Earth May Once Have Had Multiple Moons

fyc writes "A new study from NASA's Ames Research Center has suggested that the collision of Earth and a Mars-sized object that created the Moon may also have resulted in the creation of tiny moonlets on Earth's Lagrangian points. '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 longest-lasting of such Trojans could have persisted for a billion years. They would have been a few tens of kilometers in diameter and would have appeared in the sky like bright stars.

Comments

That's no moon

[sporkme]

IANAP, but this seems to illustrate a physical possibility, not evidence of past existence. The existence of the moon demands answers, which have been delivered ad nauseum, but this seems to be a bit of "well enough" not being left alone as I see it. TFA:

"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,"

The possibility of existence does not necessitate existence, but it apparently necessitates a Slashdot headline.
The real headline seems to be:
Post-collision debris from Lunar creation might have persisted a little bit longer than originally thought in these crazy gravitational slots, but no evidence is available to back up this theory, and it sure would be neat-o."
Yay.

Not an especially unique theory.

[Lord Graga]

I did a math project in university on lagrangian points and read what I could find on the net - as far as I remember, there is a similar theory that our moon was formed in one of the Earth's lagrangian points, and grew bigger with asteroid crashes (or something similar), until it grew so big that the lagrangian points couldn't hold it any more, and it flew into orbit with earth. Anyhow, this is purely speculation, but if you look closely enough into our universe, you might be able to find places where this is happening right now.

Moons? Nomeclature?

[sithkhan]

Let me see if I have this straight - Pluto is NOT a planet, because it falls beneath some arbitrary threshold for 'planet', but ANY object orbiting a planet is automagically a moon?

I have no problem with the theory, but if objects 'tens of kilometers' across are moons, then Pluto is surely a planet.

And don't call me Shirley.

Re:Perhaps the asteroid that did for the dinosaurs

[Viper Daimao]

if that were the case, there wouldn't be a k/t boundary layer would there?

Re:Perhaps the asteroid that did for the dinosaurs

[MBGMorden]

Quite true. Any "moonlet" if it had been created by the Earth/Thea collision would have bee composed of roughly the same thing as Earth is. The highly increased iridium is a signature of an asteroid and not a terrestrial rock.

Re:Maybe you are right...

[jc42]

Or has science devolved to the point where we just change the definitions to give us the answers we want, rather than looking at the evidence and following it to where it leads?

Actually, when it comes to terms like "planet", we've pretty much done just that. The original term "planeta" was from the Greek, and meant "wanderer". It was a term that referred to the celestial objects that "wandered" about the firmament, unlike the thousands of fixed stars that stayed in the same position. The list of planets included the sun and moon, but it didn't include the Earth, because from our viewpoint, the Earth doesn't wander about in the night sky.

Eventually people figured out that the Earth wasn't the center of everything, and made a revised heliocentric model. In that model, it was the sun that was stationary at the center, and the Earth became a planet that wandered about in an elliptical orbit. The moon got demoted to a different class at about the same time, because it appeared to orbit the Earth rather than the sun, putting it into a class with the four moons of Jupiter that people could see through telescopes. We went from Earth+planets+stars to sun+planets+moons+stars, and three bodies changed their classification.

So, yes, we did change the definition of "planet" back then to give us the answers we wanted. This was done because the prevailing definition of "planet" only worked for the Earth-centered model, and we'd decided to throw that model out. We didn't discard the term "planet"; we just gave it a new definition that fit the new model (and added "moon" as a classifier for a set that quickly picked up a lot of members).

In any case, there is a certain silliness to the seriousness of a debate over what is really a minor descriptive term that has little actual physical meaning. Thus, it has been pointed out that Titan is much more Earth-like than is Mercury, but Titan is called a moon rather than a planet. Earth's moon is more like Mercury than it is like Titan, including having an orbit about the sun that's nearly circular, leading some astronomers to propose calling the Earth/Luna system a "binary planet" rather than a planet and a moon. This isn't so much a serious suggestion, as it is pointing out the silliness of the argument and the irrelevancy of the terms in question.

Scientists do occasionally revise their definitions of technical terms to fit with the prevailing theories. Sometimes they make up new terms, of course. But sometimes it's easier to just tweak the definitions of the old terms.