2 Billion Years Old Meteorite From Martian Crust Found

in
http://www.nasa.gov/home/hqnews/2013...Meteorite.html
it is reported that a 2.1 billion years old meteorite
originating from the crust of Mars has been found in the
Sahara. To me, this short report raises more questions than
it answers.
As i had learned from the moderators of this group, the
Martian origin of some meteorites is proven by the oxygen
isotope ratios in small gas bubbles contained in the
meteorite amd that agrees with the isotope ratio found in
the Martian atmosphere by the two Viking landers in 1976.
(There are apparently no more recent measurements of these
isotope ratios, maybe Curiosyity will provide new results.)
However, if the age of the meteorite is correct: Why should
one expect that the isotope ratio in the atmosphere has
remained unchanged through more than 2 billion years?
Especially, if it is claimed that the meteorite left the
Martian crust during a wet period of Mars?

Most Martian meteorites appear to have been molten,
indicating a volcanic origin. As there had been volcanoes on
Mars, but e.g. not on the Moon in the last several billion
years, there is an additional argument for the Martian
origin of these meteorites. But the recently identified
meteorite is expected to come from the Martian crust.
Whereas volcanoes might be able to reach the Martian escape
velocity for parts of their ejecta, it is hard to imagine
that a grazingly incident meteorite might throw parts of the
crust into space, especially if one thinks of a maybe dense
wet atmosphere breaking the incoming meteorite and the
throen out crust material.

Presently I have no access to the paper announced in that
short communication, maybe other readers can shed some light
on this topic.

All the best
Jurgen

In article ,
Juergen Barsuhn writes:
http://www.nasa.gov/home/hqnews/2013...Meteorite.html
it is reported that a 2.1 billion years old meteorite
originating from the crust of Mars has been found in the
Sahara. To me, this short report raises more questions than
it answers.

What do you expect from a press release? The full paper is at
http://www.sciencemag.org/content/ea...e.1228858.full
but you will need a subscription or pay to read it. There may be a
preprint, but I haven't looked. The abstract is public, so you can
search on author names.

Martian origin of some meteorites is proven by the oxygen
isotope ratios in small gas bubbles

I think that's only part of the story. In any case, the Martian
orgin of NWA 7034 seems to be based mainly on Fe versus Mn, but there
are lots of other ratios that match Mars. Interestingly, NWA 7034
matches results of Mars rovers and orbiters much better than it
matches SNC meteorites, suggesting that it is more representative of
Mars' current surface than the SNCs are.

I didn't see any mention of gas bubbles, but I might have missed it.

Why should one expect that the isotope ratio in the atmosphere has
remained unchanged through more than 2 billion years?

I don't know of any evidence one way or the other, but I'm not a
planetary scientist.

Especially, if it is claimed that the meteorite left the
Martian crust during a wet period of Mars?

The data show that the meteorite contains lots of water, hence the
"wet period." Isotope ratios give its age, which I _think_ refers to
the time since the rock solidified. I don't know how that epoch
relates to other studies of Mars' climate, but the name "Amazonian
epoch" does suggest water.

Most Martian meteorites appear to have been molten,
indicating a volcanic origin.

Not sure about "most," but this one appears to be volcanic.

Whereas volcanoes might be able to reach the Martian escape
velocity for parts of their ejecta, it is hard to imagine
that a grazingly incident meteorite might throw parts of the
crust into space,

I think that's backwards: no one thinks volcanoes can eject rocks,
but impacts certainly can.

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

Steve Willner schrieb:
In article ,
Juergen Barsuhn writes:
http://www.nasa.gov/home/hqnews/2013...Meteorite.html
it is reported that a 2.1 billion years old meteorite
originating from the crust of Mars has been found in the
Sahara. To me, this short report raises more questions than
it answers.

What do you expect from a press release?

A concisely written report on the essential results of the
findings in a form that might be understood by interested
members of the public that finally finance the research work
by their taxes. Most people will never receive an
information that goes beyond of this or similar press releases.

The full paper is at
http://www.sciencemag.org/content/ea...e.1228858.full
but you will need a subscription or pay to read it.

Thank you, but indeed this location is inaccessible for me.
The abstract given lacks any closer information.
I expected this difficukty, so I hoped that somebody out of
this newsgroup might have read the cited paper and would
comment on it.

The authors claim that "their" meteorite is 2.1 billion
years old and hence by far the oldest meteorite from Mars.
As far as I have read, the other meteorites are expected to
be not older than 200 million years. So an age of more than
2 billion yeras would be an extraordinary claim.

........

Martian origin of some meteorites is proven by the oxygen
isotope ratios in small gas bubbles

I think that's only part of the story. In any case, the Martian
orgin of NWA 7034 seems to be based mainly on Fe versus Mn, but there
are lots of other ratios that match Mars. Interestingly, NWA 7034
matches results of Mars rovers and orbiters much better than it
matches SNC meteorites, suggesting that it is more representative of
Mars' current surface than the SNCs are.

I didn't see any mention of gas bubbles, but I might have missed it.

Well - this gas bubble method idea stems from a paper to
which I think Jonathan pointed me about 10 years ago. The
method sounds very complicated experimentally and maybe has
been actually performed only for a (small) part of the
Martian meteorites found in those years in the Antarctica.
Around 2000 thare was a heavy discussion in the internet,
whether these meteorites indeed originate from Mars.


Why should one expect that the isotope ratio in the atmosphere has
remained unchanged through more than 2 billion years?

If the gas bubble method were used for the Sahara-meteorite
...... But maybe other arguments have been used to validitate
its Martian origin.
.......

The data show that the meteorite contains lots of water, hence the
"wet period." Isotope ratios give its age, which I _think_ refers to
the time since the rock solidified. I don't know how that epoch
relates to other studies of Mars' climate, but the name "Amazonian
epoch" does suggest water.

OK. The rock then was formed about 2 billion years ago but
might have left the Martian surface relatively recently due
to an impact event. So this rock had not to overcome a
denser wet atmosphere when leaving the Martian surface, but
only very thin atmosphere of the presence. ?

Regards
Jurgen

Juergen Barsuhn wrote:
OK. The rock then was formed about 2 billion years ago but
might have left the Martian surface relatively recently due
to an impact event.

Yes. This rock was formed (solidifed from molten lava) about 2 billion
years ago on the surface of mars. It was blasted off the Martian surface
(by a meteor impact) quite recently, probably a few 10s of millions of
years ago.

--
-- "Jonathan Thornburg [remove -animal to reply]"
Dept of Astronomy & IUCSS, Indiana University, Bloomington, Indiana, USA
on sabbatical in Canada starting August 2012
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
-- quote by Freire / poster by Oxfam

On 09/01/2013 07:39, Steve Willner wrote:
In article ,
Juergen Barsuhn writes:

Martian origin of some meteorites is proven by the oxygen
isotope ratios in small gas bubbles

I think that's only part of the story. In any case, the Martian
orgin of NWA 7034 seems to be based mainly on Fe versus Mn, but there
are lots of other ratios that match Mars. Interestingly, NWA 7034
matches results of Mars rovers and orbiters much better than it
matches SNC meteorites, suggesting that it is more representative of
Mars' current surface than the SNCs are.

I didn't see any mention of gas bubbles, but I might have missed it.

The abstract says they determined the oxygen stable isotope ratio from
the bulk mineral and from the heat releasable water content of 0.6%
(with different delta_O17 values 0.58%o and 0.33%o respectively).

Please excuse the use of %o for per mil.

Why should one expect that the isotope ratio in the atmosphere has
remained unchanged through more than 2 billion years?

I don't know of any evidence one way or the other, but I'm not a
planetary scientist.

They are weakly dependent on the temperature and so the amount of water
locked up at the poles. Heavier isotopes of water have a slightly lower
vapour pressure and gradually concentrate in the liquid phase.

But the point here is probably that it is different enough from the
Earth's oxygen isotope ratio to rule out a terrestrial water source.

I presume that when Mars lost its magnetic field and atmosphere the
molecules containing light isotopes were more vulnerable to being swept
away by the solar wind so that what remains is enriched in heavy oxygen.

Especially, if it is claimed that the meteorite left the
Martian crust during a wet period of Mars?

The data show that the meteorite contains lots of water, hence the
"wet period." Isotope ratios give its age, which I _think_ refers to
the time since the rock solidified. I don't know how that epoch
relates to other studies of Mars' climate, but the name "Amazonian
epoch" does suggest water.

Correct. Geological dating methods depend on the radioactive decay of
certain species since the rock last solidified. The abstract doesn't say
which decay system they used to date it but Nd and Pb are popular.

The OP might find the following URL helpful as an introduction:

http://geology.cr.usgs.gov/capabilit.../geochron.html

The rare earth signature is another way to determine the type of a
meteorite with a reasonable degree of confidence. This can be done using
laser ablation with only tiny amounts of the specimen used up.

I am not a planetary scientist either but I know one or two and have
worked on software for mass spectrometry for a few decades.

--
Regards,
Martin Brown

[Mod. note: some special characters removed from no-spam From: address
in an attempt to get this posted -- mjh]