Category: Asteroids

Image credit: NASA

Researchers have built a computer simulation that better predicts how large asteroids will interact with the Earth’s atmosphere. They found that more asteroids blow up in the atmosphere than previously thought, reducing the risk of them hitting populated areas or causing tidal waves. Their model says that an asteroid has to be 200 metres in diameter or above before it can get through the atmosphere, and these only hit the Earth once every 170,000 years.

Researchers from Imperial College London and the Russian Academy of Sciences have built a computer simulation that predicts whether asteroids with a diameter up to one kilometre (km) will explode in the atmosphere or hit the surface.

The results indicate that asteroids with a diameter greater than 200 metres (the length of two football pitches) will hit the surface approximately once every 160,000 years – way down on previous estimates of impacts every 2,500 years.

The findings also predict that many more asteroids blow up in the atmosphere than previous estimates, which means the hazard posed by impact-generated tidal waves or tsunamis is lower than previous predictions. The researchers suggest that proposals to extend monitoring of Near Earth Objects (NEO) to include much smaller objects should be reviewed.

Dr Phil Bland of Imperial’s Department of Earth Science and Engineering and a Royal Society University Research Fellow, said:

“There is overwhelming evidence that impacts from space have caused catastrophes for life on Earth in the past, and will do so again.

“On the Moon it’s easier to track the number, frequency and size of collisions because there is no atmosphere, so everything hits the surface. On Earth the atmosphere acts like a screen and geological activity erodes many craters too.

“Massive impacts of the type thought to have wiped out the dinosaurs leave an indelible print on the Earth but we have not been able to accurately document the effect of smaller impacts. Now, we have a handle on the size of ‘rock’ we really need to worry about and how well the Earth’s atmosphere protects us.”

When small asteroids hit the atmosphere the two forces collide like two objects smashing together, which often breaks the asteroid into fragments. Until now, scientists have relied on the ‘pancake’ model of asteroid impact to calculate whether the asteroid will explode in the atmosphere. This treats the cascade of fragments as a single continuous liquid that spreads out over a larger area – to form a ‘pancake’. But a new model known as the ‘separate fragment’ (SF) model, which was developed by co-author of the study, Dr Natalya Artemieva of the Russian Academy of Science, has challenged this approach.

“While the pancake model can accurately predict the height from the Earth’s surface at which the asteroid will break up, it doesn’t give an accurate picture of how the asteroid will impact,” explains Dr Bland. “The SF model tracks the individual forces acting on each fragment as it descends through the atmosphere.”

To create a more accurate model of how asteroids interact with the atmosphere the researchers ran more than 1,000 simulations using both models. Objects made of either iron or stone, known as ‘impactors’, were used to reflect the composition of asteroids and experiments were run with varying diameters up to 1 km.

The researchers found the number of impacts for iron impactors were comparable using both models. For stone the pancake model significantly overestimated the survivability rate across the range used.

The SF simulations also allowed the researchers to define the different styles of fragmentation and impact rates for iron and stone, which correspond closely with crater records and meteorite data.

“Our data show that over most of the size range we investigated stony asteroids need to be 1,000 times bigger than the iron ones to make a similar sized crater. Much larger objects are disrupted in the atmosphere than previously thought.

“But we are not out of the woods yet,” added Dr Bland “asteroids that fragment in the atmosphere still pose a significant threat to human life.”

Dr Phil Bland is a member of the Meteorite and Impact Group that includes scientists from Imperial College London and the Natural History Museum.

Original Source: Imperial College News Release

Image credit: NASA

A team of researchers from Louisiana State University have uncovered a connection between a meteor strike and a mass extinction that happened 380 million years ago called the middle Devonian event. It happened at a time when small plants, wingless insects and spiders inhabited the land, and everything else lived in the sea – 40% of all life disappeared from the fossil records. They found evidence of the strike by measuring the magnetic signature of layers of rock. When a large asteroid hits the Earth, it distributes a layer of dust around the entire planet – if a strata of rock has the same magnetic signature in different parts of planet, it’s evidence of a strike.

It’s the stuff of science fiction movies. Bruce Willis, by a mighty effort, saving the world from extinction by a huge meteor.

But Bruce Willis won’t do it, and in our current state of readiness, neither will anyone else. That is why LSU geophysicist Brooks Ellwood is plumbing the geologic record, trying to correlate known mass extinctions to meteor strikes.

“When we think about the human race and life in general, what do we worry about? We worry about nuclear holocaust and major glaciation. Then we worry about the giant chunks of rock that fly past Earth all the time,” Ellwood said.

“We can’t see them till they’re here, we can’t stop one, so the question is, how often do they hit the Earth and cause major mass extinctions? Are extinctions often caused by impacts? If so, we want to be sure we are prepared.”

Ellwood and four other researchers have just published an article in the journal Science in which they tie an early mass extinction to a meteor strike. This extinction happened 380 million years ago in what is called the middle Devonian. It was a time when only small plants, wingless insects and spiders inhabited the land and everything else lived in the sea. About 40 percent of all species disappeared from the fossil record at this time.

The extinction has been known to geologists for a long time but this is the first time it has been tied to a meteor strike. This is also the oldest known impact that has been tied to a mass extinction.

Ellwood is quick to point out that because the extinction and the meteor strike happened at the same time does not prove the impact caused the extinction — but it certainly suggests it.

One of the great difficulties in determining whether an extinction happened on a global scale, or was a local event caused by a volcano or some other terrestrial force, is identifying the same strata of rock at different locations on the globe. Finding a layer of earth in Colorado, for example, and finding that same layer in Australia is no simple task.

“The same layer of earth is exposed to different conditions in different parts of the world,” Ellwood said. “Weathering, upheavals, volcanos, earthquakes and flooding all confuse the geologic record, making it incomplete and open to interpretation.”

The layers can also be extremely thin, he said, showing a picture of the location of his latest research. The layer he was looking at — near the top of a barren plateau in the Anti Atlas desert near Rissani in Morocco — was about the thickness of a felt-tipped marker and only distinguishable from the soil around it by its reddish color.

What is unique about Ellwood’s work, however, is the means he uses to identify the different layers in the geologic record: induced magnetism.

“Everything is magnetic,” he said. “If I put your finger in a magnetic coil and turn it on, your finger will be magnetized.” Ellwood uses this phenomenon to take “magnetic signatures” of geologic samples. The magnetic signature of a layer of earth will be the same anywhere in the world, making it relatively easy to identify strata, if they can be found. These signatures also make it easy to identify meteor strikes. “The magnetic pattern associated with an impact layer is often distinctive, making it easier to find in a thick sequence of strata,” he said.

Working with LSU graduate students Steve Benoist and Chris Wheeler; structural geologist Ahmed El Hassani of the University of Rabat, Morocco; and Devonian biostratigrapher Rex Crick of the University of Texas at Arlington, Ellwood was able to find high concentrations of shocked quartz, microscopic spherules and microcrysts in this layer, sure signs of a meteor impact. Benoist is a paleontologist and Wheeler is an isotope geochemist; both have since moved on.

The past 550 million years are divided up by geologists into about 90 “stages.” Each stage is distinguished from another by a change in the fossil record. To date, only four of these stages show strong evidence of a meteor strike, Ellwood’s discovery being the latest, as well as the oldest. The most recent, best known extinction is the K-T boundary at which the dinosaurs died out, about 65 million years ago. There have been five major mass extinctions and many smaller ones since then.

“We know that meteors have struck the Earth hundreds of times,” Ellwood said. “If I had to guess, I would say that once every 5 million years a meteor big enough to cause a mass extinction hits the Earth.

“We could protect ourselves if we wanted. We went to the moon, we can figure out how to destroy or deflect a meteor. All it takes is the political will — and an awareness of the threat.”

The work of Ellwood and his team, published in the prestigious journal Science, is a step in that direction.

Original Source: LSU News Release

A Japanese M-5 rocket lifted off on Friday carrying a spacecraft which will be the first to ever collect samples from the surface of an asteroid. Called Muses-C, the spacecraft will take only two years to reach asteroid 1998 SF 36 – one of the Earth?s closest space neighbours ? and then return to Earth by 2007. A grapefruit-sized marker imprinted with nearly 900,000 names will also be dropped onto the asteroid?s surface.

Image credit: NASA

Asteroid 2002 AA29 happens to share almost the same orbit as the Earth as it goes around the Sun, getting closer and further as it interacts with our planet’s gravity. On January 8, 2003, the asteroid will make its closest approach for almost a century, getting only 5.9 million kilometers away from us. There is no possibility that it can ever hit our planet, though, as interference from the Earth’s gravity keeps it at bay – causing it to trace out a strange horseshoe shape as it goes around the Sun.

The first asteroid discovered to orbit the Sun in nearly the same path as Earth will make its closest approach to our planet this month before scurrying away for 95 years.

The space rock, measuring about 60 meters (approximately 200 feet) across, is like a mouse teasing a cat. According to an international team of astronomers, including a researcher from NASA’s Jet Propulsion Laboratory in Pasadena, Calif., the asteroid approaches the Earth, first on one side and then on the other. The team’s report appeared in the October 2002 issue of the journal Meteoritics & Planetary Science.

The asteroid, named 2002 AA29, traces an unusual horseshoe pattern relative to Earth. The asteroid alternately leads and follows Earth around the Sun without ever passing it. “In some ways, the Earth and this asteroid are like two racecars on a circular track,” said JPL’s Dr. Paul Chodas, who discovered the object’s unusual motion. “Right now the asteroid is on a slightly slower track just outside Earth’s, and our planet is catching up.”

On January 8, 2003, the tiny body will come within approximately 5.9 million kilometers (3.7 million miles) of Earth, its closest approach for almost a century. “Unlike racecars, the two bodies will not pass when they approach each other,” Chodas said. “Instead, the combined gravitational effects of the Earth and Sun will nudge the asteroid onto a slightly faster track just inside Earth’s, and it will begin to pull ahead.”

In 95 years, the asteroid will have advanced all the way around to where it is catching up to Earth from behind. A similar interaction with gravity from both Earth and the Sun will then push the asteroid back onto a slower outside track, and the pattern will repeat. To an observer moving with the Earth, the asteroid appears to trace out a horseshoe pattern.

“There’s no possibility that this asteroid could hit Earth, because Earth’s gravity rebuffs its periodic advances and keeps it at bay,” said Dr. Don Yeomans, JPL manager of NASA’s Near Earth Objects Program Office. “The asteroid and Earth take turns sneaking up on each other, but they never get too close.”

The team’s calculations show that in about 600 years, the asteroid may begin looping around Earth like a tiny, distant quasi-moon. “The asteroid will appear to orbit the Earth at that time, but in fact it will be too far away to be considered a true satellite of our planet,” Chodas said. “Our calculations indicate the space rock will circle the Earth as a quasi-satellite for about 40 years before resuming its horseshoe orbital pattern.”

Other members of the team investigating this object include Dr. Martin Connors, Athabasca University, Canada; Dr. Seppo Mikkola, University of Turku, Finland; Dr. Paul Wiegert, Queen’s University, Canada; Dr. Christian Veillet, Canada-France-Hawaii Telescope, Hawaii; and Dr. Kim A. Innanen, York University, Canada.

JPL is a division of the California Institute of Technology in Pasadena, Calif.

Original Source: NASA/JPL News Release

Astronomers have discovered an asteroid in a companion orbit to the Earth. Named 2002 AA29, this 100 metre asteroid was discovered by the linear automated sky survey project in January. Although objects have been found to share the orbits of other planets, none have ever been found for the Earth. You don’t have to worry about it hitting the planet, though, as calculations of its orbit have determined that 2002 AA29 will never come closer than 4.5 million kilometres (12 times the distance from the Earth to the moon).

At a NASA-sponsored conference, a group of experts have estimated that the Earth is struck once every 1,000 years by an asteroid capable of releasing 10-megatons of energy – not a planet killer, but definitely enough to cause a terrible loss of life. NASA and the astronomical community has been systematically searching for all Near Earth Objects larger than 1 km across, and capable of crossing the Earth’s orbit. So far they’ve found 600 out of an estimated 1,000.

Amateur astronomers were given a rare treat on Sunday when asteroid 2002 NY40 passed within 530,000 kilometres of the Earth (a little further than the distance from Earth to the Moon). Over the course of a few hours, the 800 metre space rock passed through several constellations in the night sky, visible in binoculars or a small telescope. 2002 NY40 is of minor concern as astronomers believe there is a 1/500,000 chance it could strike the Earth in 2022 – the flyby will give them an opportunity to better calculate its future path.

Image credit: NASA

Researchers from the University of Queensland have discovered evidence they believe proves that the Earth was bombarded by meteorites 4 billion years ago. Although these impacts are clearly visible on the Moon, movement the Earth’s tectonic plates have obscured the evidence here. The team analyzed 3.8 billion year old rocks from Greenland, and found anomalies in the element tungsten; exactly the same as those found in meteorites.

University of Queensland researchers have for the first time discovered terrestrial evidence of a meteorite bombardment nearly 4 billion years ago.

It is widely accepted that the moon was heavily bombarded at this time, creating huge craters and basins. But although the effect of these impacts is still clearly visible on the moon today, movement of Earth?s dynamic plates over geological time have reshaped the terrestrial surface dramatically, leaving little evidence of these catastrophic events.

In a paper published in the international journal Nature, UQ researchers report evidence of the oldest impact events so far discovered on Earth.

The research team of Dr Ronny Schoenberg, Dr Balz Kamber and Professor Ken Collerson of UQ?s new Advanced Centre for Isotope Research Excellence (ACQUIRE) made the discovery by analysing 3.8 billion year old rocks from West Greenland collected by Oxford University collaborator Professor Stephen Moorbath and from Northern Labrador in Canada collected by Professor Collerson.

The researchers found these very old metamorphosed sedimentary rocks ? derived from the Earth?s early crust ? contain anomalies in the isotope composition of the element tungsten.

?Such anomalies are usually found in meteorites. To our knowledge, this is the first time these anomalies have been shown to exist in terrestrial samples? Professor Collerson said.

?There is no plausible mechanism by which tungsten isotope anomalies could have been preserved in the Earth?s dynamic crust-mantle environment. Therefore, we conclude these rocks must contain a compound derived from meteorites.?

?We have in effect found a chemical fingerprint in the earth?s oldest terrestrial rocks of a heavy meteorite bombardment 3.8 to 4 billion years ago,? he said.

?This finding has implications for the origin of life on earth as these giant impacts would have annihilated any possible existing life forms but also delivered complex molecules from carbonaceous chondrites – a type of meteorite – to the earth?s surface,? Dr. Kamber added.

?Further research on this unique collection of rocks will yield insight into the evolution of life on Earth provided provision of adequate research funding,? Professor Collerson said.

Original Source: UQ News Release

Image credit: NASA

Astronomers announced earlier last week that they had found an asteroid that could strike the Earth in 2019. More astronomers brought their equipment to bear on Asteroid NT7, however, and were able to provide enough trajectory data that NASA has eliminated the possibility of a collision in 2019; although, 2060 could still be a possible impact year (astronomers will probably rule that out eventually too). The asteroid is 2km across, so if it does ever strike the planet, it could cause significant damage.

Asteroid 2002 NT7 currently heads the list on our IMPACT RISKS Page because of a low-probability Earth impact prediction for February 1, 2019. While this prediction is of scientific interest, the probability of impact is not large enough to warrant public concern.

Discovered on July 9, 2002 by the LINEAR team, asteroid 2002 nt7 is in an orbit, which is highly inclined with respect to the Earth’s orbit about the sun and in fact nearly intersects the orbit of the Earth. While the orbits of Earth and 2002NT7 are close to one another at one point in their respective orbits, that does not mean that the asteroid and Earth themselves will get close to one another. Just after an asteroid like 2003 qq47 is discovered, the limited number of observations available do not allow its trajectory to be tightly constrained and the object’s very uncertain future motion often allows a very low probability of an Earth impact at some future date. Just such a low probability impact has been identified for February 1, 2019 and a few subsequent dates. As additional observations of the asteroid are made in the coming months, and perhaps pre-discovery archival observations of this object are identified, the asteroid’s orbit will become more tightly constrained and the future motion of the asteroid will become better defined. By far the most likely scenario is that, with additional data, the possibility of an Earth impact will be eliminated.

This is an example of the type of scenario that we can expect as some types of near-Earth objects are discovered. For some objects, their uncertain initial orbits cannot be used to immediately rule out future very low-probability Earth impacts, but when additional observations are used to refine the initial orbit, these low-probability Earth impact possibilities will go away. Other recently discovered near-Earth asteroids will be added to the Risk page until their orbits are refined and they are then dropped off the list of closely watched objects. This is how the system is expected to work and any initial indication of a low-probability Earth impact followed by a removal of that event from our IMPACT RISKS tables should not be considered a mistake. It is a natural result of the on-going process of monitoring the motions of near-Earth objects.

Original Source: NASA News Release

An asteroid the size of a football field came extremely close to the Earth last week, and scientists didn’t even know until after it passed us by. Asteroid 2002 MN is 100 metres in diameter and passed by us at a distance of only 120,000km, less than one-third the distance from the Earth to the Moon. This is one of the closest near-misses ever recorded of a spacerock this size; had it actually struck the planet it would have cause considerable destruction and loss of life.