Young asteroid tanning is big business in the Solar System (ESO)
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If you stay out in the Sun too long, you’ll eventually get a suntan (or sunburn); your skin will also get damaged and it will show signs of ageing faster. This might sound like a sunblock ad, but the same principal holds true for the small chunks of rock floating around in the Solar System. Yes, a young asteroid’s surface will age prematurely, but it’s not caused by the Sun’s ultraviolet rays, it’s caused by the solar wind…
Within a million years, an asteroid can turn from lunar grey to Martian red when left out in the solar wind. A million years is a tiny amount of time in relation to the Solar System’s lifetime. Why is this important? European Southern Observatory (ESO) researchers have realized that this finding will not only help astronomers relate an asteroid’s appearance with its history, but it can act as an indicator for after effects of impacts with other asteroids.
It turns out that the study of “space weathering” is fairly controversial, scientists have been mulling it over for a long time. Central to the problem is the fact that the appearance of the interior of meteorites found on Earth are remarkably different to the asteroids we see in space; asteroids are redder than their meteorite cousins. So what causes this redness?
“Asteroids seem to get a ‘sun tan’ very quickly,” says lead author Pierre Vernazza. “But not, as for people, from an overdose of the Sun’s ultraviolet radiation, but from the effects of its powerful wind.”
Although this is an interesting discovery, the speed at which the “tanning” occurs is astonishing. After an asteroid collision, fresh asteroid chunks are created with new surfaces. Within a million years these young asteroid surfaces will turn a dirty shade of red as the surface minerals are continuously battered by ionizing solar wind particles. “The charged, fast moving particles in the solar wind damage the asteroid’s surface at an amazing rate,” Vernazza added.
Naturally, a lot depends on the mineral composition of an asteroid’s surface, influencing how red its surface will become, but most of the tanning effect occurs in the first million years. Afterwards, the tanning continues, just at a slower rate.
Asteroid observations also reveal that the high proportion of “fresh surfaces” seen on near-Earth asteroid probably isn’t down to asteroid collisions. The frequency of collisions is far lower than the sun-tanning timescales, meaning that there shouldn’t be any “fresh surfaces” to be seen. It is far more likely that the upper layers of asteroids are renewed through planetary encounters, where the gravitational field of planets “shake off” the tanned dust.
It may not look like much, but that drawing could save a life someday — or 7 billion.
David French, a doctoral candidate in aerospace engineering at North Carolina State University is proposing a new tool for the anti-asteroid arsenal.
French said his PhD advisor Andre Mazzoleni, an associate professor of mechanical and aerospace engineering at the university, were not beholden to grant funds and “we just decided to go off on a direction that’s interesting and exciting.”
Mazzoleni has worked with tethers in other applications, and the two have now come up with a way to effectively divert asteroids and other threatening objects from impacting Earth by attaching a long tether and ballast to the incoming object.
By attaching the ballast, French explains, “you change the object’s center of mass, effectively changing the object’s orbit and allowing it to pass by the Earth, rather than impacting it.”
NASA’s Near Earth Object Program has identified more than 1,000 “potentially hazardous asteroids” and they are finding more all the time. “While none of these objects is currently projected to hit Earth in the near future, slight changes in the orbits of these bodies, which could be caused by the gravitational pull of other objects, push from the solar wind, or some other effect could cause an intersection,” French explains.
He said it’s hard to imagine the scale of both the problem and the potential solutions — but he points out that some asteroid impacts on Earth have been catastrophic.
“About 65 million years ago, a very large asteroid is thought to have hit the Earth in the southern Gulf of Mexico, wiping out the dinosaurs, and, in 1907, a very small airburst of a comet over Siberia flattened a forest over an area equal in size to New York City,” he said. “The scale of our solution is similarly hard to imagine.”
The idea is to use a tether somewhere in length between 1,000 kilometers (621 miles; roughly the distance from Raleigh to Miami) to 100,000 kilometers (62,137 miles; you could wrap this around the Earth two and a half times).
Other ideas that have emerged sound no less extreme, French notes. Those include painting the asteroids in order to alter how light may influence their orbit, a plan that would guide a second asteroid into the threatening one, and nuclear weapons.
“They probably all have their merits and drawbacks,” he said. “Nuclear weapons are already accessible; we’ve already made them. I can look at my own idea and say it’s long duration and very trackable.”
A tether effort could last in the ballpark of 20 to 50 years, he said, depending on the size and shape of the asteroid and its orbit, and the size of ballast.
French acknowledges there are “technical barriers that have to be surpassed.”
“First, you would have to mitigate the rotation of the asteroid,” he said, adding that the crescent-shaped piece connecting the poles on a globe might make a good conceptual model for a tether anchor, because it would allow for the asteroid’s rotation.
Another problem is the composition,” he added. “Some asteroids are just rubble piles.”
French said his idea was never to have all the kinks worked out on his model before presenting it; he just hoped to add another option to the asteroid-preparedness table.
“We’re opening up the concept, and we invite the broader scientific community to help us solve the issues,” he said.
Source: An NC State press release, via Eurekalert, and an interview with David French.
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Officials are now saying the bright fireball seen over Virginia in the US on Sunday was probably a natural meteor event and not part of a Russian rocket, a reversal from yesterday’s initial analysis. Space.com reported that an official from the U.S. Naval Observatory believed the loud boom and flash of light seen in the skies over Norfolk and Virginia Beach was likely the second stage of the Soyuz rocket that launched Expedition 19 to the International Space Station last Thursday. However, U.S. Strategic Command has since reported that the rocket re-entered Earth’s atmosphere near Taiwan, on the other side of the world, several hours after the reports of the fireball. So both its timing and entry location rule out the rocket as the explanation for the fireball. But the investigation is continuing to determine exactly what the object was.
The Joint Space Operations Center at Vandenberg Air Force Base in California also confirmed “the ‘bright light’ that was reported on the East Coast on Sunday, 29 March at 9:45 p.m. EST was not a result of any trackable manmade object on reentry,” according to Patricia Phillips at the Space News Examiner.
Space rocks the size of small cars plunge into Earth’s atmosphere several times a year, typically burning up before reaching the ground. “The atmosphere is very good at protecting us from falling rocks,” said Bill Cooke of NASA’s Marshall Space Flight Center. Ones that do reach the ground go unreported since they fall over uninhabited areas or in the ocean.
A few space rocks do occasionally make it to the surface though. In recent years, pieces of a bolide were found after a meteor event in western Canada, and fragments of a meteor that originated from an asteroid that blew up over the skies of Africa last October were also recovered in the Sudanese desert.
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Residents of Virginia in the US reported hearing booms and seeing flashes of light Sunday night, and originally, it was reported to be another possible meteor. But now officials from the U.S. Naval Observatory say it was likely the second stage of the Russian Soyuz rocket falling back to Earth. Parts of the rocket from last Thursday’s launch to the International Space Station would have fallen to Earth about that same time. “I’m pretty convinced that what these folks saw was the second stage of the Soyuz rocket that launched the crew up to the space station,” Space.com quoted Jeff Chester of the Naval Observatory in Washington, D.C.
Chester heard about the incident this morning and checked the listing for debris expected to enter the lower atmosphere during that time and found that second stage of the Soyuz rocket that launched last Thursday was re-enter Earth’s atmosphere during a window that started at 8 p.m. on March 29.
Chester ran a satellite tracking program that showed that the rocket debris should have come down exactly in the area where the fireball was spotted.
“This is just too much of a coincidence to be coincidence,” he said.
Chester said that U.S. Space Surveillance Network had not yet confirmed that this was the case, but said that he was “99 and four one-hundredths [percent] convinced that this is what it is.”
The descriptions of the boom and streak of light reported by local residents were “entirely consistent with re-entering space junk, especially something this big,” Chester said.
Space.com also reported that Delta airline pilot Bryce Debban reported seeing the streak of light on a flight from Boston to Raleigh-Durham when his plane was about 31,000 feet in the air.
The Soyuz rockets jettison their second stage after entering orbit in such a way that the second stage will slowly fall back to earth in a few days. But “you can control precisely where these things are going to come down,” Chester said.
It’s possible that some fragments of the rocket made it to the Earth’s surface, but they would likely have a couple of hundreds of miles east of Cape Hatteras, Chester said.
Map of the Nubian Desert of northern Sudan with the groundprojected approach path of the asteroid 2008 TC3 and the location of the recovered meteorites. Credit: P. Jenniskens, et. al
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Remember in October 2008 when Asteroid 2008 TC3 hit the scene – literally? This was the first asteroid that was predicted –and predicted correctly — to impact the Earth. Luckily, it wasn’t big enough to cause any problems, and its path was over a remote area in Africa. It streaked into the skies over northern Sudan in the early morning of October 7, 2008, and then exploded at a high 37 km above the Nubian Desert, before the atmosphere could slow it down. It was believed that the asteroid likely had completely disintegrated into dust. But meteor astronomer Peter Jenniskens thought there might be a chance to recover some of the remains of this truck-sized asteroid. And he was right.
Never before have meteorites been collected from such a high altitude explosion. Additionally, as it turns out, the assembled remnants are unlike anything in our meteorite collections, and may be an important clue in unraveling the early history of the solar system.
A meteor astronomer with the SETI Institute’s Carl Sagan Center, Jenniskens established a collaboration with Mauwia Shaddad of the Physics Department and Faculty of Sciences of the University of Khartoum. The two traveled to the Sudan. Various meteorites from 2008 TC3. Credit: P. Jenniskens, et. al. Click image for full description
Fifteen fresh-looking meteorites with a total mass of 563 g were recovered by 45 students and staff of the University of Khartoum during a field campaign on December 5-8, 2008. A second search on December 25-30 with 72 participants raised the total to 47 meteorites and 3.95 kg. Masses range from 1.5 g to 283 g, spread for 29km along the approach path in a manner expected for debris from 2008 TC3
“This was an extraordinary opportunity, for the first time, to bring into the lab actual pieces of an asteroid we had seen in space,” said Jenniskens, the lead author on a cover story article in the journal Nature that describes the recovery and analysis of 2008 TC3.
Click here for several images from NASA about the asteroid hit and the recovery of the meteorites.
Picked up by Arizona’s Catalina Sky Survey telescope on 6 October, 2008, Asteroid 2008 TC3 abruptly ended its 4.5 billion year solar-system odyssey only 20 hours after discovery, when it broke apart in the African skies. The incoming asteroid was tracked by several groups of astronomers, including a team at the La Palma Observatory in the Canary Islands that was able to measure sunlight reflected by the object.
Studying the reflected sunlight gives clues to the minerals at the surface of these objects. Astronomers group the asteroids into classes, and attempt to assign meteorite types to each class. But their ability to do this is often frustrated by layers of dust on the asteroid surfaces that scatter light in unpredictable ways.
Jenniskens teamed with planetary spectroscopist Janice Bishop of the SETI Institute to measure the reflection properties of the meteorite, and discovered that both the asteroid and its meteoritic remains reflected light in much the same way — similar to the known behavior of so-called F-class asteroids.
“F-class asteroids were long a mystery,” Bishop notes. “Astronomers have measured their unique spectral properties with telescopes, but prior to 2008 TC3 there was no corresponding meteorite class, no rocks we could look at in the lab.” Petrography of Almahata Sitta. Credit: Jenniskens, et. al. Click for full description
The good correspondence between telescopic and laboratory measurements for 2008 TC3 suggests that small asteroids don’t have the troublesome dust layers, and may therefore be more suitable objects for establishing the link between asteroid type and meteorite properties. That would allow us to characterize asteroids from afar.
Rocco Mancinelli, a microbial ecologist at the SETI Institute’s Carl Sagan Center, and a member of the research team, says that “2008 TC3 could serve as a Rosetta Stone, providing us with essential clues to the processes that built Earth and its planetary siblings.”
In the dim past, as the solar system was taking shape, small dust particles stuck together to form larger bodies, a process of accumulation that eventually produced the asteroids. Some of these bodies collided so violently that they melted throughout.
2008 TC3 turns out to be an intermediate case, having been only partially melted. The resulting material produced what’s called a polymict ureilite meteorite. The meteorites from 2008 TC3, now called “Almahata Sitta,” are anomalous ureilites: very dark, porous, and rich in highly cooked carbon. This new material may serve to rule out many theories about the origin of ureilites.
In addition, knowing the nature of F-class asteroids could conceivably pay off in protecting Earth from dangerous impactors. The explosion of 2008 TC3 at high altitude indicates that it was of highly fragile construction. Its estimated mass was about 80 tons, of which only some 5 kg has been recovered on the ground. If at some future time we discover an F-class asteroid that’s, say, several kilometers in size — one that could wipe out entire species — then we’ll know its composition and can devise appropriate strategies to ward it off.
As efforts such as the Pan-STARRS project uncover smaller near-Earth asteroids, Jenniskens expects more incidents similar to 2008 TC3. “I look forward to getting a call from the next person to spot one of these,” he says. “I would love to travel to the impact area in time to see the fireball in the sky, study its breakup and recover the pieces. If it’s big enough, we may well find other fragile materials not yet in our meteorite collections.”
Dusty debris around an old white dwarf star (NASA)
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What will happen to all the inner planets, dwarf planets, gas giants and asteroids in the Solar System when the Sun turns into a white dwarf? This question is currently being pondered by a NASA researcher who is building a model of how our Solar System might evolve as our Sun loses mass, violently turning into an electron-degenerate star. It turns out that Dr. John Debes work has some very interesting implications. As we use more precise techniques to observe existing white dwarf stars with the dusty remains of the rocky bodies that used to orbit them, the results of Debes’ model could be used as a comparison to see if any existing white dwarf stars resemble how our Sun might look in 4-5 billion years time…
A comparison of the Sun in its yellow dwarf phase and red giant phaseToday, our Sun is a healthy yellow dwarf star. If you want to be precise, it is a “G V star”. This yellow dwarf will happily burn 600 million tonnes of hydrogen per second in its core for 10 billion years, generating the light that is required to make our planet habitable. The Sun is approximately half-way through this hydrogen burning phase, so it’s OK, things aren’t going to change (for the Sun at least) for a long time yet.
But what happens then? What happens in 4-5 billion years when the supply of hydrogen runs out in the core? Although our Sun isn’t massive enough to entertain the thought of going out in a blaze of supernova glory, it will still go through an exciting, yet terrifying death. After evolving through the hydrogen-burning phase, the Sun will puff up into a huge red giant star as the hydrogen fuel becomes scarce, expanding 200 times the size it is now, probably swallowing the Earth. Helium, and then progressively heavier elements will be fused in and around the core. The Sun will never fuse carbon however, instead it will shed its outer layers forming a planetary nebula.
Once things calm down, a small sparkling jewel of a white dwarf star will remain. This tiny remnant will have a mass of around half that of our present Sun, but will be the size of the Earth. Needless to say, white dwarfs are very dense, intense gravitational pull countered not by fusion in the core (like all Main Sequence stars), but by electron degeneracy pressure.
Relative sizes of IK Pegasi A (left), IK Pegasi B (lower center; a white dwarf) and the Sun (NASA)When the Solar System reaches this phase in its evolution, what will it look like? What will become of the asteroids, gas giants, moons and rocky planets? I was very fortunate to chat with astrophysicist Dr John Debes, from NASA’s Goddard Space Flight Center, at January’s American Astronomical Society (AAS) conference in Long Beach (California) who is developing an n-body code simulating an evolving Solar System.
After the Sun has stopped hydrogen fusion in its core, it loses mass as it sheds its outer layers after the red giant phase and subsequent planetary nebula formation. It is estimated that the Sun will lose about 50% of its mass during this time, naturally affecting the Solar System as a whole. As the Sun loses mass, the outer planets (such as Jupiter) will drift outwards, increasing their orbital radii. In the simulation, Debes is very careful to ensure there is a gradual reduction in solar mass to ensure stability in the simulation.
What we are left with is an old Solar System, where little is left of the inner planets (it is likely that anything within the orbit of the Earth will have been swallowed by the Sun as it expanded through the red giant phase). Although the future white dwarf Solar System will seem very alien to present day, some things won’t change. Jupiter’s orbit might have receded with the drop in solar mass, it will remain a planetary heavyweight, causing disruption in asteroid orbits. Using known asteroid data, the motion of these chunks of rocks are allowed to evolve, and over millions of years, they may get thrown out of the Solar System, or more interestingly, pushed closer to the white dwarf. Once the whole system has settled down, resonances in the asteroid belt will become amplified; Kirkwood Gaps (caused by gravitational resonance with Jupiter) will widen, and according to Debes’ simulations, the edges of these gaps will become perturbed even more, making more asteroids available to be tidally disrupted and shredded to dust.
Artists concept of shredded asteroid around white dwarf (NASA/JPL-Caltech)The AAS conference was full of amazing research into white dwarf observations. The reason for this is that there are many white dwarf candidates out there with dusty metallic absorption lines. This means that there used to be rocky bodies orbiting these stars, but became pulverised (by tidal shear) for astronomers to analyse. These white dwarf systems can give us a clue as to what mechanisms could be supplying the white dwarfs with dusty material, even giving us a glimpse into the future of our Solar System.
“We have a physical picture for the link between planetary systems and dusty white dwarfs,” Debes said when describing his model in relation to the mysterious dusty white dwarf observations. “Dusty white dwarfs are truly a mystery! We think we know what might be going on, but we don’t have a smoking gun yet.”
However, Debes is getting close to finding a possible smoking gun, he’s basing his model on some of the key characteristics of these ancient dusty remnants to see what the Solar System could look like in billions of years time.
So, where does this dust come from? As the asteroid orbits are perturbed by Jupiter, they may get close enough to be tidally disrupted. Get too close and they will get shredded by the gravitational shear created by the steep tidal radius of the compact white dwarf. The asteroid dust then settles into the white dwarf. The presence of this dust has a very obvious signature in the absorption lines of spectroscopic data, allowing researchers to infer an accretion rate for metal-rich white dwarfs. In Debes’ model, he has set the upper limit to 1016 g/year and a lower limit to 1013 g/year, consistent with observed estimates.
Spectra of G29-38. Could this resemble the spectra of the Sun after turning into a white dwarf? (NASA/Spitzer)In his evolved Solar System model, Jupiter’s gravity controls this accretion rate, pushing asteroids toward the white dwarf and, by using a powerful supercomputer to track the perturbations and eventual shredding of known asteroids, there may be an opportunity to arrive at a profound conclusion. Debes is able to use his model to compare observations of known dusty white dwarfs with the simulated outcome of the Solar System. With reference to previous studies (in particularly Koester & Wilken, 2006 in the journal Astronomy & Astrophysics), Debes has found some similar white dwarf “Suns”.
“For G29-38, the canonical dusty white dwarf, they [Koester & Wilken] estimate a total mass of 0.55 solar masses–about what people believe the mass that our own sun will have remaining when it becomes a white dwarf,” Debes added. “But mass estimates are a bit uncertain–I’ve seen estimates ranging from 0.55-0.7 solar masses for this particular white dwarf.”
The Sun's future? The white dwarf G29-38 (NASA)“Another good candidate is a DAZ [a metal-rich white dwarf] called WD 1257+278, which does not show dust but is spot on with the mass expected for the Sun–0.54 MSun,” said Debes. “Its accretion rate is also consistent with my model predictions so far assuming an asteroid belt mass and characteristic perturbation timescale that I found in my simulations.”
Debes is continuing to make his model more and more sophisticated, but already the results are promising. Most exciting is that we may already be observing white dwarfs, like G29-38 or WD 1257+278, giving us a tantalizing glimpse of what our Solar System will look like when the Sun becomes a white dwarf star, ripping apart any remaining asteroids and planets as they stray too close to the Sun’s tidal shear. However, it also raises the question: if white dwarfs like G29-38 are being fed by the remains of tidally-blended asteroids, are there massive planets shepherding asteroids in these white dwarf systems too?
2009 FH fly past, only 85,000 km away from Earth (NASA)
[/caption]Another asteroid is set to make a close approach of 79,000 km according to NASA, a distance twice that of geosynchronous orbit around the Earth. Although the 15-20 metre-wide rock is not expected to cause any problems to Earth or satellites, some observers may be lucky to spot the faint light from 2009 FH as it passes.
Interestingly, this new object comes only two weeks after a larger (50 metre wide) asteroid was spotted passing the Earth at a similar distance. So it begs the question, why are we seeing so many asteroids lately?
“This asteroid flyby will be a good viewing opportunity for both professional and amateur astronomers,” said Don Yeomans from the Near-Earth Object Office at NASA’s Jet Propulsion Laboratory in Pasadena, California. “The asteroid poses no risk of impact to Earth now or for the foreseeable future.”
NASA is always very quick to point out these objects are harmless, passing the Earth at a very safe distance, often beyond the Moon’s orbit. However, 2009 FH will pass at a similar distance to the 50 metre-wide 2009 DD45 on March 2nd.
The orbit of 2009 FH (NASA JPL Small-Body Database Browser)In this case, 2009 FH will pass through the constellation of Gemini, as bright as a 14th magnitude star. Unfortunately there appears to be some fuzziness as to the time of observing opportunity. SpaceWeather.com reports that the best time to observe the asteroid has already passed (after sunset on March 17th, over North America), however, the NASA JPL news release states that close approach occurs at 5:17 am PST Wednesday morning. There is little more information available. However, check the 2009 FH ephemerides for more information.
This discovery was made by NASA’s Near Earth Object Observation Program, known as Spaceguard, to detect and track potentially hazardous asteroids that stray close to the Earth. It appears the Spaceguard team are getting better and better at spotting these chunks of rock. Although it might seem there are a lot more asteroids than before, this isn’t the case, we’re just getting better at finding them.
This image was taken near the point of closest approach to Mars on Feb. 17, 2009, during Dawn's gravity assist flyby. Image credit: NASA/JPL/MPS/DLR/IDA, and the Dawn Flight Team
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Recently, the Dawn spacecraft – on its circuitous route to the asteroid belt — used the gravity of Mars to provide a little ‘kick’ to the spacecraft’s velocity. Universe Today finally had the chance to catch up with the team from the Dawn mission following this maneuver to find out how things went, and how the spacecraft is doing following the gravity assist operations. “The gravity assist accomplished exactly what we needed to get on course for Vesta,” Dawn Chief Engineer Marc Rayman told UT. “In addition to the gravity assist, we decided to undertake some bonus instrument calibrations, taking advantage of flying by such a well-studied planet. In doing so, we obtained some performance data on some of our instruments.” The image seen here of Mars’ surface is one of the results of those calibrations.
Dawn will be visiting two different asteroids, Vesta and Ceres. Because of its distinctive ion engine, the spacecraft will be able to enter orbit around Vesta in August of 2011, remain there until May of 2012, then leave orbit and head to Ceres, arriving in February of 2015.
The thrusters work by using an electrical charge to accelerate ions from xenon fuel to a speed 10 times that of chemical engines. But what does this mean for a gravity assist – is there any difference between an ion engine versus and a chemical thruster in a gravity assist?
“In most ways, there is no difference,” said Rayman. “We used the ion thruster to get on course for the gravity assist, but the spacecraft coasted for most of the 4.5 months before it reached Mars. When we had to refine the trajectory, we used the ion thruster because it is so much more efficient than conventional propulsion. Moreover, because the ion propulsion affords so much flexibility in the mission, we did not have to hit as small a ‘window’ at Mars.” Dawn's trajectory. Credit: JPL
Generally, a gravity assist is used to increase a spacecraft’s velocity and propel it outward in the solar system, much farther away from the Sun than its launch vehicle would have been capable of doing.
Dawn got as close as 549 kilometers (341 miles) to the Red Planet during the Tuesday, Feb. 17, flyby. JPL said that if Dawn had to perform these orbital adjustments on its own, with no Mars gravitational deflection, the spacecraft would have had to fire up its engines and change velocity by more than 9,330 kilometers per hour (5,800 miles per hour).
At maximum thrust, each engine produces a total of 91 millinewtons — about the amount of force involved in holding a single piece of notebook paper in your hand. You would not want to use ion propulsion to get on a freeway: At maximum throttle, it would take Dawn’s system four days to accelerate from 0 to 60 miles per hour.
Using the gravity of Mars was an important part of the Dawn mission that makes going to the asteroid belt possible.
A sequence of four images reveal the motion of asteroid 2009 DD45 (at center) over 36 minutes during its discovery on February 27th. Credit: Robert McNaught / ANU / UA
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As I’m writing this (13:40 UT) a newly-discovered asteroid, 2009 DD45, is flying past Earth at only 74,800 km (46,478.5 miles or 0.000482 AU) away. That’s only about twice the height of a typical geostationary communications satellite, and well inside the moon’s orbit. According to Spaceweather.com, the 30- to 40-meter wide space rock is similar in size to the Tunguska impactor of 1908, but this time there is no danger of a collision. At closest approach on March 2nd, (which just occurred) 2009 DD45 will speed through the constellation Virgo shining as brightly as an 11th magnitude star. So if you’re in the Pacific region like Hawaii or Tahiti, go out and take a look! But this rock is moving fairly fast, and by tonight, it will only be 13th magnitude, and fading fast. UPDATE: Below see video of 2009 DD45 as seen from Australia:
(thanks to Aaron Slack for the heads up on the video)
The asteroid was only discovered three days ago by the prolific asteroid hunter Robert McNaught at Siding Spring Observatory in Australia, when the space rock was already within 2,414,016 km (1½ million miles) of Earth and closing fast. If you want to try and track it, here’s the ephemeris information from the Minor Planet Center.
Artist's depiction of the asteroid belt between Mars and Jupiter. Credit: David Minton and Renu Malhotra
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When Mars and Jupiter migrated to their present orbits around 4 billion years ago, they left scars in the asteroids belt that are still visible today.
The evidence is unveiled in a new paper in this week’s issue of the journal Nature, by planetary scientists David Minton and Renu Malhotra from the University of Arizona in Tucson.
The asteroid belt has long been known to harbor gaps, called Kirkwood gaps, in distinct locations. Some of these gaps correspond to unstable zones, where the modern-day gravitational influence of Jupiter and Saturn eject asteroids. But for the first time, Minton and Malhotra have noticed that some clearings don’t fit the bill.
“What we found was that many regions are depleted in asteroids relative to other regions, not just in the previously known Kirkwood gaps that are explained by the current planetary orbits,” Minton wrote in an email. In an editorial accompanying the paper, author Kevin Walsh added, “Qualitatively, it looks as if a snow plough were driven through the main asteroid belt, kicking out asteroids along the way and slowing to a stop at the inner edge of the belt.”
Walsh hails from the Observatoire de la Côte d’Azur in France. In his News and Views piece, he explains that the known Kirkwood gaps, discovered by Daniel Kirkwood in 1867, “correspond to the location of orbital resonances with Jupiter — that is, of orbits whose periods are integer ratios of Jupiter’s orbital period.” For example, if an asteroid orbited the Sun three times for every time Jupiter did, it would be in a 3:1 orbital resonance with the planet, he wrote. Objects in resonance with a giant planet have inherently unstable orbits, and are likely to be ejected from the solar system. When planets migrated, astronomers believe objects in resonance with them also shifted, affecting different parts of the asteroid belt at different times.
“Thus, if nothing has completely reshaped the asteroid belt since the planets settled into their current orbits, signatures of past planetary orbital migration may still remain,” Walsh wrote. And that’s exactly what Minton and Malhotra sought.
The asteroid belt easily gave up its secrets, showing the lingering evidence of planetary billiards on the inner edge of the asteroid belt and at the outer edge of each Kirkwood gap. The new finding, based on computer models, lends additional support to the theory that the giant planets — Jupiter, Saturn, Uranus and Neptune — formed twice as close to the sun as they are now and in a tighter configuration, and moved slowly outward.
“The orbit of Pluto and other Kuiper belt objects that are trapped in [orbits that resonate] with Neptune can be explained by the outward migration of Neptune,” Minton and Malhotra write in the new study. “The exchange of angular momentum between planetesimals and the four giant planets caused the orbital migration of the giant planets until the outer planetesimal disk was depleted.” Planetesimals are rocky and icy objects left over from planet formation.
“As Jupiter and Saturn migrated,” the authors continue, they wreaked havoc on the young asteroid belt, “exciting asteroids into terrestrial planet-crossing orbits, thereby greatly depleting the asteroid belt population and perhaps also causing a late heavy bombardment in the inner Solar System.”
The late heavy bombardment is proposed to have occurred about 3.9 billion years ago, or 600 million years after the birth of the Solar System, and it’s believed to account for many of the Moon’s oldest craters. Walsh said a reasonable next step, to corroborate the theory about the newly described clearings in the asteroid belt, is to link them chronologically with the bombardment.
LEAD PHOTO CAPTION: Artist’s depiction of the asteroid belt between Mars and Jupiter. Credit: David Minton and Renu Malhotra
