sábado, 31 de março de 2012

How Much Cosmic Dust Hits Earth Each Day?

So how much of this stuff – leftovers from the formation of the planets, debris from comets and asteroid collisions, etc. — encounters Earth? Satellite observations suggest that 100-300 metric tons of cosmic dust enter the atmosphere each day. This figure comes from the rate of accumulation in polar ice cores and deep-sea sediments of rare elements linked to cosmic dust, such as iridium and osmium.
But other measurements – which includes meteor radar observations, laser observations and measurements by high altitude aircraft — indicate that the input could be as low as 5 metric ton per day.
Knowing the difference could have a big influence on our understanding of things like climate change and, noctilucent clouds, as well as ozone and ocean chemistry.
“If the dust input is around 200 tons per day, then the particles are being transported down through the middle atmosphere considerably faster than generally believed,” said Plane. “If the 5-tonne figure is correct, we will need to revise substantially our understanding of how dust evolves in the Solar System and is transported from the middle atmosphere to the surface.”
When dust particles approach the Earth they enter the atmosphere at very high speeds, anything from 38,000 to 248,000 km/hour, depending on whether they are orbiting in the same direction or the opposite to the Earth’s motion around the Sun. The particles undergo very rapid heating through collisions with air molecules, reaching temperatures well in excess of 1,600 degrees Celsius. Particles with diameters greater than about 2 millimeters produce visible “shooting stars,” but most of the mass of dust particles entering the atmosphere is estimated to be much smaller than this, so can be detected only using specialized meteor radars.
The metals injected into the atmosphere from evaporating dust particles are involved in a diverse range of phenomena linked to climate change.
“Cosmic dust is associated with the formation of ‘noctilucent’ clouds – the highest clouds in the Earth’s atmosphere. The dust particles provide a surface for the cloud’s ice crystals to form. These clouds develop during summer in the polar regions and they appear to be an indicator of climate change,’ said Plane. “The metals from the dust also affect ozone chemistry in the stratosphere. The amount of dust present will be important for any geo-engineering initiatives to increase sulphate aerosol to offset global warming. Cosmic dust also fertilises the ocean with iron, which has potential climate feedbacks because marine phytoplankton emit climate-related gases.”
The CODITA team will also use laboratory facilities to tackle some of the least well-understood aspects of the problem
“In the lab, we’ll be looking at the nature of cosmic dust evaporation, as well as the formation of meteoric smoke particles, which play a role in ice nucleation and the freezing of polar stratospheric clouds,” said Plane. “The results will be incorporated into a chemistry-climate model of the whole atmosphere. This will make it possible, for the first time, to model the effects of cosmic dust consistently from the outer Solar System to the Earth’s surface.”
CODITA has received a EUR 2.5 million grant from the European Research Council to investigate the dust input over the next 5 years. The international team, led by Plane, is made up of over 20 scientists in the UK, the US and Germany. Plane presented information about the project at the National Astronomy meeting in the UK this week.

quarta-feira, 28 de março de 2012

Sixty-five million years ago a huge meteorite fell to Earth

Sixty-five million years ago, a Manhattan-size meteorite traveling through space at about 11 kilometers per second punched through the sky before hitting the ground near what is now Mexico’sYucatán Peninsula. The energy released by the impact poured into the atmosphere, heating Earth’s surface. Then the dust lofted by this impact blocked out the sun, bringing years of wintry conditions everywhere, wiping out many terrestrial species, including the nonfeathered dinosaurs. Birds and mammals thus owe their ascendancy to the intersection of two orbits: that of Earth and that of a devastating visitor from deep space.

We humans need not wait, like dinosaurs, for the next big rock to drop. We have an advanced understanding of the heavens and a spacefaring technology that could soon enable us to alter the orbits of any celestial object on a collision path with us. That capability just might come in handy.

We got a taste of the challenge in December 2004, when scientists at NASA and the Jet Propulsion Laboratory (JPL), in Pasadena, Calif., estimated there was a nearly 3 percent chance that a 30-billion-kilogram rock called 99942 Apophis would slam into Earth in 2029, releasing the energy equivalent of 500 million tons of TNT. That’s enough to level small countries or raise tsunamis [PDF] that could wash away coastal cities on several continents. More recent calculations have lowered the odds of a 2029 impact to about 1 in 250 000. This time around, Apophis will probably miss us—but only by 30 000 km, less than one-tenth of the distance to the moon.

But let’s not rejoice too quickly. We know next to nothing about that asteroid’s porosity, composition, and tensile strength. It’s possible that tidal stresses during its 2029 approach could cause it to break apart, adding to the odds of an Earth impact during another rendezvous further down the line.

There is some disagreement about the best course of action. In the United States, experts tend to want to experiment with various deflection techniques by first sending robots or even astronauts to asteroids that do not threaten Earth. But in Russia, many asteroid watchers believe the risk of a collision between Apophis and Earth has been underestimated. These analysts contend that we should therefore concentrate our experiments on this particular asteroid.

To be sure of diverting any interplanetary intruder, we would need several strings to our bow. A method that could swiftly deflect a hunk of iron might blow an icy rock into several parts, each of which could then become a danger. And the gentler method now being discussed—to vaporize part of the surface of the asteroid, creating an outpouring of gas that would generate a propulsive force—would do no more than warm a meteorite made of iron. So we’ll doubtless need to devise several strategies for dealing with threatening asteroids.

So I have proposed a new tool, one that would use the pressure of light to nudge threatening objects into safe trajectories. That I’ve been asked to explain it at all in a magazine article shows that there’s indeed one thing we can rejoice in: the enhanced awareness of the problem. The mention of killer asteroids no longer raises jeering comparisons to the cries of Chicken Little, now that we know celestial impacts are far more common than once thought.

The largest and most famous Earth impact in historical times occurred inTunguska, Siberia, in 1908, when an object perhaps 30 meters wide entered the atmosphere and exploded aboveground, with the strength of several megatons of high explosive. It leveled forests and dispersed reindeer herds, and the dust it kicked up produced colorful sunrises and sunsets throughout Europe. Fortunately, the devastated area was sparsely populated, so few people were hurt.

Astronomers now know a good deal about the nature and location of objects posing threats of both the Yucatán and Tunguska kinds. Some of these objects are comets—celestial icebergs that spend most of their time in the depths of space far from the planets. At intervals of 100 000 years or more, stars may approach our solar system closely enough to disrupt the solar orbits of some of these comets, pushing them sunward. They would then swoop through the inner solar system at great speed. It is not impossible that such a comet is what destroyed the dinosaurs.

The main threat comes from what are known as near-Earth objects. They usually reside between the orbits of Venus and Mars, although their orbits aren’t very stable. Most are eventually flung out of the solar system, but replacements wandering in from the main asteroid belt maintain their population. Some 7000 near-Earth objects have been identified so far. As many as 100 000 more, all larger than the Tunguska object, may await discovery. This guesstimate, by analysts at JPL, is based on the assumption that astronomers are far better at spotting mountains than molehills.

NASA, now joined by the European Space Agency and other space agencies, has been conducting systematic searches for these objects. The agencies hope that by 2020 they will be able to discover 90 percent of those near-Earth objects wider than 140 meters. Both terrestrial and space telescopes are involved in the effort, and amateur astronomers equipped with small, dedicated telescopes also contribute.

Most of our information on the physical properties of these objects comes from low-resolution radar images created using such devices as the 300-meter William E. Gordon Telescope at the Arecibo Observatory, in Puerto Rico. This radio telescope can reveal rotation rates and shapes, at least for the nearer objects, although there is much we must still learn. What we do know, from meteorite samples in museum collections, is that some of the interplanetary objects that strike Earth are metallic, consisting largely of iron, and that some are rocky, consisting largely of silicates. Then there are extinct comet nuclei, in which rocky layers are interleaved with volatile material—ice made of water or methane, for example.

An additional asteroid category has recently been added to the list. The Japanese space probe Hayabusa (formerly called Muse-C) arrived at asteroid Itokawa in September 2005. In a cliffhanger of a mission, the probe landed on the asteroid and retrieved samples of the surface, returning with them to Earth in June 2010.

In early 2007, I took part in a NASA Marshall Space Flight Center study of proposed deflection techniques that could be ready for use by the end of 2020. My colleagues and I assumed that by that point we’d have a heavy-lift booster capable of sending 50 000 kg or more on an Earth-escape trajectory.

We considered several strategies. The most dramatic—and the favorite ofHollywood special-effects experts—is the nuclear option. Just load up the rocket with a bunch of thermonuclear bombs, aim carefully, and light the fuse when the spacecraft approaches the target. What could be simpler? The blast would blow off enough material to alter the trajectory of the body, nudging it into an orbit that wouldn’t intersect Earth.

But what if the target is brittle? The object might then fragment, and instead of one large body targeting Earth, there could be several rocks—now highly radioactive—headed our way. Also, a lot of people might object to even the mere testing of any plan that involved lobbing 100-megaton bombs into space. The nuclear option might then be limited to a last-ditch defense of Earth, should we get little warning of an impending impact.

Another idea is to use the “kinetic” method, which essentially uses one bullet to hit another. It requires sending a small spacecraft into an orbit around the sun in the opposite direction of that of the planets and most other objects. You then maneuver this spacecraft to hit the target head-on. It would take months to accelerate something into such a retrograde orbit. Still, the job could be done using either asolar-electric [PDF] (ion) engine or a solar sail, which would use the tiny pressure that sunlight exerts on it to maneuver through space. A craft that hit the Earth-threatening rock with a relative velocity of about 60 km/s would impart a kinetic energy of 1.8 billion joules per kilogram. If the aim was perfect (no small feat at such a relative velocity), the collision could significantly alter the orbit of an asteroid—one that’s sturdy enough to take the impact without falling apart. Of course, the thing could fragment, which might just make things worse.

But if we had several decades to plan the intervention, we could apply force more gently and with better control. We could wrap a solar sail around the offending object, like aluminum foil around a potato, changing the degree to which it reflects light and thus the effective pressure that sunlight exerts on it. In this fashion, the sail could gradually alter the object’s orbit around the sun, converting an impending Earth impact into a near miss. This wrapping method ought to work for any kind of asteroid or comet.

Apollo 9 astronaut Rusty Schweickart and Bong Wie of Iowa State University have proposed yet another universally applicable solar-sail technique, called the gravity tractor [PDF]. Here a solar sail would maintain position near the threatening body for decades, exerting a small but significant gravitational attraction on that object, which over time would alter its course. The sail would move into position and remain there using the pressure of solar radiation to maneuver. This method has the advantage of working equally well on all classes of objects—metallic, stony, or rich in ice. It would take a very long time, however, to do the job.

For the 2007 NASA Marshall study I began working on yet another scheme, called the solar collector. H. Jay Melosh [PDF] of the University of Arizona and Ivan V. Nemchinov and Yu. I. Zetzer, both then affiliated with the Russian Academy of Sciences, first proposed this approach in 1994. For this strategy, the spacecraft would deploy a large parabolic reflector that would always face the sun. Although the reflector would resemble a typical solar sail, its purpose would be solely to concentrate sunlight onto a smaller flat mirror, known as a thruster sail. The thruster sail would direct concentrated sunlight onto the offending asteroid. If the object contained volatile material, the intense beam would heat things up enough to vaporize part of the surface. The gas shooting into space as a result would, over time, impart enough momentum to nudge the body’s solar trajectory away from a projected impact with Earth. It wouldn’t take much of a push, because with asteroids, unlike horseshoes, a near miss doesn’t count.

The version of this approach that I worked on for the NASA Marshall study in 2007 assumed that gas would shoot off the asteroid at a velocity of about 1 km/s. This estimate drew on an experiment Melosh and his colleagues had done long before, using a pulsed laser to heat a simulated chunk of rocky intrasolar debris. But I had some suspicions that this number was too high—that it overestimated the efficiency of this approach. So I later looked into the thermodynamics of the problem more closely.

As I described in a 2008 paper in Acta Astronautica, it turns out that much of the energy in the concentrated beam of light would simply get conducted through the rock, away from the hot spot. The beam would have to be quite powerful to ensure that the hot spot could evaporate enough volatile material to really do the job. I found that what really mattered was how deep the concentrated sunlight penetrates. Existing studies showed that most soils here on Earth allow light into just the top 100 micrometers, but measurements on extraterrestrial samples were lacking.

As an associate at the Hayden Planetarium at the American Museum of Natural History, in New York City, I was able to collaborate with Denton Ebel, curator of meteorites there. He graciously prepared two samples of the Allende meteorite, which slammed into Mexico back in 1969. It’s a carbonaceous chondrite, as are about a third of all near-Earth objects. The first sample consisted of a 30-µm-thick section epoxied to a transparent slide; the second was a finely ground simulated minimeteorite weighing just a few grams.

Both samples were loaned to the physics department at the New York City College of Technology, in Brooklyn, where I teach. There, Lufeng Leng and her student Thinh Le shone two laser beams onto the samples, one at a wavelength of 532 nanometers, in the green part of the spectrum, and the other at 650 nm, in the red part. It turned out that both samples had about the same light-penetration depths you’d expect to find in terrestrial soils. I presented those results at a meeting of the Meteoritical Society in July 2010.

Such measurements must be repeated at other wavelengths and on samples of other meteorites and, ultimately, on samples retrieved from the moon and from asteroids. That way we will be able to test extraterrestrial material that could not have been modified by a meteorite’s white-hot passage through Earth’s atmosphere.

At this stage of the analysis, it is difficult to determine how big a solar collector would be required for this strategy to work. The device would probably have to measure more than 50 meters. Building it from a thin plastic film would keep its mass down to no more than a few hundred kilograms. It would remain tightly folded on the voyage out and be unfurled only near the standoff point, at least a few hundred meters from the Earth-threatening rock. Electric propulsion would probably be necessary to maintain the collector’s position during the months or years it would take to divert the rock. Autonomous robotic control seems necessary, although astronauts could certainly monitor the process. And it might prove easier to use a number of smaller solar collectors rather than a single large one.

These are early days for designing such delicate space hardware, space sails included. But that solar sails can be manipulated in orbit and used for various purposes is no longer in doubt.

In 2010, two such sails flew in space. The more ambitious one, a square about 14 meters on a side, was launched by the Japanese space agency on an interplanetary trajectory between Earth and Venus. Called IKAROS, for Interplanetary Kite-craft Accelerated by Radiation Of the Sun, it proved that solar radiation pressure can be used both for primary propulsion and for attitude control. A follow-on craft, planned for around 2020, would use its solar sail during a close pass of the sun. There it could gain enough momentum from light pressure to swing into an orbit that would take it all the way out to explore the asteroids—called the Trojans—that trail Jupiter in its orbit.

NASA’s Nanosail-D2, approximately the same size as IKAROS but lighter, went up in late 2010 and deployed in January 2011, when the craft unfurled its sail in an Earth orbit low enough for amateur astronomers to see it. It was also low enough for atmospheric drag to affect the orbit. In this case, that was a feature, not a bug, because the point of the mission was to clean up space junk by docking with it and then using the sail to drag it down to a fiery disposal in the lower atmosphere.

It’s a good thing that solar sails have many possible uses. This helps to defray the costs of developing a technology that’s likely to be valuable should we ever discover a rogue asteroid headed our way. It also helps in overcoming the all-too-human reluctance to begin working on a problem that requires a planning horizon measured in generations or even centuries.

As with other approaches to asteroid deflection, the solar collector would not work well on all classes of interplanetary rock. If you tried to use it on an iron asteroid, the metal would instantly conduct the heat away from the hot spot. Besides, there would be no volatile material there to vaporize anyway. The asteroid would just continue on its merry way, undisturbed. A rocky body without any volatiles would also be impossible to shift in this way. So, clearly, other techniques for dealing with those kinds of asteroids must also be developed.

It does seem, though, that a solar collector could divert a 300-meter water-ice object enough to prevent an Earth impact, and while remaining on station for just a few months. Even more ambitious is the notion of using such deflection techniques to steer smaller water-ice-bearing objects into high Earth orbit, where we could mine them for materials for rocket fuel, life-support systems for space habitats, cosmic-ray shielding for such habitats, the construction of satellites to beam solar power to Earth, and other purposes. In 2010, President Obama directed NASA to prepare to send astronauts to explore near-Earth objects by the year 2025. While on that mission or on succeeding ones, astronauts could test a solar collector and other deflection techniques.

We have plenty of time to study the matter. But we do not have all the time in the world.

About the Author

Gregory L. Matloff, an emeritus associate professor of physics at New York City College of Technology, is a pioneer of what might well be termed celestial engineering. In “Deflecting Asteroids,” he discusses using solar sails to manipulate the rocks and ice balls that orbit the sun and occasionally collide with our planet. He has consulted with NASA on this idea, as well as on using sails for deep-space propulsion. He is a coauthor of Solar Sails: A Novel Approach to Interplanetary Travel (Springer, 2008).

Source: http://spectrum.ieee.org

sexta-feira, 23 de março de 2012

Meteorite, or meteor-wrong?

A Burns Lake man thinks he has possibly found three meteorite craters and is pushing for a geologist to come to Burns Lake to solve the mystery.

Joseph Driscol said to Lakes District News that he has been trying to get the word out to any level of government for well over a year, expecting that if the meteorite craters are confirmed, Burns Lake could become a tourist mecca for meteorite and rock hounds.

While Driscol thinks what he has found could be meteorite craters, he said the help of a geologist is needed to prove it.

Most come from asteroids. A small number of meteorites have been shown to be originating from Mars or the moon. In One of the Martian meteorites, known as ALH84001, found in Antarctica by an American scientist, is believed to show evidence of early life on Mars.

The largest ever found, the Hoba meteorite in Namibia, is thought to have plunged into the Earth's atmosphere a little less than 80,000 years ago. Weighing in at about 66 tons the Hoba meteorite is composed of about 84 per cent iron and 16 per cent nickel, with traces of cobalt.

The Barringer Crater, near Winslow, Arizona was formed about 50,000 years ago by an iron meteor which was about 30 to 50 meters in diameter. The crater is substantial, at 1,200 meters in diameter and 200 meters deep.

Both sites have become popular tourist destinations.

So far approximately 120 impact craters have been confirmed worldwide

Driscol said the first crater he found is on the South slope of a fairly steep hill and measures approximately 1,000 metres in diameter.

"I was searching for a snowmobile trail near our house in Tintagel using Google Earth. As I was scrolling down the BC Hydro power line, I thought I saw a 'wheel' on the line. It was only about five kilometres away at the end of Moose Road so I rode over and had a look. It was nice that it was so close. I reported it to the Geological Survey of Canada and they said it would be at least two years before they could even look at it, so I looked at it myself."

From the air, photos of the crater show a large circular depression in the ground.

Driscol said that during a visit to the Tintagel site, a rock he collected was unique.

"During a whole summer of hunting, this rock was unique among thousands I looked at. Aside from the rock, other indicators also show that a meteorite has landed here, but they don't prove it so a good geologist would be worth gold come May or June. So would a couple hundred people swinging metal detectors," Driscol said.

Raminder Singh Samara an astronomer at the H.R. MacMillan Space Centre in Vancouver examined a number of photos of the crater, but said he could not conclusively say the depression in the ground is a crater caused by a meteorite.

"There appears to be a clear depression in the ground, however the depth is difficult to estimate," Singh Samara said.

"Knowing the depth, diameter and the type of rock in the ground, it is possible to estimate the size of any meteroid that caused the depression. The rocks that should be found here should be very heavy compared to normal rocks. If there are meteorites in the area they should be very iron rich."

Singh Samara said, "An impact crater about 50 meters across would have dug into the ground and made the soil far less fertile, so you wouldn't expect anything large like trees to grow in it. It could have been that the meteoroid came at a very shallow angle from the East-North-East. However looking at the ejecta [the powder that is ejected from underground by the violent collision] we should see a distribution that is towards the west-south-west, but [in the images] it's towards the South-West in my opinion. I think it is still inconclusive from the few images I've seen to conclude that this is or is not an impact crater."

He said, " I can't say for certain if this is or is not an impact crater. The smoking gun would be finding small pebbles and stones that are very glass-like [tektites] on site due to the meteorite vaporizing some of the rock and melting other bits of it."

Driscol said the summer time satellite imagery of the crater does have greenery inside the crater, but he explained, "The reason you can see this, is because the layer of soil that has built up since it got 'cooked' only supports spruce trees because they can grow in shallow soil. Pine trees can't. It's really quite fascinating why it's two colours. I do believe it came in at the angle the astronomer [Singh Samara] described, East of North."

Singh Samara said the H.R. MacMillan space centre doesn't track impact craters or keep records, but he added that impact craters are usually confirmed, or debunked, by on site visits from a geologist.

Driscol said to Lakes District News that he has explored all avenues to get someone out to the area to assess the crater.

The other two craters are located on the Southside and are estimated to be similar in size and shape to the Tintagel crater.

"I just want to know if what I have found is a meteorite crater, if it is, this is a certainly a unique tourism opportunity for Burns Lake," he said.

Source: IDNews.net

quarta-feira, 14 de março de 2012

Queda de meteorito na Ilha Graciosa / Ofereço uma recompensa de 150 Euros a quem o encontrar

Na passada Segunda-feira, 12 de Março, por volta das 20h00 (8:00 pm) ocorreu a queda de um meteorito no interior da Ilha Graciosa, mais ou menos entre os Funchais e o Guadalupe. Trata-se de um fenómeno muito raro pois que a maioria das pessoas em geral nascem e morrem sem nunca terem observado ou testemunhado semelhante coisa à excepção de estrelas cadentes que na maioria dos casos ocorrem muito longe de nós.

Este, porém, ocorreu bastante próximo de mim (na altura eu encontrava-me no lugar da minha residência (Dores, Santa Cruz da Graciosa) e, por conseguinte, tive a felicidade de o testemunhar naquela noite mesmo do meu jardim que era onde eu me encontrava nesse momento. De salientar que esta foi a minha primeira vez e confesso que é uma experiência verdadeiramente sensacional sobretudo para alguém como eu que sou coleccionador e me dedico ao estudo destes fenómenos desde algum tempo atrás.

Creio que o meteorito, provavelmente da classe dos condritos simples (mais ou menos de 8 a 12 cm de tamanho) e pesando aproximadamente cerca de 200 a 900 (?) gramas, terá explodido durante a queda mesmo antes de atingir o solo e terá chegado ao ponto de impacto já em mais de um bocado devido à dita explosão que referi. Digo isto porque pude verificar que o fogo se apagou a sensivelmente uns 30 metros do solo e isso confirma que tenha havido de facto uma explosão fazendo com que o meteorito tenha ficado fracturado.

Aproveito para, através deste meio, pedir a todos os que tenham terras entre os Funchais e Guadalupe que se eventualmente encontrarem algum fragmento do meteorito para me contactar
o mais depressa possível para este e-mail: Galeriacores@gmail.com

Para quem nunca viu um meteorito, estes por norma são pretos no exterior e muito pesados para o tamanho que têm devido ao ferro e outros metais presentes no seu respectivo interior. O interior do meteorito normalmente costuma ser de uma cor mais clara.

Ofereço 150.00 € de recompensa a quem conseguir encontrar os fragmentos deste meteorito. Muito obrigado pela vossa atenção.

terça-feira, 13 de março de 2012

Ciência identifica partícula que terá originado a vida

As partículas elementares, que terão contribuído para o aparecimento da vida na Terra, foram identificadas, pela primeira vez, num cometa criado artificialmente, divulgou o Centro de Investigação Científica francês.

Em comunicado, o centro científico sugere que "as primeiras estruturas moleculares de vida poderão ter sido formadas num meio interestelar, antes de atingirem a Terra primitiva durante a queda de meteoritos e cometas". No entanto, a equipa responsável pela identificação das partículas admite que são necessários estudos complementares para confirmar estes resultados. O cometa artificial foi criado com a simulação das condições extremas que se encontram no espaço, onde imperam temperaturas de 200°C negativos.

Fonte: CM

segunda-feira, 12 de março de 2012

Um meteorito extremamente raro caiu no telhado de uma casa em Rodelokka, no centro de Oslo

A família Thomassen escapou por pouco de apanhar o susto das suas vidas. A sua casa pré-fabricada no centro de Oslo estava vazia quando um pedaço de meteorito atravessou o telhado, partindo-se em dois no chão. Segundo os especialistas, o pedaço de rocha, com 585 gramas, destacou-se de um meteorito maior que sobrevoou a Noruega no passado dia um de março.

É muito raro pedaços de meteorito chegarem ao solo, já que habitualmente se desintegram ao entrar na atmosfera. Mais raro ainda é quando se trata de brechas, ou seja uma pedra constituída de fragmentos de rocha, como parece ser este caso.

Estatisticamente é ainda extremamente improvável caírem em zonas habitadas. Se ainda por cima acertarem numa habitação, é quase caso único.

Mas, improvável não significa impossível, como comprovaram os Thomassen, ao darem de caras com os pedaços de meteorito no chão da sua cabana, em plena capital norueguesa.

Os dois pedaços foram identificados pelo astrofísico Knut Joergen Roed Oedegaard e pela sua mulher Anne Mette Sannes, entusiasta de meteoritos.
Brecha é uma rocha clástica formada de fragmentos grandes e angulosos, aglutinados numa massa de cimentação composta de material mais fino. Pode ter origem ígnea, sedimentar ou metamórfica (in Wikipédia)
“É sensacional sob mais de um aspeto. Por um lado, porque é raríssimo que um bocado de meteorito atravesse um teto e, por outro lado, por se tratar de uma brecha, que é ainda mais difícil de encontrar”, afirmou Sannes à Agência France Press.

Os Thomassen tiveram sorte, por a brecha não ter atingido ninguém e na sua queda ter provocado apenas estragos mínimos. Mais do que isso, os pedaços de meteorito poderão valer uma pequena fortuna.

Segundo um geofísico citado no jornal norueguês Verdens Gang, uma grama de um meteorito vindo de Marte pode valer cerca de 670 euros. Resta saber qual o valor do meteorito dos Thomassen.

Fonte: RTP

sexta-feira, 2 de março de 2012

Estudo sugere que Terra nasceu do impacto de meteoritos

O material a partir dos qual se formou a Terra poderá ser diferente daquilo que a comunidade científica até agora julgava. Um novo estudo sugere que o planeta nasceu de um grande número de colisões de meteoritos de diversos tamanhos e géneros.

Levado a cabo por investigadores franceses e publicado na revista Science, o estudo quebra com a tese anterior segundo a qual, há 4500 milhões de anos, a Terra nasceu a partir do material que sobrou da formação do sol e que se agrupou ao redor de uma estrela recém-nascida. Material que, muito lentamente, foi formando grãos, depois rochas e, finalmente, um embrião planetário que foi atraindo ainda mais material até à formação da Terra. Julgava-se também que a maioria dos materiais que se foi fundindo neste embrião terrestre era muito similar e pertencente a uma categoria de meteoritos chamada condritos estantite.

No entanto, o estudo dos geoquímicos franceses Caroline Fitoussi e Bernard Bourdon, que analisaram os isótipos de silício de amostras de rochas terrestres e amostras de rochas lunares e compararam-nas com amostras de meteoritos, quebra com esta ideia.

Utilizando modelos informáticos da formação da Terra, os cientistas chegaram à conclusão que, para produzir a mistura certa de isótopos de oxigénio, níquel e crómio encontrados nas amostras terrestres era preciso juntar pelo menos três diferentes classes de meteoritos, e não apenas uma. Ou seja, percebeu-se que não havia apenas um género de condritos, mas uma mistura, a qual levou à formação da Terra.

Fonte: DN