Since the observed fall of the famed Ensisheim meteorite in 1492, there have been 1,200 recovered meteorite falls.

A "fall" is a meteorite that was witnessed by someone as it fell from the sky, whereas a "find" is a meteorite that was not observed to fall but was later found and collected. Only a handful of witnessed meteorite falls occur each year.

The chance of finding a meteorite is exceedingly small. The chance of witnessing a meteorite fall and finding it is even smaller - and the probability that the fall is a Martian meteorite is smaller yet.

"Martian falls are extremely rare," said Laurence Garvie, collection manager for the center. "Less than 0.5% of falls are Martians. This new sample is probably one of our most prized pieces and, without a doubt, one of the most significant additions to our collection in several decades."

Consisting of specimens from about 1,700 separate meteorite falls and finds, meteorites in the center's collection represent samples collected from every part of the world. Most meteorites found on Earth come from the asteroid belt, but some from the Moon and Mars exist as well. These rare samples constitute a small but important part of the center's collection.

While a few new Martian meteorite finds are reported each year, there have been only four recovered Martian falls prior to 2011.

Fragments of the planet Mars landed in the village of Chassigny, France, in 1815. Another fell on Shergotty, India, in 1865, and a third landed at Nakhla, Egypt, in 1911. The fourth fell in Zagami, Nigeria, in 1962.

The center's newly acquired sample - named "Tissint" - is a significant meteorite, as it is only the fifth known Mars meteorite fall. The center holds small research and display pieces of each of the known Martian falls and also has six Martian finds in its collection. There are a total of 61 known distinct Mars meteorites.

To date, nearly 7 kilograms of stones have been collected from last summer's Martian meteorite fall in Morocco. The 349 gram sample the center received is one of the largest from the fall, and it is by far the center's largest Martian meteorite.

"As far as I am aware, this stone is currently the largest one from this fall in any research collection at a museum or university in the U.S.," said Meenakshi "Mini" Wadhwa, director of the center and a professor in the School of Earth and Space Exploration in ASU's College of Liberal Arts and Sciences.

"This is an important meteorite for our collection from the research and education standpoint," Wadhwa said.

"We plan to study it in our laboratories here at ASU to understand how and when it was formed on the planet Mars. We also intend to let students and the public enjoy it by highlighting it in a special display when the center moves to the new Interdisciplinary Science and Technology Building IV this spring, which will house the center's offices, meteorite preparation labs, a state-of-the-art collection storage vault and expanded gallery space for public viewing."

With the main stone to be used on display, another smaller 21-gram sample will be used for research studies.

]]> Thu, 09 FEB 2012 08:59:07 AEST Washington (AFP) Jan 18, 2012 - Rare and expensive fragments of a Mars meteorite fell from the sky in July over Morocco, a team of international scientists confirmed on Wednesday.

A fireball in the sky was observed in a remote region of southern Morocco by nomads who tracked down fragments of the seven kilogram (15 pound) meteorite, marking only the fifth time in history that a Mars rock has been seen falling to Earth.

A team of eight experts with the Meteoritical Society analyzed the pieces and determined that they are authentic chunks of the red planet, said Carl Agee, part of the team and curator at the University of New Mexico.

"This discovery is tremendously important because of the quality of the sample," Agee told AFP.

The Moroccans who found the fragments quickly sold them to dealers, and museums scrambled to purchase them at a range of $500 to $1,000 dollars per gram, said Agee, whose museum now possesses a 108 gram piece.

The price for meteorites ranges from 10 to 20 times the price of gold.

"Some of these meteorites have atmospheric gas trapped inside glassy material. When they are heated and released in the laboratory and measured it's identical to the Mars atmosphere that all the Mars probes have measured," said Agee.

"All planets, like Venus, Mars and Earth, they have very different atmospheres," he added. "It's like a fingerprint."

The meteorite was named Tissint, and its discovery was documented in the Meteoritical Society's latest bulletin issued January 17.

"At about 2:00 am local time on July 18, 2011, a bright fireball was observed by several people in the region of the Oued Draa valley, east of Tata, Morocco," it said.

"One eyewitness, Mr Aznid Lhou, reported that it was at first yellow in color, and then turned green illuminating all the area before it appeared to split into two parts. Two sonic booms were heard over the valley."

By October, "nomads began to find very fresh, fusion-crusted stones in a remote area" about 50 kilometers (30 miles) east-southeast of Tata.

Agee said such Mars meteorite events only happen about once every 50 years, with the last such event in 1962 in Nigeria. Of about 100 Mars meteorites currently in Earth collections, only five have been seen to fall.

The first known meteorite from Mars was found in France in 1815, a specimen called Chassigny that Agee described as "probably one of the most expensive meteorites in the world."

Pieces of Mars are believed to have broken loose at some time in history when a massive meteor crashed into the surface of the red planet, sending chunks hurtling through space.

Some of the debris has moved fast enough to escape the gravitational pull of Mars and eventually fall to Earth.

Agee said scientists will examine the Moroccan meteorite for radioactive signatures left by cosmic rays, signaling how long its journey has been, possibly thousands or millions of years.

]]> Thu, 09 FEB 2012 08:59:07 AEST Pasadena CA (JPL) Jan 03, 2012 - Whether you're watching from a downtown area or the dark countryside, here are some tips to help you enjoy these celestial shows of shooting stars. Those streaks of light are really caused by tiny specks of comet-stuff hitting Earth's atmosphere at very high speed and disintegrating in flashes of light.

First a word about the moon - it is not the meteor watcher's friend. Light reflecting off a bright moon can be just as detrimental to good meteor viewing as those bright lights of the big city. There is nothing you can do except howl at the moon, so you'll have to put up with it or wait until the next favorable shower.

The best thing you can do to maximize the number of meteors you'll see is to get as far away from urban light pollution as possible and find a location with a clear, unclouded view of the night sky.

If you enjoy camping, try planning a trip that coincides with dates of one of the meteor showers listed below. Once you get to your viewing location, search for the darkest patch of sky you can find, as meteors can appear anywhere overhead.

The meteors will always travel in a path away from the constellation for which the shower is named. This apparent point of origin is called the "radiant." For example, meteors during a Leonid meteor shower will appear to originate from the constellation Leo. (Note: the constellation only serves as a helpful guide in the night's sky.

The constellation is not the actual source of the meteors. For an overview of what causes meteor showers click here: Meteor Showers: Shooting for Shooting Stars)

Whether viewing from your front porch or a mountaintop, be sure to dress for success. This means clothing appropriate for cold overnight temperatures, which might include mittens or gloves, and blankets. This will enable you to settle in without having to abandon the meteor-watching because your fingers are starting to turn blue.

Next, bring something comfortable on which to sit or lie down. While Mother Nature can put on a magnificent celestial display, meteor showers rarely approach anything on the scale of a July 4th fireworks show. Plan to be patient and watch for at least half an hour. A reclining chair or ground pad will make it far more comfortable to keep your gaze on the night sky.

Lastly, put away the telescope or binoculars. Using either reduces the amount of sky you can see at one time, lowering the odds that you'll see anything but darkness. Instead, let your eyes hang loose and don't look in any one specific spot. Relaxed eyes will quickly zone in on any movement up above, and you'll be able to spot more meteors.

Avoid looking at your cell phone or any other light. Both destroy night vision. If you have to look at something on Earth, use a red light. Some flashlights have handy interchangeable filters. If you don't have one of those, you can always paint the clear filter with red fingernail polish.

These meteor showers provide casual meteor observers with the most bang for their buck. They are the easiest to observe and most active. Be sure to also check the "Related Links" box in the right margin for additional information, and for tools to help you determine how many meteors may be visible from your part of the world.

Major Meteor Showers (2012)

Quadrantids
Comet of Origin: 2003 EH1
Radiant: constellation Bootes
Active: Dec. 28, 2011-Jan. 12, 2012
Peak Activity: Jan. 4, 2012
Peak Activity Meteor Count: 120 meteors per hour
Meteor Velocity: 25.5 miles (41 kilometers) per second
Notes: A waxing gibbous moon will set at about 3 a.m. local time, allowing for several dark-sky hours of observing before dawn. This shower has a very sharp peak, usually only lasting a few hours, and is often obscured by winter weather. The alternate name for the Quadrantids is the Bootids. Constellation Quadrant Murales is now defunct, and the meteors appear to radiate from the modern constellation Bootes.

Lyrids
Comet of Origin: C/1861 G1 Thatcher
Radiant: constellation Lyra
Active: April 16-25, 2012
Peak Activity: April 21-22, 2012
Peak Activity Meteor Count: 10-20 meteors per hour
Meteor Velocity: 30 miles (49 kilometers) per second
Notes: A new moon on April 21 guarantees a dark sky in the late night and early morning hours, making this year ideal for observing from 10 p.m. to dawn. Lyrid meteors often produce luminous dust trains observable for several seconds.

Eta Aquarids
Comet of Origin: 1P Halley
Radiant: constellation Aquarius
Active: April 19-May 28, 2012
Peak Activity: May 5-6, 2012
Peak Activity Meteor Count: 10 meteors per hour
Meteor Velocity: 44 miles (66 kilometers) per second
Note: While the shower peaks an hour or two before dawn, the year's closest and largest full moon will be out all night, resulting in a moonlit sky that will wash out all but the brightest meteors. Meteor watchers in the Southern Hemisphere stand the best chance of seeing any meteors.

Delta Aquarids
Comet of Origin: unknown, 96P Machholz suspected
Radiant: constellation Aquarius
Active: July 12-Aug. 23, 2012
Peak Activity: July 28-29, 2012
Peak Activity Meteor Count: Approximately 20 meteors per hour
Meteor Velocity: 25 miles (41 kilometers) per second
Notes: It's not a good year for the Delta Aquarids - light from the August full moon make them nearly impossible to see.

Perseids
Comet of Origin: 109P/Swift-Tuttle
Radiant: constellation Perseus
Active: July 17-Aug. 24, 2012
Peak Activity: Aug. 12, 2012
Peak Activity Meteor Count: Approximately 100 meteors per hour
Meteor Velocity: 37 miles (59 kilometers) per second
Notes: Moonlight won't be as big a problem as last year, as its waning crescent won't rise until after midnight, and the shower peaks from about 10-11 p.m. local on the night of Aug. 12.

Orionids
Comet of Origin: 1P/Halley
Radiant: Just to the north of constellation Orion's bright star Betelgeuse
Active: Oct. 2-Nov. 7, 2012
Peak Activity: Oct. 21, 2012
Peak Activity Meteor Count: Approximately 25 meteors per hour
Meteor Velocity: 41 miles (66 kilometers) per second
Note: With the second-fastest entry velocity of the annual meteor showers, meteors from the Orionids produce yellow and green colors and have been known to produce an odd fireball from time to time.

Leonids
Comet of Origin: 55P/Tempel-Tuttle
Radiant: constellation Leo
Active: Nov. 6-30, 2012
Peak Activity: Night of Nov. 17, 2012
Peak Activity Meteor Count: Approximately 15 per hour
Meteor Velocity: 44 miles (71 kilometers) per second
Note: The Leonids have not only produced some of the best meteor showers in history, but they have sometimes achieved the status of meteor storm. During a Leonid meteor storm, many thousands of meteors per hour can shoot across the sky. Scientists believe these storms recur in cycles of about 33 years, though the reason is unknown. The last documented Leonid meteor storm occurred in 2002.

Geminids
Comet of Origin: 3200 Phaethon
Radiant: constellation Gemini
Active: Dec. 4-17, 2012
Peak Activity: Dec. 13-14, 2012
Peak Activity Meteor Count: Approximately 120 meteors per hour
Meteor Velocity: 22 miles (35 kilometers) per second
Note: The Geminids are typically one of the best, and most reliable, of the annual meteor showers. This year's peak falls perfectly with a new moon, guaranteeing a dark sky for the show in the nights on either side of the peak date. This shower is considered one of the best opportunities for younger viewers because the show gets going around 9 or 10 p.m.

]]> Thu, 09 FEB 2012 08:59:07 AEST Princeton, N.J. (UPI) Jan 3, 2012 - It turns out unusual crystals found in Russia weren't formed on Earth, researchers say, but rather came from outer space.

The so-called quasicrystals, with an unusual structure somewhere between crystals and glass, had only been previously created in laboratories before they were discovered in Russia's Koryak Mountains in 2009, the BBC reported Tuesday.

Now a team of researchers says the chemistry of the Russian crystals suggests they arrived in meteorites.

Quasicrystals break some of the rules of symmetry that apply to conventional crystalline structures, and it remained unknown what natural processes could create this "forbidden symmetry."

Now Paul Steinhardt of Princeton University, with Luca Bindi of the University of Florence, Italy, and his colleagues who discovered the crystals in Russia, say tests point to an extra-terrestrial origin for the minerals.

Measurements of different forms, or isotopes, of the element oxygen contained in parts of the rock sample shows the pattern of isotopes was unlike any known minerals that originated on Earth.

It was instead similar to patterns found in a type of meteorite known as a carbonaceous chondrite, meaning the quasicrystals in the Russian samples could date back to the very earliest days of the solar system, they said.

"Our evidence indicates that quasicrystals can form naturally under astrophysical conditions and remain stable over cosmic timescales," the researchers said.

]]> Thu, 09 FEB 2012 08:59:07 AEST Huntsville AL (SPX) Dec 29, 2011 - The 2012 Quadrantids, a little-known meteor shower named after an extinct constellation, will present an excellent chance for hardy souls to start the year off with some late-night meteor watching.

Peaking in the wee morning hours of Jan. 4, the Quadrantids have a maximum rate of about 100 per hour, varying between 60 and 200. The waxing gibbous Moon will set around 3 a.m. local time, leaving about two hours of excellent meteor observing before dawn.

It's a good thing, too, because unlike the more famous Perseid and Geminid meteor showers, the Quadrantids only last a few hours - it's the morning of Jan. 4, or nothing.

Like the Geminids, the Quadrantids originate from an asteroid, called 2003 EH1. Dynamical studies suggest that this body could very well be a piece of a comet which broke apart several centuries ago, and that the meteors you will see before dawn on Jan. 4 are the small debris from this fragmentation.

After hundreds of years orbiting the Sun, they will enter our atmosphere at 90,000 mph, burning up 50 miles above Earth's surface - a fiery end to a long journey!

The Quadrantids derive their name from the constellation of Quadrans Muralis (mural quadrant), which was created by the French astronomer Jerome Lalande in 1795.

Located between the constellations of Bootes and Draco, Quadrans represents an early astronomical instrument used to observe and plot stars. Even though the constellation is no longer recognized by astronomers, it was around long enough to give the meteor shower - first seen in 1825 - its name.

Given the location of the radiant - northern tip of Bootes the Herdsman - only northern hemisphere observers will be able to see Quadrantids.

]]> Thu, 09 FEB 2012 08:59:07 AEST Huntsville AL (SPX) Dec 12, 2011 - Put on the hot chocolate...find a warm, toasty location...and join us on the night of Dec. 13-14 for our "Up All Night with NASA" live Web chat about the 2011 Geminid meteor shower!

The Geminids - the final major meteor shower of the year - will be somewhat obstructed by a waning gibbous moon. Anytime between Dec. 12-16 is a valid window for Geminid-watching, but the night of Dec. 13-14 is the anticipated peak.

On Tuesday, Dec. 13, meteor experts Dr. Bill Cooke, Danielle Moser and Rhiannon Blaauw from NASA's Marshall Space Flight Center will be answering your questions about the Geminids via a live Web chat. Join them on Dec. 13 at 11 p.m. EST, then stay up until 5 a.m. EST for the meteor shower.

Joining the chat is easy. Simply return to this page a few minutes before 11 p.m. EST on Tuesday, Dec. 13. The chat module will appear at the bottom of this page.

After you log in, wait for the chat module to be activated, then ask your questions. A Ustream feed from the fireball camera network will be broadcast during the web chat. The Ustream link will be posted on this page on the afternoon of Tuesday, Dec. 13.

See you in chat!

More About the Geminids
Geminids are pieces of debris from an object called 3200 Phaethon, which is something of a mystery. Near closest approach to the Sun (perihelion), Phaethon exhibits increases in brightness similar to that of a comet; however, its orbit is characteristic of an asteroid. Extinct comet or asteroid? The debate still rages among astronomers.

In mid-December of each year, Earth runs into the stream of debris from Phaethon, which causes the Geminid meteor shower - a beautiful display of meteors for us to enjoy.

Unlike the Perseids or Leonids, the Geminids are a relatively young meteor shower, with the first reports occuring in the 1830's citing rates of about 20 per hour. Over the decades the rates have increased - it is now the best annual meteor shower - and we regularly see between 80 and 120 per hour at its peak on a clear evening.

The Moon will hamper that this year, but if your skies are clear you can still expect to see as many as 40 per hour.

One can tell if a meteor belongs to a particular shower by tracing back its path to see if it originates near a specific point in the sky, called the radiant. The constellation in which the radiant is located gives the shower its name; Geminids all appear to come from a point in Gemini, Leonids appear to radiant from Leo, and so on.

]]> Thu, 09 FEB 2012 08:59:07 AEST Washington DC (SPX) Nov 24, 2011 - An expert group of scientists, reporters, and risk management specialists have taken part in a Near Earth Object Media/Risk Communications workshop.

Output from these professionals is helping to draft a report for the United Nations Committee on the Peaceful Uses of Outer Space (UN COPUOS) Scientific and Technical Subcommittee, the Working Group dedicated to organizing an approach that counters the potential threat posed by Near Earth Objects, or NEOs.

Specifically, that UN Working Group in its deliberations is appraising establishment of an Information, Analysis and Warning Network (IAWN).

The team of workshop participants included leading journalists and writers, hazard communication authorities, artists and NEO researchers. The invite-only setting for the meeting - held November 14-15 - was the University of Colorado, Boulder's Laboratory for Atmospheric and Space Physics (LASP).

This NEO Media/Risk Communications Workshop was convened by Secure World Foundation and the Association of Space Explorers.

Reach, teach, and motivate
Among issues discussed during the two-day workshop:

+ What are effective tools to empower audiences with a tangible outreach and education plan, one that fosters accurate and timely information about the possible effects of a potentially hazardous NEO and what actionable steps can they take?

+ How best to inform the public regarding NEOs and any Earth-threatening object in a way to avoid misinformation?

+ What steps can be taken to develop an outreach and education plan, one that offers accurate and timely information about the possible effects of a potentially hazardous NEO?

Counteract consequences
Secure World Foundation has a long-standing interest for maintaining a vigilant eye on NEOs, as well as the establishment of a Planetary Defense strategy.

The consequences stemming from a NEO plowing into the Earth depends on its size and trajectory. Damage could range from destruction of an area the size of a city, to creation of tsunamis, to far greater after-effects.

"Establishment of a Planetary Defense strategy includes a number of components, from finding potentially hazardous objects, predicting their future locations, and providing warning about future impacts with the Earth," said Dr. Ray Williamson, Executive Director of Secure World Foundation.

Furthermore, a Planetary Defense strategy also includes missions to deflect impacting asteroids by changing their orbit, as well as disaster preparedness management and, in the event of a NEO strike, shaping a mitigation and recovery plan to counteract consequences.

The need for an IAWN had been identified in Asteroid Threats: A Call for a Global Response, a report prepared by an expert panel convened by the Association of Space Explorers (ASE) to assist the work of the UN COPUOS Action Team on Near-Earth Objects (AT-14), which was established in 2001.

That report is available here and additionally, you can review Executive Summary of the Workshop on a Near-Earth Object Information, Analysis, and Warning Network (IWAN).

]]> Thu, 09 FEB 2012 08:59:07 AEST St. Louis, MO (SPX) Nov 21, 2011 - Last January, two amateur meteorite hunters dropped by Randy Korotev's office at Washington University in St. Louis to show him their latest purchase, a 17-kilogram pallasite meteorite found in 2006 near Conception Junction (population 202) in northwest Missouri.

Korotev, research professor in earth and planetary sciences in Arts and Sciences and an expert in lunar meteorites, identified the stone as of a fragment of an asteroid.

His lab also analyzed crystals within the rock to help identify its body of origin, eventually referring the meteorite hunters to the University of California, Los Angeles (UCLA), for analysis of the metal in which the crystals are embedded.

The meteorite is a pallasite, a type of meteorite named for Peter Pallas, a German naturalist who first described one in 1749.

These meteorites consist of green olivine crystals embedded in an iron-nickel matrix like cherries in a pie, a rock type so odd that it was the first to be identified as extraterrestrial.

Not only are they beautiful, they are rare. The Conception Junction meteorite is only the 20th pallasite found in the United States so far.

And, like all meteorites, it carries within it a bit of the history of the early solar system. Pallasites are thought to be fragments of asteroids large enough to produce sufficient heat early in their history to partially melt and separate into a metal core and a rocky exterior.

Pallasites come from the lower mantle of these differentiated bodies and contain both metal from the core and olivine from the mantle. As such, they are miniature models of planet formation that provide clues to what lies beneath our feet.

The meteorite's story
Karl Aston, a St. Louis chemist with an interest in meteorite collecting, spotted Korotev's extensive meteorite website in 2007 and got in touch. Aston told Korotev he was trying to collect samples of all the 20-some meteorites that have been found in Missouri.

"I'm working on the St. Louis meteorite," he said. "I've got some small samples; would you like them for your museum?'"

Of course, Korotev said "Yes, please."

The St. Louis meteorite, a stony meteorite, fell through the roof of a convertible being driven down Florissant Avenue on Dec. 10, 1950. Contemporary accounts of the meteorite fall report a fireball some residents took to be an "A-bomb explosion."

But Aston also was interested in new finds, and following in the footsteps of a legendary early 20th-century meteorite hunter named Harvey Harlow Nininger, he hunted for them by advertising in local newspapers for funny-looking stones.

He got lots of bum leads. "He'd call, I'd ask what was new," Korotev says, "and he'd say, 'Oh, you know how it is. I went out and I found another hematite concretion today." (Hematite concretions, which are sedimentary rocks, are one of the stones most commonly mistaken for meteorites.)

But in 2009, Aston heard from a farmer who had found an unusually heavy stone buried deep in a hillside near Conception Junction in 2006.

The farmer, who has asked to remain anonymous, had sawed off the end of the stone, revealing an interior impossible to mistake for that of a terrestrial rock.

Aston didn't have the money to purchase the stone, so he brought in a partner, David B. Gheesling of Atlanta. Gheesling's friend, Robert Ward, of Prescott, Ariz., also joined the endeavor, directing a systematic search of the area where the stone was found, on the chance that it had broken up on entry and there were more pieces.

On their way back from Conception Junction with the newly purchased stone, Gheesling and Aston stopped by Korotev's office so that he could examine it.

Naming the stone
The meteorite hunters were eager to learn whether they had a new stone or a fragment of a known stone.

If it was a unique stone, it could be submitted for naming to the Meteoritical Society, a nonprofit organization founded in 1933 for the study of extraterrestrial materials. Naming, which follows chemical characterization and comparison to other meteorites, amounts to acceptance by the meteoritical community of the stone's validity and uniqueness.

Korotev said, "Well, that's where we might be able to help you. The composition of the olivine might tell you."

Most of the 20 pallasites found in the U.S. belong to what is called the pallasite "main group" because the elemental composition of their olivine is similar.

But, as Korotev was aware, a pallasite found by a farmer near Milton, Mo., in 2000 is "ungrouped," meaning it has a chemical composition unlike that of the main group pallasites.

"So they gave us a sample," Korotev says, "and Ryan Zeigler, PhD, then a research scientist in earth and planetary sciences, prepared it and analyzed the olivine's elemental composition.

"We got the numbers and looked at them," Korotev says, "and it was clear the stone was a main group pallasite. That meant it could be established as a unique stone only by studying the composition of the metal matrix."

Because WUSTL didn't have the tools or expertise to analyze the metal properly, Korotev referred the meteorite hunters to UCLA's John Wasson for that work.

Wasson concluded that the new stone didn't match any of the other palllasites he's analyzed - "and he's analyzed practically all of them," says Korotev. So Conception Junction was unique.

UCLA became the repository for the "type specimen" of the new meteorite. Before the Meteoritical Society will recognize a meteorite, Korotev says, a representative specimen must be deposited in a museum or other institutional collection that routinely makes material available for scholarly research.

The Nomenclature Committee of the Meteoritical Society assigned the stone the name Conception Junction on Aug. 27, 2011.

In its sliced and polished state, the meteorite is worth about $200 a gram. For comparison, the most common meteorites sometimes sell for as little as $2 or $3 a gram and pieces of the first lunar meteorite found by a private collector went for $40,000 a gram, Korotev says.

Meteorite prices depend on the type of the stone, its condition (some are unstable in Earth's atmosphere), the story that comes with it (one fetched by a dog commanded a higher price than usual) and many other factors. The meteorite market is not a good place to park your money.

"I don't know any rich meteorite collectors," Korotev says. "They do it mostly for the fun."

A wandering bit of the solar nebula
Of 1,000 meteorites that strike the Earth, 998 are from asteroids, one is from the Moon and the other one is from Mars, Korotev says.

Conception Junction was once part of an asteroid that circulated in the asteroid belt between the planets Mars and Jupiter. The gas giant Jupiter played havoc in this zone, preventing material from the primordial solar nebula from coalescing into planets.

Much of the asteroid belt's original mass has been lost since the solar system formed, with some fragments, like the Conception Junction meteorite, finding their way into Earth-crossing orbits.

Most meteorites from asteroids are from undifferentiated asteroids. But some, including Conception Junction, are from asteroids large enough that they produced sufficient internal heat to partially melt and separate into a metal core and a rocky exterior.

Meteorites blasted out of large asteroids can consist just of metal, just of stone, or - more rarely - mixtures of stone and metal, called stony irons.

The subgroup of stony irons called pallasites are thought to represent material from the boundary between the asteroid's metal core and the olivine of its lower mantle.

The boundary between Earth's mantle and core is probably similar.

"We can't break the Earth open," Korotev says, "we can't go down there and sample the rock, but we've got these pieces of broken asteroids that land on Earth, and they're made of the same stuff, they're just a lot smaller. "

]]> Thu, 09 FEB 2012 08:59:07 AEST West Lafayette IN (SPX) Nov 02, 2011 - An asteroid the size of an aircraft carrier will fly near Earth on Nov. 8. While there is no danger of it hitting the planet, a Purdue asteroid impact expert says a similar-sized object hitting Earth would result in a 4,000-megaton blast, magnitude 7.0 earthquake and, should it strike in the deep ocean, 70-foot-high tsunami waves 60 miles from the splashdown site.

NASA scientists reported this week that the asteroid 2005 YU55 will pass between the Earth and the moon and come within 201,000 miles of Earth on its closest approach.

Jay Melosh, an expert in impact cratering and a distinguished professor of earth and atmospheric sciences, physics, and aerospace engineering at Purdue, said the asteroid's orbit and trajectory mean there is no chance of an impact.

"What is unique about this asteroid flyby is that we were aware of it well in advance," Melosh said. "Before about 1980 we wouldn't know about an asteroid of this size until it was already making a close pass, but now it is unlikely that such an asteroid will approach the Earth without our knowledge."

NASA's Near Earth Object, or NEO, program celebrated a milestone earlier this year by announcing that current search programs have discovered more than 90 percent of near-Earth objects more than six-tenths of a mile in diameter. A larger number of smaller objects have yet to be found, however.

Spacewatch, a program created to discover and track all large asteroids crossing the Earth's orbit, discovered YU55 in 2005. This close approach has been expected since then, he said.

Melosh used the asteroid impact effects calculator he developed to estimate what would happen if the asteroid, which is a quarter mile in diameter, hit the Earth. The calculator, "Impact: Earth!" allows anyone to calculate potential comet or asteroid damage.

Users first enter a few parameters, such as the diameter of the approaching object, its density, velocity, angle of entry and where it will hit the Earth.

The site then estimates the consequences of its impact, including the atmospheric blast wave, ground shaking, size of tsunami generated, fireball expansion, distribution of debris and size of the crater produced. The calculator is available here.

For example, YU55 would strike with a velocity of 11 miles per second. Although it would begin to disintegrate as it passed through the atmosphere, the fragments would strike in a compact cluster that would blast out a crater 4 miles in diameter and 1,700 feet deep, Melosh said.

Sixty miles away from the impact site the heat from the fireball would cause extensive first-degree skin burns, the seismic shaking would knock down chimneys and the blast wave would shatter glass windows.

If YU55 were to strike a large city like Chicago, it would obliterate the entire city and leave few survivors. Fortunately, the chance of a large impact targeted on a city is very small, he said.

According to NASA, the last time an asteroid this size came close to Earth was in 1976, and the next known approach of such a large asteroid will be in 2028.

The most recent impact of this size is not known, but there are about 20 similar craters known in the geologic record, including the Wetumka crater in Alabama and the Rock Elm crater in Wisconsin.

Of the known large craters, the most recent are the six-mile-wide Bosumtwi crater in Ghana, which is about 1 million years old, and the nine-mile-diameter Zhamanshin crater in Kazakhstan, which is about 900,000 years old, Melosh said.

"Impacts from asteroids of this size are very rare," he said. "They occur about once every 100,000 years, so the chances of an actual collision with an asteroid like YU55 is about 1 percent in the next thousand years. Apophis, a similar-sized asteroid about one-third of a mile in diameter is the biggest threat in our near future. It has a tiny chance of striking the Earth in 2036."

Melosh is a co-author of a 2010 NRC report "Defending Planet Earth" that explores the feasibility of detecting all Earth-crossing asteroids down to a diameter of 140 meters, or about one-tenth of a mile, and of ways to mitigate their hazard.

]]> Thu, 09 FEB 2012 08:59:07 AEST Princeton, NJ (SPX) Oct 21, 2011 - Seeking to better understand the level of death and destruction that would result from a large meteorite striking the Earth, Princeton University researchers have developed a new model that can not only more accurately simulate the seismic fallout of such an impact, but also help reveal new information about the surface and interior of planets based on past collisions.

Princeton researchers created the first model to take into account Earth's elliptical shape, surface features and ocean depths in simulations of how seismic waves generated by a meteorite collision would spread across and within the planet.

Current projections rely on models of a featureless spherical world with nothing to disrupt the meteorite's impact, the researchers report in the October issue of Geophysical Journal International.

The researchers - based in the laboratory of Jeroen Tromp, the Blair Professor of Geology in Princeton's Department of Geosciences - simulated the meteorite strike that caused the Chicxulub crater in Mexico, an impact 2 million times more powerful than a hydrogen bomb that many scientists believe triggered the mass extinction of the dinosaurs 65 million years ago.

The team's rendering of the planet showed that the impact's seismic waves would be scattered and unfocused, resulting in less severe ground displacement, tsunamis, and seismic and volcanic activity than previously theorized.

The Princeton simulations also could help researchers gain insight into the unseen surface and interior details of other planets and moons, the authors reported. The simulations can pinpoint the strength of the meteorite's antipodal focus - the area of the globe opposite of the crater where the energy from the initial collision comes together like a second, smaller impact.

The researchers found this point is determined by how the features and composition of the smitten orb direct and absorb the seismic waves. Scientists could identify the planet or moon's characteristics by comparing a crater to the remnants of the antipodal point and calculating how the impact waves spread.

Lead author Matthias Meschede of the University of Munich developed the model at Princeton through the University's Visiting Student Research Collaborators program with co-authors Conor Myhrvold, who earned his bachelor's degree from Princeton in 2011, and Tromp, who also is director of Princeton's Institute for Computational Science and Engineering and a professor of applied and computational mathematics. Meschede describes the findings as follows:

"We have developed the first model to account for how Earth's surface features and shape would influence the spread of seismic activity following a meteorite impact. For the Earth, these calculations are usually made using a smooth, perfect sphere model, but we found that the surface features of a planet or a moon have a huge effect on the aftershock a large meteorite will have, so it's extremely important to take those into account.

"After a meteorite impact, seismic waves travel outward across the Earth's surface like after a stone is thrown in water. These waves travel all the way around the globe and meet in a single point on the opposite side from the impact known as the antipode.

"Our model shows that because the Earth is elliptical and its surface is heterogeneous those waves travel with different speeds in different areas, changing where the waves end up on the other side of the world and the waves' amplitude when they get there. These waves also are influenced by the interior. The effect on the opposite side is a result of the complete structure.

"We began by asking whether the meteorite that hit the Earth near Chicxulub could be connected to other late-Cretaceous mass-extinction theories. For example, there's a prominent theory that the meteorite triggered huge volcanic eruptions that changed the climate.

"These eruptions are thought to have originated in the Deccan Traps in India, approximately on the opposite side of the Earth from the Chicxulub crater at the time. Because North America was closer to Europe and India was closer to Madagascar during the Cretaceous period, however, it seemed questionable that the Deccan Traps were at the Chicxulub impact's antipode.

"Regarding the mass extinction, we saw from our measurements that a Chicxulub-sized impact alone would be too small to cause such a large volcanic eruption as what occurred at the Deccan Traps.

"Our model shows that the antipodal focusing of the seismic wave from such an impact was hugely overestimated in previous calculations, which used a spherical-Earth model.

"The Earth's maximum ground displacement at this point has been calculated to be 15 meters, which is extreme. The first outcome of our model was that this is reduced by a large amount to about three to five meters. On the spherical model, all the waves come together at exactly one point and, as a result, have a huge amplitude.

"We found the waves are disturbed by surface features and take on a more ragged structure, meaning less energy is concentrated at the antipode.

"But our results go beyond Chicxulub. We can, in principle, now estimate how large a meteorite would have to have been to cause catastrophic events. For instance, we found that if you increase the radius of the Chicxulub meteorite by a factor of five while leaving its velocity and density the same, it would have been large enough to at least fracture rocks on the opposite side of the planet.

"Our model can be used to estimate the magnitude and effect of other major impacts in Earth's past. A similar model could be used to study other examples of antipodal structures in the solar system, such as the strange region opposite the gigantic Caloris Basin crater on Mercury.

"Also, such a model can help examine the interior of a moon or planet by comparing the size of the crater to the amount of antipodal disruption - you only need two pictures, basically.

"One could correlate a certain impact magnitude with the observed antipodal effect - which is dependent on the object's surface features - and better understand the heterogeneity of the surface by how the energy was distributed between those two points. That can reveal information about not only the surface structure of the body at the time of the impact, but also the interior, such as if the planet has a hard core."

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