[meteorite-list] Helium Helps Trace the Origin of the Los AngelesMeteorite

From: Matt Morgan <mmorgan_at_meteoritecentral.com>
Date: Thu Oct 28 12:58:19 2004
Message-ID: <007501c4bd0f$1a6bd490$5f01040a_at_cgsjnm3p212k>

This is interesting. How far back can we use Helium before it completely
decays?
Matt
<><><><><><><>
Matt Morgan
Mile High Meteorites
http://www.mhmeteorites.com
PO Box 151293
Lakewood, CO 80215 USA
ebay id: mhmeteorites
----- Original Message -----
From: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Sent: Thursday, October 28, 2004 10:51 AM
Subject: [meteorite-list] Helium Helps Trace the Origin of the Los
AngelesMeteorite


>
>
> http://www.yaledailynews.com/article.asp?AID=27007
>
> Helium helps trace the origin of Martian meteorite
> BY ASHLEY FOX
> Yale Daily News
> October 28, 2004
>
> While cleaning out his rock collection in 1999, Los Angeles resident and
> rock-enthusiast Bob Verish came across two unusual looking stones he had
> picked up on a hike in the Mojave Desert 20 years earlier. The stones,
> which Verish named "Miguel" and "Gabriel," were soon recognized by UCLA
> scientists as remnants of a meteorite from Mars.
>
> Four researchers from Yale's Geology and Geophysics Department, led by
> post-doctoral fellow Kyoungwon Kyle Min, have taken up the quest to
> uncover the story behind these unlikely space travelers, a story that
> began around three million years ago.
>
> "We wanted to know the time-temperature history of meteorites, not just
> when they were formed," said Peter Reiners, a member of the Yale team
> and a professor of geology and geophysics. "This tells us about their
> history in space and on other planets. We want to know how often things
> bump into each other and how hard."
>
> In order to draw such conclusions about the Martian meteorite, now
> referred to as the "Los Angeles" or "LA," the team had to think outside
> the box -- or, in this case, outside the planet. They identified a
> method of helium dating which is used on terrestrial rocks and applied
> it to the meteorite from Mars, Reiners said.
>
> The team knew that a meteor had hit Mars prior to the time that the LA
> was ejected from the red planet, Min said. When this meteor hit Mars, it
> caused a change in the constitution of the rock on the planet, known as
> impact-related shock metamorphism. The team was fortunate that the
> interior of the LA meteorite preserved its original Martian signatures,
> including those from the original Martian impact, making the LA a
> virtual time capsule from the impact of the meteorite on Mars, Min said.
>
> During the impact, helium atoms, products of spontaneous uranium and
> thorium decay, would have been completely diffused out of the rock,
> Reiners said. As a result, the team, which also included Yale
> researchers Stefan Nicolescu and James Greenwood, was able to determine
> when the meteorite hit Mars by measuring the uranium, thorium and helium
> content of the sample.
>
> Min said the study was innovative in its use of helium measurements from
> only single grains of the meteorite. By employing this method, Min and
> his colleagues discovered that the impact occurred on Mars around three
> million years ago. They were also able to conclude that the maximum
> temperature of impact was between 450 and 500 degrees Celsius, Reiners
said.
>
> The helium age was then compared to the LA's exposure age, the amount of
> time that the sample has been exposed to cosmic rays. Since the LA was
> underground until its ejection from Mars, the exposure age equals the
> amount of time since it left Mars, Min said. The exposure age was also
> found to be about three million years. He said a main conclusion of the
> study was the similarity of the helium and exposure ages.
>
> "Thus, we showed that the impact that launched it [the LA] off the
> planet also heated it up to pretty high temperatures," Reiners said.
>
> According to the study, this new method of meteorite analysis allows
> scientists to better understand the time and temperature impact
> processes. The method has a variety of applications to terrestrial and
> extraterrestrial materials, higher thermal sensitivity than other
> techniques and an accessible age range that spans from the birth of the
> solar system to the beginning of modern human history, according to the
> study.
>
> Although Min's technique cannot directly answer the question of
> extraterrestrial life, it could aid scientists in this search.
>
> "It could tell us about how material that could potentially contain
> traces of life from Mars could or could not be transported to earth,"
> Reiners said.
>
> By accurately determining the temperature, pressure and time of shock
> metamorphism, scientists can gauge the probability of finding evidence
> of life in meteorites, Min said.
>
>
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Received on Thu 28 Oct 2004 12:56:13 PM PDT