Re: Moon was produced by head-on collision?

From	willner@cfa.harvard.edu (Steve Willner)
Newsgroups	sci.astro, sci.physics
Subject	Re: Moon was produced by head-on collision?
Date	2016-02-01 22:27 +0000
Organization	Harvard-Smithsonian Center for Astrophysics
Message-ID	<n8om4s$gp6$1@dont-email.me> (permalink)
References	<dPqdnSyaPpEcxjDLnZ2dnUU7-b3OydjZ@giganews.com>

Cross-posted to 2 groups.

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In article <dPqdnSyaPpEcxjDLnZ2dnUU7-b3OydjZ@giganews.com>,
 Yousuf Khan <bbbl67@spammenot.yahoo.com> writes:
> Moon was produced by head-on collision | Astronomy.com
> http://www.astronomy.com/news/2016/01/moon-was-produced-by-head-on-collision

The UCLA press release is at
http://newsroom.ucla.edu/releases/moon-was-produced-by-a-head-on-collision-between-earth-and-a-forming-planet
and the article in _Science_ is at
http://science.sciencemag.org/content/351/6272/493.full

I couldn't find a preprint, but there might be one somewhere.

> The Theia Theory used to talk about a glancing blow between the early 
> Earth and a Mars-sized Theia, perhaps at 45 degrees. New data suggests 
> that Theia might have actually hit head-on with the Earth. That's 
> because the percentage of Oxygen 16/17/18 isotopes between the Earth and 
> Moon are nearly identical,

Specifically, the new data show the isotope ratios (actually a ratio
of differences) is the same within 2 ppm.  A paper last year
http://science.sciencemag.org/content/344/6188/1146

found apparent differences at the 18 ppm level.  The new paper
suggests that was sample selection, i.e., the rocks analyzed earlier
were not characteristic of the whole Moon.

>  indicating that they came from the same source.

If the isotope ratios are identical, _either_ Earth and Theia had
identical ratios to begin with (possible but not very likely) _or_
the present Earth and Moon have identical fractions of Theia
material. That last would require a head-on collision with everything
getting mixed; a glancing collision would put a larger fraction of
Theia material into the Moon.

I'm very much an outsider here, but this looks to me like a highly
technical insider dispute that most of us shouldn't worry about.

> My question is, if the isotopic evidence which was used to create the 
> Theia Hypothesis in the first place, due to a previously perceived 
> difference in isotopic abundances,

The isotope ratios are _at least_ very similar, now seemingly
identical within measurement accuracy.  This tends to support the
Theia hypothesis.  If the Moon formed on its own and was somehow
captured by the Earth, it would be expected to have very different
isotope ratios.

> so now that that isotopic evidence has disappeared, why keep the
> Theia Hypothesis? There were other theories prior to that, which
> were discarded due to the isotopic evidence.

That evidence being the _similarity_ of ratios, which is now stronger
than before.  The argument now seems to be about the details of the
collision, but as I say, I'm an outsider.

For a different hypothesis to be viable, it will have to be
consistent with not only the isotope ratios but also the element
ratios and other evidence.  As with all scientific hypotheses, it
will have to be testable (falsifiable) to receive scientific
consideration.

-- 
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner            Phone 617-495-7123     swillner@cfa.harvard.edu
Cambridge, MA 02138 USA

Thread

Moon was produced by head-on collision? Yousuf Khan <bbbl67@spammenot.yahoo.com> - 2016-01-30 19:55 -0500
  Re: Moon was produced by head-on collision? Sam Wormley <swormley1@gmail.com> - 2016-01-30 22:17 -0600
  Re: Moon was produced by head-on collision? dlzc <dlzc1@cox.net> - 2016-01-31 07:25 -0800
  Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-01-31 09:44 -0800
    Re: Moon was produced by head-on collision? dlzc <dlzc1@cox.net> - 2016-01-31 17:02 -0800
    Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-01-31 23:10 -0800
      Re: Moon was produced by head-on collision? Yousuf Khan <bbbl67@spammenot.yahoo.com> - 2016-02-01 03:13 -0500
        Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-01 10:36 -0800
  Re: Moon was produced by head-on collision? willner@cfa.harvard.edu (Steve Willner) - 2016-02-01 22:27 +0000
    Re: Moon was produced by head-on collision? Yousuf Khan <bbbl67@spammenot.yahoo.com> - 2016-02-01 19:44 -0500
      Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-01 23:12 -0800
        Re: Moon was produced by head-on collision? dlzc <dlzc1@cox.net> - 2016-02-02 05:57 -0800
        Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-02 15:59 -0800
          Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-02 22:14 -0800
            Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-03 14:23 -0800
          Re: Moon was produced by head-on collision? Martin Brown <|||newspam|||@nezumi.demon.co.uk> - 2016-02-04 11:40 +0000
            Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-04 11:35 -0800
              Re: Moon was produced by head-on collision? moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-02-05 03:18 +0000
                Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-04 20:42 -0800
                Re: Moon was produced by head-on collision? Martin Brown <|||newspam|||@nezumi.demon.co.uk> - 2016-02-05 08:46 +0000
                Re: Moon was produced by head-on collision? moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-02-05 15:26 +0000
                Re: Moon was produced by head-on collision? R Kym Horsell <kym@kymhorsell.com> - 2016-02-05 15:39 +0000
                Re: Moon was produced by head-on collision? dlzc <dlzc1@cox.net> - 2016-02-05 12:55 -0800
                Re: Moon was produced by head-on collision? willner@cfa.harvard.edu (Steve Willner) - 2016-02-05 21:48 +0000
                Re: Moon was produced by head-on collision? R Kym Horsell <kym@kymhorsell.com> - 2016-02-05 22:31 +0000
                Re: Moon was produced by head-on collision? Martin Brown <|||newspam|||@nezumi.demon.co.uk> - 2016-02-05 22:50 +0000
                Re: Moon was produced by head-on collision? willner@cfa.harvard.edu (Steve Willner) - 2016-02-11 19:44 +0000
                Re: Moon was produced by head-on collision? Sam Wormley <swormley1@gmail.com> - 2016-02-06 12:41 -0600
                Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-06 01:20 -0800
                Re: Moon was produced by head-on collision? moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-02-06 18:37 +0000
                Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-06 12:53 -0800
                Re: Moon was produced by head-on collision? moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-02-07 01:28 +0000
                Re: Moon was produced by head-on collision? dlzc <dlzc1@cox.net> - 2016-02-07 07:06 -0800
                Re: Moon was produced by head-on collision? moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-02-08 02:58 +0000
                Re: Moon was produced by head-on collision? dlzc <dlzc1@cox.net> - 2016-02-08 06:35 -0800
                Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-07 13:54 -0800
                Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-07 15:11 -0800
                Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-07 16:16 -0800
                Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-08 21:36 -0800
                Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-09 11:37 -0800
            Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-04 12:39 -0800
      Re: Moon was produced by head-on collision? willner@cfa.harvard.edu (Steve Willner) - 2016-02-03 22:16 +0000
        Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-03 22:22 -0800
          Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-03 22:38 -0800
            Re: Moon was produced by head-on collision? The Starmaker <starmaker@ix.netcom.com> - 2016-02-04 11:46 -0800
              Re: Moon was produced by head-on collision? the_shadow <the_shadow@xcoxx.net> - 2016-02-06 07:30 +0000
          Re: Moon was produced by head-on collision? dlzc <dlzc1@cox.net> - 2016-02-04 07:52 -0800

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