Re: New Study Claims Mars Dry for 4 Billion Years

Joseph Lazio wrote:
> >>>>> "m" == msadkins04 <msadkins04@xxxxxxxxx> writes:
>
> m> The study is based upon argon decay analysis of the remaining argon
> m> content of seven meteorites "known to have arrived from Mars after
> m> millions of years in space". The study relies on a formula for
> m> argon decay that varies with temperature. [...]
>
> Not decay, diffusion. (Of course, this confusion may have been
> generated by the space.com article.) Decay implies a nuclear
> reaction, which shouldn't be affected by temperature (at least not at
> the temperatures of interest here).
>
> Diffusion, OTOH, can be affected by temperature. The hotter a rock
> is, the easier it is for gasses to diffuse through it.

Yes, the term "decay" appeared in the space.com summarizing the (then
unpublished) Science article. I thought it was a bit odd, but assumed
(wrongly, as it turned out) that the senior science writer at a media
outlet devoted to astronomical issues would get it right, and supposed
that it was some obscure but proper nomenclature.

>
> m> Offhand, there seem to be a number of assumptions to be justified.
> m> Whether the study does so successfully remains to be seen, though
> m> the fact that these represent elementary issues suggests that they
> m> wouldn't be overlooked.
>
> Always be careful about assessing the validity of a scientific paper
> based on its press coverage.

Excellent point.

>
> m> First, how is it known that the rocks weren't in space for merely
> m> "millions of years" but perhaps for billions of years? [...]
>
> Cosmic ray exposure. There is a host of material about this on the
> Web, but, simply put, the longer a rock is in space, the more cosmic
> rays to which it is exposed, and the more isotopes are produced in the
> rock from nuclear reactions.

Might they have floated through space for billions of years without
appreciable cosmic ray exposure because they were interior portions of
much larger Martian rocks? By the time a meteorite reaches the surface
of the Earth, it is likely to be much smaller than before it entered
the atmosphere. Furthermore, it is not unthinkable that during several
billion years of drifting through the solar system, in belts to which
meteoritic debris is drawn, that collisions may have occurred. Now,
here are two alternative scenarios, which incidentally are not mutually
exclusive: (a) Eleven million years ago the rocks in question were
liberated, in space collisions, from much larger rocks of which they
were interior pieces, and which had previously limited their cosmic ray
exposure; (b) These rocks are the remaining core pieces of a larger
rock (or multiple larger rocks) whose exterior portions were burned
away (and/or broke away) during entry into Earth's atmosphere and/or
upon impact, and the appearance of eleven million years worth of cosmic
ray exposure is really the result of a much longer exposure shielded by
the layers of rock surrounding them for most of their space travel.

>
> m> Second, what were the climate patterns on Mars up until the time
> m> these rocks became spaceborn? Could they have originated in a part
> m> of Mars that was "very cold" without implicating the same climate
> m> for all the rest of the planet?
>
> I suppose that is the case. Of course, as one would sample more and
> more meteorites, this case would become less and less likely.

Well, at the present time, I believe something like seven rocks were
sampled. Even assuming the cosmic ray dating method is appropriate,
that number is not statistically significant, particularly if they were
found in the same area (on Earth), since such a grouping might be
interpreted as evidence that they shared a common orbit and hence,
perhaps, a common origin.

>
> --
> Lt. Lazio, HTML police | e-mail: jlazio@xxxxxxxxxxx
> No means no, stop rape. | http://patriot.net/%7Ejlazio/
> sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

Mark Adkins
msadkins04@xxxxxxxxx

.

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