What this effort reminds me off, is just how much carbon in powdered
form actually arrived with the comet that produced the Pleistocene
Nonconformity. Inches of material is
sometimes found associated with the geologic contact and even assuming
accumulation in the environment an assumption of a sizable milometer or even a
lot more is totally reasonable.
This allows us to make some educated guesses. All the carbon is formed from solar heated
outgassed cometary material so it is reasonable that the arriving volume itself
represents a significant fraction of the original mass itself. I would assume better that one percent since
the comet likely also broke up in a close pass through the heliosphere.
Thus a ten thousand kilometer square distribution puts around as much
as a hundred cubic kilometers into play which appears to be right in the ball
park of what I would expect from a survivable comet event. This actually more of an upper limit but we
certainly find ourselves in the proper magnitude range.
Meteorites from giant
fireball over California found
Tiny meteorites found in
northern California were part of a giant fireball that exploded over the
weekend with about one-third the explosive force of the atom bomb dropped on
Hiroshima in World War II, scientists said on Wednesday.
Robert Ward displays one of
two pieces of a meteorite he found at a park in Lotus, Calif.
6:30AM BST 26 Apr 2012
The rocks each weighed about
10 grams, or the weight of two nickels, said John T Wasson, a longtime
professor and expert in meteorites at UCLA's Institute of Geophysics and
Planetary Physics.
Experts say the flaming
meteor, dating to the early formation of the solar system 4 to 5 billion years
ago, was probably about the size of a minivan when it entered the Earth's
atmosphere with a loud boom early Sunday. It was seen from Sacramento,
California, to Las Vegas and parts of northern Nevada.
An event of that size might
happen once a year around the world, said Don Yeomans of Nasa's Near-Earth
Object Program Office at the Jet Propulsion Laboratory in Pasadena, California.
But most of them occur over the ocean or an uninhabited area, he said.
"Getting to see one is
something special," he said. He added, "Most meteors you see in the
night's sky are the size of tiny stones or even grains of sand, and their trail
lasts all of a second or two."
The meteor probably weighed
about 70,000 kilograms, said Bill Cooke, a specialist in meteors at Nasa's
Marshall Space Flight Center in Huntsville, Alabama. At the time of
disintegration, he said, it probably released energy equivalent to a 5-kiloton
explosion. The Hiroshima bomb was 15 kilotons.
"You don't often have
kiloton rocks flying over your head," he said.
The boom, another expert said,
was caused by the speed with which the space rock entered the atmosphere.
Meteorites enter Earth's upper atmosphere at speeds of up to 44,000mph – faster
than the speed of sound, thus creating a sonic boom.
The friction between the rock
and the air is so intense that "it doesn't even burn it up, it
vaporises," said Tim Spahr, director of the Minor Planet Center at Harvard
University.
Wasson said one meteorite was
found near the town of Coloma, northeast of Sacramento. "I'm sure more
will be found, I'm hoping, including some fairly big pieces," he said.
"The fact that two pieces
already have been found means one knows where to look," Wasson said.
Bits of the meteor could be
strewn over an area as long as 10 miles, most likely stretching west from
Coloma, where James W. Marshall first discovered gold in California, at Sutter's
Mill in 1848.
Robert Ward of Prescott,
Arizona, who has been hunting and collecting meteorites around the world for
more than 20 years, said he found the first piece about 10am. Tuesday in
between a baseball field and park on the edge of the town of Lotus.
Ward said he "instantly
knew" it was a rare meteorite known as "CM" – carbonaceous
chondrite – based in part on the "fusion crusts from atmospheric
entry" on one side of the rock. He actually has two rocks that he suspects
were part of the same small meteorite that split on impact.
"It was just, needless to
say, a thrilling moment," he said.
"It is one of the oldest
things known to man and one of the rarest types of meteorites there is,"
he said. "It contains amino acids and organic compounds that are extremely
important to science."
Yeomens confirmed this type of
meteorite is one of the more primitive types of space rocks out there, dating
to the origin of the solar system 4 to 5 billion years ago. And it's
"actually kind of unusual," he said.
Yeomens said it's got two of
the most important chemicals that scientists look for: carbon and a form of
water. In fact, this type of space rock is likely full of water and would have
made a good candidate for the new space company announced Tuesday that plans to
mine asteroids, he said.
"And this one landed in
their backyard for a lot less than they planned to spend," he said.
The minivan sized asteroid
wasn't on NASA's lengthy list of near Earth objects that they track coming
close to the planet, so it took scientists by surprise. "There are
millions of objects of that size that we don't know about," he said.
"They're too small to image unless they're right up on top of you."
Ward and others tracked the
meteorites' possible location based on estimates by, among others, scientists
with the Meteor Group at the Western University of Ontario in Canada that the
fireball likely had exploded in the upper atmosphere above California's Central
Valley.
Wasson suspected hundreds of
dealers and collectors already have joined the search. He said it was important
to recover the meteorites soon because any rain will cause them to degrade,
losing their sodium and potassium.
"From my viewpoint as a
meteorite researcher," he said, "I'm hopeful some big pieces are
found right away."
No comments:
Post a Comment