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Earliest rocky planets

  1. Mar 1, 2013 #1
    I'm looking for a more or less definitive answer for the earliest time when rocky planets could form. I saw one thread in this forum that addressed this, but there was no resolution. My guess is two to three billion years from the start to allow for several generations of supernovae to put out enough metal to allow metal-rich protoplanetary disks. Anyone have any hard info?

    Thanks --

  2. jcsd
  3. Mar 1, 2013 #2

    Simon Bridge

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    You won't get one. Any claimed definitive answer would be highly suspicious.

    Anyway - where are you measuring time from?
    From when time separated out?

    What would you recognize as "definitive"?
  4. Mar 2, 2013 #3
    I'd be happy to take a consensus guess of cosmologists who have considered the question.

    I'm measuring time from the big bang.

    Thanks --

  5. Mar 2, 2013 #4


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    post number 3105934 by Deuterium2H had something about this.


    I have seen several estimates that Population 1 (metal-rich) stars could have formed as early as 9 billion years ago. In this post however, Deuterium2H merely says that the oldest Pop 1 stars are "6-9 billion years" old.

    Planets have been found orbiting a Pop 11 (metal-poor) star--there was an MPIA announcement in 2011 about that--but these would presumably not be ROCKY planets.

    I think Deuterium2H knows what he is talking about and since I do not have an authoritative peer-review source for you I would only suggest that you write a PM to him and ask him for a source on the oldest Pop 1 stars. If you are lucky he will refer you to some pre-print at arxiv.org and give a link. If he just gives you an author name, journal and publication year, then come back here and ask. People will help find an online copy.

    It's an interesting question.
    Last edited: Mar 2, 2013
  6. Mar 2, 2013 #5
    Another factor that may help in an estimate. One of the oldest Jupitor like planets Gas giants. Is Methuselah PSR B1620-26B.
    The estimates for this planet is 12.7 billion years ago. Keep mind this is a gas giant. So is its companion planet in this system.
    How much later was their enough heavier material to form rocky planets I would have no idea. If I were to guess it would be around 2 to 3 billion years later. However thats a very rough guess based solely on the previous gas giant
  7. Mar 2, 2013 #6
    Lol I posted the above in the wrong thread unfortunetely I can't delete it from my phone ah well.
  8. Mar 2, 2013 #7

    Simon Bridge

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    Hmmm... do you need metals to have "rocks"?
    Anyway - question asked for metals.

    Related discussion:

    ... the kinds of planets under consideration would form along with pop I stars right? So the question would be "how long to pop I stars?" The oldest pop I stars are supposed to be 5-6 billion years old... that would be a pretty definitive time frame despite my earlier comments. So... somewhere between 4.5 and 7billion years ago?
    Is that a narrow enough range ... subtract from 13.77 billion years to get time from big bang... looks like rocky planets may have first formed roughly half the Universes lifetime ago.

    NGC 118 mentioned in the (above) link.
    The age of NGC 118 stars.
    Last edited: Mar 2, 2013
  9. Mar 3, 2013 #8
    You seem confused. Any element other than hydrogen and helium is metal, so Yes, you need metals to have "rocks".

    On a more relevant note, can we really rule out Pop II? They are metal poor but not metal free Pop III. Even with one in billion chance, they should have rocky planets before Pop I came to existence.
  10. Mar 3, 2013 #9

    Simon Bridge

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    Oh right - I was thinking in terms of chemistry, not astronomy.
    http://en.wikipedia.org/wiki/Periodic_table_(metals_and_nonmetals [Broken])
    ... and a big gas giant can have "metallic hydrogen" ... probably dosn't count ;)
    I think that is a call for OP as it depends on what the information is wanted for.

    I have encountered this sort of question in the context of SciFi - where the interest is in ancient spacefaring civilizations ... and from theists in the context of the argument from improbability.

    If we interpret the question as asking for the literal earliest possible planetary formation out of material that includes elements other than hydrogen and helium then we would certainly not exclude pop II stars. But I think the term "rocky" needs a bit more than that.
    Last edited by a moderator: May 6, 2017
  11. Mar 3, 2013 #10
    OP speaks

    The information is not requested as part of an astronomy project. Specifically, I'm looking for the earliest likely time for a planet to exist with the possibility of evoloving some form of life; I'm making the leap that that calls for a "rocky" planet. It's one of a list of dates I'm researching that includes things like adult lactose tolerance, invention of the brick, formation of our solar system (that's pretty well known of course) and a bunch of other items.

    I must say everyone has been very helpful. If I understand what I'm reading, "conventional" thinking had it around 6 or 7 billion years FBB; newer thinking and evidence may have it as 3 to 4 billion years FBB. If that's more or less the case, then I'm happy.

  12. Mar 3, 2013 #11
    Those estimates I would consider reasonable.
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