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Hitchhiker to the Outer System?

Years ago at the Aosta conference on interstellar studies, Greg Matloff told attendees about an interesting way to travel the Solar System. If the goal is to get to Mars, for example, it turns out that there are two objects — 1999YR14 and 2007EE26 — that pass close to both Earth and Mars, each with transit time of about a year. Let me quote from Greg’s paper:

Since orbital characteristics are known for a few thousand NEOs, it is reasonable to assume that about 0.1% of the total NEO population could be applied for Earth-Mars or Mars-Earth transfers during the time period 2020-2100. Because a few hundred thousand NEOs must exist that are greater in dimension than 10m, hundreds of small NEOs must travel near-Hohmann trajectories between Earth and Mars or Mars and Earth. It seems likely that a concerted search will find one or more candidate NEOs for shielding application during any opposition of the two planets.

The notion is provocative. Could we somehow hitch a ride on one of these objects, taking advantage of its capabilities as a radiation shield by digging into its surface and exploiting its resources along the way? And maybe we can look further than Mars. In 2014, a NEO called 2000WO148 swings by the Earth enroute to the main belt asteroid Vesta in 2043. The question becomes, are there other NEOs on interesting trajectories that might be of use in our explorations?

I was reminded of the NEO hitchhike idea this morning while reading about another interesting object. NEOWISE detected 2016 WF9 in late November of 2016. Here we have a true sightseer. 2016 WF9 approaches the orbit of Jupiter at its furthest point from the Sun, and then, over just under five years, swings inward, coming in past the main asteroid belt and the orbit of Mars to move just inside the orbit of the Earth before heading back out.

We get closest approach to Earth’s orbit on February 25th of this year, although at 51 million kilometers, this object hardly poses a danger to our planet, nor will it in the foreseeable future. Whether 2016 WF9 is an asteroid or a comet is not known. What we know is that it is between 0.5 and 1 kilometer across, and has low reflectivity, as do many dark objects in the main asteroid belt. Although in a comet-like orbit, 2016 WF9 lacks the dust and gas we normally associate with a comet. James ‘Gerbs’ Bauer (JPL) is deputy chief investigator for NEOWISE:

“2016 WF9 could have cometary origins. This object illustrates that the boundary between asteroids and comets is a blurry one; perhaps over time this object has lost the majority of the volatiles that linger on or just under its surface.”


Image: An artist’s rendition of 2016 WF9 as it passes Jupiter’s orbit inbound toward the sun. Credit: NASA/JPL-Caltech.

Another object recently spotted by NEOWISE is indeed thought to be a comet, releasing dust as it nears the Sun. In the first week of the new year, C/2016 U1 NEOWISE will be in the southeastern sky shortly before dawn as seen from the northern hemisphere, reaching perihelion on January 14 inside the orbit of Mercury. Although it’s impossible to say for sure, it may become bright enough to be visible in binoculars, according to this JPL news release.

Since NEOWISE was reactivated in December of 2013, it has discovered either 9 or 10 comets, depending on what 2016 WF9 turns out to be. It 2016 WF9 is found to be an asteroid, then it would be the 100th discovered since reactivation. The original mission, the asteroid and comet-hunting part of the Wide-Field Infrared Survey Explorer (WISE) mission, discovered 34,000 asteroids. 31 of its discoveries pass within 20 lunar distances, and 19 are thought to be more than 140 meters in size, but reflect less than 10 percent of incident sunlight. They are objects as dark as new asphalt, absorbing most visible light but re-emitting energy at infrared wavelengths that the NEOWISE detectors can readily study.

For those interested in digging into these matters further, the NEOWISE data release, with access instructions and supporting documentation, is here. And on the fictional side, Kim Stanley Robinson’s novel 2312 looks at terraformed asteroids in terms of both habitats and intra-system transportation in an evolving space infrastructure.


Comments on this entry are closed.

  • ljk January 4, 2017, 10:24

    For whatever this is worth, the White House is at least aware and paying some attention to NEOS…

    National Near-Earth Object Preparedness Strategy:


    Full document here:


  • Michael January 4, 2017, 10:24

    I see this as a great way to move more safely through the solar system and building all the time.

    Here is a nice orbit calculator, just cut and paste or type an object in and you can see its orbit animation.


    For 1999YR14 it is,


  • Larry Kennedy January 4, 2017, 10:49

    As one sympathetic to those speaking against ” planet chauvinism” I’m all for developing some of these bodies into space and materials research centers with a plus side of cycler.
    And so once again I will plug the need for orbital experiments with short arm centrifuges, although for many of these bodies the “short” arm could be significantly larger.

  • Neil S January 4, 2017, 11:22

    This is exciting; it could be the answer to near-term human space flight beyond the earth-moon region.

    Radiation seems to be the last big obstacle to flying to other planets. Carrying enough shielding to be pretty safe is likely to be very fuel-intensive. Flying out to meet one of these asteromits and creating shelters inside it would cut way down on the exposure. As time goes by it would also give the travelers a lot more room and facilities. The down side is that you’d have little control over when you had to fly to meet it and when you’d fly from it to your destination but those would presumably be relatively short flights.

    I can see important bases being established on these objects. There are lots of stories to be written about them.

    • DJ Kaplan January 4, 2017, 14:25

      Wouldn’t burrowing under an asteroid’s surface be plenty fuel-intensive?

      • Michael January 5, 2017, 8:39

        Asteroids and comets are mostly rubble, regolith and ices which is easy to move around in the low ‘G’ environment. I can also see these hitchhikers as jump off points around the solar system. We could potential refuel using water and solar energy on the trip and then eventually use them to jump off in a part of the objects orbit.

        • Alex Tolley January 5, 2017, 11:48

          The refueling adds to Neil’s point below. A ship that can refuel at the base saves energy simply by not needing the fuel to accelerate the fuel needed for orbit insertion at the end of the journey. This further reduces the needed mass of the “taxi”.

        • DJ Kaplan January 5, 2017, 13:33

          Some are solid rock of course. And we haven’t begun to characterize these two bodies yet. I wouldn’t get all giddy just yet. ;)

  • RobFlores January 4, 2017, 12:37

    Riding on a comet or comet remnant, would be far more advantageous.
    You have the option of building a feris wheel type station(actually a wheel with an inner tube which spins living quarters) and bury it a few tens of meters deep With CHO present and modest other amounts nutrients added, it would save on infrastructure costs (no water recycling systems to start with) and Blue Green Algae could be grown as a base feed stock. It’s great if you are only doing exploration.
    The most interesting thing about hitchiking imo, is the possibility
    of reaching Jupiter and Saturn and their moons. The abundant lesser moons would be perfect to jump off into, so exposure to space hazzards would be limited. (For scientific exploration, those would be lifetime missions, years of travel waiting for a return “Body” 20 years possibly, and return to write papers. Colonization is a bit trickier unless colonization target is one of these ice/rock moons of lesser size. It would still be tough to colonize a larger moon, you would have to use lesser moons as a safe space while preparing a colony site on a larger moon.
    Overall the NEO’s could speed solar system exploration/development up by decades if dedicated infrastructure were designed.

  • Marshall Eubanks January 4, 2017, 12:37

    Here is a rather large recently discovered hitchhiker:


    “The newly discovered asteroid 2016 YN2 has an absolute magnitude of H=14.8, suggesting a diameter of 3.3-6.5 km. This makes it the largest NEA discovery since (242450) 2004 QY2, and one of the 50 largest objects in the Near Earth asteroid population.”

    This body at present goes from near the orbit of Jupiter down to just outside the Earth’s orbit, but it reaches perihelion near the L3 Lagrange point (i.e., the opposite side of the Sun from the Earth) and has an orbital period of very close to 5 years (meaning it will stay in this out of sync orbit for decades, at least, although it is hard to see how this could be any sort of resonance with the Earth).

  • Alex Tolley January 4, 2017, 13:44

    Clarke missed the benefits of this when he argued about the fallacy of hitching a ride on an asteroid. (Astronautical Fallacies”):

    A number of writers have fallen into the another gravitational trap by proposing that space travelers use asteroids or comets to give them free rides. Some asteroids, they point out, have passed within a few hundred thousand miles of earth and then gone on to cut across the orbits of other planets. Why not hop aboard such a body as it makes its closest approach to earth, and then jump off at a convenient moment when passing mars? In this way your spaceship would only have to cover a fraction of the total distance. The asteroid would do all the real work.

    While Clarke was right about the fallacy, he missed the value of such an approach for shielding (not expected to be a problem when he wrote this) and local resources.

    Comets might be ideal in that they could be gently nudged into the most convenient orbits using their own mass as propellant. As my colleague Brian McConnell and I have argued with the Spacecoach idea, abundant water resources would make space travel far more safe and comfortable. Rotating habitats buried beneath the surface would make for Earth-like living conditions. Contra-rotating habs would not exert any net torque on the comet so that anchoring the structure would be easier. If fusion power is achievable, then the comet would offer abundant heavy hydrogen isotopes to power the reactor. Over time, I would expect the comet’s structure to change from a fluffy snowball with a dusty surface to carved ice covered in reflective foils, offering a strong structure and possibly a sunlit interior for parts of its orbit.

    • DJ Kaplan January 5, 2017, 13:36

      I think that maybe Clarke was remarking on the “the asteroid would do all the real work” when of course, once you get to a matching velocity, you are basically coasting, whether you’re on a rock or on your own. The momentum of an asteroid is not likely to make the trip any faster or easier.

      • Michael January 8, 2017, 14:38

        Easier? it will protect the crew, that means mass or energy saved.

  • ljk January 4, 2017, 15:13

    Planetoids get the luck of the draw for the latest NASA Discovery missions:


    To quote:

    “This is an opportunity to explore a new type of world – not one of rock or ice, but of metal,” said Psyche Principal Investigator Lindy Elkins-Tanton of Arizona State University in Tempe. “16 Psyche is the only known object of its kind in the solar system, and this is the only way humans will ever visit a core. We learn about inner space by visiting outer space.”

  • Christian G January 4, 2017, 18:57

    A couple obvious questions:

    What’s the Delta-v getting from LEO to matching orbits with a likely hitch-hiker?


    Do we know if any of these are solid objects that can be tunneled into or just gravity-bound piles of rubble?

    • Neil S January 5, 2017, 0:15

      I’d think the delta-v would be the same as it would be taking that briefly accelerated route out-sysstem in the ship. But the delta-(mv) would be a lot less because the ship wouldn’t need as much radiation shielding and it could be a lot smaller; you’re not planning on spending one or more years in it but rather in whatever size tunnels and halls have been made in the asteromit.

      • Michael January 5, 2017, 11:24

        I suppose we could have a tunnel complex all made up and then when we get to a rubble/regolith pile we just ‘pour’ it around the structure with ports to the outside.

      • Alex Tolley January 5, 2017, 11:43

        That is a good and often overlooked point. The ships can be much more basic as they are only needed as short duration taxis. The asteroid/comet would provide all the roomy accommodation for the trip.

        Depending on the orbit it might be possible that several rendezvous would be made with other ships on te journey, not just at the start and end.

        In addition, if you are moving bulk resources such as water and other volatiles around the system, the orbit of the resources has already saved some of the delta-v involved in relocating the resources compared to those in approximately circular orbits.

  • Sean Meaney January 4, 2017, 19:16

    We wont be able to alter the mass of these objects or we will change their orbits. On the upside we could change their orbits and position Astronomy systems on them to provide us with an unobstructed viewpoint.

  • Frank Smith January 5, 2017, 9:08

    @ Christian:

    AFAIK, it would take just as much fuel to match the orbit of a hitch-hiker as it would to get to a planet on your own.

    That neglects the other benefits mentioned in the article such as shielding and using the object to possibly provide water and other resources.

  • Marshall Eubanks January 5, 2017, 11:08

    This makes some sense if you can find asteroids near cycler orbits.

    Consider a habitat in the orbit of one of the Mars “cyclers” proposed by Buzz Aldrin (and others). If the cycler was ISS sized, it might have a habitat surface area of 4000 m^2. If each square meter had a shielding of 1 m of water, that’s 4000 tons of water (plus some piping and tubing etc. which could be 3-D printed or brought from Earth). The question then becomes, is it easier to extract 4 kilotons of water (a sphere with a radius of 10 meters) and move it to the cycler from a remote body, or move the body itself to the cycler orbit and extract 2 kilotons of water there (as you could use the mass of the asteroid for 1/2 your shielding by just placing the habitat on the surface of the asteroid).

    (Note – 1 m of water may not be enough. If you need N meters thickness, just multiply the above masses by N. Even with 1 meter it is a lot of water.)

    • Michael January 5, 2017, 14:21

      We could give it a magnetic field which reduces the mass need.

  • Dani Eder January 5, 2017, 11:09

    You don’t have to restrict yourself to NEO’s that happen to be in the right orbit at the right time. Since we already know of 15,000 NEO’s, and the number is rapidly growing, for any desired orbit there will always be some that are close, in terms of delta-V and timing.

    For example, if you want to set up a cycling orbit “Transfer Station”, which travels repeatedly between Earth and Mars, you can first send an asteroid tug with electric propulsion to a suitable nearby NEO. It gathers some hundreds of tons of asteroid rock scraped off the surface, then carries it to the desired orbit. You then launch crew modules and processing equipment to meet the tug, the next time it passes near Earth. Some of the rock gets distributed in a shell around the crew modules, for radiation protection. The rest can be processed for water, fuel, and other products. If you run low on raw rock, the first tug, or another one, can go get more. The advantage of keeping a tug at the station is cycling orbits are not naturally stable, and you therefore need course corrections.

    Advantages of this approach include:

    * Shielding mass, once placed in the correct orbit, can be used for multiple trips. The mass per use then becomes low. Crew exposure is minimized to the short time between planet and habitat as it passes.

    * Crew have something useful to do with their time for the 6-8 months between planets. They can be making fuel, growing food, etc.

    * The transfer habitat can be expanded incrementally each time it gets near Earth. Extra modules and equipment can be later dropped off at Phobos as a “forward base” to reaching the surface.

    * Producing supplies en-route reduces the total mass that has to come from Earth, and therefore mission cost. The asteroid tugs can be self-fueling, since typical delta-V’s are on the order of 1 km/s, which only requires 2% propellant/delivered rock mass. Chondrites contain up to 20% water and carbon compounds.

  • Alex Tolley January 5, 2017, 11:58

    The solar system is big. I suspect there are not many bodies that are in convenient orbits to act as good bases to hitchhike on. To really make this a useful approach, we are going to need to convert the orbits of many such bodies to useful ones to service destinations.

    If we do, can the habitats in these bodies be made attractive enough to serve as long-term, even permanent, accommodation for personnel to manage and maintain them?

  • Charley January 5, 2017, 16:21

    With regards to the problem of the velocities and what was stated earlier:

    @DJ Kaplan
    “I think that maybe Clarke was remarking on the “the asteroid would do all the real work” when of course, once you get to a matching velocity, you are basically coasting, whether you’re on a rock or on your own. The momentum of an asteroid is not likely to make the trip any faster or easier.”

    I’m not at all certain that that is a true statement. The reason I say that is one could be on a intersection course with the near Earth object, such that the object to be captured could be in a ballistic capture type of situation. This was stated many months ago by the individual who advocated that a gentle ballistic capture of an object at it’s apihelion with regards to a Mars type probe.
    Such a gentle ballistic capture of an Earth probe near a earth orbit crossing body would be equally able to be achieved and would require probably a minimal amount of Delta V to achieve necessary capture. If the object to be captured was in fact actually in front of the asteroid or comet and the difference in velocity was not too great, you could even allow the asteroid to impact in a gentle fashion and achieve capture that way. I would expect that this would not be a situation such as a fly flying in front of a steaming locomotive and then there would be a sudden splat type of impact. And I’m certain that someone could figure out a way to achieve a relatively soft landing.

    As for the idea of using these bodies as troop transports (if you’ll allow me to use that analogy here). I think is an extremely poor idea in all aspects. I see absolutely no reason whatsoever that this should be allowed to use this natural bodies is any type of personnel transport type mechanism. I think primarily it would be a matter of cost, and as has been carefully pointed out here the radiation shielding and production of personnel would probably be extremely costly. In addition, whenever you have people involved, you’re going to have to provide a lot of and ancillary type of items to keep them alive. And I just don’t think that’s a reasonable use of resources for this type of particular situation.

    However, I would and definitely advocate utilizing such bodies as transport platforms for enormous quantities of supplies that could be cycled between Earth and your target body. Use the land thousands of tons of needed supplies on this body and then at closest approach (or whatever situation would best serve you.) A gentle nudge off the body and allow ballistic capture of the needed supplies at your target. Obviously, transportation of materials doesn’t require any type of special shielding and at the same time you could have robot wardens scour the object and if need be, and possibly feasible mine the body for any type of consumables that might be useful and store them to be jettisoned with the other supplies at the rendezvous point.

    Also overlooked. I believe is the fact that these natural bodies. Not only can be used as transport vehicles, but they could be exploration platforms in their own right. Some of these objects will cross Earth orbit and go far into the icy comet belts that lie beyond Pluto. With a robotic probe firmly attached to the object. It can serve as a marvelous platform to do scientific studies and you don’t even require any type of additional gravity assist to do your work for you. At least this is my take on what should be done with these bodies as a way to exploit them, not only for resources, but for transportation and exploration.

  • douglas dwyer January 8, 2017, 20:04

    Expoition of FRB echoes as radar sources may be possible because our knowledge of the direction of origin of the reflecting stellarbody, the reversal of the degree of dispersion and the ability to set up an antenna pointed in the direction of a potential source of re-radiated signal could all be done in anticipation of reception of the vanishingly small re-radiated signal (echo) from bodies within light months or years
    Information carried by the reradiated FRB will be carried as sidebands on the FRB and may be obtined by comparing the echo with the original FRB
    One way of looking at the FRB is to regard it as originating as a sub microsecond pulse that is stretched to a length of a few milliseconds as the result of travelling through a weakly ionised environment. Any non-uniformity in the environment will provide historic information |as dispersion on the space through which it has passed.