[meteorite-list] New Antarctic lunar

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Wed Sep 13 10:47:31 2006
Message-ID: <pf6gg21hv533igrpdgi4d9iv0fdm15o9nb_at_4ax.com>

http://www.cleveland.com/news/plaindealer/index.ssf?/base/news/115813624740920.xml&coll=2


Case team finds moon meteorite
Wednesday, September 13, 2006
John Mangels
Plain Dealer Science Writer
The Antarctic equivalent of a hurricane had been blowing for nearly a week, and
geologist Ralph Harvey was beginning to wonder if his team would ever get out of
their rattling tents and onto the ice.

It was early December 2005. Members of the Antarctic Search for Meteorites
program, based at Case Western Reserve University, were on their annual trek to
the planet's best hunting grounds - vast ice fields, where rocks that scorch
down from the heavens stand out against the featureless white plain.

Finally, the winds calmed and on Dec. 11 the searchers eagerly headed out on the
Miller Range. Within a half-mile of camp, they spotted a golf ball-sized lump
half-buried in the snow. The sun glinted off its shiny black surface, a sure
sign the rock had been exposed to intense heat, enough to partially melt it.

The shiny coating is called fusion crust, and Harvey jokes that it's a
meteorite's party clothes, "because it hides as much as it reveals." When
scientists back in the United States chipped away the crust and examined the
rock's interior, they got a big surprise. This wasn't just space rubble. It was
a piece of the moon, and an old one too, possibly blasted off the lunar surface
by an asteroid impact soon after the moon's formation 4.5 billion years ago.

The sample, whose discovery was announced Tuesday, is exceedingly rare, one of
less than 50 lunar meteorites found on Earth, and only the second of its
geologic type. Further analysis of the innocuous tan rock known as MIL 05035 may
shed light on the moon's violent early history.

"It's not the most photogenic meteorite we've ever seen, but it's maybe one of
the most interesting," said Tim McCoy, curator of the Smithsonian Institution's
National Meteorite Collection, who has examined the sample.

The rock is volcanic, a product of the moon's once-molten interior. Rather than
being belched to the surface as lava, however, MIL 05035's big crystals suggest
it cooled slowly, smothered deep in the moon's crust.

Then, something smashed it from the moon's grip. Scientists surmise this because
a component called plagioclase feldspar has been transformed to glassy
maskelynite. "The conversion of feldspar to glass only happens when you impact
the heck out of it, really shock it," said Harvey.

Only one other lunar meteorite has that shocked feldspar glass. Analysis has
shown that the meteorite, Asuka 881757, is one of the moon's most ancient
volcanic rocks. Its age, at least 3.7 billion years, is close to the time called
the late heavy bombardment, when the inner solar system was relentlessly pelted
by asteroids and comets.

Such impacts could have shattered pieces of the moon's crust, which Earth's
gravity could eventually capture and pull down to the Antarctic ice. "Asuka
looks like part of this heavy bombardment," Harvey said. Considering its
similarity to MIL 05035, "it's our hope this rock is another representative of
that time period."

Only further analysis will tell. Like their counterparts scooped from the lunar
dust by the Apollo astronauts more than a generation ago, MIL 05035 and the
other meteorites shed by the moon hold tantalizing secrets about their home
world.

Until America's planned resumption of lunar landings in 2020, the meteorites
"are really the best source of new information about what the moon's surface is
like," said McCoy. "They're asking all sorts of questions that our return will
help us answer."

To reach this Plain Dealer reporter:

jmangels_at_plaind.com, 216-999-4842
Received on Wed 13 Sep 2006 10:48:10 AM PDT