Starship Asterisk*

http://news.discovery.com/space/meteor-the-size-of-a-minivan-exploded-over-california-120423.html wrote:

[b][color=#0000FF]Location of the atmospheric breakup[/color][/b]

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Asteroid the 'Size of a Minivan' Exploded over California
by Ian O'Neill, Apr 23, 2012, Discovery News

<<The source of loud "booms" accompanied by a bright object traveling through the skies of Nevada and California on Sunday morning has been confirmed: it was a meteor. A big one.

It is thought to have been a small asteroid that slammed into the atmosphere at a speed of 15 kilometers per second, turning into a fireball, delivering an energy of 3.8 kilotons of TNT as it broke up over California's Sierra Nevada mountains. Bill Cooke, head of NASA's Meteoroid Environment Office, classified it as a "big event."

"I am not saying there was a 3.8 kiloton explosion on the ground in California," Cooke told Spaceweather.com. "I am saying that the meteor possessed this amount of energy before it broke apart in the atmosphere. (The map) shows the location of the atmospheric breakup, not impact with the ground."

Cooke went on to say that the meteor likely penetrated very deep into the atmosphere, producing the powerful sonic booms that rattled homes across the region. According to Reuters, car alarms in Carson City, Nev., were even triggered.

After some rough calculations, Cooke has been able to estimate the mass of the incoming object -- around 70 metric tons. This was a fairly hefty piece of space rock. From this estimate he was also able to arrive at an approximate size of the meteor: "Hazarding a further guess at the density of 3 grams per cubic centimeter (solid rock), I calculate a size of about 3-4 meters, or about the size of a minivan."

Although there were numerous reports of sightings in Nevada and California, there was little immediate clue as to where the fireball ended its journey. But with the help of two infrasound stations, the source of the explosion could be resolved.

"Elizabeth Silber at Western University has searched for infrasound signals from the explosion," said Cooke. "Infrasound is very low frequency sound which can travel great distances. There were strong signals at 2 stations, enabling a triangulation of the energy source at 37.6N, 120.5W. This is marked by a yellow flag in the map (above)."

Interestingly, the estimated size of the California fireball is bigger than the small 3-meter wide asteroid that exploded over Sudan in 2008. That one delivered an energy of 1.1–2.1 kilotons of TNT. Asteroid 2008 TC3 was actually the first ever space rock to be detected before it hit the Earth's atmosphere. With astonishing accuracy, astronomers at Mount Lemmon telescope in Arizona managed to spot the tiny asteroid and infrasound stations in Kenya triangulated the location where the asteroid hit. Using this information, meteorite hunters were able to recover fragments of the impact.

This time, however, we didn't spot the California-bound asteroid coming, but we know where it ended up. Perhaps it's a good time to dispatch meteorite hunters to the Sierra Mountains.>>

http://astrobob.areavoices.com/2012/04/23/california-fireball-excitement-plus-sweet-sights-in-the-western-sky/ wrote:
California fireball excitement plus sweet sights in the western sky
Posted on April 23, 2012 by astrobob

<<People in California and Nevada yesterday didn’t have to bother looking to know a meteor crashed through their sky. Yesterday around 8 a.m. a fireball brighter than the full moon shot across the sky at supersonic speeds creating a sonic boom that rattled windows and nerves alike. Check out these incredible photos taken by Lisa Warren over Reno.

Most meteoroids – what meteors are called before they burn up as meteors – are the size of chocolate chips or small pebbles, but the ones the size of baseballs and softballs we call fireballs. You’ll never forget the sight if you’re lucky enough to see one.

Eye witnesses described the fireball’s brightness as somewhere between the full moon and sun. You know it had to be bright because the meteor was seen in full daylight around 8 a.m. Many witnesses reported loud booms that shook their homes. Check out the American Meteor Society’s Fireball Reports and you’ll see that more than 40 people hopped online to share their impressions.

Like objects in your side view mirror, most meteors appear closer than they are. That’s all the more true when they’re exceptionally bright. Studies show however that meteors burn up at least 50 miles overhead. If big enough to survive and land on the ground, the pieces go completely dark 5-12 miles high during the “dark flight” phase. Only if you see a fireball directly overhead would it lie within that distance. Most sightings are well off toward one direction or another, so you have to add your horizontal distance to the meteor’s height to get a true distance. While some meteors are bright enough to make us think they landed over the hill, almost all are many miles away.

According to Bill Cooke, head of NASA’s Meteoroid Envronment Office, the source of the blast was a meteoroid about the size of a minivan. Did any fragments survive and land as meteorites? Hard to say just yet. It may have completely disintegrated. I suspect meteorite hunters will now be on the ground talking to eyewitnesses and studying Doppler weather data to determine a trajectory and possible fall site. Fireball sightings aren’t uncommon and many don’t lead to meteorites, but some do. If this is one of those, I’ll be touch with news of the hunt.>>

http://astrobob.areavoices.com/?blog=78068 wrote:

[b][color=#0000FF]Closeup of the first meteorites found by Robert Ward from the California fall. Notice the bumpy fusion crust on the piece at right. CM chondrites like the California fall are also nearly black inside and out. Perhaps, just perhaps, they’re pieces from a long ago shattered comet. Credit: Dave Gheesling[/color][/b]

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California fireball drops rare meteorites
Posted on April 25, 2012 by astrobob

<<The first fragments of the California-Nevada daylight fireball were recovered Tuesday by Robert Ward, one of the most prolific meteorite hunters in the world. Ward lives in Arizona and has been fascinated by meteorites since witnessing a fireball as a boy in 1986. In the late 1980s he found his first meteorite and today his collection of personal finds includes space rocks from almost 500 localities.

Ward and other meteorite hunters would be looking for black stones that stand out from the native rocks. Freshly-fallen meteorites are coated in a thin layer of black, melted rock called fusion crust from heat generated by friction and pressure with the air as they fall to Earth. He may also be using a metal detector as many meteorites contain specks of iron-nickel metal.

After a preliminary assessment, it appears that the California fall is a particularly rare type of meteorite called a CM carbonaceous chondrite. I know that’s a mouthful so bear with me. CMs are rich in carbon and contain water and complex organic compounds including amino acids. Here on Earth, amino acids are used by our cells to build the proteins that make and power our bodies. One of the most famous CM chondrites (KON-drites) fell on September 28, 1969 near the town of Murchison, Australia. Some 254 lbs. or 100 kg of specimens were recovered from the Murchison fall. Local people who picked up the pieces right after the fall said the meteorite smelled like methanol (a form of alcohol), a sure sign that it contained organic compounds. While most meteorites trace their origins to asteroids, CM chondrites like the California fall might be fragments of a comet, which are rich in water and have similar compositions. At the center of all comets is a several-mile-diameter, irregularly shaped “nucleus” made of ice and dust. And it’s as black as a charcoal briquette. Everything we associate with a comet – the glowing head and bright tail – are created when heat and light from the sun boil off and illuminate ice, dust and other rocky materials from the nucleus. Comets are fragile and known to regularly break into pieces under the stress of solar heat and gravity.>>

http://astrobob.areavoices.com/?blog=78068 wrote:

[b][color=#0000FF]A slice of the carbonaceous chondrite NWA 3118 from the Sahara Desert. The round dots are chondrules. They were formed from the original dust of the solar nebula that evolved into the planets. Early on, the dust was flash-heated and congealed into tiny spheres. The white mineral, called a calcium-aluminum-inclusion, is slightly older than the chondrules. Photo: Bob King[/color][/b]

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Meteorite hunters scour hills near
Sutter’s Mill, site of California gold rush
Posted on April 26, 2012 by astrobob

<<There’s been lots of excitement about the meteorites that fell from the California fireball. Hunters have converged around the town of Coloma, home of the famed Sutter’s Mill where the California gold rush started. Is there a more fitting place for the start of a “meteorite gold rush”?

According to meteorite hunter Mike Farmer of Arizona, as of Thursday morning only about 15 grams or about half an ounce of material has been found. Rattlesnakes and tough terrain have made looking for space rocks no easy task.

Sunday’s fall is only the 3rd witnessed fall of a meteorite in California. The other two were Red Canyon Lake on August 11, 2007 and San Juan Capistrano on March 15, 1973. The first was a single stone weighing picked up by a hiker that weighed just 18.4 grams; the second fall dropped two small stones. One of them penetrated the roof of a carport in a mobile-home park and was picked up on the floor several hours later. Both falls were much more common stony meteorites compared to the rare carbonaceous or carbon-rich variety from the current fall.

You may have heard the new meteorites called by several names: Sutter’s Mill, Lotus, Coloma. While one of these may ultimately be chosen by the Meteoritical Society as the formal name, for now they’re best guesses and convenient handles. Often when there’s high interest in a particular meteorite fall like the one in California, the space rock gets named and classified more quickly. As you might guess, I’m rooting for Sutter’s Mill. It was there that carpenter James W. Marshall, while working on the construction of the mill, found several gold nuggets in January 1848 that would lead to the gold rush so many of us remember from our grade school history books.

In 2009, a widely witnessed meteorite fall happened near West, Texas. For a long time it was referred to as the West meteorite until receiving its official name Ash Creek. I hunted the April 2010 fall in southern Wisconsin near the town of Livingston. Many of us referred to the fragments by that name until the Society designated it as Mifflin after another nearby town where specimens were found.

[b][color=#FF00FF]An endpiece of the stony meteorite NWA 869 from the Sahara. Most stony meteorites like this one originate from the crusts of asteroids. Credit: H. Raab[/color][/b]

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Here are the Society’s basic guidelines for naming a new meteorite whether from a fresh fall or one that’s been there a long time and just recently discovered. Most are named after the nearest town or feature of the landscape: * A new meteorite shall be named after a nearby geographical locality. Every effort should be made to avoid unnecessary duplication or ambiguity, and to select a permanent feature such as a town, village, river, bay, cape, mountain or island which appears on widely used maps and is sufficiently close to the recovery site to convey meaningful locality information. In sparsely populated areas with few place names, less permanent features such as ranches or stations or, in extreme cases, local unofficial names of distinctive quality may be used, provided the latitude and longitude of the recovery site are well determined.

The rules go into much more depth to cover other circumstances like the glut of meteorites from the Sahara Desert that appear in marketplaces in Morocco and other North African countries or were sold to dealers in Europe and the U.S. Specific locations for these orphan meteorites were often not recorded, so they’re all classed as NWA (Northwest Africa) followed by a number. One of the best known Saharan meteorites is NWA 869, classified as an L4-6 chondrite. There’s been a tremendous number of meteorites coming out of the Sahara since around the year 2000. Numbered NWAs are currently approaching 8000!

One last point. I’m often asked where a person can send a suspected meteorite to have it tested. You’ll find a list of testing services at Found A Meteorite? The site reminds readers that real meteorites are found in less than 1% of submitted samples.>>