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Space Science

The Second Moons of Earth 92

Posted by samzenpus
from the that's-no-moon dept.
Hugh Pickens writes "Despite a large body of work on satellite capture by the gas giants, mainly Jupiter and Saturn, there has been little published about the Earth's natural satellites other than the moon. Now Scientific American reports that although the moon has been with us for billions of years, Earth has also had countless other satellite companions and probably has one right now. These 'second moons' are boulders from the large population of near-Earth asteroids that get snagged by our gravity, orbit the Earth for a few months, then escape and move on. Known as 'Temporarily-Captured Orbiters' (TCOs), the irregular natural satellites are hard to see but astronomers spotted one such transient satellite in 2006. Dubbed 2006 RH120, the asteroid was a few meters in diameter, was captured by Earth for about a year and made four Earth orbits before being ejected after its June 2007 perigee back to interplanetary space. But TCOs are not just of academic interest. 'Once TCOs can be reliably and frequently identified early enough in a capture event they create an opportunity for a low-cost low-delta-v meteoroid return mission. The scientific potential of being able to first remotely characterize a meteoroid and then visit and bring it back to Earth would be unprecedented (PDF).'"
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The Second Moons of Earth

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  • by Anonymous Coward on Monday January 02, 2012 @01:34PM (#38564428)

    not the best idea... (i think they're dangerous)

  • Better ideas (Score:5, Interesting)

    by vlm (69642) on Monday January 02, 2012 @01:36PM (#38564454)

    But TCOs are not just of academic interest. 'Once TCOs can be reliably and frequently identified early enough in a capture event they create an opportunity for a low-cost low-delta-v meteoroid return mission.

    Boring. I'd put a whole freaking base on it while its in earth orbit, then see where it goes. If not a manned base, at least a robot research station. Should be pretty interesting to see where it ends up. At least a radio beacon?

    • Re:Better ideas (Score:4, Informative)

      by Grishnakh (216268) on Monday January 02, 2012 @01:40PM (#38564478)

      I'd put a whole freaking base on it while its in earth orbit, then see where it goes. If not a manned base, at least a robot research station.

      Did you miss the part in the description that said the last such meteoroid was only a few meters across? Are you going to send Lilliputians up there to build a base on it?

      Should be pretty interesting to see where it ends up. At least a radio beacon?

      I'm sure they can calculate exactly where it'll go once they know enough about its position and velocity. Even if it makes it out of the Solar System, it's going to be rather slow; if you want to send a probe out of the solar system, it's probably a lot faster to just build one and send it out there with rockets. To be captured by Earth's gravity, these things can't be going very fast.

      • Re:Better ideas (Score:5, Interesting)

        by Nyeerrmm (940927) on Monday January 02, 2012 @02:11PM (#38564724)

        Actually, trajectories of small bodies like that are quite interesting. Two things stand out to me (I did some of my graduate work looking at missions to small-ish asteroids like Apophis which is ~300 meters, so bigger than this but smaller than large asteroids).

        1. If this is loosely captured by Earth with multi-month orbits it is on the edges of the Earth's sphere of influence where the Earth and the Sun's gravity really interplay in weird ways and small uncertainties in its current state could turn into huge uncertainties later.

        2. For a very small asteroid, the surface-area-to-mass ratio is very high, meaning effects of solar pressure and the Yarkovsky effect will cause it to behave very differently. The ability to track an asteroid like this could greatly inform models of these effects.

        If you could find many of these and have a spacecraft able to rendezvous and deposit a tracker on new ones as we find them, it could greatly benefit studies of near-Earth objects. Of course, a mission to do that sounds extremely challenging (but very interesting to work on).

        • by Grishnakh (216268)

          2. For a very small asteroid, the surface-area-to-mass ratio is very high, meaning effects of solar pressure and the Yarkovsky effect will cause it to behave very differently. The ability to track an asteroid like this could greatly inform models of these effects.

          If you could find many of these and have a spacecraft able to rendezvous and deposit a tracker on new ones as we find them, it could greatly benefit studies of near-Earth objects. Of course, a mission to do that sounds extremely challenging (but ve

          • Re:Better ideas (Score:4, Interesting)

            by Nyeerrmm (940927) on Monday January 02, 2012 @02:30PM (#38564850)

            Understanding the effects for a small asteroid could inform our understanding of how larger asteroids would behave as well, thus serving to help us better predict contintent-killers like Apophis.

            Of course, I'd much rather bring them in closer and mine them, but that would be more difficult, so tracking would probably happen first (and be good practice for eventual capture missions).

            As far as allocation of resources go, that really depends. I'd have to see detailed studies on what a mission like this would cost.

            • by mcgrew (92797) *

              Why would we go to the expense of mining asteroids when it's far cheaper, easier, and safer to mine here on Earth? I mean, until an asteroid made of unobtainium comes close.

          • by vlm (69642)

            Doesn't this:

            It seems like it'd be more useful to capture them and exploit them for their mineral content.

            Depend directly on what you don't seem to like:

            This is interesting and all, but I have to ask, how useful is this knowledge?

            • by Grishnakh (216268)

              Not exactly. I was just saying that if you're going to mess around with a puny asteroid in the first place, it'd be better to just capture it and use it for mineral resources. But realistically, it probably isn't worth it unless the thing is 50% gold or something, and that isn't very likely. If you're going to mine asteroids, it'd be much more economically feasible to go after much larger asteroids rather than something that's the size of a car. Yes, to learn if these asteroids are filled with gold or p

              • is because idiots at JP Morgan, Goldman Sachs, Morgan Stanley, and others are 1. hoarding it, 2. looting and pillaging the paper money system of the planet.

                in essence -- you act like the 'free market' should govern our societies big ideas. well, the free market doesnt. free will does. and we have decided to throw it down the toilet, on wars, on stupid financial crimes, on smoke and mirrors. gold's value is false.

                the value of scientific research is real, it is fundamental. you can feel it. you can feel it in

                • by Grishnakh (216268)

                  Forget gold then, there's lots of other materials that are intrinsically valuable for their industrial uses. Even gold is highly useful for electrical applications due to its corrosion resistance, but copper would be a lot more useful.

                  Scientific research is nice and all, but finding ways of improving peoples' quality of life is better, and for that you need technology and materials and resources to build that technology.

          • got started up in 2002? Where are you when we spend a trillion a year on boondoggles like Trailblazer or Turbulence? How about the VIPR teams - know how much we spent on those last year?

            Answer: enough to hire a crapload of scientists to study rocks and tell us the future of the planet. you know, that big ball where we actually live, that gives us food and water and everything we need to survive.

          • by stevelinton (4044)

            The attraction is the ability to study a steady stream of asteroidal rocks extremely cheaply. Bigger rocks either don't come along as often or don't come as close (close in the sense of the amount of fuel needed to reach them). The only exception is the Moon, which is (a) just one rock and (b) so big that you need significant fuel to land on it and take off again.

            Assuming you're talking unmanned, which seems likely, a mission to lurk somewhere suitable and study (and perhaps "tag" with a radar reflector) as

        • 2. For a very small asteroid, the surface-area-to-mass ratio is very high, meaning effects of solar pressure and the Yarkovsky effect will cause it to behave very differently. The ability to track an asteroid like this could greatly inform models of these effects.

          That is interesting. Would you equate that to an analogue of a Reynolds number in fluids?

        • by Hentes (2461350)

          You don't need an asteroid to shoot a tracker into those orbits. The tracker being "on" the asteroid doesn't change anything, as its gravity is practically zero. It's not like you can "hitchhike" an asteroid, you have to match its speed before landing.

          • by Nyeerrmm (940927)

            Actually it does.

            The second aspect of my statement focuses particularly on non-gravitational forces on the asteroid, which would not be measured by a free-floating beacon.

        • by stevelinton (4044)

          At the cost of slightly perturbing the orbits, couldn't you "harpoon" them with a transponder (or laser reflector) on a penetrator? Probably only needs to mass a few kg, could be launched from LEO by a modest solid fuel booster, and would just need a very small thrusters to make sure it hit point first. We can track the missile and the target with radar from here, aim for an impact velocity enough to lodge a hardened spike in rock.

          The much more difficult mission is to recover one. One approach would be to w

      • Re:Better ideas (Score:5, Interesting)

        by dotancohen (1015143) on Monday January 02, 2012 @03:05PM (#38565136) Homepage

        I'm sure they can calculate exactly where it'll go once they know enough about its position and velocity.

        No, all we know is that it is in a possibly-unstable orbit. If the orbit were simply enough that we could calculate it long term, then it would be stable enough to not be reejected. In fact, landing on the object in order to enjoy it's boost out of Earth orbit would require matching its orbit exactly, which would put the lander on an escape orbit itself. No chuck of iron necessary.

        If you didn't notice from the summary, one item made four orbits in a year, that is one orbit every three months. By Kepler's laws, that means that the object's distance from the Earth is twice the moon's distance. You would already be at escape velocity there, seeing as it just butts up against the Earth's Hill sphere. And all that is assuming a circular orbit, which is very unlikely. More likely, apogee is outside the Hill sphere and the only reason that the object stays in "orbit" is when the apogee is opposite the sun. As soon as the orbit rotates a bit, the object is lost.

        • by Grishnakh (216268)

          Ok, so we can't predict where it'll go very well. But even so, who cares where it'll go? It's so small that it really isn't useful for much, unless it's made of gold or platinum. A chunk of iron the size of a car isn't all that valuable. So what if it leaves Earth's orbit and travels to Alpha Centauri in 10k years? That's interesting and all, but it's not very useful. If we want to go to AC, we can just send a purpose-built probe there ourselves (although it'd still take a really long time). If we wa

          • A chunk of nickle iron meteor would give us something to practice zero G refining techniques on. Obviously robotic missions. Building/inflating a parabolic mirror would be step 1. (Profit would not be till much later then step 4. If ever.)

            It would give us an excuse to start. I'd set an ambitious goal of blowing a small nickle-iron bubble.

          • If we had tracking stations on these things, then we could use them to get a much better estimation of the distribution of mass in our solar system at any given time.
          • by ianare (1132971)

            Isn't being curious about the world enough of a reason ? Not everything has to apply to money or immediate use. Frankly, I'm disappointed to see this kind of position on a "geek" website.

            • by Grishnakh (216268)

              No, merely being curious is not enough of a reason: resources are limited, and there's a LOT of things out there to be curious about. So you need to pick carefully what you devote your research resources to. I am glad to see several other responses showing why this is a good thing to research (like the bit about these small asteroids being closer and more common than the big ones, so needing much less fuel to launch a probe to), but no, curiosity alone is never a good reason to investigate something.

              Just

            • by mcgrew (92797) *

              Not everything has to apply to money or immediate use.

              Mammon worship demands that, and money is the US's predominant religion. There are far too many, even at slashdot, who equate "free" with "worthless" who don't realise that the one theing they need more than anything else is free (air). Those who equate "having more stuff" with "being a better person" ("How much are you worth?")

              These folks are flabberghasted by the likes of me, who are happy with a roof over their head, food, clothes, and transportation

          • Could give us some insight into unknown gravity field configurations throughout our solar system. That could prove to be pretty useful one day. Right now we mostly have only analytical models of our system's gravity field. If we could get some hard data of paths that we have not commonly traveled, we might find something useful.
    • by n5vb (587569)
      Radio beacon with telemetry and a ranging transponder would be intriguing and probably not all that hard to deploy .. :)
      • by Toonol (1057698)
        The trouble is that if you can match courses with the object to drop a beacon, you can just dispense with the object and let the beacon follow the course on its own. It doesn't gain anything by being mounted on an asteroid... at least unless we make a beacon sophisticated enough it can somehow use the asteroid's resources.
        • by vlm (69642)

          Not true, the asteroid is a bigger heatsink than the beacon, unless you're tracking something really small.

    • by thue (121682)

      > Should be pretty interesting to see where it ends up.

      This is Newtonian mechanics. We can calculate where it ends up pretty accurately.

    • by Hentes (2461350)

      Why do you need an asteroid for that? You can just put a probe in the same orbit whenever you like, it's not like an asteroid makes that any easier.

    • by lievendp (872547)

      I would mount it with a small engine and remote control to have it do my bidding.

  • by Dexter Herbivore (1322345) on Monday January 02, 2012 @01:38PM (#38564466) Journal
    I really hope this does lead to capture of a metal rich meteoroid, it may cause havoc on the world metal markets but in the long run cheap minerals have to be good for the world economy.
    • by Hentes (2461350)

      It's not cheap anymore if you have to go up for it.

    • You are a space nut, and this is good. Yep, what more tempting target than an asteroid with hundreds of tons of metals difficult to achieve on Earth as rare earths, titanium, chromium, etc.? Maybe even silver and gold. The problem is that unfortunately many people think:

      1) can be transformed into a weapon?
      2) can be transformed into a weapon? (not repeated unintentionally, seriously)
      3) When will I profit from it in a month?
      • by Skapare (16644)

        Hundreds of tons would not be worth it. But some of the objects out there probably have trillions of grams. That's a 't', the 20th letter of the English alphabet which implies a number with at least thirteen digits in decimal.

        • by artor3 (1344997)

          Offtopic, but what is the point of the metric system if no one ever uses the prefixes? I have never once heard someone talk about teragrams or gigameters. It doesn't work that way in the other direction... people talk about nanometers or micrograms all the time. But in the large direction, people get to kilo and stop. In fact, they go out of their way to avoid the big prefixes, using phrases like "metric ton" instead of megagram.

          Just think how much clearer your post would be if the convention was to say

      • You are a space nut, and this is good. Yep, what more tempting target than an asteroid with hundreds of tons of metals difficult to achieve on Earth as rare earths, titanium, chromium, etc.? Maybe even silver and gold. The problem is that unfortunately many people think: 1) can be transformed into a weapon?

        Yes, witness "the moon is a harsh mistress" [wikipedia.org] by Robert Heinlein, circa 1966

        2) can be transformed into a weapon? (not repeated unintentionally, seriously)

        Ditto

        3) When will I profit from it in a month?

        the moment you'll find a technology to extract the reverse Delta-V [wikipedia.org]to produce propellant.

      • Having looked into this a bit, it appears that most of the metals that might be found would probably not be economical to bring back to Earth for various reasons (we can't just toss them down as big, dangerous meteorites), but will be invaluable as raw materials for space development.

    • by jc42 (318812)

      So do we have any credible estimates of the costs of capturing such near-Earth objects and mining them? Would it really be profitable with our current technology?

      I've read a few wide-eyed "sci-fi" suggestions about this, but nothing that would convince the management of any mining company to invest in it. Of course, I could have missed 99% of what's been written on the topic, and some of it might actually be accurate.

      • From my limited study of this, it appears unlikely to be cost-effective to bring back to the Earth's surface, but could be invaluable for building things in space.

    • by khallow (566160)
      They aren't that big. Would be an interesting source of materials for orbital activities, but the asteroid they spotted, if it were metal rich, would be a few dozen to few hundred tons, mostly iron and chromium.
    • by Anonymous Coward

      I want to tell Astrologists about this, just to watch them panic.

    • by Baron_Yam (643147)

      I don't think we have the technology to make a profit on bringing a metal-rich rock to Earth, even if it is in orbit just a light second or two away.

      How were you planning on bringing it down without risking a huge impact crater where we don't want one?

  • And at least one .. (Score:5, Interesting)

    by n5vb (587569) on Monday January 02, 2012 @01:47PM (#38564544)
    .. is man-made [wikipedia.org] .. :)
    • And David Icke will tell you that the earth's moon is hollow, was placed there by aliens, etc.

      Certainly not man-made, but manufactured by a super species (not God.)

      cheers,

      me

    • by Anonymous Coward

      that's no moon.

  • by Hatta (162192) on Monday January 02, 2012 @02:12PM (#38564742) Journal

    What causes these things to be only temporarily captured? If they escape orbit by their own momentum, they were never really in orbit in the first place. So either this is a misnomer, or there's some external force causing these objects to leave orbit. What is it? Tidal effects from the moon?

    • Yeah, pretty much actually. I'm not an astrophysicist, so I'm sure one will give you the details, but for any object to have a stable orbit around the earth it's got to get into some harmonic resonance with the moon or else be kicked out by the moon's gravity eventually.
      • Re: (Score:3, Funny)

        by Anonymous Coward

        That's exactly it. There's a very nice animated gif here [nasa.gov] of the old Saturn V third stage captured out of the blue a few years ago (mentioned by n5vb earlier in the thread). You can see that every time it gets near the moon, it gets either slowed down or sped up depending on if it comes before or after. On the final and sixth orbit, it comes just behind the moon which slingshots it away completely.

    • by Trepidity (597) <delirium-slashdot AT hackish DOT org> on Monday January 02, 2012 @02:38PM (#38564920)

      If I understand the paper correctly, there are configurations where the zero-velocity surfaces [wikipedia.org] of the sun and a planet coincide at some points, so an object orbiting the sun can transfer to a planetary orbit at one of the intersections without any other energy input, and then transfer back out again at the same or another intersection, again without any other energy input. Figure 1 on page 8 of the PDF [arxiv.org] has an illustration of some cases.

    • by thrich81 (1357561)
      I'm not an expert either but these objects are loosely "captured" by the Earth due to interactions mostly with the Sun I think. Even without the Moon this can happen. If the Earth were totally isolated then this couldn't happen via Newtonian mechanics but the presence of the Sun makes the whole system a three body problem with chaotic effects such as temporary captures. The definition of "temporary" depends on your timeframe -- not much in the Solar System is eternally stable due to multi-body gravitatio
      • by asjk (569258)
        Great explanation. The relevent section is found in the PDF: 3.6 Orbit characteristics and residence-time distributions for temporarily-captured orbiters. Quoting in part "A geocentric two-body orbit is not adequate for describing the motion of TCOs even for relatively short time periods".
    • by TubeSteak (669689)

      If they escape orbit by their own momentum, they were never really in orbit in the first place.

      You're confusing "orbit" with "stable orbit"

      If it goes around [object] at least once, it was in orbit.
      If it stays in orbit around [object], it's in a stable orbit.
      If it leaves [object]'s orbit (either back into space or crashing into [object]) it was in an unstable orbit.

    • by KenSeymour (81018)

      From my college physics:

      Two bodies = stable elliptical orbits
      more bodies -> ejection possible if they get too close.

      The planets we have are the ones that are left. They don't cross paths much.
      Asteroids, comets, Oort-cloud objects can be ejected from the solar system.

  • That's no moon....

  • I say we snag it, bag it and tag it.

  • That is interesting. That would give us enough time to put an ion engine on it or two and try to control it to keep it in orbit. It would not only be a simple way to capture an asteroid, but give us loads of practice at what it will take. A couple of meters in diameter is a bedroom sized item, so not that easy to control. But since it is here, if we can bring it down and then play with it, R&D it, that is great experience for going to large asteroids and mining them. Heck, if we are going to an astero
  • How difficult is it to exploit this resource vs exploiting moon resources? I would think that the energy requirements would be smaller for a rock in orbit then going into the moon's gravity well and returning to earth. Of course any mining would require moving the body into a stable orbit.

    I've read science fiction where solar reflectors are used to smelt nickel iron rocks in vacuum. Are there any technical studies about the feasibility of this? With automated processing, would it be economically feasible t

  • Maybe, with some luck we can use one of them as a counterweight for a space elevator. Changing orbits is a hell of an energy drain, I know, but if it's already up there there are some slow but cool tricks [wikipedia.org] to change it's orbit over a long period of time. Get it into a closer orbit (just outside geostationary) and get a cable to it. Since this is quite far from the moon the thing may remain stable for a long time (centuries) getting us time to get the tether up, devise a way to keep it outside geostationary b

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