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Earth's Moon is a Rarity
Posted by
Zonk
on Thu Nov 22, 2007 06:35 PM
from the lucky-to-have-you-luna-old-sod dept.
from the lucky-to-have-you-luna-old-sod dept.
Smivs writes "Scientists have concluded that moons like the Earth's are actually quite rare. Only 5-10% of planetary systems are likely to contain moons formed by planetary collisions. 'By the time the Earth's moon formed, when the Sun was 30 million years old, the planet formation process in our Solar System should have been approaching its end. In the latest study, Dr Gorlova's team looked at the heat signature of stars using the infrared. This allows astronomers to predict how much of that heat comes from the star itself and how much is re-emitted by dusty material encircling it.'"
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Submission: Earth's moon is a rarity by Anonymous Coward
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What's also rarer. (Score:5, Funny)
Re:What's also rarer. (Score:5, Funny)
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I believe the most unique thing about our moon is the orbiting bovine...
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Re:What's also rarer. (Score:5, Funny)
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Asimov? (Score:5, Interesting)
Side note: In The End of Eternity, we developed time travel before space travel, and so never colonised the galaxy until we eventually discovered hyperspace in the 130,000th century and found that the galaxy was already full of other species and we had no room to expand. Eventually those from near the human extinction altered history to make sure time travel was not invented and thus ensure the expansion into a galactic empire. Apparently the idiots who wrote the sequel trilogy a few years ago failed to read this book (or Robots and Empire), and retcon'd the robots in as Eternals who killed off all competing intelligences in a bizarre and nonsensical addition.
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Not convinced (Score:5, Interesting)
1. Radiation. Actually, Earth probably has the least radiation problem in the solar system, because of its strong magnetic field.
Venus, for example, started extremely similar to Earth but was doomed because its dynamo stopped (and was probably weaker to start with). So the solar wind stripped away all hydrogen, leaving it with an atmosphere of CO2.
Mars hardly has a dynamo because its core froze already. Fat lot of good it did for intelligent life there.
Mercury. Ditto. Its magnetic field is at a whole 0.1% of Earths.
So even when you factor in the different mass and conditions, it seems to me like Earth is unique in having too _strong_ shielding, not in needing some plot device to weaken it.
2. (Or 1a.) If allowing more radiation in was better, you don't need a moon for that. Just rotate slower.
(And indeed the way I remember it, the collision theory says that the same collision that created the moon actually accelerated Earth's rotation a lot.)
Or lose your water, which stops plate tectonics, which kills off the dynamo. Easy.
In fact, you need a whole bunch of special conditions to _keep_ your shielding. Losing it seems more like the norm for a rocky planet in the right band to not turn into a snowball. If the moon's positive influence were punching a hole in our shield... heh... then a lot of planets would get there without a moon just as well.
3. Mutations. Longer text, so have patience please.
Well, this is stuff that happens anyway, simply because some UV gets through, there are radioactive elements in the soil, and even because simply errors happen when transcribing DNA. Especially look again at the last parts: even if you kept something under a slab of lead, without UV or cosmic radiation at all, it would still mutate.
Most of the history of life (except for virii, some bacteria and your immune system) was about _preventing_ mutations. Your cells have layers upon layers of defenses against that kind of thing. Starting with the very fact that you're DNA instead of RNA based, and all the repair proteins, and it goes on and on.
Heck, even the fact that you age is a defense against cancer, i.e., against mutation. Your cells start with a max division counter and literally count divisions. So if that mechanism didn't break down too, a tumour would reach a maximum size and stop. Unfortunately that also means that as more and more of your cells reach that limit natuarally, there's more and more damage which can't be repaired, and you discover the fun of old age.
At any rate, any multi-cellular kind of life, actively fights off mutations. Simply because you can't exceed a certain complexity without preventing mutations. You can't have a body consisting of gazillions of cells, if they don't obey the rules. If cells in your palm randomly tried to evolve into a nose, your left foot tried to become a palm, etc, your body would break apart pretty fast.
You also have to understand that this all happens on a "good enough" basis. Your body could evolve even more fool-proof defenses -- and through the billions of years it has, slowly -- but beyond a point they wouldn't be worth the extra complexity and energy requirements. Plus, in the long term, perfect repairs would also mean an inability to evolve. So anything that got too good at it just disappeared later in the next glaciation, when it was unable to evolve.
And in rare cases, even conversely: if it's of advantage to mutate faster (if still in a controlled manner), mechanisms evolve to create just that. E.g., there are cells in your immune system which actively mutate certain genes randomly, to try to produce a protein that exactly matches a target protein. (E.g., a piece of a new virus's capsid.) There's literally an enzyme in there whose sole role is to junk a random codon (think: byte) of DNA, so the repairs would kick in and some of them would get i
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There's a book mostly intended as a resource for sf writers, What if the Moon didn't Exist? [amazon.com] , which details many of the poor consequences for creatures like us given the absence of a large moon for earth. Its been years, but I remember two of the big ones.
First, without tidal interaction with a large moon, the earth would spin a great deal faster on its axis, resulting in much stronger and consistent winds. It would be hard for anything to be more than a few inches tall except in the windshadow of tall
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And I might as well throw my other comments in here as well:
1. The slowing of the Earth's rotation due to tidal friction is well established. It's good physics and there is even some evidence for slowing of about 2 hours in the past 370 million years based
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Sure your body has lots of defenses against mutation, because like you said, if the cells just do what they want _after_ you are born, then, as you said, it falls apart very quickly.
But it is a different story when the body is still being "designed" when the DNA that makes up the new life has mutations, THAT's when
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Asimov did say it first, and not just in fiction (Score:5, Interesting)
As noted in the parent post, Asimov will often incorporate real science into his fiction.
So, what's this about how the Earth's moon is unique? Is this something new?
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Re:Asimov did say it first, and not just in fictio (Score:5, Informative)
Earth and Pluto are similar in having a moon which is a decent fraction of their own mass. The two moons of Mars, and the moons of the four gas giant planets are minute in comparision to their primary bodies.
Earth and Pluto are sometimes called binary planets for this reason. And there is no easy way to show how they formed in this way, other than invoking chance impacts shortly after formation.
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Re:Asimov did say it first, and not just in fictio (Score:4, Informative)
IMBO, the earth-moon system can still be called a binary planet as no other major body in the solar system except Pluto has a satellite with as large a mass fraction as the moon is to earth.
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Re:Asimov did say it first, and not just in fictio (Score:4, Informative)
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It's been a while since I read those, but, IIRC, it was Asimov himself who wrote that line and, in the book, it was told as a legend that has been told for countless generations.
As such, it could have some resemblance to reality, bu also include many elements of fiction.
And
I thought this was commonly known? (Score:5, Informative)
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The evidence brought forth by this science is looking at the current (relative) stars that are forming and finding what percentage are likely to have moon formation occurring at around the time that our moon was formed. The figure is surprisingly low - but like most c
More assumed than known (Score:2)
Re:Why this might matter (Score:5, Interesting)
Uranus doesn't point one pole at the sun year round. It points one pole at the same area in its "sky" year round.
Imagine if our north star wasn't Polaris, but instead, say, Aldebaran (Which is in Taurus). When the sun is in Taurus, the North pole would point at the sun. 6 months later, the South pole would point at the sun. In "spring" and "autumn" the sun would be over the equator.
So north and south of the equator, you'd have 6 months of darkness (read: COLD) and 6 months of light (read: HOT). On the equator, the sun would, over the course of a year, go from the southern horizon to the northern horizon, and back. When it was significantly above the horizon, it would rise and set in much the way it does now.
No idea if that'd be habitable or not, but it would assuredly not be "fairly stable"
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It surprised me they can detect and not detect dust around nearby stars, but still have a hard time doing the same with Earth-sized objects, but maybe the "dimming" of their light is noticeable enough, or should be according to the theories, and the observations don't follow...
Oblig: The "Moon" - A ridiculous liberal myth (Score:5, Funny)
Documentaries such as Enemy of the State have accurately portrayed the elaborate, byzantine network of surveillance satellites that the liberals have sent into space to spy on law-abiding Americans. Equipped with technology developed by Handgun Control, Inc., these satellites have the ability to detect firearms from hundreds of kilometers up. That's right, neighbors
Of course, this all works fine during the day, but what about at night? Even the liberals can't control the rotation of the Earth to prevent nightfall from setting in (only Joshua was able to ask for that particular favor!) That's where the "moon" comes in. Powered by nuclear reactors, the "moon" is nothing more than an enormous balloon, emitting trillions of candlepower of gun-revealing light. Piloted by key members of the liberal community, the "moon" is strategically moved across the country, pointing out those who dare to make use of their God-given rights at night!
Yes, I know this probably sounds paranoid and preposterous, but consider this. Despite what the revisionist historians tell you, there is no mention of the "moon" anywhere in literature or historical documents -- anywhere -- before 1950. That is when it was initially launched. When President Josef Kennedy, at the State of the Union address, proclaimed "We choose to go to the moon", he may as well have said "We choose to go to the weather balloon." The subsequent faking of a "moon" landing on national TV was the first step in a long history of the erosion of our constitutional rights by leftists in this country. No longer can we hide from our government when the sun goes down.
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Yeah, I know you were joking, but 1950? I've got a copy of Jules Verne's 1865 "From Earth to the Moon", and 1870's "Around the Moon" both published prior to 1950.
I'm sure there are people with bibles published a couple hundred ago, all with a few dozen mentions of the moon
Huge moon (Score:5, Insightful)
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But we don't really know that much about planetary formation. Last I read, none of our planetary formation models generated our own solar system, though there has no doubt been progress since I last read. Still, until we can study some sample of solar systems (note the plural) in detail, we really won't have a very good handle on what's going on. At the moment about all we can detect are bodies too big to really be of interest, unless we're really looking for E
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Scientists talking about the moon?!? (Score:5, Funny)
Rare defined as 5 - 10 percent ? (Score:5, Insightful)
Theres 200 people in the room..10 to 20 of them have a birthmark on their left cheek... how RARE.
Theres 2000 people in the room..100 to 200 of them have a birthmark on their left cheek... how RARE.
Given distances between galaxies 5 to 10 percent seems rare, but if distance didn't matter then this percentage is hardly RARE considering the vastness of the universe, and number of galaxies.
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Binary planetary system (Score:2)
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http://en.wikipedia.org/wiki/Double_planet [wikipedia.org]
Earth's Moon is a Rarity? (Score:4, Funny)
Pluto/Charon? (Score:2, Interesting)
So potentially 2/9 so far...
A rarity also in terms of a lottery win (Score:3, Interesting)
Giant Space Mouse (Score:3, Funny)
Anyhow, that's why our moon and its delicious Swiss Cheese core are still around, while other planets with their lame Brie-mantled moons were pillaged by the Giant Space Mouse.
Moon's diameter as viewed from Earth (Score:5, Interesting)
The amazing thing, to me, is that the Moon's diameter as viewed from the Earth is almost exactly the same as that of the Sun. I've heard that, of the moons in the Solar System, only a handful subtend the same arc as the Sun when viewed from their primary's surface (though of course "surface" is a tricky concept when we're talking about the gas giants), and of those, I don't think many of them are spherical. The kind of diamond rings we get during eclipses are probably quite rare.
Re:Moon's diameter as viewed from Earth (Score:5, Interesting)
and please forgive my woo here,
but i also find it weird that the human menstrual cycle so closely matches the lunar,
while pretty much every other mammal's doesn't.
i'm as science-minded as they come,
but these are each eyebrow-raisingly coincidental.
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News for you (Score:5, Funny)
That's no moon. and you're on Alderaan. buckle up.
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Re:Wrong, sir. (Score:5, Informative)
Antiope [wikipedia.org]
Orbit of the Moon [wikipedia.org]
Barycenter(Centre of mass) [wikipedia.org]
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If I remember correctly, the center which they both orbit around is *inside* the Earth (but not at the center). Some have suggested that the difference between "moon" and "double planet" could be defined by whether the center of gravity is inside the larger body or on the outside (between them).
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Re:Is it established now, Luna was created by impa (Score:2)
Of course, it could be that the moon was moved into position
in order to make the planet more stable for future use.
Re:Eventually (Score:5, Informative)
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