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Read the text 'russdill linked in another comment: "Most (99 percent) of the meteorite inventory on Earth comes from the main asteroid belt, between the orbits

by acqq 9y ago

Read the text 'russdill linked in another comment: "Most (99 percent) of the meteorite inventory on Earth comes from the main asteroid belt, between the orbits of Mars and Jupiter. A small fraction of meteorites come from Mars (about 180) and the Moon (about 275). Some meteorites have been suspected to come from comets. Famous astronomer Carl Sagan once said, “It is unlikely that a single meteorite of extrasolar origin has ever reached the surface of the Earth.” Numerical calculations suggest that the possibility of exchange of meteoritic fragments between stellar systems is highly unlikely. Indeed, extrasolar meteorites have not been identified in our meteorite collections." So it's still highly probable that it's still from the stuff of our solar system, it's just the question how homogeneous the stuff was and did the stuff coalesce before or after the Sun was formed. But we know that stuff formed in the cold, from the University of Johannesburg press release: https://www.uj.ac.za/newandevents/Pages/UJ%E2%80%99s-newest-A-rated-researcher-shows-Hypatia-stone-questions-formation-of-solar-system-.aspx https://www.uj.ac.za/newandevents/Pages/UJ%E2%80%99s-newest-... "What we do know is that Hypatia was formed in a cold environment, probably at temperatures below that of liquid nitrogen on Earth (-196 Celsius). In our solar system it would have been way further out than the asteroid belt between Mars and Jupiter, where most meteorites come from. Comets come mainly from the Kuiper Belt, beyond the orbit of Neptune and about 40 times as far away from the sun as we are. Some come from the Oort Cloud, even further out. We know very little about the chemical compositions of space objects out there. So our next question will dig further into where Hypatia came from."

saalweachter 9y ago
Was that quote from Sagan basically saying "panspermia is very unlikely"?
- pbhjpbhj 9y ago
  Universes are very unlikely. Life is very unlikely. Applying statistical analysis to single instances of things always seems like a major flaw to me - it being unlikely means that if we have a million earths few will have extra-solar matter on them. It doesn't really help when you have one Earth.
  - mnx 9y ago
    Well, this is about establishing priors. If something seems unlikely, maybe our understanding of it is wrong? Concepts like Anthropic principle have been introduced to deal with the fact that we exist, however unlikely it may seem.
wiz21c 9y ago
I'm not very knowledgeable about all of this but : >> A small fraction of meteorites come from Mars (about 180) and the Moon (about 275). How come that the moon being closer to earth, we have just 50% more meteorites Mars ? And how come we have so many more from the asteroid belt ?
- fovc 9y ago
  Mars is about 10 times the mass of the moon, so maybe that helps. Though the Kuiper Belt is about the same mass as Mars, so not sure if that's the answer
- adrianN 9y ago
  Mars is much bigger than the Moon, so it's hit more often by stuff that could send rocks our way. In terms of delta-v, Mars is not so much farther away than the Moon.
- api 9y ago
  The energy required for a transfer orbit from Mars is only a bit more than the Moon. Energy matters more than distance or time.
- Symmetry 9y ago
  You have to leave Mars's surface at 6300 m/s to get to Earth, ignoring slowing down at the end which is accomplished by the atmosphere. To get to Earth from the Moon takes 5670 ms/s. The Moon is much closer in Cartesian space, but that just means that the delay from an object leaving the Moon's surface to getting to the Earth's is much smaller, it affects latency but not throughput and on geologic timescales both latencies are small. EDIT: See this map of the solar system in delta-v terms: http://i.imgur.com/AAGJvD1.png http://i.imgur.com/AAGJvD1.png EDIT2: Argh, I messed up my calculations and the distance from the moon is just 2410 m/s. You have to factor in how often Mars gets hit by stuff and the speed at which stuff is going given Mars's gravity well.
  - bostonpete 9y ago
    It seems like your comment ignores the relevance of proximity in the likelihood that an ejected object with the necessary velocity ends up at Earth. Wouldn't the probability of such an object hitting Earth from Mars would be many orders of magnitude smaller than one from the Moon (like trying to hit a target from 100x further away)? I always understood the large numbers of meteorites from Mars to be related to the fact that Mars is closer to the asteroid belt and therefore has had a lot more impacts historically...
ChuckMcM 9y ago
I would have loved to hear Sagan reconsider his statement when he learned that a large oblong extra-solar object (Oumuamua) passed through.
- blacksmith_tb 9y ago
  I would guess that he would have loved it, too! But in fairness, while it is 'passing through' Oumuamua isn't leaving any minerals on the surface of the Earth, either.
- earenndil 9y ago
  > a large oblong extra-solar object (Oumuamua) passed through Just the one. What are the odds that another passes through our solar system, and another, and what are the odds that any of those lands on earth? Close to 0.
  - nkoren 9y ago
    We've just seen the one, but we've only had the capability to detect something like that for ~5 years. So in the absence of further data, it's reasonable to conclude that `Oumuamua-like objects pass through the solar system once every 10 years. Of course smaller and larger interstellar objects will also pass through the solar system. Objects half the size -- which presently we'd be quite lucky to detect -- should pass through with ~5 times the frequency, assuming a size/frequency distribution similar to asteroids. Objects with a quarter the size (currently almost impossible to detect) should be ~25 times as frequent, etc. There is presumably a lower bound to this: at some minimum size, interstellar objects will be repelled by light pressure and the solar wind. I have no idea what this size might be, but for argument's sake let's say that is 1/8th the size of `Oumuamua. So for any given year, the probability of interstellar objects passing through the solar system, should be as follows, (where `Oumuamua is size=1): Size | Annual probability -------+------------- 0.125 | 12.5 0.25 | 2.5 0.5 | 0.5 1 | 0.1 2 | 0.02 4 | 0.004 8 | 0.0008 ...there's not really an upper bound, but I can make my point without one. My point is, in any given year, based on current observations, there should be roughly 16 interstellar objects passing through the inner solar system. Multiplying that by the ~4 billion years that the Earth has been around to run into, and you get a very large number. It seems certain that some small fraction of that large number would have run into Earth. So based on this back-of-the-envelope analysis, either the actual probabilities are MUCH lower -- as in thousands of times lower -- and we were unbelievably lucky to see `Oumuamua when we did, or Carl Sagan was wrong.
cwkoss 9y ago
I wonder if two comets (within our solar system) colliding at high speed could have created some of the substances found in this.

by acqq 9y ago

saalweachter 9y ago

Was that quote from Sagan basically saying "panspermia is very unlikely"?

pbhjpbhj 9y ago
Universes are very unlikely. Life is very unlikely. Applying statistical analysis to single instances of things always seems like a major flaw to me - it being unlikely means that if we have a million earths few will have extra-solar matter on them. It doesn't really help when you have one Earth.
- mnx 9y ago
  Well, this is about establishing priors. If something seems unlikely, maybe our understanding of it is wrong? Concepts like Anthropic principle have been introduced to deal with the fact that we exist, however unlikely it may seem.

wiz21c 9y ago

I'm not very knowledgeable about all of this but : >> A small fraction of meteorites come from Mars (about 180) and the Moon (about 275). How come that the moon being closer to earth, we have just 50% more meteorites Mars ? And how come we have so many more from the asteroid belt ?

fovc 9y ago
Mars is about 10 times the mass of the moon, so maybe that helps. Though the Kuiper Belt is about the same mass as Mars, so not sure if that's the answer
adrianN 9y ago
Mars is much bigger than the Moon, so it's hit more often by stuff that could send rocks our way. In terms of delta-v, Mars is not so much farther away than the Moon.
api 9y ago
The energy required for a transfer orbit from Mars is only a bit more than the Moon. Energy matters more than distance or time.
Symmetry 9y ago
You have to leave Mars's surface at 6300 m/s to get to Earth, ignoring slowing down at the end which is accomplished by the atmosphere. To get to Earth from the Moon takes 5670 ms/s. The Moon is much closer in Cartesian space, but that just means that the delay from an object leaving the Moon's surface to getting to the Earth's is much smaller, it affects latency but not throughput and on geologic timescales both latencies are small. EDIT: See this map of the solar system in delta-v terms: http://i.imgur.com/AAGJvD1.png http://i.imgur.com/AAGJvD1.png EDIT2: Argh, I messed up my calculations and the distance from the moon is just 2410 m/s. You have to factor in how often Mars gets hit by stuff and the speed at which stuff is going given Mars's gravity well.
- bostonpete 9y ago
  It seems like your comment ignores the relevance of proximity in the likelihood that an ejected object with the necessary velocity ends up at Earth. Wouldn't the probability of such an object hitting Earth from Mars would be many orders of magnitude smaller than one from the Moon (like trying to hit a target from 100x further away)? I always understood the large numbers of meteorites from Mars to be related to the fact that Mars is closer to the asteroid belt and therefore has had a lot more impacts historically...

ChuckMcM 9y ago

I would have loved to hear Sagan reconsider his statement when he learned that a large oblong extra-solar object (Oumuamua) passed through.

blacksmith_tb 9y ago
I would guess that he would have loved it, too! But in fairness, while it is 'passing through' Oumuamua isn't leaving any minerals on the surface of the Earth, either.
earenndil 9y ago
> a large oblong extra-solar object (Oumuamua) passed through Just the one. What are the odds that another passes through our solar system, and another, and what are the odds that any of those lands on earth? Close to 0.
- nkoren 9y ago
  We've just seen the one, but we've only had the capability to detect something like that for ~5 years. So in the absence of further data, it's reasonable to conclude that `Oumuamua-like objects pass through the solar system once every 10 years. Of course smaller and larger interstellar objects will also pass through the solar system. Objects half the size -- which presently we'd be quite lucky to detect -- should pass through with ~5 times the frequency, assuming a size/frequency distribution similar to asteroids. Objects with a quarter the size (currently almost impossible to detect) should be ~25 times as frequent, etc. There is presumably a lower bound to this: at some minimum size, interstellar objects will be repelled by light pressure and the solar wind. I have no idea what this size might be, but for argument's sake let's say that is 1/8th the size of `Oumuamua. So for any given year, the probability of interstellar objects passing through the solar system, should be as follows, (where `Oumuamua is size=1): Size | Annual probability -------+------------- 0.125 | 12.5 0.25 | 2.5 0.5 | 0.5 1 | 0.1 2 | 0.02 4 | 0.004 8 | 0.0008 ...there's not really an upper bound, but I can make my point without one. My point is, in any given year, based on current observations, there should be roughly 16 interstellar objects passing through the inner solar system. Multiplying that by the ~4 billion years that the Earth has been around to run into, and you get a very large number. It seems certain that some small fraction of that large number would have run into Earth. So based on this back-of-the-envelope analysis, either the actual probabilities are MUCH lower -- as in thousands of times lower -- and we were unbelievably lucky to see `Oumuamua when we did, or Carl Sagan was wrong.

cwkoss 9y ago

I wonder if two comets (within our solar system) colliding at high speed could have created some of the substances found in this.