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and mapping of find sites. Then, on 18 January, Ian
wanted to see the Near and Middle Western Icefields, so
the whole group rode to the Near Western and proceeded
to search systematically and collect meteorites. Snow
began coming down about noon so Cassidy, Crozaz, and
Fudali rode back to camp while John Schutt guided Ian
Whillans to the Middle Western Icefield. There, at the
edge of the ice, they noted a small stone about the size of
a golf ball (See the arrow pointing to the edge of the
Middle Western Icefield in Figure 1.10). Schutt, who was
keeping the notes, described the stone:
ad hoc committee of scientists who were familiar with
meteorites and lunar rocks but did not intend to submit
sample requests. On 4 December 1982, Cassidy held a
special meeting in Houston to assess which lines of
research would be the most definitive of lunar origin. Of
the requests for samples submitted to the committee,
those that were granted proposed to investigate one of
the following six lines of research: oxygen isotope ratios,
noble gas measurements, cosmogenic nuclides, nuclear
particle tracks in feldspar grains, neutron activation anal-
ysis, and rare-earth element analyses. The committee
itself solicited two more studies: measurement of the
magnetic properties of several small chips, and passive
counting of a major piece of the specimen for
aluminum-26, which indicates how long a meteorite has
been lying on the Earth's surface. It sounds like a lot of
material, but the total weight of the eight samples allo-
cated summed up to 2.6 g.
At the annual Lunar and Planetary Science Conference,
held in Houston in March of 1983, 16 scientists presented
evidence that this was a lunar meteorite. In his topic
[2003] on page 158,
Cassidy
reports that at the end of a
long session of papers supporting a lunar origin, Randy
Korotev of Washington University at St. Louis announced
that he would like to present some evidence for why we
believe ALH A81005 is
not
from the Moon. A hush fell
over the room. Then Randy added: “Unfortunately, we
were unable to find any such evidence, so I will have to
talk about something else.”
The very existence of even one meteorite from the
Moon forced new lines of thought in planetary science.
No longer could it be argued that lunar craters could not
be due to meteorite impacts. Nor could it be argued that
inasmuch as we have no meteorites from the nearby
Moon, we certainly cannot have any from Mars. And it
weakened the argument that the force of an impact
required to send a martian meteorite into an earth-crossing
orbit would totally destroy the rock. In fact, rather quickly
after the verification of ALH A81005, studies redoubled
of the strangely youthful, 180 million to 1.3 billion
(instead of 4.5 billion) -year-old meteorites called
shergottites, nakhlites, and chassignites until it was
demonstrated that bubbles in the glass of EET A79001
(Plate 70) contain the martian atmosphere.
Some meteoriticists saw this Antarctic expedition as
being of equal importance to an
Apollo
Mission, two of
which had been cancelled within the previous year.
#1422—Strange meteorite. Thin, tan-green fusion crust, ~50%,
with possible ablation features. Interior is dark grey with numerous
white to grey breccia (?) fragments. Somewhat equidimensional
at
~
3 cm.
They went on to collect 10 more meteorites, but that
first one made history. It would prove to be the world's
first recognized meteorite from the Moon. Some reports
honor John Schutt as the finder and some pass the baton
to Ian Whillans. In fact, they discovered it together. When
the stone arrived in Houston, months later, it was seen by
some of the world's leading experts on lunar rocks. They
assigned to it the number ALH A81005 (Figure 1.12; see
also Plate 64). When Brian Mason saw the thin section,
he put in writing what many had been thinking: “Some of
the clasts resemble the anorthositic clasts described from
lunar rocks.” There it was, all 31.4 g of it, almost certainly
a meteorite from the Moon, but specific measurements
would be required to prove it.
Cassidy, who was chairing the Meteorite Working
Group, realized that numerous members of that
committee would submit requests for a research sample,
which meant there would be a series of absences while
their requests were discussed. So he decided to form an
With the
Apollo
18 mission cancelled,
the ANSMET expedition of 1981-1982
to the Allan Hills of Antarctica
collected lunar meteorite
ALH A81005
and changed the history
of planetary science.
Figure 1.12.
The lunar meteorite ALH A81005 after one chip
has been taken off at Houston. (NASA photo)
