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Pluto/Charon: A Dangerous Arrival?

We’ve often considered the effect of interstellar dust on a spacecraft moving at a substantial percentage of the speed of light. The matter becomes even more acute when we consider an interstellar probe arriving at the destination solar system. A flyby mission moving at ten percent of the speed of light is going to encounter a far more dangerous environment just as it sets about its critical observations, which is why various shielding concepts have been in play to protect the vehicle. But even at today’s velocities, spacecraft can have unexpected surprises when they arrive at their target.

We’re now looking toward a 2015 encounter at Pluto/Charon. New Horizons is potentially at risk because of the fact that debris in the Pluto system may not be found in a plane but could take the form of a thick torus or even a spherical cloud around the system. We don’t yet know how much of a factor impactors from the Kuiper Belt may be, but strikes at 1-2 kilometers per second would kick up fragments moving at high velocity, generating debris rings or clouds we have yet to see. For that matter, are there undiscovered satellites in this system that could pose a threat?

Image: Pluto’s newest found moon, P4, orbits between Nix and Hydra, both of which orbit beyond Charon. Finding out whether there are other moons or potential hazards near Pluto/Charon was the subject of a recent workshop that is gauging the dangers involved in the encounter. Credit: Alan Stern/New Horizons.

Working on these questions is the job of a team that met at the Southwest Research Institute (Boulder, CO) in early November. The New Horizons Pluto Encounter Hazards Workshop had plenty on its agenda. As principal investigator Alan Stern notes in this report on the New Horizons mission, the group was composed of about 20 of the leading experts in ring systems, orbital dynamics and the astronomical methods used to observe objects at the edge of the Solar System.

The Hubble Space Telescope will play a role in the search for undiscovered moons and possible rings, aided by ground-based telescopes that will study the environment between Pluto and Charon, space through which New Horizons is slated to move. Stern also notes that the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope will be able to make thermal observations of the system, all of which should give us a better idea of the situation ahead even as plans go forward to consider alternate routes in case the current trajectory starts to look too dangerous. From Stern’s report:

Studies presented at the Encounter Hazards Workshop indicate that a good ‘safe haven bailout trajectory’ (or SHBOT) could be designed to target a closest-approach aim point about 10,000 kilometers farther than our nominal mission trajectory. More specifically, a good candidate SHBOT aim point would be near Charon’s orbit, but about 180 degrees away from Charon on closest-approach day. Why this location? Because Charon’s gravity clears out the region close to it of debris, creating a safe zone.

New Horizons is now approaching 22 AU out and has been brought out of hibernation until November 15 for regular maintenance activities. Tracking a spacecraft on its way to a dwarf planet we have never visited is intriguing enough, but the recent workshop was inspired at least partially by discoveries made after launch, such as the existence of the moon P4, which was found this summer. Stern mentions some evidence for still fainter moons that have not yet been confirmed, but it’s clear that space ahead may have more surprises in store.

Stern adds “it is not lost on us that there is a certain irony that the very object of our long-held scientific interest and affection may, after so many years of work to reach her, turn out to be less hospitable than other planets have been.” Indeed. Then factor in how much work went into getting this mission funded, built and flown — the payload aboard New Horizons is a precious thing indeed. We can only hope — and assume — that the observing campaign to verify the path ahead will be successful.


Comments on this entry are closed.

  • Ole Burde November 9, 2011, 15:19

    The best and easiest and cheapest way to protect an interstellar probe against debris at the target star , must be to send two or more identical probes with only a slight variation in the programming of final aproach strategi . The chance of several probes getting hit is much , much smaller .
    The whole idea of such a probe is , that it should be as fast as possible , and therefore lightweight . Heayy shieldig does not go well with any kind of sail-design, but there is another survival strategy that does . If critical control and sensor funktions are distributed in “nodes” all aroud the sailarea , and if each one of these are made small enough to be DUBLICATED i several copies or back up systems in different locations , then the system can take a great number of hits from big pieces of spacerock without loosing any ability . Each of the nodes might have som protection against the general effect of space dust , but only against very small particles . Add to all this a relatively simple maitenance “spider” capable of reconncting damaged wiring , and we have a robust system designed for ” damage control ” .
    Another advantage of distributed functions are the much lower structural demands this puts to the saildesign .

  • Kevin Blair November 9, 2011, 17:24

    Will private space explorations ever be able to reach pluto? Can humans land on pluto? Sorry if thats stupid, I’m new to the blog

  • Paul Gilster November 9, 2011, 17:35

    Kevin, we’re a long way from private missions to Pluto — New Horizons is the first spacecraft dedicated to a Pluto mission, and there is no current follow-up being planned. However, commercial space is opening up starting with trips from companies like Virgin Galactic, and companies like SpaceX are showing how viable commercial boosters can be. It’s not inconceivable that in the future — down the road a good bit — private companies will operate deep space vehicles.

  • Lepton November 9, 2011, 17:42

    I can understand a safe aim point is around Charon orbit, but why 180 degrees away? Was that due to they want NH path to intersect both shadows of Pluto and Charon?

  • Laurel Kornfeld November 9, 2011, 18:23

    Whether public or private or some combination of both, I hope the next mission will be a Pluto orbiter similar to Cassini, which has been orbiting the Saturn system for several years.

  • Christopher Phoenix November 9, 2011, 19:04


    Will private space explorations ever be able to reach pluto? Can humans land on pluto? Sorry if thats stupid, I’m new to the blog

    We are a long way away from manned flights to Pluto, but companies like SpaceX and Virgin Galactic are working on the goal of private deep space flight. In the nearer future I can imagine commercial SSTO’s, private space stations, and commercial moon bases. In the farther future, private companies might even operate interplanetary craft.

    Before a private space firm can try to reach Pluto, orbital and cis-lunar space will already be thoroughly crowded with commercial ventures, and we will doubtless have Mars colonies and manned flights to Saturn. Private companies will be operating spacecraft with nuclear propulsion- be it nuclear electric rocket, nuclear pulse rockets, or some variant of the fusion rocket. Obviously this is down the road a good bit.

    Any flight to the outer solar system faces many problems. You need much better propulsion to reach your destination quickly. There are various radiation and microgravity hazards, and the ship will be on its own for a while. Such missions will not be undertaken until space technology has matured significantly.

    We’ll have already built a city on Mars before we try growing potatoes on Pluto or any other Kuiper belt object.

  • Daniel Suggs November 10, 2011, 0:08

    @Christopher Phoenix- I hope that the people who build the cities on Mars come from Earth orbiting stations and fly ships built on Luna. Even better, if it were to happen in my lifetime.

  • jkittle November 10, 2011, 12:09

    I would imagine that the extended carbon monoxide gas envelop around Pluto would create drag to remove very small objects and dust orbiting Pluto (over a few millions year time frame, if not sooner). the surviving objects would have to be larger, large enough to be observed as the crft approaches. Worth study, not worth worry.
    and welcome Kevin- In theory there is no reason that any Kuiper belt object is out of reach! icy and inviting!

  • John Koziol November 10, 2011, 16:26

    I can’t think of a good reason a commercial enterprise to Pluto would be contemplated unless something unforeseen and tremendously valuable was there. I think the 1st two extraorbital commercial ventures would likely involve lunar or asteroidal mining.

  • andy November 10, 2011, 19:25

    I think the 1st two extraorbital commercial ventures would likely involve lunar or asteroidal mining.

    I have yet to see any convincing economic justification for either lunar or asteroid mining. The costs of getting to and from the moon or the asteroids are far too great to make these activities worthwhile, even if we are wildly optimistic about what resources we’d be able to obtain from them.

  • William November 10, 2011, 23:44

    What’s being presented in this article as a problem near the destination star, is in fact a problem *everywhere* on the multiple-light-year path from Sol to there. There’s (probably) all kinds of stuff in interstellar space, not just dust: comets in each star’s respective Oort cloud, comets wandering outside these, free-floating planets, rocks ranging in size from dust grains to dwarf-planet size, etc.

    In the Kuiper Belt, there are an estimated 1^15 objects around 100 meters in diameter. Let’s suppose there are similar objects and similar numbers of them out into the Oort clouds and outside these clouds in true interstellar space. They would be in far lower density than in the Kuiper Belt. But with the enormous number of these out there, and the fact that an interstellar vehicle is going to be travelling at such a speed, they are going to be a huge problem.

    IMO this problem — which could be the show-stopper for interstellar flight — is generally just glossed over.

  • Eniac November 11, 2011, 7:08

    @Andy: If there were lumps of pure platinum flying around, you could probably make a business from cutting them up and dropping them to Earth in safe portions. More likely, though, you are right and asteroids are not that much more valuable than ordinary rocks.

    The use of asteroids to supply a space industry is a Catch-22: There will only be a space industry after we have gone into space, thus the mining of asteroids for space industry cannot be the motivation to go there in the first place. It is like the pilgrims leaving for America to set up a business selling hot dogs to pilgrims.

  • Interstellar Bill November 13, 2011, 6:40

    The economic value of space has already been established by the hundreds of Earth-orbiting satellites, particularly comsats, now making money.
    Read the works of O’Neill concerning solar-power satellites as the basis for a space manufacturing industry.
    A 1 km nickel-iron asteroid could supply all the Earth’s steel for a century, with no Earthside pollution, while the Moon could supply all our titanium.
    Though it would take decades to establish them, such space industries would under-price any Earthside competition.

    After 50 years in space, the reason we don’t now have such an industry is that the governments of the world make it impossible for any private entities both to amass unconfiscated capital and to financially plan for future decades free of arbitrary and capricious government dictats. Otherwise the world’s steel companies would have done it already.

    Space fans must wake up to the dismal fact that unless economic literacy suddenly illuminates world governments, space will never be conquered.

    It’s no coincidence that the current regime, while exploding the U.S. national debt, has cancelled the Shuttle and all planetary probes not already started. (Did you know Kepler will soon be shut off? Don’t bother protesting: the money is being re-routed to promote Islamic self-esteem.)

    You see, there are much more efficient ways to buy votes than funding aerospace projects staffed by $100K/yr engineers who are politically unreliable because of their ability to think. That same $100K can buy several brain-dead government dependants who will vote the statist ticket every time, firmly believing in their masters’ intellectual swill (e.g.,’fairness’).

    Hey, I think I just solved the Fermi Paradox:
    Leftism as Cosmic Antidote,
    preventing civilizations
    from ever escaping their home-worlds

  • Eniac November 13, 2011, 14:26


    A 1 km nickel-iron asteroid could supply all the Earth’s steel for a century, with no Earthside pollution, while the Moon could supply all our titanium.

    Even better, the Earth can supply all our steel AND titanium, and it is much easier to reach.

    A pound of steel is $0.20, titanium is ~$6. That includes mining, refining, and transportation, on Earth. Mining, refining, and transportation of metals from asteroids or the moon has never been done, but surely it will be more expensive than this for a quite a while. Or perhaps you could explain how you would do it at these prices.

    Now, a pound of platinum is about $24,000, so there the chance of breaking even is quite a bit better, although currently even that is way out of reach.

  • Christopher Phoenix November 14, 2011, 1:54


    Now, a pound of platinum is about $24,000, so there the chance of breaking even is quite a bit better, although currently even that is way out of reach.

    We’re using asteroid resources already. All the gold, cobalt, iron, manganese, molybdenum, nickel, osmium, palladium, platinum, rhenium, rhodium, ruthenium, and tungsten that humans are currently mining from Earth’s crust originally came from the rain of asteroids that hit Earth after the crust cooled. This is because Earth’s gravity pulled all the siderophilic (iron loving) elements down into the planet’s core before the crust cooled. Initially, the Earth’s crust was completely depleted of these valuable elements (all of which are vital for technological and economic progress). Asteroid impacts re-infused the Earth’s crust with these elements.

    In the future, asteroid miners might even export valuable elements like platinum and cobalt to Earth for profit. The asteroids are full of valuable elements that modern industry needs. However, the cost of returning asteroidal materials to Earth far outweighs their market value with current technology. Once the space technology is there, asteroid miners will have to compete with terrestrial sources of metals.

    The sea floor contains plenty of valuable minerals that are probably easier to extract and transport. I am worried about the possible environmental damage deep-sea mining might do, though. The hydrothermal vents are a unique environment host to unusual creatures that could be harmed by such efforts. Asteroid mining is cleaner, environmentally speaking.

    It is likely that asteroid miners will be selling to people who are in space, such as habitats or various settlements. Going now would be a bit like sailing to America to sell hot dogs to Pilgrims before the Pilgrims arrive, as you said.