Did the asteroid that hit the Earth, creating the Moon, originate from one of Earth's Lagrangian points? (ESA)
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Two solar telescopes launched to study coronal mass ejections and the solar wind have been sent to do an entirely different task. Currently, the Solar Terrestrial Relations Observatory (STEREO) probes are flying in opposite directions; one directly in front of Earth’s orbit and the other directly behind. This unique observatory is intended to view the solar-terrestrial environment in unprecedented detail, allowing us to see the Sun from two vantage points.
This might sound like an exciting mission; after all, how many space-based observatories have such a unique perspective on the Solar System from 1 AU? However, both STEREO probes are currently moving further away from the Earth (in opposite directions), approaching a gravitational no-man’s land. STEREO is about to enter the Earth-Sun Lagrangian points L4 and L5 to hunt for some sinister lumps of rock…
The Lagrangian points of a two-body system, such as the Earth and the Sun.Lagrangian points in planetary systems are islands of gravitational stability. They are volumes of space where the gravity of two massive bodies cancel out. The first two Lagrangian points in the Earth-Sun system are fairly obvious. The L1 point is located directly between the Earth and Sun, about 1.5 million km from the surface of the Earth, the point at which the gravitational pull of the Sun and Earth cancel each other out.
The L2 point is located at approximately the same distance, but on the opposite side of the Earth. In this case, the Earth is constantly eclipsing the Sun. The L3 point is on the opposite side of the Sun from the Earth, at approximately 1AU. Now this is where it starts to get a little strange. The L4 and L5 points are located 60° in front and 60° behind the Earth’s orbit. The 4th and 5th Lagrangian points are also the most gravitationally stable regions, primordial debris lurks, trapped in the Lagrangian prisons. Although the L1 point is often considered to be the most stable of the Lagrangian points (as it’s directly locked between the gravity of the Sun and Earth), even space observatories (such as SOHO and ACE) have to carry out complex orbits to remain in place. Otherwise the delicate balance will be lost and they will drop away from L1.
L4 and L5 are in fact the most stable locations, balanced by a complex cage of competing gravitational components from the Earth and the Sun. It is thought that these two regions have trapped lumps of rock and dust all the way through the evolution of the Solar System, making them a very interesting place to send a space mission. And the two solar probes of STEREO are currently racing toward L4 and L5, about to explore the gravitational dead zone, whether they like it or not.
It is a known fact that other planets in the Solar System possess these islands of gravitational calm, and asteroids have been observed sitting in stable locations in front and behind of Jupiter’s orbit for example (called “Trojans” and “Greeks”). Does Earth have a swarm of asteroids sitting in its L4 and L5 points? Scientists believe this is a certainty. However, no asteroids have ever been observed.
Although millions of kilometres across, L4 and L5 can only be observed at dawn and dusk. Any possibility of spotting a large asteroid diminishes rapidly as they are obscured by the Sun. So, the STEREO space telescopes are going to take the dive into L4 and L5 to see, first hand, what lies in wait.
Artist impression of the STEREO probes going their separate ways (NASA)Early on in the STEREO mission, scientists discussed the possibility of stopping the spacecraft inside the two islands of calm to provide an advanced warning of incoming charged particles from coronal mass ejections during solar maximum. However, slowing the craft down would have cost the mission too much fuel, so the decision was made to let the solar telescopes pass straight through. It will take a few months to complete the journey through the huge Solar System badlands, but it will serve a valuable purpose, STEREO has become NASA’s makeshift asteroid hunting mission.
Although STEREO wasn’t designed for this work, the mission already has a team of volunteer near-Earth asteroid hunters at the ready and their optics are more than capable of looking out for large lumps of rock invisible from Earth.
“The close-up investigation of L4 and L5 is completely new. That makes it something we should be driving,” says Richard Harrison of the Rutherford Appleton Laboratory in Oxfordshire, UK and a member of the STEREO project. “Wouldn’t it be spectacular if we actually backed past an asteroid? Saw it come creeping into view around the camera.” Now that would be a huge discovery.
This isn’t simply out of academic curiosity however. The Earth’s Moon is thought to have been formed after a huge cosmic impact with a small planetary body. The problem comes when trying to explain where the offending planetary body could have come from; too far away and it will have had too much energy. Rather than punching into the side of the Earth it would have shattered our planet. So the body must have formed a lot closer to our planet.
Did this body evolve in either the L4 and L5 points? If it did, and then somehow got kicked out of the gravitational island, perhaps careering toward the Earth, causing the cataclysmic impact that seeded the formation of the Moon.
It is exciting to think that STEREO may make some ground-breaking discoveries not Sun related. I just hope they don’t bump in to any chunks of rock, it could be pretty crowded out there…
Bolide in Italy. Credit: Ferruccio Zanotti of Ferrara, Italy, via Spaceweather.com
A fireball seen over Texas during the daytime on Sunday, Feb. 15th, triggered widespread reports that debris from the recent satellite collision was falling to Earth. The FAA even issued a statement that airplanes should watch for falling debris. However, those reports and statements were premature. Researchers have studied video of the event and concluded that the object was more likely a natural meteoroid about one meter wide traveling more than 20 km/s–much faster than orbital debris. Meteoroids hit Earth every day, and the Texas fireball was apparently one of them. Additionally, a spokeswoman for U.S. Strategic Command said the fireball spotted in the Texas skies Sunday was unrelated to the satellite collision. And as always, the Bad Astronomer was on top of it from the beginning, so check out his first post here (which includes several updates as the news broke), and a follow-up here. There were other fireballs, too….
There was one bolide event in central Kentucky on Friday, February 13. People heard loud booms, felt their houses shake, and saw a fireball streaking through the sky. This occurred just hours after another fireball at least 10 times brighter than a full Moon lit up the sky over Italy. Although it is tempting to attribute these events to debris from the Feb. 10th collision of the Iridium 33 and Kosmos 2251 satellites, the Kentucky and Italy fireballs also seem to be meteoroids, not manmade objects. Italian scientists are studying the ground track of their fireball, which was recorded by multiple cameras, and they will soon begin to hunt for meteorites.
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Air Force Major Regina Winchester said that Joint Space Operations Center at California’s Vandenberg Air Force Base has been monitoring the debris from the collision, and that could not have caused the dramatic sight. She also said the fireball was not related to the estimated 18,000 man-made objects that the center also monitors.
“There was no predicted re-entry,” Winchester said about the objects in Earth’s orbit.
She said it was likely a natural phenomenon such as a meteorite.
Image where PHA 2009 BD81 (left) was discovered. PHA 2008 EV5 is on the right. Image courtesy Robert Holmes.
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While observing a known asteroid on January 31, 2009, astronomer Robert Holmes from the Astronomical Research Institute near Charleston, Illinois found another high speed object moving nearby through the same field of view. The object has now been confirmed to be a previously undiscovered Potentially Hazardous Asteroid (PHA), with several possible Earth impact risks after 2042. This relatively small near-Earth asteroid, named 2009 BD81, will make its closest approach to Earth in 2009 on February 27, passing a comfortable 7 million kilometers away. In 2042, current projections have it passing within 5.5 Earth radii, (approximately 31,800 km or 19,800 miles) with an even closer approach in 2044 2046. Data from the NASA/JPL Risk web page show 2009 BD81 to be fairly small, with a diameter of 0.314 km (about 1000 ft.) Holmes, one of the world’s most prolific near Earth object (NEO) observers, said currently, the chance of this asteroid hitting Earth in 33 years or so is quite small; the odds are about 1 in 2 million, but follow-up observations are needed to provide precise calculations of the asteroid’s potential future orbital path.
In just the past couple of years, Holmes has found 250 asteroids, 6 supernovae, and one comet (C/2008 N1 (Holmes). However, he said he would trade all of them for this single important NEO discovery.
“I was doing a follow up observation of asteroid 2008 EV5,” Holmes told Universe Today, “and there was another object moving right next to it, so it was a pretty easy observation, actually. But you just have to be in the right place at the right time. If I had looked a few hours later, it would have moved away and I wouldn’t have seen it.” A map generated by Holmes showing the path of 2009 BD 81. Credit: Robert Holmes
A few hours later, teacher S. Kirby, from Ranger High School in Texas, who was taking part in a training class on how to use the data that Holmes collects for making observations used Holmes’ data measuring 2008 EV5 and also found the new object. Shortly after that, a student K. Dankov from the Bulgarian Academy of Science, Bulgaria who is part of ARO education and public outreach also noticed the new asteroid. Holmes listed both observers as co-discovers as well as another astronomer who made confirmation follow-up observations of what is now 2009 BD81.
Holmes has two telescopes, a 24-inch and 32-inch. Holmes' 24 inch telescope. Courtesy Robert Holmes
He works night-after-night to provide real-time images for the IASC program, uploading his images constantly during the night to an FTP site, so students and teachers can access the data and make their own analysis and observations from them. IASC is a network of observatories from 13 countries all around the world.
Holmes is proud of the work he does for education, and proud of the students and teachers who participate.
“They do a great job,” he said. “A lot of the teachers are doing this entirely on their own, taking it upon themselves to create a hands-on research class in their schools.” Holmes said recently, two students that have been involved with IASC in high school decided to enter the astrophysics program in college.
“I feel like we are making a difference in science and education,” he said, “and it is exciting to feel like you’re making a contribution, not just following up NEO’s but in people’s lives.”
Holmes also owns some of the faintest observations of anyone in the world.
“My telescopes won’t go to 24th magnitude,” Holmes said, “but I’ve got several 23rd magnitudes.”
“Getting faint observations is one of the things NASA wants to achieve, so that’s one of the things I worked diligently on,” Holmes continued. The statistics on the site bear that out clearly, which shows graphs and comparisons of various observatories.
To what does Holmes attribute his success? “It’s obviously not the huge number nights we have in Illinois to work,” Holmes said. The East-Central region of Illinois is known for its cloudy winter weather, when we often have our poorest astronomical “seeing.”
“However, I work every single night if it’s clear, even if it’s a full moon,” he said. “Most observatories typically shut down three days on either side of a full moon. But I keep working right on through. I found that with the telescopes I work with, I’ve been able to get to the 22nd magnitude even on a full moon night. Last year, I got about 187 nights of observing, which is the same number as the big observatories in the Southwest, when you take off the number of cloudy nights the 6 nights a month they don’t’ work around full moons. Sometimes you just have to work harder, and work when others aren’t to be able to catch up. That’s how we are able to do it, by working every single chance we have.”
He works alone at the observatory, running the pair of telescopes, and doing programming on the fly. “I refresh the confirmation page of new discoveries every hour so I can chase down any new discovery anyone has found,” he said. “If I just pre-programmed everything I wouldn’t have a fraction of the observations I have each year. I’d miss way too many because some of the objects are moving so fast.”
Holmes said some objects are moving 5,000 arc-seconds an hour on objects that are really close to Earth. “I’ve seen them go a full hour of right ascension per day and that’s pretty quick. They can go across the sky in four or five days,” said Holmes. “And there have been some that have gone from virtually 50 degrees north to 50 degrees south in one night. That’s was a screaming fast object, and you can’t preprogram for something like that, you actually have to be running the telescope manually.”
Overhead view of 2009 BD81's path. Courtesy Robert Holmes
2009 BD81 is listed as a “risk” object on the NASA/JPL website. This is the 1,015th PHA discovered to date.
“It ranks high as a NEO in general,” said Holmes, “although not in a super-high category as far as the Torino scale,” which categorizes the impact hazard of NEOs. “At this point it’s considered a virtual impactor and that is typically is as high of a rating that you get at this point.”
“Because it is a virtual impactor, it will remain on that webpage and ask for observations every single night until it is removed as a virtual impactor or becomes too faint to see,” said Holmes. “In the past year, we’ve removed 23 virtual hazardous objects, which means there have been enough observations that the orbit of that object is no longer considered a threat to our planet.” 2009 BD81. Courtesy Robert Holmes
Because of the small number of observations of of 2009 BD81, the current chance of it hitting Earth is small. “The odds are really small right now,” said Holmes, “however, the smaller your orbital arc is the wider the path is at that point is of potential impact. The longer the arc gets, the narrower the cone of opportunity of impact becomes, and once that cone is no longer pointing at earth in the future, it is removed as a possible impactor.”
Holmes said the excitement of this discovery has been exhilarating. “It’s been a lot of fun. The energy level gets pretty high when you have something like this show up,” he said. “It’s pretty rare, and this is the first time I’ve ever had a NEO discovery. I’ve had several hundred asteroids, and just since the beginning of the school year we have had about 40 asteroids that students and teachers have discovered in the program. So having this as a NEO is kind of a nice thing.”
Holmes said he’ll track 2009 BD81 as long as he possibly can.
Holmes previously was a commercial photographer who had over 4,500 photographs published worldwide in over 50 countries. “At first astronomy was just a hobby in the evening,” said Holmes. “I worked with schools, who used the data and made some discoveries of supernovae and asteroids. It came to a point where it was really hard to work all day as a photographer and work all night in astronomy getting data for students.” So, he chose astronomy over photography.
Holmes now works under a grant from NASA to use astrometry to follow-up new asteroid discoveries for the large sky surveys and help students look for new asteroid discoveries for educational outreach programs.
One would assume that as a former commercial photographer, Holmes would attempt to capture the beauty of the night sky in photographs, but that’s not the case.
“The only thing I’m really interesting in is the scientific and educational aspect of astronomy,” said Holmes. “I’ve never taken a single color, pretty picture of the sky in the half a million images I’ve taken of the sky. It’s always been for research or education.”
Holmes is considered a professional astronomer by the Minor Planet Center and International Astronomical Union because he is funded by NASA, so that means he wasn’t eligible to receive the Edgar Wilson award when he found a comet last year.
Because of Holmes outstanding astronomical work, he is also an adjunct faculty member in the physics department at Eastern Illinois University in Charleston, Illinois.
Artist’s impression of the asteroid (234) Barbara. Thanks to a unique method that uses ESO’s Very Large Telescope Interferometer, astronomers have been able to measure sizes of small asteroids in the main belt for the first time. Their observations also suggest that Barbara has a complex concave shape, best modelled as two bodies that may possibly be in contact. Credit: ESO/L. Calçada
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It’s one thing to know the position of an asteroid out in space. It’s quite another to know the size and shape of a particular asteroid that might be heading our way. A team of French and Italian astronomers have devised a new method for measuring the size and shape of asteroids that are too small or too far away for traditional techniques by using ESO’s Very Large Telescope Interferometer (VLTI). This will increase the number of asteroids that can be measured by a factor of several hundred, and provide the ability to resolve asteroids as small as about 15 km in diameter located in the main asteroid belt, 200 million kilometers away. This is equivalent to being able to measure the size of a tennis ball a distance of a thousand kilometers.
“Knowledge of the sizes and shapes of asteroids is crucial to understanding how, in the early days of our Solar System, dust and pebbles collected together to form larger bodies and how collisions and re-accumulation have since modified them,” says Marco Delbo from the Observatoire de la Côte d’Azur, France, who led the study.
Direct imaging with adaptive optics on the largest ground-based telescopes such as the Very Large Telescope (VLT) in Chile and space telescopes, or radar measurements are currently the best methods of asteroid measurement. However, direct imaging, even with adaptive optics, is generally limited to the one hundred largest asteroids of the main belt, while radar measurements are mostly constrained to observations of near-Earth asteroids that experience close encounters with our planet. Another double asteroid. Credit: ESO
Delbo and his colleagues have devised a new method using interferometry that will not only increase the number of objects that can be measured, but, more importantly, bring small asteroids that are physically very different from the well studied larger ones into reach.
The interferometric technique combines the light from two or more telescopes. Astronomers proved their method using ESO’s VLTI, combining the light of two of the VLT’s 8.2-metre Unit Telescopes.
“This is equivalent to having vision as sharp as that of a telescope with a diameter equal to the separation between the two VLT Unit Telescopes used, in this case, 47 meters,” says co-author Sebastiano Ligori, from INAF-Torino, Italy.
The researchers applied their technique to the main belt asteroid (234) Barbara, which was earlier found, by co-author Alberto Cellino, to have rather unusual properties. Although it is so far away, the VLTI observations also revealed that this object has a peculiar shape. The best fit model is composed of two bodies each the size of a major city – with diameters of 37 and 21 km – separated by at least 24 km. “The two parts appear to overlap,” says Delbo, “so the object could be shaped like a gigantic peanut or, it could be two separate bodies orbiting each other.”
If Barbara proves to be a double asteroid, this is even more significant: by combining the diameter measurements with the parameters of the orbits, astronomers can then compute the density of these objects. “Barbara is clearly a high priority target for further observations,” concludes Ligori.
The team will now begin a large observing campaign to study small asteroids.
2009 BD is approximately 400,000 miles from Earth (NASA)
[/caption]A 10 meter-wide asteroid named 2009 BD discovered earlier this month is making a slow pass of the Earth, coming within 400,000 miles (644,000 km) of our planet. The near-Earth asteroid (NEO) poses no threat to us, but it is an oddity worth studying. Astronomers believe the rock is a rare “co-orbital asteroid” which follows the orbit of the Earth, not receding more than 0.1 AU (15 million km) away. It is stalking us.
On looking at the NASA JPL Small-Body Database orbital plot, it is hard to distinguish between the orbital path of the Earth and 2009 BD, showing just how close the asteroid is shadowing the Earth on its journey around the Sun…
In 2006, NASA announced that Earth’s “second moon” was an asteroid called 2003 YN107 (with a diameter of about 20 meters) and it was about to leave the vicinity of Earth, leaving its “corkscrewing” orbit around our planet for seven years, only to return again in 60 years time. 2003 YN107 was of no threat (and wont be in the future), but it is interesting to study these bodies to understand how they interact with Earth. Having NEOs in stable orbits around the Earth could be of benefit to mankind in the future as missions can be planned, possibly sending mining missions to these rocky visitors so we can tap their resources.
The orbital path of 2009 BD (blue line) (JPL Small Body Database)
So far, little is known about the new 10 meter asteroid in our near-Earth neighbourhood, but it provides us with an exciting opportunity to track its laborious orbit to see whether it will eventually be ejected after making a close pass to the Earth’s gravitational field (as was the case with 2003 YN107 in 2006). From preliminary observations, 2009 BD is projected to shadow our planet for many months (possibly years) to come. Until November 2010 at least, the asteroid will hang around the Earth, within a distance of 0.1 AU.
It is worth emphasising that 2009 BD is of no threat to the Earth, its closest approach takes it 644,000 km from us. For comparison, the Moon’s apogee is 400,000 km, so 2009 BD is stalking us from afar, beyond lunar orbit.
As time goes on, astronomers will be able to track 2009 BD’s orbit with more precision (for updates, keep an eye on the JPL Small-Body Database), but for now, we have a micro-second moon following the Earth on its orbit around the Sun…
Pan-STARRS 1 prototype, part of the Panoramic Survey Telescope and Rapid Response System, Haleakala mountain, Maui. Photo / MIT Lincoln Laboratory
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A prototype telescope with an enhanced ability to find moving objects will soon be operational, and its mission will be to detect asteroids and comets that could someday pose a threat to Earth. The system is called Pan-STARRS (for Panoramic Survey Telescope and Rapid Response System) located on Haleakala mountain in Maui,Hawaii, and is the first of four telescopes that will be housed together in one dome. Pan-STARRS will feature the world’s largest and most advanced digital camera, providing more than a fivefold improvement in the ability to detect Near Earth Asteroids and comets. “This is a truly giant instrument,” said University of Hawaii astronomer John Tonry, who led the team developing the new 1.4-gigapixel camera. “We get an image that is 38,000 by 38,000 pixels in size, or about 200 times larger than you get in a high-end consumer digital camera.” The Pan-STARRS camera will cover an area of sky six times the width of the full moon and it can detect stars 10 million times fainter than those visible to the naked eye.
The Lincoln Laboratory at the Massachusetts Institute of Technology (MIT) developed charge-coupled device (CCD) technology is a key enabling technology for the telescope’s camera. In the mid-1990s, Lincoln Laboratory researchers developed the orthogonal-transfer charge-coupled device (OTCCD), a CCD that can shift its pixels to cancel the effects of random image motion. Many consumer digital cameras use a moving lens or chip mount to provide camera-motion compensation and thus reduce blur, but the OTCCD does this electronically at the pixel level and at much higher speeds.
The challenge presented by the Pan-STARRS camera is its exceptionally wide field of view. For wide fields of view, jitter in the stars begins to vary across the image, and an OTCCD with its single shift pattern for all the pixels begins to lose its effectiveness. The solution for Pan-STARRS, proposed by Tonry and developed in collaboration with Lincoln Laboratory, was to make an array of 60 small, separate OTCCDs on a single silicon chip. This architecture enabled independent shifts optimized for tracking the varied image motion across a wide scene.
“Not only was Lincoln the only place where the OTCCD had been demonstrated, but the added features that Pan-STARRS needed made the design much more complicated,” said Burke, who has been working on the Pan-STARRS project. “It is fair to say that Lincoln was, and is, uniquely equipped in chip design, wafer processing, packaging, and testing to deliver such technology.”
The primary mission of Pan-STARRS is to detect Earth-approaching asteroids and comets that could be dangerous to the planet. When the system becomes fully operational, the entire sky visible from Hawaii (about three-quarters of the total sky) will be photographed at least once a week, and all images will be entered into powerful computers at the Maui High Performance Computer Center. Scientists at the center will analyze the images for changes that could reveal a previously unknown asteroid. They will also combine data from several images to calculate the orbits of asteroids, looking for indications that an asteroid may be on a collision course with Earth.
Pan-STARRS will also be used to catalog 99 percent of stars in the northern hemisphere that have ever been observed by visible light, including stars from nearby galaxies. In addition, the Pan-STARRS survey of the whole sky will present astronomers with the opportunity to discover, and monitor, planets around other stars, as well as rare explosive objects in other galaxies.
Ever since our recent encounter with asteroid 2008 TC3 — the first asteroid that was correctly predicted to hit our planet — I’ve had impact craters on the brain. Earth has about 175 known impact craters, but surely our planet has endured more bashing than that in its history. All the other terrestrial planets and moons in our solar system are covered by impact craters. Just look at our Moon through a telescope or binoculars, or check out the recent images of Mercury sent back by the MESSENGER spacecraft, or pictures of Mars from the armada of spacecraft orbiting the Red Planet, and you’ll see that impact craters are the most common landforms in our solar system.
But since two-thirds of Earth is covered by water, any asteroid impacts occurring in the oceans are difficult to find. And even though Earth’s atmosphere protects us from smaller asteroids, just like in the case of 2008 TC3, which broke up high in the atmosphere, weathering, erosion and the tectonic cycling of Earth’s crust have erased much of the evidence of Earth’s early bombardment by asteroids and comets. Most of Earth’s impact craters have been discovered since the dawn of the space age, from satellite imaging. In fact, a geologist recently discovered an impact crater using Google Earth!
Here’s my list of Earth’s Ten Most Impressive Impact Craters, starting with #1. the largest and oldest known impact crater, Vredefort Crater, shown above, located in South Africa. It is approximately 250 kilometers in diameter and is thought to to be about two billion years old. The Vredefort Dome can be seen in this satellite image as a roughly circular pattern. What an impact that must have been!
Manicouagan Reservoir. Credit: NASA 2. Manicouagan Crater: fifth largest known impact crater. This crater is located in Quebec, Canada. It was created about 212 million years ago. Now, it is an ice-covered lake about 70 km across. This image, taken by space shuttle astronauts, shows an outer ring of rock. Close up, the rock reveals clear signs of having been melted and altered by a violent collision. The original rim of the crater, though now eroded away, is thought to have had a diameter of about 100 km.
Chicxulub Crater. 3. Chicxulub Crater, third largest and possible dinosaur killer. The third largest impact crater lies mostly underwater and buried underneath the Yucatán Peninsula in Mexico. At 170km (105 miles) in diameter, the impact is believed to have occurred roughly 65 million years ago when a comet or asteroid the size of a small city crashed, unleashing the equivalent to 100 teratons of TNT. Likely, it caused destructive tsunamis, earthquakes and volcanic eruptions around the world, and is widely believed to have led to the extinction of dinosaurs, because the impact probably created a global firestorm and/or a widespread greenhouse effect that caused long-term environmental changes.
Aorounga Crater. Credit: NASA 4. Aorounga Crater: possible triple crater. The main Aorounga Crater in Chad, Africa, visible in this radar image from space, shows a concentric ring structure that is about 17 kilometers wide. But, this crater might have been formed as the result of a multiple impact event. A second crater, similar in size to the main crater, appears as a circular trough in the center of the image. And a third structure, also about the same size, is seen as a dark, partial circular trough on the right side of the image. The proposed crater “chain” could have formed when a 1 km to 2 km (0.5 mile to 1 mile) diameter object broke apart before impact. Ouch! Clearwater craters. Credit: NASA 5. Clearwater Craters: two for the price of one. Twin, lake-filled impact craters in Quebec, Canada were probably formed simultaneously, about 290 million years ago, by two separate but probably related meteorite impacts. The larger crater, Clearwater Lake West has a diameter of 32 km, and Clearwater Lake East is 22 km wide.
Barringer Crater. 6. Barringer Crater: well preserved. While this crater isn’t all that big, what’s most impressive about Barringer Crater in Arizona (USA) is how well preserved it is. Measuring 1.2 km across and 175 m deep, Barringer Crater was formed about 50,000 years ago by the impact of an iron meteorite, probably about 50 m across and weighing several hundred thousand tons. Most of the meteorite was vaporized or melted, leaving only numerous, mostly small fragments with in the crater and scattered up to 7 km from the impact site. Only about 30 tons, including a 693-kg sample, are known to have been recovered. Wolfe Creek Crater 7. Wolfe Creek Crater, well preserved, too. Another relatively well-preserved meteorite crater is found in the desert plains of north-central Australia. Wolfe Creek crater is thought to be about 300,000 years old and is 880 meters across and and about 60 meters deep. It’s partially buried under the wind-blown sand of the region, and although the unusual landform was well-known to the locals, scientists didn’t find the crater until 1947. Deep Bay Crater. Credit: NASA 8. Deep Bay Crater: deep and cold. Deep Bay crater is located in Saskatchewan, Canada. The bay is a strikingly circular 13 km wide impact crater and is also very deep (220 m). It is part of an otherwise irregular and shallow lake. The age of the crater is estimated to be 99 million years old.
Kara-Kul Crater. Credit: NASA 9. Kara-Kul Crater: high altitude crater. This crater was formed about 10 million years ago, and is located in Tajikistan, near the Afghan border. In total, the crater is about 45 km in diameter and is partially filled with a 25 km-wide lake. This might be the “highest” impact crater, almost 6,000 m above sea-level in the Pamir Mountain Range. It was found only recently from satellite images.
Bosumtwi Crater. 10. Bosumtwi Crater: built of bedrock. The last crater on our tour of impressive impact craters is this located in Ghana, Africa. It is about 10.5 km in diameter and about 1.3 million years old. The crater is filled almost entirely by water, creating Lake Bosumtwi. The lakebed is made of crystalline bedrocks.
The long-lasting persistent train after the impact of 2008 TC3 over the Sudanese skies (NASA)
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A month after asteroid 2008 TC3 hit the Earth’s atmosphere, the first ground-based image of the event has surfaced on the Internet. Admittedly, it’s not the fireball everyone has been waiting to see, but it is visual evidence that something hit us above Sudan on October 7th. The image above was taken from a frame of video that was being recorded by Mr. Mohamed Elhassan Abdelatif Mahir in the dawn following the asteroid impact with the atmosphere. The smoky feature is the remnant of the fireball as the 3 meter-wide asteroid blasted through the upper atmosphere, eventually exploding. The long-lasting persistent train is seen hanging in the air, high altitude winds causing it to twist in the morning sunlight.
We may not have a dazzling fireball re-entry video of 2008 TC3, but this striking image provides the first ground-based evidence of the direct hit, and may help refine the search for any meteorites from the disintegrated asteroid…
Although details are sketchy, it would appear that a person on the ground observed the skies of Sudan shortly after 2008 TC3 exploded in the upper atmosphere. It is unclear whether the observer was part of a meteorite-hunting team, or a Sudanese resident videoing the scene, but it is very fortunate he captured this footage. Dr. Muawia H. Shaddad of the University of Karthoum communicated this single frame, and the picture is being showcased as the November 8th NASA Astronomy Picture of the Day.
It is currently the only ground-based evidence that something hit the Earth at the right time and right location as predicted by scientists using the Mount Lemmon telescope in Arizona as part of the NASA-funded Catalina Sky Survey for near-Earth objects. However, as Nancy reported on October 13th, indirect support for an atmospheric fireball came from a webcam on a beach in Egypt. Also, at 02:43 UTC on that Tuesday morning, an infrasound array in Kenya detected an explosion in the atmosphere (with an energy equivalent of 1.1–2.1 kT of TNT). These observations were backed up by the European weather satellite METEOSAT-8, capturing the fireball from orbit. The pilot of a KLM airliner also witnessed a bright flash, 750 miles from the impact location.
This was the first time that an asteroid has been discovered before it hit the Earth, thereby proving an early-warning system for future asteroid impacts is possible. Although there are 5-10 space rock collision events per year, this is the first time we knew something about it before it happened. This is an amazing achievement as 2008 TC3 was only 3 meters in diameter.
To aid the search for any 2008 TC3 debris, SpaceWeather.com is hoping this image of the aftermath of the October 7th impact will jog any potential witness memories of the African skies a month ago:
[/caption]Was there a third Martian moon orbiting the planet? Did Phobos and Deimos have a triplet sibling? According to the discovery of two elliptical impact craters, there might just have been another moon, but it ploughed into the Red Planet’s surface a long time ago. The moonlet would have been approximately 1.5 km wide (0.9 miles), and it will have succumbed to the Mars gravity, entering the atmosphere at a shallow angle. As it tumbled through the atmosphere it broke in two, hitting the surface and creating two elongated impact craters, near-perfectly aligned.
It is thought that the “third moon” of Mars dropped from orbit a billion years ago and the same will happen with Phobos in a few million years. However, there might be another explanation, with no third moonlet in sight…
Observations of the Martian surface, just north of Olympus Mons, show two oval-shaped craters (pictured top). Usually impact craters are approximately circular, so the elongated craters indicate the impactor(s) entered the atmosphere at a very shallow angle. This isn’t the only strange characteristic of these two craters. They lie 12.5 km (7.8 miles) apart and they are almost exactly aligned from east to west (they are off-alignment by only 3.48°). The larger crater is 10 km (6.2 miles) wide at its longest point, and the smaller crater is 3km (1.9 miles) wide.
There are two possible answers to this puzzle, but researchers are having a hard time in agreeing on which one. In a recent publication, John Chappelow and Rob Herrick of the University of Alaska, Fairbanks, have calculated that the impact craters were caused by a small moon that entered the atmosphere, broke into two (due to atmospheric drag) and then struck the surface at an oblique angle of 10° or less. The moonlet would have been 1.5 km (0.9 miles) in diameter. This sounds feasible, after all for both craters to be aligned, one would think they came from the same mass, right?
The lunar Messier craters (NASA)This moon-impact theory has a few drawbacks however. The first problem is that the impact craters are located at 40° latitude in Mars’ northern hemisphere. One would expect natural satellites to orbit around the equatorial plane if their orbits are stable (hovering around 0° latitude). “Any close natural satellite must, like Phobos, orbit in Mars’s equatorial plane,” said Jay Melosh, a crater expert at the University of Arizona in Tucson, who is highly sceptical of Chappelow and Herrick’s findings.
However, Herrick believes that the moonlet may not have established a stable orbit, above the equator. “We don’t know the details of the [moonlet’s] capture mechanism, so I don’t know that we can definitively say that the object must have moved to an equatorial orbit before spiralling in,” countered Herrick.
Artist impression of binary asteroid 90 Antiope (ESO)Melosh argues that the craters may have been caused by a binary asteroid (or “double asteroids”) entering the Martian atmosphere at a very shallow angle. After all, there is a confirmed example of a binary asteroid impact on the Moon (a.k.a. the Messier craters on the Moon, pictured above). Chappelow however disputed this claim saying, “In such a case, the craters should be oriented randomly.” After all, wouldn’t the binary asteroid have a randomly oriented orbital plane?
Apparently not. It appears that over hundreds of thousands of years of asteroid evolution, the effect of sunlight has a huge role to play in the dynamics of binary asteroid formation. A process known as the “Yarkovsky-O’Keefe-Radzievskii-Paddack Effect,” or the YORP Effect, causes the uneven heating of an asteroid. Carrying a tiny jolt of momentum, photons are emitted from the surface in jets, eventually causing the asteroid to spin. Eventually a piece of rock breaks loose, forming the binary asteroid. It would appear there is an observed trend for the majority of binary asteroids to orbit in the same plane as the rest of the Solar System.
So it seems possible that a binary asteroid could create the two elongated and aligned impact craters after all.
Regardless, whether a third moon or binary asteroid hit Mars, it will be of little comfort to Phobos. The moon (with a mean radius of 11 km) is slowly dropping in altitude due to tidal forces. In about 11 million years it will either crash into Mars or be ripped apart through gravitational shear. Either way, Phobos is a doomed moon.
Asteroid-2008-tc3. From Kite Power El Gouna web cam.
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One of the big news items last week was the prediction that an asteroid was on a collision course with Earth. Although it was a small space rock – estimates ranged from 1-5 meters (3-15 feet), scientists were excited because this was the first time an asteroid was discovered with an imminent known impact. Granted, we’d all probably feel a little safer if we knew about this asteroid, named 2008 TC3, days or months ahead of time instead of only 19 hours, but it’s a step in the right direction. Astronomers even predicted correctly the asteroid would come through the atmosphere over Africa. So with this prediction, many were hoping someone with a camera would be watching the skies of Sudan. But the flight path of the object was over a remote area and so far the only ground-based image that has surfaced is the one shown here, taken by a webcam from a beach in Egypt. (The words on the image indicate the objects on the beach — which were illuminated by the fairly distant explosion low on the horizon. try to find the tiny bright spot in the center of the image — that’s the asteroid.) But we do have satellites constantly monitoring Earth’s atmosphere and a few of them captured images and data about 2008 TC3. However, it’s not known if any parts of the meteoroid hit the ground.
The explosion was recorded directly by the cameras of a European weather satellite called METEOSAT-8. This was taken in infrared, and the temperature scale on the right is in Kelvin. Asteroid 2008 TC3 seen from space in infrared. Credit: EUMETSAT
Data from this satellite helped determine the asteroid entered Earth’s atmosphere at a velocity of 12.8 kilometers per second. “As it entered the Earth’s atmosphere, it compressed the air in front of it. The compression heated the air, which in turn heated the object to create a spectacular fireball, releasing huge amounts of energy as it disintegrated and exploded in the atmosphere, dozens of kilometers above ground,” the Eumetsat website explains. Meteostat also took a visible image:
Also, according JPL’s Near Earth Object Program, an undisclosed U.S. system has monitored the airburst and yielded a precise time (02:45:45 UTC) and explosive energy equivalent (0.9 to 1.0 kT of TNT). The NEO office also said, “Tthe follow-up astrometric observations from professional and sophisticated amateur astronomers alike were rather extraordinary, with 570 observations from 26 observatories being reported between the time of discovery by the Catalina Sky Survey to just before the object entered Earth’s shadow (57 minutes prior to impact).” These observations revealed a tumbling, rotating object. The CAST astronomical observatory created a “movie” of their observations of the asteroid before it entered into Earth’s shadow. CAST astronomical obervatory in Italy created this 2008tc3 animation.
Also, SpaceWeather.com reported the crew of an airplane saw a flash in the sky which may have been from this object. But beyond that, sadly, there’s not many images available related to this extraordinary event. If any surface, we’ll be sure to post them.
