# Could Earth Capture a SECOND Satellite the size of the Moon?

by Taymith
Tags: capture, earth, moon, satellite, size
 P: 1 I'm doing a research paper based on mining asteroids or near earth objects. I was wondering, could we pull/move a relatively large asteroid About half as large as the moon could we use is as an anchor to launch missions? Thanks!
 P: 2 Well I'm not sure if you already saw this link but http://www.universetoday.com/92022/earths-other-moons/ Based on this article there have already been other natural satellites of the earth in the past. The question is whether it would be possible to keep the satellite in orbit for long enough to mine or launch missions from it.
 P: 82 There are no asteroids half as large as the moon so that would be a big no.
 P: 2 Could Earth Capture a SECOND Satellite the size of the Moon? True all the asteroids in the Asteroid Belt would not equal the size of our moon. I was taking the questions as a theoretical one. Why couldn't you have the missions launched from out moon itself instead? That would seem more feasible.
 P: 712 I think capturing something half the size of the Moon, whether by mass or by radius, is pretty close to crazy talk. Adding any sort of useful ΔV against that much inertia would be beyond daunting. For more sensible-sized asteroids, have a look at these: http://www.nss.org/settlement/asteroids/capture.html http://www.kiss.caltech.edu/study/as...nal_report.pdf Also, the largest asteroid is Ceres, with less than third of the Moon's radius and 1/100th of its mass.
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 Quote by glappkaeft There are no asteroids half as large as the moon so that would be a big no.
There are, since Pluto was demoted and branded with a number.
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 Quote by snorkack There are, since Pluto was demoted and branded with a number.
It was demoted to dwarf planet, not to asteroid, though.
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 Quote by glappkaeft There are no asteroids half as large as the moon so that would be a big no.
There aren't any such objects in the solar system but there may be such objects in interstellar space with trajectories that will bring them through our solar system at some time.
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Quote by glappkaeft
There are no asteroids half as large as the moon so that would be a big no.

 Quote by mrspeedybob There aren't any such objects in the solar system but there may be such objects in interstellar space with trajectories that will bring them through our solar system at some time.
@Glappkaeft: Good point.

@Mrspeedybob: Nearly 70% of the mass of the interstellar medium is made up of hydrogen atoms. The rest is mostly helium and heavier atoms, molecular clouds, and dust. Asteroids orbit the Sun, and most of them are inside the orbit of Jupiter.
 Emeritus Sci Advisor HW Helper Thanks PF Gold P: 6,547 Pluto is still bigger than the biggest asteroid, Ceres. Pluto has a mass of about 18% of the Moon, while Ceres is only about 1.25% as massive as the moon. Ceres has been estimated to contain about 1/3 of the entire mass of the asteroid belt. http://en.wikipedia.org/wiki/Ceres_%28dwarf_planet%29 http://en.wikipedia.org/wiki/Pluto
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 Quote by TumblingDice Asteroids orbit the Sun, and most of them are inside the orbit of Jupiter.
Correction. Most *known* asteriods are inside the orbit of Jupiter.

Kuiper belt is quite farther out than Jupiter.

While we detected many sub-kilometer object inside the orbit of Jupiter, in KB we only detected some of the largest stuff - and already we know about six objects larger than Ceres (>1000 km in diameter). It looks like in reality, "most asteriods are outside of orbit of Neptune".
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 Quote by Bandersnatch I think capturing something half the size of the Moon, whether by mass or by radius, is pretty close to crazy talk. Adding any sort of useful ΔV against that much inertia would be beyond daunting. For more sensible-sized asteroids, have a look at these: http://www.nss.org/settlement/asteroids/capture.html http://www.kiss.caltech.edu/study/as...nal_report.pdf Also, the largest asteroid is Ceres, with less than third of the Moon's radius and 1/100th of its mass.
Thank you for posting important links! These are really helpful to know.

Best Regards!
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 Quote by glappkaeft There are no asteroids half as large as the moon so that would be a big no.
You are right. :)
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 Quote by nikkkom Correction. Most *known* asteriods are inside the orbit of Jupiter.
That doesn't make sense. If there were more *unknown* asteroids, how could you know?

 Quote by nikkkom Kuiper belt is quite farther out than Jupiter. It looks like in reality, "most asteriods are outside of orbit of Neptune".
That's quite the opposite of what NASA/JPL indicates and Wiki clarifies
 ...as minor planets in the outer Solar System were discovered, their volatile-based surfaces were found to resemble comets more closely and so were often distinguished from traditional asteroids. Thus the term asteroid has come increasingly to refer specifically to the small bodies of the inner Solar System out to the orbit of Jupiter.
Whatever the bodies outside of Neptune are called, most Kuiper belt bodies are made up of ices. Those wouldn't remain solid anywhere near Earth.
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 Quote by TumblingDice Whatever the bodies outside of Neptune are called, most Kuiper belt bodies are made up of ices. Those wouldn't remain solid anywhere near Earth.
Most of them are not massive enough to melt near Earth.
 P: 543 When you ask, "Could Earth capture..." you have to add more about whether it is being guided with direct manipulations (meaning space tugs or whatever), or whether (at least in the final approach) it is allowed to try to insert into Earth orbit "hands off". With enough technology, I think it could be done with direct manipulation. But, another way of interpreting the question would be, could we manipulate the motion of a distant large object so that it naturally approaches the Earth and inserts into a stable orbit? This is similar to asking if a passing large body could enter the solar system, approach the Earth, and adopt a stable orbit. For these later cases of the object "passively" (at least for the final approach ) inserting into a stable orbit without direct additional manipulation, I'm not so sure... especially if the body is coming from higher than the Earth's orbit around the Sun. Imagine an object that is already in stable Earth orbit... now imagine how you would move it out of that orbit - you would have to apply an acceleration to do so. To me I think this means that the body had to decelerate in order to insert into the orbit... What would cause a body approaching the Earth and increasing attraction with approach to decelerate other than direct manipulation?
 Admin P: 23,592 Large satellites orbiting planets have some interesting properties when it comes to the dynamics of the system. I believe I have read somewhere (possibly even on PF) that lack of other satellites of the Earth is due to the fact Moon interferes with their orbits, effectively ejecting them into space. IOW, it is not just a matter of putting something on the orbit, it is also a matter of keeping it in that orbit and not destroying the already existing system.
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 Quote by Borek Large satellites orbiting planets have some interesting properties when it comes to the dynamics of the system. I believe I have read somewhere (possibly even on PF) that lack of other satellites of the Earth is due to the fact Moon interferes with their orbits, effectively ejecting them into space. IOW, it is not just a matter of putting something on the orbit, it is also a matter of keeping it in that orbit and not destroying the already existing system.
This is what I understand to be a major "problem" in having a second large satellite in the Earth system. As moons go, our Moon is quite dense and massive, and simply inserting a large satellite into the system isn't going to fly. Small objects for mining and the like seem feasible, since they could possibly be constantly manipulated to keep them in orbit, but putting, say, Ceres into orbit, not even considering the energy required to do that, seems destined for failure over the long term. The interaction between the Earth, the moon, and the smaller, yet large satellite would, I think, end up with the smaller object getting booted out.

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