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Earth may once have had three moons
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Until now, the accepted view had been that our anomalously large Moon had always been a lone wolf. It is believed to have formed some 4.4 billion years ago in the aftermath of a chance encounter between a Mars-sized planetary embryo and our early Earth.
But the paper’s co-authors, planetary scientists Jack Lissauer, at NASA Ames Research Centre in Mountain View, California, USA and John Chambers at the Carnegie Institution in Washington DC, believe the moonlets (named ‘Trojans’ after similar captured satellites of Jupiter) may have formed simultaneously with the larger impact.
Earth may once have had three moons | COSMOS magazine
3 Comments
Kevin Dement
May 24th, 2008
at 2:32pm
That is absurd.
Given your position as a well-known and respected astrophysicist, I defer to your opinion wholeheartedly.
shedtroll
May 24th, 2008
at 3:01pm
Yeah, and there are still three moon apparently. The two other moons are small they can only be seen with a telescope.
teddgcm
May 26th, 2008
at 8:06pm
No one will truly know if the Moon (or moons) were created by an impact with an early Earth, or a rouge planetoid captured by our planet’s gravity. The jury will always be out on this one. I tend to think that it is the latter, though I am no scientist.
Actually, we have a pretty good idea, based on isotopes of oxygen, relative densities of the bodies, etc. (Recall, we have been there and brought back pieces of Luna, so it’s not just wild-eyed speculation.) To say that we will “never know” (unless you wish to imply that we will never know First Causes) is pretty risky, given that we are planning on further Lunar expeditions to determine, among other things, the answer to precisely this question. Considering that scientific theories are different from the popular concept of a theory as something much in doubt*, we will likely know the answer to a very high degree of probability in a few years’ time.
The most widely-accepted theory at present is that, at the time Earth formed 4.5 billion years ago, other smaller planetary bodies were also growing. One of these hit earth late in Earth’s growth process, blowing out rocky debris. A fraction of that debris went into orbit around the Earth and aggregated into the moon. (See Giant Impact Theory: http://en.wikipedia.org/wiki/Moon)
The mini-satellites, on the other hand, are far more likely to have been captures from the original Solar accretion ring or from the Earth’s.
*In popular usage, a theory is a vague idea yet to be shown true or false. In scientific usage, a theory refers to a body of fact that leads strongly to a given conclusion. Misunderstanding of this crucial difference is the cause of much confusion among non-scientists.