[meteorite-list] 'Baby' Moon Rock Studied

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Dec 20 01:46:07 2004
Message-ID: <200412200636.WAA01402_at_zagami.jpl.nasa.gov>

http://www.abqtrib.com/albq/news/article/0,2564,ALBQ_19855_3409276,00.html

'Baby' moon rock studied
By Sue Vorenberg
Albuquerque Tribune
December 18, 2004

A rock 2.85 billion years old might not sound young, but in the
planetary science world, it's just an infant.

Scientists at the University of New Mexico Institute of Meteoritics just
finished studying a moon rock of that age and have concluded it's the
youngest lava rock yet found from that body.

"It sounds like a long time ago, but compared to other things in the
solar system, 2.85 billion years ago is very recent," said Lars Borg, a
researcher at the institute. "Most of the things we have from outer
space have very ancient ages. The fact that we're getting younger and
younger ages from moon rocks shows the moon might be more geologically
active than we thought."

Scientists generally agree that the solar system is about 4.6 billion
years old.

>From counting the rate of cratering on the moon, some have estimated it
could have been volcanically active as recently as 1 billion years ago.
So far, however, they haven't had younger rock samples available to test
that theory, Borg said.

Understanding how volcanic processes work on the moon might help
scientists better understand how such processes work on Earth and other
planets, said Chip Shearer, another institute researcher.

"The moon is very asymmetrical, with lots of (volcanic rock) basalts on
the Earth-facing side and very little on the other side," Shearer said.
"Studying those volcanic processes could help us study other
asymmetrical bodies in the solar system."

The rock came from the Earth-facing side of the moon, Shearer added.

The youngest magma rocks from the moon before this sample were 3.1
billion years old, Borg said.

"The moon is thought to have basically coalesced and formed a magma
ocean that eventually cooled over time," Borg said. "All planets in the
solar system do that - including Earth."

After those rocks cooled, pockets of radioactive elements remained,
which likely heated up surrounding rock enough to make smaller lava
flows that continued long after the rest of the planet was solid rock,
Borg explained.

"It appears that there were more radioactive elements in the lunar
mantle on the Earth-facing side of the moon that caused more heat and
more vulcanism there than on the far side," Shearer said. "Why that is,
is a question we're still trying to answer."

The 2.85 billion-year-old moon rock had significant quantities of
uranium and thorium in it, indicating it was from the Earth-facing side
and that it was heated by a pocket of radioactive elements, Borg said.

"We'd love to find younger samples than that, but unfortunately we don't
have people walking around the moon picking up samples like we do on
Earth," Borg said. "If more robotic or human missions to the moon are
approved, we think we'll find younger samples."

The rock was found in northwest Africa - it probably reached Earth after
another meteorite hit the moon. It is owned by the Natural History
Museum in London. Scientists asked the museum for a sample and have been
analyzing it for the past two years, Borg said.

"We asked for 100 milligrams of the rock - which is about the size of
half an aspirin," he said. "We grind it up and separate out elements,
then analyze minerals to calculate an age. It takes one person months to
do that."

Borg and three other UNM scientists published a paper on their findings
last month in the journal Nature.
Received on Mon 20 Dec 2004 01:36:34 AM PST