Northwest Africa 482 (NWA 482) was originally part of the moon.
In order to understand the history of this lunar meteorite, we
must first understand the origin of the moon.
The most accepted theory on how the moon was created is referred
to as the "Giant Impact" theory. Most scientists believe the
moon was created when a small planet-sized body impacted the Earth.
This happened during the very early history of the Earth
about 4.5 billion years ago. This
impacting body was destroyed during the collision,
ejecting material from itself as well as Earth, into space.
The fragments from this event were trapped by the
Earth’s gravity, orbiting in a large array of debris. Through a
gravitational process called accretion, the pieces were brought back together to form the moon.
We know from observation and the Apollo missions that there are
two main classes of rocks from the moon. The first type is referred
to as "mare" (meaning "sea"), pertaining to the
darker areas of the moon mainly composed of ancient (3.0 to 3.8 billion year old) basalt lava flows.
The second type referred to as "highlands" pertains to the lighter colored
areas of the moon mainly composed of feldspar-rich anorthosite rocks. NWA 482 is
a highlands-breccia (meaning a type of rock made of fragments of other
rocks and composed mainly of anorthosite). The moon is believed to be
about 4.5 billion years old and for about 600 million years during its
early history was bombarded by pieces left over from formation of the
planets. Impacts continued to pulverize the surface of the moon at a decreasing
rate, creating the heavily cratered surface.
During this time, melting of the lunar mantle produced basalt
magma that erupted into the larger basins producing the dark
areas of the moon, again referred to as "mare".
Knowing this history of the moon, we know that NWA 482 is over four billion years old, making it older
than most known Earth rocks.
The next period of NWA 482’s existence was relatively quiet, with
moderate impact events creating what is referred to as lunar regolith
(soil created by fragmentation of rocks). These events caused brecciation of NWA 482 and also remelted most
of it, producing its distinctive matrix. This also created the
brecciated composition of NWA 482 as noted by some impacting material
left over from prior impact events in its matrix. Then came a larger
impact event that ejected this rock from the moon. According to cosmogenic radionuclide and noble gas concentration tests,
this happened 900 thousand years ago plus or minus 200 thousand years.
After floating for about one million years in space, NWA 482 intercepted the
Earth’s orbit and was pulled in by its gravity. At first it was probably
the size of a grapefruit. When it hit the Earth’s atmosphere at cosmic
velocity (an estimated 11-30 kilometers per second) the surface began to heat up. As it
heated up, it gave off light, making it a meteor (a shooting star).
At this point, material began to ablate from its surface and spalled
off as a glowing trail of meteoritic material. During this entry phase
into the atmosphere it lost about half of its mass, eventually becoming the
size of a potato. It also oriented itself during its few moments of
entry, meaning that it stabilized during its flight rather than tumbled
randomly. We know this because of the nice flow lines and a characteristic
called a lip-over rim on the trailing edge of this lunar meteorite.
Oriented meteorites are rare, and NWA 482 is the only known lunar example
that displays this property. Eventually the atmosphere, acting as a brake,
slowed it down to about 300 kilometers per hour at about 12 – 16 km altitude, arresting
the ablation process. Most meteoroids do not survive this part of the trip thus
never becoming meteorites. NWA 482 dropped to Earth only under the influence
of gravity, landing in the sands of Northwest Africa and thus becoming a meteorite.
Because a terrestrial age of 60-120 thousand years was measured, we know how long it lay in the desert.
This age is remarkable considering how well preserved this specimen is. The glass crust and dry Sahara
desert conditions have preserved this meteorite well.
Terrestrial History
Northwest Africa 482 was found somewhere in the Northwestern
African desert by a Berber nomad in late 2000. The most likely
place of the find is Algeria because the nomad who sold the
meteorite to a fossil dealer in Morocco stated this is where
he made most of his finds. NWA 482 was then purchased from the
Moroccan dealer by two American meteorite dealers, Mike Farmer
and Jim Strope, on January 9th 2001 (incredibly, during a
complete lunar eclipse), on their fourth expedition to the area.
Several kilograms of meteorites have been brought back from these
trips, financed by private individuals, to be serialized,
classified and then divided among the investors. Most of these
meteorites turn out to be ordinary chondrites, worth very little
on the open market. Sometimes a rare type will be discovered,
making the entire process worthwhile.
NWA 482 is one of those rare types that make these trips worth
the effort. The fresh glassy fusion crust, the flow lines and
the orientation of this particular piece caused excitement when
it was brought to Dr. Alan Rubin of UCLA for study. A
sample was sent to Dr. David Kring of the Lunar and
Planetary Laboratory of the University of Arizona. After studying
a thin section, Dr. Kring stated that it appeared lunar in
origin. The electron microprobe analysis performed at UCLA showed
that all the parameters fit a lunar origin as well.
Another sample was sent to
Dr. Robert Clayton at the University of Chicago for oxygen isotope
analysis to confirm its lunar origin by comparison with Apollo lunar samples.
On February 2nd 2001, Dr.
Rubin stated that it classified as a lunar impact melt. On
February 13th Dr. Kring confirmed Dr. Rubin’s findings,
calling it a lunar impact melt (polymict, crystalline) breccia.
The entire mass weight was 1015 grams, making it the second largest
lunar meteorite ever found. After donating 42 grams for classification,
the rest of NWA 482 was distributed among the 11 investors at the
Tucson Gem and Mineral show. Approximately 20.5% of the mass, or
208 grams, was lost during cutting due to the great number of slices
that had to be cut for the investors. This left 765 grams to be
distributed among the shareholders. The largest shareholders, Adam
and Greg Hupé, financed 40% of Expedition 4, bringing back the largest
piece, the 312 gram main mass. The Hupé family then purchased another
63.25 grams from other shareholders, giving them a total of 375.25 grams.
Approximately 100 grams has been traded to museums at this point, leaving
only 290 grams of this material available for possible private purchase.
During the Tucson show, the Hupé brothers met with famous meteorite explorer
Robert Haag, the first private individual to own a lunar meteorite
(Calcalong Creek), with a scant 7 gram main mass. NWA 482 and Calcalong
Creek were brought together in the same room on January 27th 2001, making
history for two reasons. One, due to the extreme value of these exceedingly
rare objects (nine in private hands), no private individuals have brought
two together. Two, Calcalong Creek was the first privately found lunar and
NWA 482 is the most recent.
Upon returning to Seattle, the Hupé brothers arranged a private viewing
session with scientists from the University of Washington. Dr. Anthony Irving,
a former NASA scientist, and Dr. Donald Brownlee, lead scientist
on NASA's Stardust Mission, examined the main
mass and five slices. Both agreed it would be a shame not to thoroughly study
the slices before they were broken up any more. Adam Hupé was told that once
the pieces were broken or sliced, valuable scientific information would be
lost forever. The Hupé brothers, having great respect for academics, allowed the University of Washington to map the pieces even though there
was some material losses due to preparation.
After examining a small slice provided by Adam Hupé, Dr. Irving claimed
it to be a lunar highland piece resembling a sample (sample number 60015)
returned from the Apollo 16 mission in 1972.
The Hupé brothers then sent one complete and four part slices weighing a total
of 62 grams to the University of Washington for polishing and preparation for
large scale characterization mapping under a scanning electron microscope.
Five grams more were sacrificed, in the name of science, for the preparation
of three thin sections bringing the total of lab-prepared thin sections in the world to only five.
The Hupé brothers announced the arrival of NWA 482
(the freshest lunar meteorite in existence) on April 14th, at the University of Washington.
This occurred after a public lecture series sponsored by NASA Washington Space Grant,
Penford Corporation and the University of Washington Dept. of Earth & Space Sciences
titled "Pieces of Asteroids, The Moon and Mars: The Latest on Meteorites"
with special guest Dr. Michael Zolensky from NASA Johnson Space Center in Houston Texas.
