The Second Moons of Earth

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Posted by samzenpus on Monday January 2, 2012 @05:31AM 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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metroid capture by Anonymous Coward · 2012-01-02 05:34 · Score: 4, Funny

not the best idea... (i think they're dangerous)
1. Re:metroid capture by superslacker87 · 2012-01-02 07:36 · Score: 2
  
  Tell that to Samus Aran.
  
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  I run Ubuntu skinned to look like a Mac on a PC. Go figure.
Better ideas by vlm · 2012-01-02 05:36 · Score: 5, Interesting

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?

--
"Science flies us to the moon. Religion flies us into buildings." - Victor Stenger
1. Re:Better ideas by Grishnakh · 2012-01-02 05:40 · Score: 3, Informative
  
  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.
2. Re:Better ideas by n5vb · 2012-01-02 05:43 · Score: 2
  
  Radio beacon with telemetry and a ranging transponder would be intriguing and probably not all that hard to deploy .. :)
3. Re:Better ideas by Nyeerrmm · 2012-01-02 06:11 · Score: 5, Interesting
  
  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).
4. Re:Better ideas by Anonymous Coward · 2012-01-02 06:25 · Score: 3, Insightful
  
  What about the n-body problem?
5. Re:Better ideas by Nyeerrmm · 2012-01-02 06:30 · Score: 3, Interesting
  
  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.
6. Re:Better ideas by dotancohen · 2012-01-02 07:05 · Score: 5, Interesting
  
  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.
  
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7. Re:Better ideas by dotancohen · 2012-01-02 07:18 · Score: 2
  
  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?
  
  --
  It is dangerous to be right when the government is wrong.
8. Re:Better ideas by Grishnakh · 2012-01-02 07:28 · Score: 2
  
  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 want to send probes to asteroids, it seems like we should be sending them to big ones like Apophis, both to see what they're made of and also to help predict their trajectories better so we can make sure we're not on a collision course.
9. Re:Better ideas by Anonymous Coward · 2012-01-02 08:37 · Score: 2, Insightful
  
  What about the n-body problem?
  Use numerical methods
10. Re:Better ideas by HornWumpus · 2012-01-02 10:25 · Score: 2
  
  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.
  
  --
  John McAfee 'It was like that time I hired that Bangkok prostitute; to do my taxes, while I fucked my accountant'
At the risk of being declared a space nut by Dexter+Herbivore · 2012-01-02 05:38 · Score: 4, Insightful

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.
1. Re:At the risk of being declared a space nut by TheDarkMaster · 2012-01-02 06:08 · Score: 2
  
  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?
  
  --
  Religion: The greatest weapon of mass destruction of all time
2. Re:At the risk of being declared a space nut by daem0n1x · 2012-01-02 06:12 · Score: 3, Funny
  
  I think Heavy Metal is not allowed by the regime, because it's satanic and pollutes youth's minds.
3. Re:At the risk of being declared a space nut by Skapare · 2012-01-02 06:26 · Score: 2
  
  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.
  
  --
  now we need to go OSS in diesel cars
4. Re:At the risk of being declared a space nut by artor3 · 2012-01-02 06:50 · Score: 2
  
  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 "Hundreds of megagrams wouldn't be worth it, but some objects out there may have teragrams."
5. Re:At the risk of being declared a space nut by garyebickford · 2012-01-02 08:20 · Score: 2
  
  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.
  
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And at least one .. by n5vb · 2012-01-02 05:47 · Score: 5, Interesting

.. is man-made .. :)
Temporarily captured? by Hatta · 2012-01-02 06:12 · Score: 3

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?

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1. Re:Temporarily captured? by Trepidity · 2012-01-02 06:38 · Score: 4, Informative
  
  If I understand the paper correctly, there are configurations where the zero-velocity surfaces 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 has an illustration of some cases.
  
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  10 PRINT CHR$(205.5+RND(1)); : GOTO 10
2. Re:Temporarily captured? by thrich81 · 2012-01-02 06:41 · Score: 2
  
  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 gravitational effects anyway.
3. Re:Temporarily captured? by TubeSteak · 2012-01-02 06:50 · Score: 2
  
  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.
  
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4. Re:Temporarily captured? by asjk · 2012-01-02 06:58 · Score: 2
  
  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".
5. Re:Temporarily captured? by Anonymous Coward · 2012-01-02 10:15 · Score: 3, Funny
  
  That's exactly it. There's a very nice animated gif here 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.
Oblig xkcd by 16384 · 2012-01-02 06:22 · Score: 5, Funny

http://xkcd.com/307/
where were you people when the Iraq War by decora · 2012-01-02 08:50 · Score: 2

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.
Re:the only reason gold is 'valuable' by Grishnakh · 2012-01-02 09:38 · Score: 2

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.