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Mars Had an Ancient Impact Like Earth
quixote9 writes "The BBC reports on a set of Nature articles showing that Mars had an impact about four billion years ago by a huge asteroid. This was about the same time that a much bigger object slammed into the Earth, throwing material into orbit around our infant planet. This material is thought to have coalesced to form the Moon. 'It happened probably right at the end of the formation of the four terrestrial planets — Mercury, Venus, Earth and Mars,' said Craig Agnor, a co-author on the Francis Nimmo study. 'In terms of the process of the planets sweeping up the last bits of debris, this could have been one of the last big bits of debris.' There's a theory that having a big moon is important to the development of life, because the much bigger tides create a bigger intertidal zone, but people used to think having a huge Moon like ours was a once-in-a-universe event."
I reckon ther's not sucha a thing as a once-in-a-universe event!
Dawkins Revisited: A person is shit's way of making more shit -- Steve Barnett, anthropologist.
What is the evidence pro and con that Mars and Earth are the ones that actually collided, creating the Moon, and then they went spinning away from each other to settle in their current orbits.
Had that happened, Mars's orbit would not be nearly so circular as it is.
Having a single big moon is supposed to be ultra rare? I'm really curious why that is. Given what we know of our solar system, moons are far from rare. We may only have one example of a large unitary moon, but come on, that's out of a sample size of 9 (8 now I guess) from a universe with presumably a nearly limitless number of planetoids. The argument almost strikes me as one of those arguments for Humans being the only intelligent species in the entire universe because it must be almost impossible for life to occur. Arguments that are grounded entirely in conjecture.
I read the internet for the articles.
people used to think having a huge Moon like ours was a once-in-a-universe event.
And I should hope that they still think so, seeing as Mars does not have a huge Moon like ours... Despite evidence of an impact that COULD have created one, and yet didn't.
That would make it a once-in-a-solar-system event. There's nothing to say this isn't a common occurrence elsewhere. Unless of course you've observed the complete planetary composition of many other solar systems, which no one else has.Developers: We can use your help.
[troll]lets nit-pick things to look cool![/troll]
It means rare. I doubt it's never happened before, it's just a very rare set of events. The size of space (as noted so accuratly in hitchhikers) is big. Really big. That big makes the odds that one rock or the exact size will 'just happen to' hit a young planet of the exact size at the exact direction, while not destabalizing their orbits by increasing the mass.. blah blah... really long odds.
and to add life to that, add the odds that this planet is in the 'livable zone'... add to this the odds that it contains the right materials... add to this the odds that the right chemicals are accessable in just the right places at the right times... add to this that all of that happens at the right time in the planets life... add to that few enough asteroid strikes to prevent obliterating it every few thousand years (Jupiter saves our asses on this)... add to that a bit of luck.
Another effect of the 'really big' portion is that we have a nearly limitless number of chances for this ultra rare occurance to happen.
Of course, to us it seems like it has to happen all the time... I mean hell, we're sitting right here watching it!... but the 99.999~% of planets who were just off the mark will never talk to us about how they see the odds differently.
Beware of he who would deny you access to information, for in his heart, he dreams himself your master.
#2 rotational speed. The moon has kept our rotation from slowing as much as it should have. Shorter day/night cycles are important for environmental management.
Um... Just the opposite. It has slowed down the Earth's rotational period over time. There's a few other things you mention that I find slightly questionable, which may be due to how you stated them, but that one is just flat wrong.
How it does/did that is discussed widely on the net and elsewhere, so I won't even bother pulling up a Wikipedia link for you.
While it didn't appear in the article, I've seen quite a bit of stuff suggesting that a big moon could be a necessity.
The fact is, no one knows how likely it is for a planet to develop life, or intelligent life. We can speculate, but it's a wild guess at best. There's just too much uncharted wilderness out there and we have only one positive event with which to draw conclusions.
To offer a horrible analogy, SETI is like a team or researchers looking for an unknown bacteria up in the Himalayas by standing in a basement in Wichita, Kansas and shouting one time "Where are you?"
Stop Global Warming!
Just say no to irreversible processes!
Let's take Venus and Earth, for example. Venus' orbital period is 224.7 days, and its orbital radius (assuming the orbit was circular) is about 108 million km. Using 2*pi*r/t, we get about 35km/s. For Earth, we get an orbital period of 365.25 days, and an orbital radius of 149.6 million km. This gives an average velocity of 29.8km/s.
This is why in orbital mechanics you add velocity to allow something to catch up to you, and reduce velocity if you want to catch up to something. It's totally counter-intuitive, but in the grand scheme, that's how it works.
I've never heard this before -- do you have some source that describes this in more detail?Note to self: Stop putting jokes in my insightful comments so I can get something other than +1 Funny!