Found! Fresh moon crater from LADEE spacecraft impact

Before and after photos show the new crater blasted out by the impact of the LADEE spacecraft. It’s the white spot a short distance to the upper right of the prominent crater in the center and measures less than 10 feet (3-m) across.  Credit: NASA/Goddard/Arizona State University

I’d love to see that ad on Craigslist. Using before and after photos taken by NASA’s Lunar Reconnaissance Orbiter Camera (LROC), Mark Robinson, LROC principal investigator, discovered a tiny crater within one-fifth of a mile (300-m) of the predicted impact zone. And I do mean tiny. The impact of the refrigerator-sized spacecraft at the relatively leisurely speed of 3,800 miles an hour (1,699 meters per second) excavated a hole under 10 feet across or as big as your bathroom.

LRO close up photo of the LADEE impact site on the eastern rim of Sundman V crater. The bright area highlights what has changed between the time of the two images, specifically the impact point and the ejecta. The ejecta pattern spreads to the northwest, consistent with the direction the spacecraft was traveling when it smacked into the surface. Credit: NASA/Goddard/Arizona State University

NASA’s LADEE or Lunar Atmosphere and Dust Explorer’s mission studied dust hovering in the Moon’s extremely rarefied atmosphere called the exosphere. Much of the dust sputters off the surface during meteorite impacts, but some may be lofted into the sky by electrostatic forces active when the sun rises along the day-night borderline called the terminator. As the probe used up the last of its fuel, engineers lowered its orbit to study the lunar environment in ever greater detail. Variations in lunar topography and gravity soon brought it crashing to the surface on April 17 this year on the farside of the Moon.

LADEE only had so much fuel to conduct operations at the moon. When that was used up, the mission was complete. The vending-machine-sized probe broke apart as it heated up upon impact. Credit: NASA Ames/Dana Berry

The small size of the LADEE crater relates to the relatively slow impact speed (meteorites strike at a much higher velocity) as well as the craft’s small size and low density. To find it, investigators had to develop special software that compared before and after images to find the slightest changes between them. The impact popped into view much the same way before and after images of the sky are compared to detect moving asteroids.

Despite the crater’s tiny dimension, the crashing spacecraft managed to eject a plume of bright lunar dust 656-984 feet (200-300 meters) from the impact site. Future astronauts will likely find metal shrapnel from the probe mingled with lunar dust downstream from the impact.

“I’m happy that the LROC team was able to confirm the LADEE impact point,” said Butler Hine, LADEE project manager at Ames Research Center in California. “It really helps the LADEE team to get closure and know exactly where the product of their hard work wound up.”

In a memorable mess of an impact that will remain visible for millions of years.

Mars got a black eye this March

A large, fresh crater on Mars resulting from an impact sometime on March 27-28 this year. The main crater’s 159 by 143 feet (49-meter diameter). It’s surrounded by secondary craters (circled) probably formed from impact debris crashing down on the surface after the crater was excavated. Click to enlarge. Credit: NASA/JPL/Univ. of Arizona

Let’s face it. We’re all sitting ducks. Planets get whacked routinely by space debris. Most of it gets burned up in our atmosphere; a few pieces occasionally fall to the ground every year as meteorites. Mars is in the same boat. With a difference. It’s atmosphere is much thinner than Earth’s, allowing smaller meteoroids to penetrate to the surface.

This pair of images was taken 1 day apart by the lower resolution weather camera on NASA’s Mars Reconnaissance Orbiter (MRO). The left image was taken during Martian afternoon on March 27, 2012; the right one on the afternoon of March 28, 2012.The dark area in the “after” image is about 5 miles (8 kilometers) wide and marks the spot of the new crater. Credit: NASA/JPL-Caltech/MSSS

NASA’s orbiters have to date discovered about 400 fresh craters on the Red Planet using before and after photos taken from orbit. Recently, the largest ever impact crater in the solar system confirmed by this method was spotted on Mars by a scientist Bruce Cantor who studies the daily images taken with the Mars Reconnaissance’s weather-monitoring camera. His eye caught a dark spot in late March that wasn’t there the last time he looked.

Before and after pictures taken with the Context camera on MRO. Left photo was taken on Jan. 16, 2012; right photo on April 6. The dual-impact crater stands out clearly. Credit: NASA/JPL-Caltech/MSSS

When the more powerful cameras on Mars Reconnaissance Orbiter zoomed in for a look, they revealed a fresh impact scar half as long as a football field (49-meters) with a good-sized secondary crater biting into the main crater’s south rim. Scientists suspect the original meteoroid broke up into many pieces on atmospheric entry creating not only the secondary crater but a smattering of smaller craters (circled above) in the vicinity. It’s also possible that chunks of crust blown out by the impact fell back and gouged out some of the smaller depressions.

Fresh landslides created by the shock wave from the impact darkened the slopes in the 5-mile area surrounding the new craters. Credit: NASA/JPL-Caltech/MSSS

Working through older images, Cantor was able to narrow the time of the crater’s formation to sometime between the afternoon of March 27 and the following afternoon March 28. This is the narrowest time interval in which a crater-forming event has ever been observed.

Alfred McEwen, principal investigator MRO’s high resolution camera, estimates the impact object measured about 10 to 18 feet (3 to 5 meters) long, or less than a third the estimated length of the asteroid that hit Earth’s atmosphere near Chelyabinsk, Russia last year.

Sentinel Mission would spy ‘city-killing’ asteroids in the nick of time

B612 foundation video showing locations of 26 asteroid impacts between 2000 and 2013

Poor Earth. Always getting whacked by asteroids. Now it’s time to do something about it. This week, the B612 Foundation, a private organization dedicated with protecting the planet from potential asteroid impacts, announced plans to build the Sentinel Infrared Space Telescope to detect Earth-approaching asteroids long before they get here.

The Chelyabinsk meteoroid / asteroid, here seen from a dashcam video, was the largest impact in Earth’s atmosphere recorded by the nuclear test ban treaty network’s infrasound’s sensors since 2000. Before it exploded into smaller pieces, the asteroid measured about 65 feet across.

Data recently released from the Nuclear Test Ban Treaty Organization, which operates a network of sensors that monitors Earth around the clock listening for the low frequency infrasound signature of nuclear detonations, recorded 26 large explosions in the atmosphere not from weapons but rather from small asteroid impacts. The largest of them was the headline-making Chelyabinsk fireball that exploded in the atmosphere with the force of 600-kilotons of TNT on Feb. 15, 2013. To put this in perspective, the atomic bomb that destroyed Hiroshima had the energy of 15 kilotons.

Another fireball over Murmansk, Russia reminiscent of Chelyabinsk occurred Saturday night April 19. No sounds or explosions were heard but the object burned briefly as bright as the full moon. Video courtesy: Alexandr Nesterov

Most of the 26 impacts were smaller than Chelyabinsk and detonated high in the atmosphere over uninhabited regions like the oceans. Asteroid impacts greater than 20 kilotons occurred over South Sulawesi, Indonesia in 2009, the Southern Ocean in 2004, and Mediterranean Sea in 2002.

“While most large asteroids with the potential to destroy an entire country or continent have been detected, less than 10,000 of the more than a million dangerous asteroids with the potential to destroy an entire major metropolitan area have been found by all existing space or terrestrially-operated observatories,” stated Lu, CEO and co-founder of B612. “Because we don’t know where or when the next major impact will occur, the  only thing preventing a catastrophe from a “city-killer” sized asteroid has been blind luck.”

Sentinel would circle the sun inside Earth’s orbit and look outward to spy incoming Earth-crossing asteroids. The B612 Foundation hopes to raise private money to build the probe. Credit: B612 Foundation

The B612 Foundation (named after the asteroid in the novella “The Little Prince”) will partner with Ball Aerospace to privately build the Sentinel spacecraft that would launch in 2018 into a Venus-like orbit on a 6.5 year mission to find and track 90% of the asteroids larger than 460 feet (140 meters) with orbits that intersect Earth’s. It will also search for smaller asteroids in the 30-45 meter range, large enough to destroy a major city should our luck go bad. B612 estimates an asteroid this size strikes the planet about every hundred years.

Potentially hazardous asteroid 4179 Toutatis photographed by the Chang’e 2 spacecraft during a 2012 flyby. The asteroid is 2.8 miles long. Credit: CNSA

Sentinel will create a comprehensive map detailing the paths of asteroids during the next 100 years, giving earthlings decades of notice to alter their course through one of several imaginative but untested methods.

The Foundation believes that asteroid impacts rates have been underestimated and are 3-10 times more common than previously thought. While some would argue that number is overstated, there’s no denying that discovering more potentially hazardous objects is a good thing. Sentinel scientists hope to find some 500,000 large enough to pose a threat.

This is no fly-by-night operation. B612 was co-founded by Ed Lu, a former Shuttle and Soyuz astronaut, and has links with NASA, which will provide communications, navigation and tracking for the mission with its Deep Space Network.

To learn more about the topic, click HERE for a FAQ on hazardous asteroids and HERE to donate money to the mission.

Forbidding Planet: Scientists find remains of monster asteroid impacts on early Earth

Artist’s view of Earth several billion years ago during the Late Heavy Bombardment, when the planet is thought to have been battered by impacts of comets and asteroids. Credit: Chris Butler/SPL

Earth 3.5 billion years ago was a terrifying place. Picture a rocky landscape pounded by meteorites and asteroids with a surface resembling that of the moon. Volcanoes spewed water vapor but also a toxic mix of carbon dioxide, sulfur dioxide and methane. If you could whisk yourself back to this world by time machine, you’d need to be fully protected by a spacesuit and lucky enough to not get picked off by a falling space rock. Oh, and bring a boat too. Hot-water oceans likely covered a fair portion of the planet back then.

This time-lapse illustration of the Nice (pronounced ‘neece’) model of solar system evolution shows how outer planet migrations kick asteroids into the inner solar system

Scientists call the period from about 3.8 billion to 1.8 billion years ago the Late Heavy Bombardment (LHB), a time when the number of asteroids and their fragments pelting the inner planets and their moons spiked. Why then? No one’s absolutely certain, but the leading theory posits that the migration of the giant outer planets to their present positions “stirred the gravitational pot”, slinging boatloads of asteroids into the inner solar system, where they rained down on Earth and its neighbors in hellish monotony for millions of years.

Anyone with a small telescope can see resulting devastation to this day. Just take a long look at the moon’s battered and cratered surface and thank your lucky stars you’re around during a more peaceful time. Finding Earth’s craters is trickier because water and wind erosion, along with the continual recycling of much of our planet’s crust through plate tectonics, has erased much of our violent past.

The Vredefort Dome – these concentric hills, which rebounded after the impact that created Vredefort Crater – are what remains after an asteroid about 3-6 miles wide struck Earth 2 billion years ago. Credit: NASA

About 180 craters are known on Earth today, but we’re aware of only three resulting from the Late Heavy Bombardment. The oldest, estimated at 3 billion years old and 62 miles (100 km) wide, is also the most recently discovered. Found in western Greenland in 2012, all that remains of the impact are rocks rattled by the massive shock wave that penetrated 15 miles (25 km) deep within Earth’s crust.

You can still see the remains of the impacts that formed the 112-mile-wide (180 km) Vredefort Crater in South Africa, which is 2 billion years old, and the youngest LHB member, the 155-mile (250-km) Sudbury crater in Canada dated at 1.85 billion years.

Map of South Africa with the Barberton greenstone belt shown in red. Shock waves from the impact of an asteroid 3.26 billion years ago created telltale formations within the belt. No one knows yet where the impact happened.

Now, a group of scientists have announced they’ve found evidence for an even older impact, one that occurred 3.26 billion years ago and left its signature in a South African region known as the Barberton greenstone belt.

A recent press release describes the huge impactor as between 23 and 36 miles wide (37- 58 km). Colliding with the planet at 12 miles per second, the jolt delivered was bigger than a 10.8 magnitude earthquake and propelled seismic waves hundreds of miles through the Earth, breaking rocks and setting off other large earthquakes. Tsunamis thousands of feet deep swept across the oceans that covered most of the planet at that time.

A graphical representation of the size of the asteroid thought to have killed the dinosaurs (left), and the crater it created, compared to an asteroid thought to have hit the Earth 3.26 billion years ago and the size of the crater it may have generated. A new study reveals the power and scale of the event some 3.26 billion years ago which scientists think created geological features found in a South African region known as the Barberton greenstone belt. Credit: American Geophysical Union

“We knew it was big, but we didn’t know how big,” Donald Lowe, a geologist at Stanford University and a co-author of the study, said of the asteroid.

The collision would have blasted out a crater some 300 miles (500 km) wide, filled the atmosphere with fiery rock vapor and set the surface of the ocean a-boil. We’re talking serious cataclysm. Somehow life found a way through the heat and crater-punching to gift us with the rolling green hills, coral reefs and forests that characterize Earth today.

Table from the book “Near Earth Objects – Finding Them Before They Find Us” by Donald Yeomans showing average asteroid impact results and probabilities by size. Credit: Donald Yeomans

I try to imagine the dark days of the LHB to help me appreciate these calmer times. Yet we know in our gut – and in fact, thanks to probability – that we’ll never truly be out of the woods. Asteroids lurk in the deep that could one day cause a similar scenario. Don’t let it worry you too much – the chance of a 10-mile-wide space rock striking Earth is once every 89 million years. You’ve still got time to take a nap, catch a show and enjoy a few nights out on the town. Probably.

Lunar eclipse will give NASA moon orbiters the shivers

Artist’s view of Earth eclipsing the sun next Tuesday morning April 15 as seen from the Lunar Reconnaissance’s Orbiter’s perspective. For several hours, it and NASA’s LADEE dust explorer will be cut off from sunlight. Back on Earth, we see the moon slide into our planet’s shadow. Credit: NASA

While we’re all bundled up for next Monday’s late night total eclipse of the moon, NASA will be taking special precautions to ensure its two moon probes survive the deep chill they’ll experience when the moon dives into Earth’s shadow.

NASA’s LRO has been orbiting, mapping and studying the moon since 2009. Credit: NASA

The Lunar Reconnaissance Orbiter (LRO), launched in 2009, has spent the past four-plus years photographing and mapping the moon in great detail from an orbit dipping as low as 31 miles (50 km). One of its goals is to determine future lunar landing sites. The craft also examines the moon’s radiation environment and maps the concentration of hydrogen – the main ingredient of water – across the globe. Hydrogen “hot spots” imply potential locations of water ice beneath the surfade or bound to moon rocks.

LRO will orbit the moon twice in Earth’s shadow. All instruments will be shut down since they would otherwise drain the batteries which can’t recharge without sunlight. Credit: NASA

LRO depends on sunlight to keep its batteries charged and instruments running. During the upcoming lunar eclipse, the moon will be either partially or fully within Earth’s shadow for several hours. With no sunlight reaching the probe’s solar panels, recharging the batteries isn’t possible.

To prevent damage to the either instruments or batteries, NASA plans to shut down all of LRO’s science instruments next Monday night for the duration of the eclipse. As soon as the event is over, the sun will slowly recharge the batteries and mission control will bring everything back online.

While LRO’s no stranger to eclipses,this time the spacecraft will have to pass through the complete shadow twice before the eclipse ends – longer than in any previous event.

“We’re taking precautions to make sure everything is fine,” said Noah Petro, Lunar Reconnaissance Orbiter deputy project scientist. “We’re turning off the instruments and will monitor the spacecraft every few hours when it’s visible from Earth.”

Understanding lunar eclipses

During other briefer eclipses, scientists have used the opportunity to study how the moon’s surface cools during these events, shedding light on the composition of the lunar crust. During the June 15, 2011 eclipse, temperatures on some areas of the moon dropped 180 degrees F compared to sunny, pre-eclipse conditions.

While LRO is expected to emerge from the shadow with flying colors, the forecast for NASA’s Lunar Atmosphere and Dust Explorer (LADEE) spacecraft is sketchy. The probe was never designed to withstand hours in the deep freeze of a shadowed moon.

“The eclipse will really put the spacecraft design through an extreme test, especially the propulsion system,” said Butler Hine, LADEE project manager.

Prior to impact on or before April 21, ground controllers at NASA’s Ames Research Center in Moffett Field, Calif., are maneuvering the spacecraft to fly approximately 1 to 2 miles (2-3 km) above the lunar surface to gather science measurements at the lowest altitude possible. Credit: NASA

LADEE (pronounced ‘laddie’) has been circling the moon studying dust in its extremely rarefied atmosphere since last fall. Much of the dust sputters off the surface during small meteorite impacts. If it survives the eclipse, LADEE will perform additional week of science before the mission is terminated. Rather than just shutting the probe off, mission control will direct it to crash into the moon near on or around April 21. LRO will locate study the impact site when it makes its next flyover a few months later.

Meanwhile, NASA invites you to  “Take the Plunge Challenge” and guess  what date LADEE will slam into the surface. Winners will be announced after impact and e-mailed a commemorative, personalized certificate from the LADEE program. The submissions deadline is 5 p.m. CDT tomorrow April 11.

For more information on the April 14-15 total eclipse of the moon including viewing times for your time zone, please see my earlier blog.

Boom! Watch a record-breaking meteorite strike the moon

Lunar impact blast September 11, 2013

Wish I’d been over in Europe staring at the waxing crescent moon last September 11. On that evening, a meteoroid weighing an estimated 900 pounds (400 kg) struck Mare Nubium (Sea of Clouds) at 38,000 mph at 8:07 p.m. Greenwich Time.

The flash from the impact occurred in the “dark” portion of the moon not illuminated by sunlight, providing excellent contrast against the landscape.  Anyone looking up at our satellite at that moment would have easily seen it as a star-like point of light of magnitude 2.9, nearly as bright as the stars comprising the Big Dipper.

Still frame from the video taken September 11, 2013 shows the bright flash in Mare Nubium from the small asteroid impact. Credit: J. Madiedo / MIDAS

It was dutifully recorded by two telescopes equipped with CCD cameras in the Moon Impacts Detection and Analysis System (MIDAS) program in southern Spain. Astronomer Jose M. Madiedo, who was operating the telescopes at the time, reports that the event was not only the brightest but the longest-lasting confirmed lunar impact flash; the afterglow of the explosion lasting fully 8 seconds. Estimated at between 2 and 4 feet across (about 1 meter), the little asteroid struck the moon with the equivalent of 15 tons of TNT, hollowing out a 131-foot (40-meter) diameter crater.

NASA video of the March 17, 2013 lunar meteorite impact 

The energy released was three times more powerful than the previous largest impact observed with NASA telescopes last March 17. NASA has recorded more than 300 lunar strikes, almost all much smaller than this one. Over half come from meteor streams like the Perseids or Geminids – the rest originate from random meteorite and comet shards called sporadics.

Once NASA’s Lunar Reconnaissance Satellite gets into position, it should have no problem photographing this large of an impact scar. We hope the new crater will soon be targeted.

The moon and approximate location of the big impact as seen from southern Spain around 8 p.m. September 11, 2013. Stellarium

The moon has virtually no atmosphere, so meteorites strike its surface at full speed without suffering break up. Similar sized rocks pelt our planet but our atmosphere renders most of them harmless; air pressure and atmospheric heating shatters and slows them down, leaving mostly small pieces traveling at low velocity.

You can read more about the discovery in Madiedo’s complete article published the Monthly Notices of the British Astronomical Society.

Mini Asteroid 2014 AA hits Earth on New Year’s Day

Animation shows the Earth as observed from asteroid 2014 AA shortly before impact. The asteroid approaches from the night side and enters Earth’s shadow cone at approximately 7:45 p.m. CST January 1; a little more than an hour later it entered the atmosphere. Click for more information. Credit: Pasquale Tricarico

I know, I know. That’s a scary headline, but we’re all safe. A very small asteroid estimated at between 3 and 13 feet across (1-4 meters) named 2014 AA headed straight for Earth around 9 p.m. CST on Jan. 1. It likely broke apart in the atmosphere with pieces scattering somewhere along a path stretching from Central America across the Atlantic Ocean to West Africa.

Possible impact zone of the asteroid 2014 AA. It was the first new asteroid discovered in 2014. Map credit: NASA

The reason for the uncertainty is that only a few measurements of of 2014 AA’s position were possible before it literally disappeared from view. Richard Kowalski of the Catalina Sky Survey out of Tucson, Ariz. picked up the object on New Year’s Eve in northern Orion as a tiny twinkle of 19th magnitude. At the time, the asteroid was only 300,000 miles from Earth. When it hit the atmosphere some 22 hours later, it must have created a spectacular fireball.

This sequence of four images taken about every 30 seconds shows 2014 AA’s movement across northern Orion on the evening of Dec. 31. Credit: Catalina Sky Survey / NASA

2014 AA was similar in size to 2008 TC3, the only other asteroid discovered and tracked before impact. That one, estimated at 13 feet across, fragmented in Earth’s atmosphere over the Nubian Desert in Sudan on October 7, 2008.

Later, dozens of fragments with a total weight of 8.7 pounds (3.95 kg) were recovered as the Almahata Sitta meteorite.

Meteor researcher Peter Jenniskens finds a fragment of meteorite dropped by asteroid 2008 TC3 in the desert in Sudan. Credit: Peter Jenniskens

Right now, signals from the global network of infrasound stations are being analyzed to see if they can be correlated with an impact. There are no visual sightings of the asteroid … Perhaps a surveillance satellite snagged it or we’ll hear of a airplane pilot seeing something. Stay tuned!

UPDATE Jan. 3: Three weak infrasound signals have been detected pointing to an impact near 12 degrees north, 40 degrees west latitude about 1,900 miles (3,000 km) east of Caracas, Venezuela in the Atlantic Ocean.

Biggest Chelyabinsk meteorite caught on video crashing into Lake Chebarkul

Security camera video showing the impact of the largest piece of the Chelyabinsk meteorite striking Lake Chebarkul on Feb. 15, 2013. Credit: Nikolaj Mel’nikov

While it may not be much to look at, the simple fact that it was recorded at all makes it an incredibly rare and invaluable document of the great Russian meteorite fall.  You’ll recall that a house-sized meteoroid created a gigantic fireball over Chelyabinsk in Russia’s Ural Mountain region on Feb. 15 this year. It was probably the most photographed fireball in history thanks to all the dashcams that recorded the scene as people headed to work on that clear, cold morning.

Five Chelyabinsk meteorite fragments weighing a total of just 7 grams. Credit: Bob King

The meteoroid or tiny asteroid that entered Earth’s atmosphere that day was the size of a five-story building, but it broke up into thousands of much smaller pieces from the pressure and shock of hitting our protective blanket of air at over 41,000 mph (66,960 km/hr) or 60 times the speed of sound.

Frame grab from the video showing the movement of the ice and snow cloud created by the impact of the 1/2-ton meteorite. I still can’t be sure of seeing the meteorite itself but the cloud isn’t too hard to spot.

One of those pieces – the largest found to date – punched a 20-foot-wide (6-meter) hole in Lake Chebarkul about 43 miles southwest of Chelyabinsk. No one witnessed the moment of impact, but divers using special equipment discovered a half-ton meteorite buried in the muck in the bottom of the lake. The rock was finally fished out with great effort on Oct. 16 and taken ashore to be weighed. As it was lifted in


The 20-foot hole in the ice of Lake Chebarkul from the impact of a large hunk of Chelyabinsk meteorite. Credit: AP

Meteors leave brilliant trails that make a great spectacle; large ones like Chelyabinsk leave trails that linger for many minutes, providing countless opportunities for photos. But what about the stuff that survives the fiery plunge and makes it to the ground as meteorites?

Very rarely does anyone ever see a meteorite strike the ground. Video or still picture recordings are rarer still. That’s why it’s worth a minute to study the Chebarkul video to appreciate what you’re seeing. It recently popped up on Youtube as part of an online presentation on the Chelyabinsk airburst by Peter Jenniskens, noted meteorite expert and senior research scientist at the SETI Institute. You can watch Jenniskens’ full report HERE.

Biggest hunk of Chelyabinsk meteorite pulled from Lake Chebarkul

When you watch the video, make it “full-screen” and focus your attention on the area to the left of the small, rectangular ice fishing shack at the top middle of the image. In the slowed-down part of the footage you’ll see a cloud of ice and snow blow up and quickly drift to the right of the shack immediately after impact. Can you see it? If not, I grabbed the video frame showing the moment-by-moment sequence. Give this a look and watch the video again.

Bizarre green meteorite NWA 7325 may be from Mercury

Wow, that’s what I call green! Green, glassy fusion crust coats one side of Ralew’s new meteorite. This is the largest of the 35 fragments, weighing just over 100g. Cube at right is 1 cm across. Click for larger version. Credit: Stefan Ralew

In April 2012 Stefan Ralew, a meteorite collector from Berlin, found himself staring at a spread of 35 green meteorite fragments for sale by a dealer in Morocco

“It was offered as a Martian (meteorite) but for me it was simply far too green,” said Ralew. Moroccan meteorite always keep an eye out for green rocks in the belief that they’re of Martian origin. Sometimes however they turn out to be nothing more than Earth rocks. Since this one was expensive, Ralew would have normally declined, but he noticed that the pieces had fusion crust, that frothy, typically dark coating of melted rock that forms when a meteorite is heated during its fall through the atmosphere.

Stefan Ralew Credit: Mirko Graul

“It was a big risk because of the high price,” said Ralew, but he sealed the deal and mailed off a piece to Dr. Tony Irving at the University of Washington, well-known for his expertise in meteorites from other planets.

After chemical analysis, Irving discovered that Ralew’s green rock was a completely new type of achrondrite (ay-KON-drite), a class of igneous meteorite that forms deep within the crust of larger asteroids and planet-sized bodies. In fact, Ralew’s green meteorite shared similarities with the planet Mercury, making it a one-of-a-kind.

Many of the more familiar achondrites that scientists and meteorite hunters have picked up here on Earth were blasted from the surface of Vesta by meteorite and asteroid impacts. Still others have been liberated from the moon and Mars. They drift through space until swept up by the ceaseless Earth. Scientists have done the math and arrived at the conclusion that meteorites from Mercury impacts should also by lying around in the deserts of the world, preserved by arid air and lack of rain. But no one had definitely identified a rock from Mercury until the green meteorite entered the scene.

A closeup of a polished, cut face of NWA 7325 shows striking green crystals of chromium diopside (a silicate mineral with chromium) and gray crystals of plagioclase, a rock also common in Earth’s crust. Click for larger version. There are a total of 345 grams (about 12 ounces) mostly in small fragments. Credit: Stephan Ralew

Other classes of achondrites called aubrites and angrites were once believed to have originated on the innermost planet, but further research points to their home on a yet-unknown asteroid or planet.

Mercury photographed by MESSENGER. The planet’s crust lacks iron and is pockmarked by countless craters. One of these impacts possibly sent NWA 7325 our way. Credit: NASA

Stefan’s meteorite, now classified as NWA 7325 (NWA=Northwest Africa, its find location), is a near-match for rocks examined from orbit by Mercury MESSENGER space probe. NWA 7325 is rich in magnesium, calcium and a silicate material laced with chromium that lends it an emerald sparkle, but it lacks iron. And that’s the key. Surface rocks on Mercury are likewise igneous and depleted in iron.

The match isn’t perfect. NWA 7325 has more calcium than it should and lacks the silicate mineral enstatite (common on Mercury), but that doesn’t worry scientists too much. Because the rock was excavated from deeper down in the crust, it would be expected to have its own unique qualities.

Mars meteorites show evidence of shock from impact in their crystal structures, and the same would be expected for rocks delivered to us from Mercury. Plagioclase, a very common mineral in Earth’s crust, and found in abundance in NWA 7325, has been completely melted, likely due to shock from the impact that sent it flying from the planet long ago.

Bubbly fusion crust on another fragment of Stefan’s meteorite. Click for larger version. Credit: Stefan Ralew

While the evidence points to a Mercury origin, we won’t really know for certain whether Ralew’s rock originated from the innermost planet until further studies are done. Scientists are still working to determinewhen those gorgeous green crystals formed as well as how long the rock coasted through space before arriving on Earth.

“Ultimately, only a sample return from Mercury may provide an answer,” wrote Irving in his group’s recent report on NWA 7325. In the meantime, Stefan’s meteorite stands as one of the most singular finds to date. It couldn’t have happened to a better guy. Ralew has a been a great friend of meteorite collectors and the scientific community for years. You can check out his website HERE.

New asteroid book good medicine for the doomsday blues

Don Yeoman’s new book on asteroids is a great read. Photo: Bob King

I just finished reading Donald Yeomans’ excellent new book “Earth-Approaching Asteroids: Finding Them Before They Find Us” and figured many of you might enjoy hearing about it. The book is published by Princeton University Press and available from Amazon for $15.73.

Author Donald Yeomans might be known to some of you already for his youtube video debunking 2012 doomsday predictions.  He works as a senior research scientist at the Jet Propulsion Lab, where he manages NASA’s Near-Earth Object Program Office. His book offers an excellent introduction to the layperson on near-Earth asteroids (NEAs), those objects that can potentially pass within about 29 million miles of Earth as they orbit around the sun.

Yeomans’ primary focus is on a smaller group within the NEAs called the PHAs or potentially hazardous asteroids. These pass within 4.65 million miles of the planet and span at least 500 feet across, large enough to cause significant destruction should they impact Earth. Close-approaching comets are also discussed.

The book is 161 pages long and divided into 10 chapters, starting with asteroid and comet basics and moving on to how astronomers calculate orbits and name names. Next is an overview of the new Nice model (developed in Nice, France) of the solar system’s evolution, where we learn that the giant planets did not form where they now reside.

Author Donald Yeomans

Gravitational interactions of Jupiter, Saturn, Uranus and Neptune with each other and the small asteroid-like building blocks of the solar system called planetesimals caused the outer planets to migrate over time. As they moved to their current locations, they scattered planetesimals hither and yon to form the current main asteroid belt between Mars and Jupiter and the distant Kuiper Belt beyond Neptune. It’s a fascinating read and goes far in explaining the present-day layout of the solar system.

With the Nice model as background, Yeomans delves into how asteroids from the main belt – the origin of nearly all NEAs – are delivered into Earth-crossing orbits through a combination of the Yarkovsky effect and gravitational nudges from Jupiter and Saturn. Heat absorbed by a rotating asteroid from the sun radiates back into space, giving it a little push and causing the asteroid to spiral toward or away from the sun – this is the Yarkovsky effect. Once the asteroid crosses into a “resonance” point with Jupiter or Saturn, it can then get tossed into the near-Earth neighborhood.

Because near-Earth objects, both comets and asteroids, are composed of primitive materials from early days of the solar system’s history, Yeomans believes they’re critical to understanding our origins. These small bodies may well have delivered much of the water and organic (carbon-containing) compounds necessarily for life to have evolved on Earth.

Plot showing the rapid increase in near-Earth asteroid (NEA) discoveries beginning in the late 1990s due to the increase in telescopic surveys and use of CCD technology. Credit: Alan Chamberlain, NASA-JPL/Caltech

The first near-Earth asteroid, 433 Eros, was discovered in 1898, while the first dedicated survey to hunt for them didn’t begin until 1973, when Gene Shoemaker and Eleanor Helin used the 18-inch Schmidt telescope on Mt. Palomar to search for small, fast-moving asteroids.

Yeomans describes accelerating efforts to find and track NEAs in the 1980s and 1990s thanks to workshops and papers by asteroid researchers, the discovery of the dinosaur extinction-asteroid connection and introduction of CCD technology (electronic cameras) that allowed for much more rapid and efficient surveys.

As scientists and legislators realized the potential destruction power of near-Earth objects, part of NASA’s budget was directed toward creating the Near-Earth Objects Observations Program in 1998. Its goal: to detect, track and characterize 90 percent of near-Earth asteroids 1 km and larger. The lower limit for an asteroid or comet to cause a global disaster is 0.9 miles (1.5 km).

Especially interesting is how the notification system works should a potential threat be detected during a survey run. I’ll leave it for you to read, but let’s just say, there are many checks before an announcement would be made.

Table from the book showing average asteroid impact results by size. Credit: Don Yeomans

Yeomans describes asteroids’ and comets’ compositions and how we might mine near-Earth asteroids for materials to build space ports and rockets. Much of our planet’s metal content long ago sank to the core or is otherwise deep beneath the surface. Asteroids wear their metals on their sleeves so to speak, with abundant iron, nickel and precious metals like platinum and rhodium much more easily available.

Later chapters go into detail about the potential threats of near-Earth objects, how orbits are refined through continued observation and the protocols in place should an alert need to be issued. Already about 90 percent of NEAs 0.9 mile and larger have been discovered; no known asteroids of this size will impact Earth for at least the next 100 years.

The final chapter describes what we’d do to deflect a potentially threatening asteroid. The slow-pull gravity tractor method (changing its trajectory by “towing” into a safer orbit via gravity from a neighboring spacecraft) and detonating a nuclear device on or near an asteroid are explored.

I highly recommend the book. Since it covers so many aspects of these fascinating asteroids, I found it comprehensive and a great read. While Yeoman covers a topic that some of us worry about, he provides the facts needed to stay cool yet informed. One very small criticism – a list of web resources on the topic in the index would have been nice addition.

I liked the occasional touches of humor, such as when the author wondered why there wasn’t a “rhodium” credit card yet, since that metal’s even more precious than the vaunted “platinum”. We’ll finish with the book’s final sentence:

“Near-Earth objects are among the smallest members of the solar system, but their diminutive size is in no way proportional to their importance. When it comes to their role in the development and future of humankind, next to the sun itself, theirs is the most important realm.”