Debris still a threat as New Horizons approaches Pluto

Impact unlikely but mission team members are taking all possible precautions.
By Laurel Kornfeld | Apr 16, 2015
As NASA's New Horizons speeds toward Pluto, the mission team is paying careful attention to debris in the planet's vicinity that could prove hazardous to the spacecraft in the event of an impact.

The grand piano-sized probe has traveled more than three billion miles in nearly nine-and-a-half years since its launch in January 2006.

Its closest flyby of the Pluto system will occur in just three months, on July 14-15 of this year.

Pluto has one large moon, Charon, that is half its size, and four smaller moons, Nix, Hydra, Styx, and Kerberos. Nix and Hydra were discovered the year before New Horizons launched while Styx and Kerberos were found only a few years ago.

The Pluto system may contain even more, smaller moons, plus a ring system.

Pluto's Kuiper Belt neighborhood is home to numerous tiny icy bodies. If any of those objects collide with one or more of Pluto's small moons, the impact would generate debris that could hit the spacecraft, which is traveling approximately 31,000 miles per hour (50,000 km per hour).

Unlike Pluto and Charon, the smaller moons do not have sufficient gravity to trap debris from such an impact on their surfaces. Instead, the debris is released back into space.

If enough debris from past collisions was released, it could have formed rings around Pluto.

Whether individually or as part of a ring system, even one particle of debris could prove fatal to New Horizons.

"Even tiny particles the size of a grain of rice can be lethal to the New Horizons spacecraft because we are traveling so fast," emphasized mission principal investigator Alan Stern.

Recognizing the potential danger from debris, Stern put together a hazard analysis team four years ago.

Their analysis determined the spacecraft has only a one percent chance of being hit by debris on approach to Pluto.

But because New Horizons is the only probe heading for Pluto, even that small chance generated precautionary measures.

For example, starting May 11, mission team members will use instruments onboard the spacecraft to search for rings, additional moons and loose debris.

Should any danger be found in the current trajectory, the team has designed two alternate approaches to the Pluto system.

The alternate routes would reduce the amount of science New Horizons can do but would save the spacecraft.

NASA director of planetary science Jim Green stated, "This is no simple flyby. We are flying into the unknown."

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