Could The Earth Capture Another Moon?

[Moontanman]

Is it possible the Earth Moon system could capture another moon? Plausibility of a Ceres sized body being captured by the Earth moon system and the possibility of the Earth Moon system capturing a small body say 20 kilometers in size.

 

Is it possible to calculate this mathematically? Is it possible but so unlikely the universe couldn't exist long enough kind of possible or reasonable?

 

Would the body, if captured, orbit the Earth or the moon? Could it orbit the moon? I am full of questions tonight I don't know how to answer.

[LaurieAG]

Is it possible the Earth Moon system could capture another moon? Plausibility of a Ceres sized body being captured by the Earth moon system and the possibility of the Earth Moon system capturing a small body say 20 kilometers in size.

 

Is it possible to calculate this mathematically? Is it possible but so unlikely the universe couldn't exist long enough kind of possible or reasonable?

 

Would the body, if captured, orbit the Earth or the moon? Could it orbit the moon? I am full of questions tonight I don't know how to answer.

 

They are called quasi moons and usually swap between orbiting the earth and orbiting the sun.

 

http://www.newscientist.com/article/dn4814-earths-quasimoon-is-wayward-asteroid.html

[Guest MacPhee]

Is it possible the Earth Moon system could capture another moon? Plausibility of a Ceres sized body being captured by the Earth moon system and the possibility of the Earth Moon system capturing a small body say 20 kilometers in size.

 

Is it possible to calculate this mathematically? Is it possible but so unlikely the universe couldn't exist long enough kind of possible or reasonable?

 

Would the body, if captured, orbit the Earth or the moon? Could it orbit the moon? I am full of questions tonight I don't know how to answer.

 

This is something I've wondered about - why has Mars got two small moons, Phobos and Deimos, orbiting around it - whereas the Earth hasn't any equivalents.

 

Shouldn't we have some small moons like Phobos and Deimos? These are supposed to be "captured" asteroids. That makes sense in a way, because Mars is nearer to the asteroid belt than Earth. So Mars could more easily pull in stray asteroids, and convert them into moons (Though they ought to be in eccentric and highly elliptical orbits, unlike Phobos and Deimos, which have quite close and circular orbits. Which seems a bit puzzling).

 

Anyway, assuming that Mars has managed to capture a couple of asteroids, why hasn't Earth been able to do so too.

 

Our planet has a much stronger gravitational pull than Mars. So even though we're further out from the asteroid belt, we should have captured at least a few, surely?

[CraigD]

Is it possible the Earth Moon system could capture another moon? Plausibility of a Ceres sized body being captured by the Earth moon system and the possibility of the Earth Moon system capturing a small body say 20 kilometers in size.

 

Is it possible to calculate this mathematically?

A good start is to calculate circular orbit speeds and require speed changes (delta Vs) for a Hohmann transfer orbit from Ceres to Earth orbit. I’ve got a calculator just for this – here’s its inputs and outputs:

u: 132712440018000000000 m^3/s^2 (standard gravitation parameter of Sun)

r1: 413690604000 m (orbit of Ceres)

v1: 17910.92389423411936

r2: 149982660000 m (orbit of Earth + Luna)

v2: 29746.46010869811399

dv1: -4845.009927609523874

dv2: -6292.678286800170623

 

The circular orbit speed of the Moon is about 1022 m/s

 

So to insert Ceres into the Moon’s orbit, you’ve got to change its speed, in the direction opposite its orbit, by about 4845 m/s, wait for it to reach its insertion point, and change its speed again in the direction opposite its orbit by about 5271 m/s.

 

These numbers assume the velocity changes happens instantly, which can’t really happen, and the transfer occurs in only half an orbit, which is faster than it need be, but are close enough for approximation purposes. The differences in numbers assuming more realistic maneuvers – that is, many smaller transfers using smaller delta Vs – increases the total deltaV by less than 7%.

 

The trick is figuring out how to get all that delta V.

 

Barring obviously exotic, artificial approaches like giant rocket motors, for the initial dv1, the only feasible scenario I can see is a gravitational boost. This pretty much rules out dwarf planets like Ceres, as it’s in a fairly circular orbit where it’s the most massive body around. A dwarf-planet mass candidate body to transfer to Earth orbit needs, then, to either have an orbit eccentric enough to intersect Earth’s orbit, or pass near one of the outer giant planets. There simply is no such body. So, for Earth to get a captive moon, it’d have to be a small body, “ejected” from it’s usual orbit into a transfer orbit by a much larger body, such as Ceres.

 

For the final dv2, the obvious candidate is aerobraking with the Earth’s atmosphere. For this, we need a sturdy, heat-resistant body.

 

Something like this is believed to be how Mars got its 2 little moons – this wikipedia section has a good explanation, including a nice animation.

 

As fortune would have it, the 15 Feb 2013 Chelyabinsk meteoroid is at least somewhat close to such a candidate. In its ultimately self-destructive passage through the Earth’s atmosphere, it aerobraked away essentially all of its velocity. It could, conceivably, have entered the atmosphere at a higher altitude and/or shallower angle, and have shed just enough speed to enter Earth orbit. Though necessarily initially very elliptical, it could through repeated aerobraking, as illustrated in this post by LaurieAG, have become more circular, and a true, though at around 20 m diameter, a very tiny, captive moon.

 

They are called quasi moons and usually swap between orbiting the earth and orbiting the sun.

As I explained in the last part of this post, a quasi satellite isn’t a temporary captive moon, because it never truly orbits the “quasi-primariy” with which it nearly shares its orbital period.

 

Once captured, the only way a moon can get un-captured is to change its velocity to transfer to an orbit of another primary, such as the Sun, or considering an extreme, achieve a Solar escape velocity. Solar escape speed for a body around Earth’s orbit is about 42100 m/s, several times that of the Ceres-to-Earth transfer orbit delta Vs above, so transfers to solar orbit are the much more likely scenario.

[Hellboy]

No, the earth can't capture another moon. Frederic petit, director of toulose observatory was the 1st to claim that earth has two moons. He even discovered that the one moon was revolving around the moon and another was going to another direction. This was dismissed by his peers that it was demos, satellite of venus. No another moon has been discovered yet. If it existed, the gravity of 2 moons would fuse to release great gravity and the earth instead had to revolve around the moon. The moon would even be luminuous due to production of infrared rays. The moon would even release flares like sun. We can be saved from the flares of sun due to the magnetic field in lethosphere. But the moon is too close that it might break the force of lethosphere and it might destroy the whole civilization. So the news of existance of 2 moons could be a threat to the life of earth!

[Moontanman]

No, the earth can't capture another moon. Frederic petit, director of toulose observatory was the 1st to claim that earth has two moons. He even discovered that the one moon was revolving around the moon and another was going to another direction. This was dismissed by his peers that it was demos, satellite of venus. No another moon has been discovered yet. If it existed, the gravity of 2 moons would fuse to release great gravity and the earth instead had to revolve around the moon. The moon would even be luminuous due to production of infrared rays. The moon would even release flares like sun. We can be saved from the flares of sun due to the magnetic field in lethosphere. But the moon is too close that it might break the force of lethosphere and it might destroy the whole civilization. So the news of existance of 2 moons could be a threat to the life of earth!

 

 

Venus has no satellites, and it would take almost 100 moons to equal earths mass, i suggest you use google, it is your friend..

Edited February 6, 2014 by Moontanman

[Boerseun]

Sure the Earth can capture another moon. Provided the body in question approaches the Earth at the right speed and angle so that a successful orbital configuration can be established. The resultant orbit of the Earth/Moon1/Moon2 system will not look like the original setup, however, everything depends on the angle and speed at which the new moon is captured, as well as the new moon's mass. The capturing process might slow the Earth down around the sun, or even speed it up, both of which would result in a change in the oval form of the Earth's orbit. Speed it up enough and the Earth might even be flung out of the solar system. Slow it down enough and the Earth might even fall into the sun. The Earth might end up grazing the sun in its new orbit, to be flung far out beyond the orbits of the outer planets on a trajectory that might take hundreds of years to complete - once again, all depending on the initial variables of the new moon's capture.

 

But keep in mind that the moon isn't orbiting the Earth. And the Earth isn't orbiting the moon. They're both orbiting the system's centre of mass, which is just below the Earth's surface and not at the planet's core. A second, or third (or 67th - look at Jupiter!) moon will merely move the system's centre of mass around, and all the bodies in the system will alter their orbits accordingly. Whether this will result in a stable system all depends on the initial conditions. But it is by no means impossible. Disastrous for life on Earth, maybe, but nobody said life was a bed of roses.

[Moontanman]

At the time of this question I was toying with the idea of a moon orbiting our moon and how stable it would be. A large object like Ceres would have to orbit quite close to our moon to be stable would be the assumption I was making...