Pluto May Live in a Rough Neighborhood


When NASA’s New Horizons mission flies past Pluto in 2015, will the dwarf planet have a nasty surprise in store? This question is pondered in a recent update by New Horizons principal investigator Alan Stern. And for the moment, he doesn’t know how hazardous the flyby could be.

The problem is that recent observations have shown Pluto to have more moons than previously known. In July, a fourth natural satellite — temporarily designated “P4″ — was discovered by the Hubble Space Telescope. P4, a moon measuring between 8 to 21 miles wide, joined Pluto’s other three moons: Charon, Nix and Hydra. (For a comparison, Charon is 648 miles wide; Nix and Hydra are between 20 and 70 miles wide.)


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Now, according to Stern, other satellite candidates are being identified. “When we discovered P4 this summer, along with possible evidence of a couple of still-fainter moons (something we need more study to confirm or reject), we began to worry about just how many tiny moons Pluto might have and whether we might have to dodge them,” said Stern in his Nov. 7 mission update.

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Space may be big, but say if the Plutonian system has more than just moons knocking around?

“Even more worrisome than the possibility of many small moons themselves is the concern that these moons will generate debris rings, or even 3-D debris clouds around Pluto that could pose an impact hazard to New Horizons as it flies through the system at high speed,” he adds.

Imagine driving down a freeway at 70 miles per hour only to hit a lane filled with nails — you’d be lucky to walk away from your car with just a blow-out. Now imagine driving straight into a cloud of nails. That probably wouldn’t end so well.

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Now, if you scale the situation up to spacecraft speeds, a serious problem presents itself. According to Stern: “…at our 14-kilometer-per-second (31,300 miles per hour) flyby speed, even particles less than a milligram can penetrate our micrometeoroid blankets and do a lot of damage to electronics, fuel lines and sensors.”

In light of the very real risk of the high-speed New Horizons getting punctured by an errant piece of rocky debris — or slamming into the surface of a much larger object (a mile-wide previously unnoticed moon, say) — the New Horizons team hosted a workshop on Nov. 3-4 at the Southwest Research Institute’s offices in Boulder, Colo. 20 experts in ring systems, orbital dynamics and astronomical observing techniques gathered to put together a plan of action ahead of the flyby in three years time.

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Using Hubble and other large ground-based observatories, the workshop advised that as much information about Pluto’s neighborhood should be gathered as possible and should more hazards be uncovered, alternate flyby routes for the spacecraft will be planned.

Interestingly, one of the “safe zones” for a flyby could be through the orbit of Charon, Pluto’s largest moon. As Charon has a dominant gravitational field in that zone, a clear path from debris can be expected.

So let’s hope any clouds of debris or small moons are identified before New Horizons reaches Pluto’s orbit, because as any Star Wars fan knows, collision avoidance is usually best handled with Han Solo at the helm:

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