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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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  • Better ideas (Score:5, Interesting)

    by vlm (69642) on Monday January 02, 2012 @12:36PM (#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?

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

    by n5vb (587569) on Monday January 02, 2012 @12:47PM (#38564544)
    .. is man-made [wikipedia.org] .. :)
  • Re:Better ideas (Score:5, Interesting)

    by Nyeerrmm (940927) on Monday January 02, 2012 @01:11PM (#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).

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

    by Nyeerrmm (940927) on Monday January 02, 2012 @01:30PM (#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.

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

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

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