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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 con
by 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.
- earenndil 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 No it's not. It's impossible to deduce anything from a sample size of 1. (And yes I realise that this invalidates my point as well.)
- nkoren 9y agoToss a coin (known to be non-evenly-weighted) five times. It comes up heads once. Can you now estimate the probability of the coin coming up heads? Of course you can. What you can't do is put error-bars on that estimate: you might have just seen the only "heads" that you'll see in the next ten thousand tosses. So the error bars are essentially infinite, but you can make a first-order estimate. Analogously, we've had the capability to to detect `Oumuamua-like objects for ~5 years, and after searching for 5 years, have found one such object. That's good enough to start making first-order estimates of probabilities. Such estimates will obviously change, possibly significantly, as more observation time goes by. Absent error bars, you can't be certain of that first-order estimate is even approximately correct. But if it's not even vaguely correct, then that means your initial "heads" observation was very, very, unlikely. Hence my conclusion is valid: either we got extraordinarily lucky in detecting `Oumuamua when we did, or Carl Sagan is wrong.