Did Earth Once Have 3 Moons?

[Andy44]

Article in the New Scientist (yeah, I know, but this one passed my smell test) about how the formation of Luna via collison would likely have resulted in multiple satellites, collecting at the L-points:

http://space.newscientist.com/article/dn13836-did-earth-once-have-multiple-moons.html

Did Earth once have multiple moons?

• 05:00 06 May 2008
• NewScientist.com news service
• Ker Than

The ancient catastrophe that gave birth to the Moon may have produced additional satellites that lingered in Earth's skies for tens of millions of years.
A new model suggests moonlets may have once occupied the two Earth-Moon Lagrangian points, regions in space where the gravitational tug of the Earth and the Moon exactly cancel each other out. Objects trapped in these points are called Trojans and can remain stationary forever if left undisturbed.
Scientists think the Moon was created when Earth was struck by a Mars-sized object some 4.5 billion years ago.
"The giant impact that likely led to the formation of the Moon launched a lot of material into Earth orbit, and some could well have been caught in the Lagrangian points," says study team member Jack Lissauer of NASA Ames Research Center in California, US.
Once captured, the Trojan satellites likely remained in their orbits for up to 100 million years, Lissauer and co-author John Chambers of the Carnegie Institution of Washington say. Then, gravitational tugs from the planets would have triggered changes in the Earth's orbit, ultimately causing the moons to become unmoored and drift away or crash into the Moon or Earth.
"The perturbations from the other planets are very, very tiny," Lissauer said. But they change the shape of Earth's orbit, which changes the effect that the Sun's gravity has on the moons. "[That] is what ultimately destabilises the Trojans," Lissauer told New Scientist.
Separate modelling work by Matija Cuk, an astrophysicist at the University of British Columbia in Canada, suggests small, asteroid-sized objects a few tens of kilometres across would have lasted the longest as Trojan satellites. Cuk estimates these 'lost moons' might have circled Earth for a billion years or more after the Moon's formation.
"They would have looked more like Jupiter or Venus in the sky than a satellite," Cuk told New Scientist. "They would have resembled very bright stars."
Journal reference: Icarus (vol 195, p 16)

 

[Scarecrow]

The only problem with that theory is that the moon being created by a collision between Earth and a Marsish object seems very unlikely, as anything launched into orbit from that collision would either be in a hyperbolic orbit, and never be seen again, or in a elliptical orbit with the perigee at an altitude pretty close to the surface. It seems unlikely that you could collect a large amount of matter in a ball in a very high altitude, near circular orbit around the earth.

Then again, if someone could explain why I'm wrong, I'd be much obliged.

 

[Ghostrider]

Earth actually used to have a dozen small moons, but it didn't look good on postcards so we settled on one big Moon.
Besided, think of the chaos the Space Race would have been with multiple moons: instead of having one small step, one giant leap we would have had to hop like mad from one moon to the other with people going to the ludicrous extremes of wanting to set foot on orbiting pebbles.
"First man to step on a small rock somewhere" just isn't cool enough.

 

[Piet Barber]

Then again, if someone could explain why I'm wrong, I'd be much obliged.

Ya pretty much completely wrong. Sorry. When you get an impact like that, the resultant objects are in the zillions and all behave a little bit differently than the billiard-balls and orbital mechanics principles you might be used to. But you're right, it is pretty hard to get the impact "just right" in order to make a resultant moon, instead of an escaped object. The trick is that the original object, named Theia, was in one of the Earth-Sun LaGrange points, and "fell-in"

The Discovery channel had a really cool program about earth-moon formation a few years ago which talked about this at length. This Wikipedia article will get you started (link below) The link below also has a cool movie that shows the molten slag orbiting proto-earth after the collision; the ring of material made Earth have rings for a few million years. Since the junk was outside the Roche limit, it formed a moon, instead of spiraling into the proto-earth.

http://en.wikipedia.org/wiki/Giant_impact_hypothesis
http://en.wikipedia.org/wiki/Roche_limit

 

[mrspacely]

however she was formed, Luna (amongst other things) has made life possible for us! I always wonder the real history of our system..

did you know there is an abundance of helium particles from the sun (hydrogen too I think) on the moon? and supposedly there is water ice too, making me think the moon was formed in the same period that earth got its oceans.. who really knows tho right?

 

[willy88]

...

Tex! Release the hounds! We got another one!

 

[makulay]

what an interesting theory.

_____________________
airport limousine San Francisco

 

[ar81]

The only problem with that theory is that the moon being created by a collision between Earth and a Marsish object seems very unlikely, as anything launched into orbit from that collision would either be in a hyperbolic orbit, and never be seen again, or in a elliptical orbit with the perigee at an altitude pretty close to the surface. It seems unlikely that you could collect a large amount of matter in a ball in a very high altitude, near circular orbit around the earth.

Then again, if someone could explain why I'm wrong, I'd be much obliged.

If you see the simulation on collision effects, you notice that Earth changed its shape during 48 hours, and heavy materials remain on Earth and Moon keeps the lighter materials. The problem with other theories is that composition of moon is not the same of Earth.

The theory of moon coming out from Earth matter without collision has a problem, since Moon remains a few thousand km from Earth during the closest point.

The collision theory also explains Earth Rotation.
It was not just a close pass with some fragments falling, it was a full planet killer that changed the shape of Earth.

I do not know which theory is right, but the collision theory sounds convincing.

Or could moon be implanted by aliens using planetary engines?

 

[BigDAS]

One theory and the one I'm most inclined to believe is that satellites are created from the cosmic material ringing a planet as it being formed.

 

[Whatu]

Or could moon be implanted by aliens using planetary engines?

Remember we are being observed by an alien race with wormhole-travel capabilities, but they dont want us to be aware because they study us in their struggle to know how life begun. We are a really good "experiment" for them. And they put there the moon and the other planets so that we just could name the days of the week. (at least in spanish ).

Well, that can be true unless we prove its wrong...