3 ms·

Ask HN: Is it possible to estimate the age of the moon from its crater count?

1 points by keepamovin 3y ago

If we know the approximate rate of impacts (and can cross check across the rate of different sizes with the count of craters of different sizes), shouldn't we be able to get a good picture of its age? How does this correspond to the age estimate through other methods? :)

gregjor 3y ago
We probably can't know the rate of impacts, or the sizes of the objects that impacted the moon. Assuming the moon had no impact craters at some point and then accumulated them, the missing piece of data needed turns out to be: how old is it? That's implicit in the "rate" part of your hypothesis -- rate includes a duration of time. Fortunately scientists have found other ways to determine the age of the moon. https://www.space.com/35291-moon-age-pinned-down.html https://www.space.com/35291-moon-age-pinned-down.html
- keepamovin 3y ago
  > We probably can't know the rate of impacts Why not? We can track impacts on Earth. And objects in the solar system. We should be able to estimate the rate, at least with error bars. Why do you say we can't know it? Hahaha! :) Also why do you say we can't know the sizes??? :) haha
  - gregjor 3y ago
    We can only track impacts on the earth if we witness them or find evidence. The majority of objects that get through the earth's atmosphere without burning up will impact in the ocean, which covers 70% of the surface, and leave no trace. And we can't observe or know about impacts that occurred prior to human beings keeping track of them. We just have estimates. We have no way to know how many objects struck the moon since it formed, if the solar system contained fewer or more such objects that might strike the moon during all of that time, with no one observing or measuring. It's possible that 90% of the impact craters on the moon happened in the first million years after it was formed, then the supply of objects in intersecting orbits got exhausted, and the rate of impacts declined. How could we guess at that? And supposing we did guess, how would that help us derive the age of the moon -- your original question? Besides an estimate of the rate of impacts since the moon was formed, we would still need to know how long the moon existed to sustain those impacts. Other problems occur to me, mainly that later impacts would wipe out traces of earlier impacts, so we can't even count the impact craters. The size of an impact crater depends both on the mass of the object that struck the moon and its velocity, so just knowing the rate of impact without knowing the masses and velocities doesn't tell us enough. And we're still left not know over what period of time the moon accumulated those impact craters -- its age -- which would have to be part of any calculation involving a rate. Do you understand that rate means the number of incidents happening over a given duration of time?
    - keepamovin 3y ago
      All of these are valid questions and uncertainties, but they're the kind of things that can be studied, and even quantified as error bars. Hahaha! :) To say it's impossible is like avoiding the question. I don't mean my question..I mean the science process. Oh well hahah :)
      - gregjor 3y ago
        Knock yourself out.
        keepamovin 3y ago
        Hahaha. Nope. You try tho, and refute it. Hahaha! :) Seriously tho, I mean it's not my job. What's your background? Astronomy related? Anyway, someone should be studying it hahaha! :)
  - DemocracyFTW2 3y ago
    it's the haha guy again
    - keepamovin 3y ago
      > it's the haha guy again Hahaha! :) I don't remember you. What guy are you? Some kind of abuser, right? Haha :) In my experience, it's the people who rush to label others that are normally pretty toxic people themselves. hahahaha :) So you're against laughter??? Hahahaha! :) I'm not laughing at you...Hahahahaha! :) Well....maybe a little bit, now. I wasn't tho hahahahahaha! :)
gus_massa 3y ago
IIRC we have done that, but in the (long) past there were more asteroids, so the calculation is more complicated.
- keepamovin 3y ago
  Hei, cool man, thank you! :) haha. I will look it up edit: Oh, look at this: 1975: https://adsabs.harvard.edu/full/1975LPSC....6.2597N https://adsabs.harvard.edu/full/1975LPSC....6.2597N BTW I love this document system whatever it is. Very interesting: https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?db_key=AST&bibcode=1975LPSC....6.2597N&letter=0&classic=YES&defaultprint=YES&whole_paper=YES&page=2597&epage=2597&send=Send+PDF&filetype=.pdf https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_que... cratering in the Earth-moon system: consequences for age determination by crater counting