zones.

According to Stern, the best route would zip through Charon's orbit, but on the opposite side of the planet from the moon since the large body constantly clears debris from its path. This makes it a safe route for New Horizons to pass through.

The risk, however, is heightened if the debris will not remain in a plane, similar to Saturn's rings, but orbits Pluto in a cloud.

Stern said that if New Horizons encounters dirt and dust from the moons, it could put an abrupt end to the first mission to Pluto.