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Freitag, 25. Oktober 2013 - 08:45 Uhr

In eigener Sache!

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Freitag, 25. Oktober 2013 - 07:45 Uhr

Astronomie - Sind Schwarze Löcher von Wänden aus Feuer umgeben?

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25.08.2013

Are black holes surrounded by walls of fire? Does this imply that one (or more) of our most cherished physical principles—and here I’m talking about biggies like quantum theory, the conservation of information or Einstein’s equivalence principle—is wrong? Any may our savior come in the form of wormholes? These are the questions consuming some of the world’s foremost theoretical particle physicists as they argue about potential solutions to what has become known as the “black hole firewall” problem—perhaps the most important paradox in physics since Stephen Hawking proposed his first black hole information paradox nearly four decades ago.

Every black hole has an event horizon. Nothing that moves inside a black hole’s event horizon will ever escape, not even light. Yet we’ve always understood event horizons to be less than dramatic—if you were to cross one, you wouldn’t notice anything immediately amiss.

Event horizons are important, however, for a number of reasons. Consider that according to the laws of quantum mechanics, a pair of virtual particles can jump into existence. Ordinarily, they quickly come back together and annihilate one another, but if the process happens near an event horizon, one particle can get sucked into the hole, leaving the other to drift into space. This implies that black holes radiate particles, a curious fact that Stephen Hawking pointed out many years ago. Eventually black holes lose so many particles that they shrink and die, having spewed their mass out into the cosmos in a stream of Hawking radiation.

Looking at the situation another way, black holes swallow matter—a star here, a wayward astronaut there—then, over time, spit it back out into the cosmos as Hawking radiation. But because information can not be destroyed—only scrambled—the Hawking radiation must contain all the information about the stuff that fell in to the black hole. And the only way that this can happen is if all the Hawking radiation is entangled—that is, every particle’s quantum state co-depends on the quantum states of all the other particles in the Hawking radiation. (Entanglement is a weird and important quantum concept. If you’d like to know more, I recommend this short video.)

Remember, though, that Hawking radiation only exists because a pair of virtual particles popped into existence. One fell in, the other drifted out. These two particles must also be entangled. Unfortunately, the laws of quantum mechanics forbid promiscuous entanglements—a particle can be entangled with its twin, or the rest of the radiation coming out of the black hole, but not both.

And so we have a dilemma. In order for information to be conserved, particles in the Hawking radiation must be entangled each other. But in order to get the Hawking radiation in the first place, these particles must be entangled with the particles falling in to the black hole. Physicists used to think this might be OK, since no single observer could detect both entanglements. But AMPS noticed that a particle coming out of the black hole could be turned around and sent in to the black hole, illuminating the double quantum correlations and causing no end of quantum mischief. To avoid this, they suggest that as the particle crosses the event horizon, the original quantum correlation breaks, producing a burst of energy. The net effect: a wall of fire.

(For more on the firewall paradox, I’d recommend reading Jennifer Ouellette at Cocktail Party Physics, Dennis Overbye in the New York Times, Zeeya Merali in Nature, Caltech’s John Preskill and UCSB’s Joe Polchinski, who first came up with the paradox along with his colleagues Ahmed Almheiri, Don Marolf and James Sully—the quartet now known as AMPS.)

The black hole firewall paradox has caused no small amount of wonder and confusion amongst particle physicists. It appears as though one of our core beliefs about the universe is wrong: Either particles can be promiscuously entangled, leading to quantum disaster (basically no one takes this option seriously; quantum theory and the no-promiscuous-entanglement rule are far too well supported by decades of experimental evidence), or information is not conserved (another non-starter), or black holes have firewalls (even Polchinski considers this a reductio ad absurdum), or… we just don’t fully understand what’s really going on.

And so in an effort to sort the mess out, physicists gathered this week at the Kavli Institute for Theoretical Physics at UCSB to talk over the options. (They’ve been doing a great job uploading videos of all the talks, so if you’re interested in watching smart folks try to hash out knotty thought experiments in near-real time, you can follow along at home.) One of the most intriguing possibilities for a solution comes from Juan Maldacena and Leonard Susskind, building on the ideas of Mark Van Raamsdonk and Brian Swingle. Maldacena and Susskind posit that the solution to the firewall problem may come in the form of wormholes.

Wormholes! I feel like we haven’t talked about them since the ’90s. Basically, wormholes are theoretical objects that connect two different points in space. They’re allowed as possible solutions to Einstein’s equations for general relativity—indeed, Einstein and his colleague Nathan Rosen first discovered wormholes, which is why they’re also called Einstein-Rosen bridges. Unfortunately, wormholes aren’t perfect—Einstein’s equations also imply that nothing with nonnegative energy (that is to say: nothing that we know of) can traverse a wormhole, so they’re not going to make for useful intergalactic portals anytime soon.

Maldacena and Susskind, following Van Raamsdonk, posit that any time two quantum particles are entangled, they’re connected by a wormhole. They then go on to say that the wormhole connection between particles inside a black hole (the infalling virtual particles) and the particles outside of a black hole (the Hawking radiation) soothes out the entanglement problems enough so that we can avoid the firewall at the event horizon.

Note that this requires a profound rethinking of the fundamental stuff of the universe. Entanglement, a deeply quantum phenomenon, is fundamentally wound into to the geometry of the universe. Or, to flip it around, quantum weirdness may be stuff that creates the substrate of spacetime.

Of course, nothing is settled yet. As Maldacena and Susskind write towards the end of their paper:

At the moment we do not know enough about Einstein-Rosen bridges involving clouds of Hawking radiation to come to a definite conclusion…. The AMPS paradox is an extremely subtle one whose resolution, we believe, will have much to teach us about the connection between geometry and entanglement. AMPS pointed out a deep and genuine paradox about the interior of black holes.

And if there’s one great thing about paradox, it’s that their resolutions require radical breakthroughs. The equipment we build for the job may take us to places we’ve never dreamed.

Quelle: Scientific American

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Update: 25.10.2013

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Physicists Euphoric but Confused about Black Hole Paradox

The recently proposed idea of “black hole firewalls” has physicists questioning some of their most cherished ideas

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“The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘eureka!’ but ‘that's funny,’” Isaac Asimov once said. Well, something seriously funny is going on in theoretical physics these days. A recent conundrum about black holes is threatening to overturn some of the most basic tenets of physics, and many scientists are nothing but thrilled.
“To me it’s the best thing that’s happened in awhile,” says University of California, Berkeley, physicist Raphael Bousso of the so-called “black hole firewall paradox,” which concerns what happens at the boundary of a black hole. “This is a 9 on the Richter earthquake scale—it’s by far the most shocking and surprising thing that has happened in my career.” The quandary prompting such jubilation is an idea first put forward in July 2012, which was extended in a paper published October 21 in Physical Review Letters. Physicists have long assumed that space is smooth at a black hole’s event horizon—the point of no return where nothing that passes through can escape. A person crossing over that line shouldn’t immediately notice anything amiss, however, and neither should a distant observer watching that person. But physicists have also assumed that information can never be destroyed. The new work says those two ideas are mutually incompatible. “It’s a paradox because several things we believed were true can’t all be true,” says Joseph Polchinski of the Kavli Institute for Theoretical Physics and U.C. Santa Barbara, one of the main architects of the firewall idea.
Polchinski and his colleagues conclude that not only is space not smooth at a black hole horizon—at that point the laws of physics completely break down. Instead of an unobtrusive boundary, the scientists argue that there must actually be a sharp division they call a firewall. “The firewall is kind of a wall of energy—it could be the end of spacetime itself,” Polchinski says. “Anything hitting it would break up into its fundamental bits and effectively dissolve.” At first, many physicists strenuously objected to the bizarre idea of firewalls. “I tried very hard to get rid of them, but I don’t think it’s likely that will happen,” Bousso says. “I’ve decided that the most promising thing for me is to assume there are firewalls, and look into why they form.” Even the main authors of the idea aren’t completely onboard. “There is a group of people, including me half the time, that thinks there must be some subtle assumption that we’ve made that’s not valid,” Polchinski says. Yet he and everyone else admit they haven’t identified a flaw in the reasoning so far.
The first argument for firewalls, put forward by Polchinski and his U.C. Santa Barbara, colleagues Ahmed Almheiri, Donald Marolf and James Sully, relied on the complex quantum mechanical concept of entanglement, where two particles can be separated over a distance but retain a profound connection. The new paper strengthens and simplifies the case for firewalls by sidestepping the issue of entanglement altogether, Marolf says. “It shows very clearly that some things you might have worried about are red herrings and not relevant to the argument.”
The new paper is far from the last word on the subject, though. In the year since the firewall idea was proposed, more than 100 papers have addressed the idea, and firewalls have been the subject of three conferences and workshops. “The last year has witnessed the kind of development we live for,” Columbia University physicist Brian Greene says. “It’s where the rubber hits the road.”

Quelle: Scientific American




Tags: Black Hole Paradox Schwarze Löcher 

3123 Views

Donnerstag, 24. Oktober 2013 - 15:39 Uhr

Raumfahrt -Weltraumforschung öffnet ethisches Dilemma

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The Daily Wildcat Christopher Impey, a University of Arizona Distinguished Astronomy Professor, gave a lecture on Monday, Oct. 14 about ...

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In “Star Trek,” Starfleet officers are required to swear an oath to follow the Prime Directive, which states that personnel will not interfere with the natural development of alien cultures or civilizations while they explore the universe and “boldly go where no man has gone before.”
While the Prime Directive is a fictional rule for one of the most popular science-fiction franchises, there may be some merit to the philosophical and ethical issues the rule brings up, especially in regards to the future of space exploration.
In a lecture given last Monday, Christopher Impey, a UA distinguished astronomy professor, discussed the social and ethical implications involved with exploring the universe — namely those associated with astrobiology, which deals with the search and study of life elsewhere in space.
The subject is not new to Impey, who recently worked as an editor on the book “Encountering Life in the Universe: Ethical Foundations and Social Implications of Astrobiology.”
“Astrobiology begs a series of very profound questions about the nature of life, the role of life in the universe and our relation to any sort of life in the universe,” he said.
While we haven’t found life anywhere other than Earth, Impey remains positive that such a major discovery will happen soon, due to the number of Earth-sized planets being discovered in the habitable zones of their stars.
But while the discovery of new life would be one of the most significant findings in our lifetimes, theorizing what that new life could be like may be one of the greatest challenges we face — simply because we may be limited by our own imaginations.
“It’s hard to imagine how strange life could be in the universe,” Impey said. “It has to be tethered, at some point, in the familiar.”
For us, that familiarity means that life must be made of carbon and have access to water. Essentially, for us to recognize it, life must be like us, despite the fact that there is very little evidence to support that all life does fit such a narrow definition.
The lack of understanding about the possibilities of life, however, hasn’t stopped scientists from looking for life within our solar system. The moons Titan and Europa are prime candidates in the search for extraterrestrial life, and the recent discovery of water on Mars could also indicate the possibility of life on the red planet, Impey said.
The discovery of water opens up the possibility of terraforming Mars as well, in order to make it habitable for humans. But while establishing life on other planets would be a significant scientific achievement, it also brings up a multitude of moral and ethical questions.
“Here comes the moral dilemma within the solar system,” Impey said. “What is our right, or our obligation, to not just find life elsewhere, but to make a place right for us or for our life or to alter it so it becomes living?”
According to Impey, these questions are going to incite debate about astrobiology and ethical space travel within our lifetimes, especially with private sector space travel becoming a greater rival to institutions like NASA.
“I’ve always been a believer in the spirit of adventure and the spirit of exploration,” said Thomas Fleming, an astronomer and senior lecturer at the UA. “I just have to hope in the innate goodness of the individual humans who perform some of these adventures in the future, that they will do the right thing — because there is no sheriff in space.”
Others are less optimistic about the answers to the ethical issues posed by astrobiology.
“I don’t have much hope for human ethics if you take a look back at what we’ve done to other species and to our own species,” said Maliha Khan, a journalism freshman who attended Impey’s lecture.
While NASA may be no closer to forming its own Starfleet Academy than it was when “Star Trek” first aired, it may consider creating its own version of the Prime Directive before the decade is through.
Quelle: University of Arizona.

3372 Views

Donnerstag, 24. Oktober 2013 - 13:20 Uhr

Astronomie - Feuerkugel am Samstag über Süddeutschland und Österreich

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20.10.2013

 

 

Feuerkugel bei Vollmond 19.10.2013

 

20:02 MESZ

 

Richtung Nordost

1 Stunde nach Mondaufgang mit 99,4 %
beleuchteten Mond

Aufnahme: Hermann Koberger / Österreich

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Update: 24.10.2013

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Feuerkugel über dem Landkreis

Weilheim-Schongau - Eine Feuerkugel ist am Montagabend über den Landkreis geflogen. EIn besonderes Himmelsphänomen - das sogar fotografiert wurde.

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Die Feuerkugel, die auch im Landkreis zu sehen war, fotografierte Hermann Koberger am Montag um 22.51 Uhr. fkn
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Hans Gattinger beobachtete am Montag um 22.52 Uhr vor seiner Garage in Untersöchering ein seltsames Himmelsphänomen: Südöstlich am Horizont erschien über der B 2 ein heller Himmelsstreif, der sich dann orange-gelb verfärbte und auflöste. „Das muss was Besonderes gewesen sein“, dachte sich der 64-Jährige und wandte sich an die Heimatzeitung.
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Das, was Gattinger gesehen hat, war eine Feuerkugel, wie mit Hilfe des Weilheimer Astronomen Helmut Hornung zu ermitteln war. Dieser fand über die DLR (Institut für Planetenforschung) heraus, dass zum exakt gleichen Zeitpunkt der Oberösterreicher Hermann Koberger den Lichtstreif mit seiner Meteorkamera fotografiert und dem DLR gemeldet hatte. „Feuerkugeln sind über hunderte Kilometer zu sehen, deshalb ist es sicher, dass es dasselbe war“, so Hornung. Feuerkugeln seien im Grunde riesige Sternschnuppen: tennis- bis fußballgroße Gesteinsbrocken aus dem All, die in 10 bis 50 Kilometern über der Erde verglühen. Mehrmals im Monat seien solche Lichtstreife zu beobachten. sw
Quelle: Merkur, 23.10.2013


 



Tags: Feuerkugel 19.10.2013 über Süddeutschland 

5679 Views

Donnerstag, 24. Oktober 2013 - 13:13 Uhr

Astronomie - Aufbau von weltweit größten Amateur-Teleskop in Utah.

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SALT LAKE CITY — A Utah man has set a record by building the world's largest amateur telescope, and he plans to travel the country to allow others to use it.
By day, Mike Clements drives a truck to Idaho and back. However, by night, he's preoccupied with something much less down-to-earth.
Clements is an amateur astronomer who, after years of planning, finished constructing the world's largest amateur telescope in September. The telescope is as long as a school bus, and weighs about 900 pounds. It also houses a mirror that is 70 inches wide.
"I still am in a state of disbelief," Clements said after completing his project. "I'm mad. I'm simply mad. It's something I had to do."
In 1988, a group of amateur astronomers named Group 70 attempted to build just such a telescope, but ran out of money, according to their website. Clements wears a souvenir Group 70 t-shirt given to him by a friend. It bears a large "1.8" to represent the 70-inch mirror.
The heart of Clements' telescope is a government surplus 70-inch mirror. It was produced originally for a Cold War-era spy satellite.
"It was designed for looking down and I guess reading license plates in Russia," he said.
Clements began began building a steel structure to house the mirror in 2012. He did it without formal training in telescope construction or welding and without any blueprints.
"He's got nothing on paper," said Clements' friend, Steve Dodds. "He did make a model out of popsicle sticks."
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Dimensions of Telescope:
The telescope is as long as a school bus
Weighs about 900 pounds
Has a 70-inch mirror
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Clements finished the telescope and in late September, he said he put a reflective coating on the mirror with a weed sprayer.
"It was grass roots from beginning to the end," he said.
"Mike is a very positive, 100 mph type guy," said his friend, Charlie Green. "He sets his goals and he jumps on things and you can see that in his telescope."
One cold fall night, Clements took his first real glimpses though the telescope. He said The Ring Nebula, a small blur in a normally-sized telescope, filled a large portion of his field of view. Clements said that conditions were not optimal due to heat waves radiating from the earth and distorting the view, but the sight was still impressive.
Clements plans to eventually buy a trailer and haul his telescope — designed to be disassembled — to parks to show people the night sky.
"I'm gonna take it around the country and show people," Clements said. "It's also portable. I don't know if I mentioned that."
Clements said years ago, he got the nickname "One-Meter Mike" when he built a large telescope with a diameter of one meter and hauled it around the country in the back of a pickup. He took it to national parks and rest stops and showed off the stars and planets.
Clements may be getting a new nickname with his latest project.
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Quelle: KSL

3282 Views

Donnerstag, 24. Oktober 2013 - 10:28 Uhr

Raumfahrt - Cassini erhält neue Bilder von Titan´s Land der Seen

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PASADENA, Calif.-- With the sun now shining down over the north pole of Saturn's moon Titan, a little luck with the weather, and trajectories that put the spacecraft into optimal viewing positions, NASA's Cassini spacecraft has obtained new pictures of the liquid methane and ethane seas and lakes that reside near Titan's north pole. The images reveal new clues about how the lakes formed and about Titan's Earth-like "hydrologic" cycle, which involves hydrocarbons rather than water.

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Bird's Eye View of the Land of Lakes
The vast hydrocarbon seas and lakes (dark shapes) near the north pole of Saturn's moon Titan sprawl out beneath the watchful eye of NASA's Cassini spacecraft. Scientists are studying images like these for clues about how Titan's hydrocarbon lakes formed. Titan is the only world other than Earth that is known to have stable bodies of liquid on its surface.
This view was made from near-infrared images of Titan obtained by Cassini's imaging science subsystem. Bright material seems to surround the lakes, which could help explain why currently almost all large bodies of liquid are found here, at Titan's north pole, rather than other parts of Titan. The imaging data suggest the surface here is unique. Explanations range from the collapse of land after a volcanic eruption to karst terrain, where liquids dissolve soluble bedrock. Karst terrains on Earth can create spectacular topography such as the Carlsbad Caverns in New Mexico
The largest of the dark shapes, at the upper right, is Kraken Mare, Titan's largest sea and about the size of the Caspian Sea and Lake Superior put together. To its left lies Ligeia Mare (about 300 miles or 500 kilometers across), the second largest sea. Punga Mare (about 240 miles or 380 kilometers across) is below Ligeia Mare and just above its leftmost finger is the north pole.
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Titan's Northern Lakes: Salt Flats?
This false-color mosaic, made from infrared data collected by NASA's Cassini spacecraft, reveals the differences in the composition of surface materials around hydrocarbon lakes at Titan, Saturn's largest moon. Titan is the only other place in the solar system that we know has stable liquid on its surface, though its lakes are made of liquid ethane and methane rather than liquid water. While there is one large lake and a few smaller ones near Titan's south pole, almost all of Titan's lakes appear near the moon's north pole.
Scientists mapped near-infrared colors onto the visible color spectrum. Red in this image was assigned a wavelength of 5 microns (10 times longer than visible light), green 2.0 microns (four times longer than visible light), and blue 1.3 microns (2.6 times longer than visible light).
The orange areas are thought to be evaporite -- the Titan equivalent of salt flats on Earth. The evaporated material is thought to be organic chemicals originally from Titan's haze particles that once dissolved in liquid methane. They appear orange in this image against the greenish backdrop of Titan's typical bedrock of water ice.
In this mosaic, Kraken Mare, which is Titan's largest sea and covers about the same area as Earth's Caspian Sea and Lake Superior combined, can be seen spreading out with many tendrils on the upper right,. The big dark zone up and left of Kraken is Ligeia Mare, the second largest sea. Below Ligeia, shaped similar to a sports fan's foam finger that points just up from left, is Punga Mare, the third largest Titan Sea. Numerous other smaller lakes dot the area. Titan's north pole is located in the geographic location just above the end of the "finger" of Punga Mare.
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Dark Lakes on a Bright Landscape
Ultracold hydrocarbon lakes and seas (dark shapes) near the north pole of Saturn's moon Titan can be seen embedded in some kind of bright surface material in this infrared mosaic from NASA's Cassini mission.
The bright area suggests that the surface here is different from the rest of Titan, which might help explain why almost all of the lakes are found in this region. Titan's lakes have very distinctive shapes -- rounded cookie-cutter silhouettes and steep sides -- and a variety of formation mechanisms have been proposed. The explanations range from the collapse of land after a volcanic eruption to karst terrain, where liquids dissolve soluble bedrock. Karst terrains on Earth can create spectacular topography such as the Carlsbad Caverns in New Mexico.
Titan is the only world in the solar system other than Earth that is known to have stable bodies of liquid on the surface. Titan's, however, are composed of liquid ethane and methane rather than liquid water. While there is one large lake and a few smaller ones near Titan's south pole, almost all of Titan's lakes appear near the moon's north pole. Scientists are using images like these to understand why.
The north pole is at the upper right in this view, marked with a cross. The largest of the dark shapes, at the upper right, is Kraken Mare, which is about the same size as Earth's Caspian Sea and Lake Superior put together. To its upper left lies Ligeia Mare, the second largest sea (about 300 miles, or 500 kilometers, across). Directly below Ligeia Mare, Punga Mare (about 240 miles, or 380 kilometers, across) lies near the north pole.
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Titan's North: The Big Picture
Almost all of the hydrocarbon seas and lakes on the surface of Saturn's moon Titan cluster around the north pole, as can be seen in this mosaic from NASA's Cassini mission. This mosaic, made from near-infrared images of Titan obtained by Cassini's imaging science subsystem, shows a view from the north pole (upper middle of mosaic) down to near the equator at the bottom. Here, the seas and lakes appear as dark shapes, embedded in some kind of bright terrain. Titan is the only world in the solar system other than Earth that is known to have stable bodies of liquid on the surface. Titan's, however, are composed of liquid ethane and methane rather than liquid water.
The bright area suggests the surface material around the lakes is unique and might explain why almost all of Titan's lakes are found in this region. It appears to cover much of the surface north of 65 to 70 degrees north latitude on this side of Titan. Titan's lakes have very distinctive shapes -- rounded cookie-cutter silhouettes and steep sides - and a variety of formation mechanisms have been proposed. The explanations range from the collapse of land after a volcanic eruption to karst terrain, where liquids dissolve soluble bedrock. Karst terrains on Earth can create spectacular topography such as the Carlsbad Caverns in New Mexico.
The north pole is in the upper middle in this view. The largest of the dark shapes, at the upper right, is Kraken Mare, which is about the size of the Caspian Sea and Lake Superior put together. To its left lies Ligeia Mare, the second largest sea, which measures about 300 miles (500 kilometers) across. And below them is Punga Mare, which lies near the north pole and is about 240 miles (380 kilometers) across.
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While there is one large lake and a few smaller ones near Titan's south pole, almost all of Titan's lakes appear near the moon's north pole. Cassini scientists have been able to study much of the terrain with radar, which can penetrate beneath Titan's clouds and thick haze. And until now, Cassini's visual and infrared mapping spectrometer and imaging science subsystem had only been able to capture distant, oblique or partial views of this area. 
Several factors combined recently to give these instruments great observing opportunities. Two recent flybys provided better viewing geometry. Sunlight has begun to pierce the winter darkness that shrouded Titan's north pole at Cassini's arrival in the Saturn system nine years ago. A thick cap of haze that once hung over the north pole has also dissipated as northern summer approaches. And Titan's beautiful, nearly cloudless, rain-free weather continued during Cassini's flybys this past summer. 
The images are mosaics in infrared light based on data obtained during flybys of Titan on July 10, July 26, and Sept. 12, 2013. The colorized mosaic from the visual and infrared mapping spectrometer, which maps infrared colors onto the visible-color spectrum, reveals differences in the composition of material around the lakes. The data suggest parts of Titan's lakes and seas may have evaporated and left behind the Titan equivalent of Earth's salt flats. Only at Titan, the evaporated material is thought to be organic chemicals originally from Titan's haze particles that once dissolved in liquid methane. They appear orange in this image against the greenish backdrop of Titan's typical bedrock of water ice. 
"The view from Cassini's visual and infrared mapping spectrometer gives us a holistic view of an area that we'd only seen in bits and pieces before and at a lower resolution," said Jason Barnes, a participating scientist for the instrument at the University of Idaho, Moscow. "It turns out that Titan's north pole is even more interesting than we thought, with a complex interplay of liquids in lakes and seas and deposits left from the evaporation of past lakes and seas." 
The near-infrared images from Cassini's imaging cameras show a bright unit of terrain in the northern land of lakes that had not previously been visible in the data. The bright area suggests that the surface here is unique from the rest of Titan, which might explain why almost all of the lakes are found in this region. Titan's lakes have very distinctive shapes -- rounded cookie-cutter silhouettes and steep sides -- and a variety of formation mechanisms have been proposed. The explanations range from the collapse of land after a volcanic eruption to karst terrain, where liquids dissolve soluble bedrock. Karst terrains on Earth can create spectacular topography such as the Carlsbad Caverns in New Mexico. 
"Ever since the lakes and seas were discovered, we've been wondering why they're concentrated at high northern latitudes," said Elizabeth (Zibi) Turtle, a Cassini imaging team associate based at the Johns Hopkins Applied Physics Laboratory, Laurel, Md. "So, seeing that there's something special about the surface in this region is a big clue to help narrow down the possible explanations." 
Launched in 1997, Cassini has been exploring the Saturn system since 2004. A full Saturn year is 30 years, and Cassini has been able to observe nearly a third of a Saturn year. In that time, Saturn and its moons have seen the seasons change from northern winter to northern summer. 
"Titan's northern lakes region is one of the most Earth-like and intriguing in the solar system," said Linda Spilker, Cassini project scientist, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We know lakes here change with the seasons, and Cassini's long mission at Saturn gives us the opportunity to watch the seasons change at Titan, too. Now that the sun is shining in the north and we have these wonderful views, we can begin to compare the different data sets and tease out what Titan's lakes are doing near the north pole." 
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the mission for NASA's Science Mission Directorate, Washington. The California Institute of Technology in Pasadena manages JPL for NASA. The VIMS team is based at the University of Arizona in Tucson. The imaging operations center is based at the Space Science Institute in Boulder, Colo. 
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High Above Saturn
This portrait looking down on Saturn and its rings was created from images obtained by NASA's Cassini spacecraft on Oct. 10, 2013. It was made by amateur image processor and Cassini fan Gordan Ugarkovic. This image has not been geometrically corrected for shifts in the spacecraft perspective and still has some camera artifacts.The mosaic was created from 12 image footprints with red, blue and green filters from Cassini's imaging science subsystem. Ugarkovic used full color sets for 11 of the footprints and red and blue images for one footprint.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.
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Quelle: NASA

Tags: Cassini Saturn-Mond Titan 

2614 Views

Donnerstag, 24. Oktober 2013 - 09:54 Uhr

Astronomie - Die entfernteste Galaxie entdeckt: Galaxy von Epoche 700.000.000 Jahre nach dem Big Bang gesehen.

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This Hubble Space Telescope image shows the most distant galaxy discovered to date. The green panel zooms in on the galaxy, which is observed as it existed only 700 million years after the Big Bang.

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Astronomers have identified the most distant galaxy found to date.
The galaxy, z8_GND_5296, sits 13 billion light-years from Earth, so astronomers see the object as it existed only 700 million years after the Big Bang. Steven Finkelstein of the University of Texas at Austin and his colleagues describe the discovery October 23 in Nature.
The extremely distant galaxy, observed in a patch of sky near the Great Bear constellation, makes new stars more than 100 times faster than the Milky Way, the astronomers report. The observation suggests that the early universe may have more areas with relatively high star formation than astronomers expected. The results also raise questions about the conditions of the early universe and how that environment influences astronomers' hunt for the first galaxies ever formed. 
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Quelle: ScienceNews
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UC Riverside Astronomers Help Discover the Most Distant Known Galaxy

Galaxy is seen as it was just 700 million years after the Big Bang

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RIVERSIDE, Calif. — University of California, Riverside astronomers Bahram Mobasher and Naveen Reddy are members of a team that has discovered the most distant galaxy ever found. The galaxy is seen as it was just 700 million years after the Big Bang, when the universe was only about 5 percent of its current age of 13.8 billion years.
Results appears in the Oct. 24 issue of the journal Nature.
In collaboration with astronomers at the University of Texas at Austin, Texas A & M University, and the National Optical Astronomy Observatories, Mobasher and Reddy identified a very distant galaxy candidate using deep optical and infrared images taken by the Hubble Space Telescope.  Follow-up observations of this galaxy by the Keck Telescope in Hawai’i confirmed its distance.
In searching for distant galaxies, the team selected several candidates, based on their colors, from the approximately 100,000 galaxies identified in the Hubble Space Telescope images taken as a part of the CANDELS survey, the largest project ever performed by the Hubble Space Telescope, with a total allocated time of roughly 900 hours. However, using colors to sort galaxies is tricky because some nearby objects can masquerade as distant galaxies.
Therefore, to measure the distance to these galaxies in a definitive way, astronomers use spectroscopy — specifically, how much the wavelength of a galaxy’s light has shifted towards the red-end of the spectrum as it travels from the galaxy to Earth, due to the expansion of the universe. This phenomenon is called “redshift.” Since the expansion velocity (redshift) and distances of galaxies are proportional, the redshift gives astronomers a measure of the distance to galaxies.
“What makes this galaxy unique, compared to other such discoveries, is the spectroscopic confirmation of its distance,” said Mobasher, a professor of physics and observational astronomy.
Mobasher explained that because light travels at about 186,000 miles per second, when we look at distant objects, we see them as they appeared in the past. The more distant we push these observations, the farther into the past we can see.
“By observing a galaxy that far back in time, we can study the earliest formation of galaxies,” he said.  “By comparing properties of galaxies at different distances, we can explore the evolution of galaxies throughout the age of the universe.”
The discovery was made possible by a new instrument, MOSFIRE, commissioned on the Keck Telescope. Not only is the instrument extremely sensitive, but it is designed to detect infrared light — a region of the spectrum to where the wavelength of light emitted from distant galaxies is shifted — and could target multiple objects at a time. It was the latter feature that allowed the researchers to observe 43 galaxy candidates in only two nights at Keck, and obtain higher quality observations than previous studies.
By performing spectroscopy on these objects, researchers are able to accurately gauge the distances of galaxies by measuring a feature from the ubiquitous element hydrogen called the Lyman alpha transition. It is detected in most galaxies that are seen from a time more than one billion years from the Big Bang, but as astronomers probe earlier in time, the hydrogen emission line, for some reason, becomes increasingly difficult to see.
Of the 43 galaxies observed with MOSFIRE, the research team detected this Lyman alpha feature from only one galaxy, z8-GND-5296, shifted to a redshift of 7.5. The researchers suspect they may have zeroed in on the era when the universe made its transition from an opaque state in which most of the hydrogen is neutral to a translucent state in which most of the hydrogen is ionized (called the Era of Re-ionization).
“The difficulty of detecting the hydrogen emission line does not mean that the galaxies are absent,” said Reddy, an assistant professor of astronomy. “It could be that they are hidden from detection behind a wall of neutral hydrogen.”
The team’s observations showed that z8-GND-5296 is forming stars extremely rapidly — producing each year ~300 times the mass of our sun. By comparison, the Milky Way forms only two to three stars per year. The new distance record-holder lies in the same part of the sky as the previous record-holder (redshift 7.2), which also happens to have a very high rate of star-formation.
“So we’re learning something about the distant universe,” said Steven Finkelstein at the University of Texas at Austin, who led the project. “There are way more regions of very high star formation than we previously thought. There must be a decent number of them if we happen to find two in the same area of the sky.”
“With the construction and commissioning of larger ground-based telescopes — the Thirty Meter Telescope in Hawai’i and Giant Magellan Telescope in Chile — and the 6.5 meter James Webb Space Telescope in space, by the end of this decade we should expect to find many more such galaxies at even larger distances, allowing us to witness the process of galaxy formation as it happens,” Mobasher said.
Other team members include Mark Dickinson of the National Optical Astronomy Observatory; Vithal Tilvi of Texas A&M; and Keely Finkelstein and Mimi Song of the University of Texas at Austin.
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This image from the Hubble Space Telescope CANDELS survey highlights the
most distant galaxy in the universe with a measured distance, dubbed
z8-GND-5296. The galaxy’s red color alerted astronomers that it was
likely extremely far away, and thus seen at an early time after the Big
Bang. The magnified image results from stacks of optical and infrared images taken, respectively, by the Advanced Camera for Survey (ACS) and Wide-Field Camera 3 (WFC3) on board the Hubble. The galaxy has a mass of ~109 times the mass of the Sun and is at a distance of ~13 billion light years from us, forming stars nearly 150 times more rapidly than our galaxy. Image credit: V. Tilvi, S.L. Finkelstein, C. Papovich, STScI/NASA.
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Quelle: University of California, Riverside

2650 Views

Mittwoch, 23. Oktober 2013 - 23:40 Uhr

Astronomie - Bergung des Tscheljabinsk-Meteoriten

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16.08.2013

Im Gebiet Tscheljabinsk wird die Bergung des im Februar in einem See abgestürzten Meteoriten ausgeschrieben, berichtet die Zeitung „Moskowski Komsomolez“ am Donnerstag.

Die Behörden wollen umgerechnet etwa 70 000 Euro in die Bergung investieren. Der künftige Auftragnehmer  muss „einen ovalen Körper mit einem Durchmesser von 0,3 bis einem Meter und einen Gewicht von bis zu 600 Kilogramm aus einer Tiefe von mindestens 16 Metern heben“. Interessierte Auftragnehmer müssen sich bis zum 19. August melden. Die Ausschreibung beginnt am 23. August.

Der Meteorit war am 15. Februar im Gebiet Tscheljabinsk abgestürzt. Auf dem Grund des Tschebarkulsees soll das größte Fragment des Himmelkörpers liegen. Die bisherige Suche blieb bislang erfolglos – nicht zuletzt wegen der drei Meter dicken Schlammschicht auf dem Grund des Sees.

Auch andere Länder boten ihre Hilfe an, konnten den Meteoriten allerdings auch nicht an die Oberfläche holen. Experten aus Tschechien wollten Meteoriten im Wasser einfrieren und ihn anschließend heben. Andere Experten wollten einen Betonschacht bauen und anschließend Wasser und Schlamm abschöpfen.

Nach mehreren gescheiterten Bergungsversuchen bat der Bürgermeister der Stadt Tschebarkul russische und internationale Organisationen um Hilfe. Der Gouverneur des Gebiets Tscheljabinsk, Michail Jurewitsch, lehnt jedoch die  fremde Hilfe ab.

Das regionale Umweltministerium will den Meteoriten nach seiner Bergung dem Tscheljabinsker Landeskundemuseum übergeben. „Der Himmelskörper wird im Gebiet Tscheljabinsk bleiben. Er ist eine wichtige Sehenswürdigkeit. Wie der Meteorit geborgen wird, steht noch nicht fest. Zunächst muss der Grund des Sees untersucht werden. Dann werden die genauen Koordinaten und Charakteristiken des Himmelskörpers bestimmt. Erst danach wird er gehoben“, betonte die Sprecherin der Umweltministeriums.

Quelle: RIANOVOSTI

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Update: 13.09.2013

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Bei Tscheljabinsk sind die Arbeiten an der Bergung des größten Fragments des Meteoriten begonnen worden, der über den Köpfen der Stadtbewohner am 15. Februar 2013 vorbeigeflogen und direkt in den See Tschebarkul gelandet war.

Die Größe des Meteoriten, der im Wasser liegt, macht bei einer Masse von 600 Kilogramm von 0,3 bis einem Meter aus.

 Er ist ein Splitter eines größeren Himmelskörpers, der die Erdatmosphäre betreten und eine Explosion verursacht hat, die in vielen Regionen von Russland und Kasachstan zu sehen war.
Quelle: Stimme Russlands


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Update: 25.09.2013 
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Tiny Chelyabinsk Meteorite Fragment Found, Big to Be Lifted Soon

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YEKATERINBURG, September 25 (RIA Novosti) – While removing silt in an effort to fish out a huge chunk of meteorite from the bottom of a lake in Russia’s Urals, divers recovered a smaller meteorite on Tuesday, scientists said.
A meteorite, estimated to weigh about 10,000 metric tons, exploded over the Chelyabinsk Region in February. The biggest of chunks that the celestial body fragmented into ended up in the local Chebarkul Lake, and silt is now being pumped from the lakebed to recover it.
According to scientists, the huge chunk, weighting hundreds of metric tons, is buried under a 2.5-meter (8.2-foot) layer of silt. Scientists expect to remove the silt around it on Wednesday evening.
However, divers came across a smaller one on Monday evening, but were unable to recover it because of a huge amount of silt on the lakebed. The rock was eventually recovered early on Tuesday.
“A meteorite chunk roughly the size of a human fist has been lifted from the depth of 13 meters [43 feet] in Lake Chebarkul,” the Urals Federal University said in a statement.
Viktor Grokhovsky, the founder and longstanding leader of the university’s meteorite expedition, said he studied the images of the smaller meteorite and confirmed its space origin.
“I received images of this object, which according to members of the expedition has slight magnetic properties and has a brown crust with traces of smelting. I confirmed that this indeed was a meteorite,” he said.
The celestial body, later named the Chelyabinsk meteorite, exploded above the city on February, 15, leaving about 1,500 injured, mostly due to glass shattered by the shockwave. Scientists said the space rock was a typical chondrite (non-metallic meteorite).
 
Quelle: RIANOVOSTI

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Update: 27.09.2013 

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Probable Fragments of Chelyabinsk Meteorite Lifted From Lake

 

 

YEKATERINBURG, Divers have lifted from a Ural Mountain lake five rocks thought to be fragments of the meteorite that exploded in February near the Russian city of Chelyabinsk, a local environment ministry said Thursday.
The fragments, ranging from 10 to 30 centimeters in diameter, will now be handed over to scientists for a thorough examination, the Chelyabinsk Region’s Radiation and Environmental Safety Ministry said in an online statement.
The entire meteorite is estimated to have weighed 10,000 metric tons. Divers have been working to fish out a huge chunk – thought to weigh several hundred kilograms – buried under a 2.5-meter (eight-foot) layer of silt at the bottom of Lake Chebarkul.
Currently, silt is being pumped out of the lakebed to free that piece and possibly find others. The environment ministry’s head, Alexander Galichin, has said he believes that the large chunk will be recovered by October 4.
The meteorite exploded on February 15, leaving about 1,500 people injured, mostly due to glass shattered by the shockwave. Scientists have said the space rock was a typical chondrite, a stony, non-metallic meteorite.
Quelle: RIANOVOSTI

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Update: 28.09.2013

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Almost 5-kilo meteorite piece retrieved from Chebarkul Lake

CHELYABINSK.  Divers have retrieved another fragment of the meteorite that landed in the Chebarkul Lake in the Chelyabinsk region in February, Chebarkul city administration press secretary Lyubov Rudometova told Interfax on Friday.

"Divers have retrieved the largest meteorite fragment so far with a weight of 4.8 kilograms," she said.

The divers are searching for meteorite fragments at the depth of 16 meters. The water depth is ten meters and the rest is silt, Rudometova said.

The meteorite exploded in the sky above Chelyabinsk on February 15. The blast wave broke windows and damaged roofs of apartment, industrial and social buildings. More than 1,600 people were wounded and the material damages sustained amounted to nearly one billion rubles.

A large part of the meteorite is believed to be lying at the bottom of Chebarkul Lake.

Reportedly, the meteorite fragment of 50 to 90 centimeters is stuck in the silt at an approximate depth of nine meters. Divers have found several fragments and the largest piece is expected to be retrieved by October 4.

A previous large meteorite fragment of 3.4 kilograms was found by a local resident near the town of Timiryazevsky in the Chelyabinsk region in May.

Quelle: Interfax

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Update : 30.09.2013. 

Das Geheimnis verbirgt sich tiefer als gedacht

Im Gebiet Tscheljabinsk in Russland gehen die Arbeiten zum Bergen eines Meteoriten fort. Es wird angenommen, dass ein Teil des Himmelkörpers, der im Februar dieses Jahres über der Stadt Tscheljabinsk explodiert war, in einen See in der Nähe der Ortschaft Tschebarkul gestürzt ist. Den Tauchern ist es bereits gelungen, mehrere Bruchstücke zu bergen. Das Gewicht des größten von ihnen beträgt rund fünf Kilo. Fachleute sind sich dessen sicher, dass auf dem Seegrund noch einige Fragmente liegen.
Die spezielle Plattform, von der aus sich die Taucher in die Tiefe begeben, ist vom Seeufer von der Seite des Städtchens Tschebarkul kaum zu sehen. An die weiße Kuppel der Tauchstation kommen die Taucher mit Motorbooten mehrere Male am Tag gefahren. Gearbeitet wird ohne arbeitsfreie Tage und ohne Pausen, erzählte dem Korrespondenten des Rundfunksenders STIMME RUSSLANDS Nikolai Mursin, der Generaldirektor des Unternehmens „Aleut“, das sich mit der Bergung des Meteoriten beschäftigt. In den letzten Tagen hätten die Taucher tiefer als das voraussichtliche Niveau tauchen müssen. Doch würden alle Arbeiten im etatmäßigen Modus ausgeführt, stellte Nikolai Mursin fest:
„In der Tiefe von neun Meter beginnt eine Schlammschicht, und weiter folgt unsere Auffahrung. Gegenwärtig wird in einer Tiefe von 16 bis 18 Metern gearbeitet. Die Arbeiten schreiten voll und ganz in Übereinstimmung mit dem Plan voran, der bei uns vorliegt. Es geschieht nichts Außerordentliches. Wir halten die Termine ein, die im Vertrag festgesetzt worden sind: 28 Tage seit dem Datum der Unterschreibung des Vertrages. Alles, was es dort gibt, lassen wir nach oben schaffen, in welcher Art, das lässt sich nur schwer sagen. Wir verfügen über spezielle Vorrichtungen, die uns befähigen, in metertiefen Schlammablagerungen zu arbeiten. Über alle geborgenen Bruchstücke informieren wir unverzüglich den Auftraggeber und übergeben sie laut Protokoll.“
Die einzige Schwierigkeit, mit der sich die Fachleute bisher konfrontiert sehen, ist die erhöhte Aufmerksamkeit für ihre Arbeit von Seiten der Journalisten. Doch ist es gelungen, auch dieses Problem operativ zu lösen.
„In den letzten Tagen unserer Arbeit, als es uns gelungen war, mehrere Fragmente vom Seegrund zu bergen, kamen Fernsehleute zu uns. Danach begann eine regelrechte Pilgeraktion der Bevölkerung auf Booten. Doch half uns die Staatliche Inspektion für kleinere Wasserfahrzeuge (russische Abkürzung: GIMS) aus der Not. Seit drei Tagen verrichten sie ihren Dienst bei uns. Wir dürfen ja niemandem das Fahren verbieten.“
In Tschebarkul selbst gibt es keinerlei Rummel wegen der Bergungsarbeiten, obwohl jeder Einwohner der Stadt ganz genau wissen will, wo der Himmelskörper niedergegangen sei. Zeugen behaupten, dass er abgeschossen worden sei. Allerdings ist es unklar, von wem und womit. Versionen dafür gibt es genug, von Vertretern außerirdischer Zivilisationen und UFOs bis hin zu den Raketen der Luftabwehr. Tschebarkuls Einwohner Dmitri behauptet, die Explosion mit eigenen Augen gesehen zu haben:
„Es hat ein Leuchten durch den Niedergang des Meteoriten gegeben, wonach ihn etwas abgeschossen hat. Es knallte laut. Doch meiner Meinung nach ist das Gros des Meteoriten in Richtung Ufa weitergeflogen. Das wäre, was ich gesehen habe. Und die weiße Rauchschleife vom Meteoriten war noch etwa eine halbe Stunde am Himmel zu sehen. Ehrlich gesagt, wir haben nicht verstanden, dass der Meteorit in unseren See gestürzt ist.“
Heute regt die Einwohner von Tschebarkul und dessen Umgebung mehr nicht etwa auf, wann man den Meteoriten bergen würde, sondern ob der Gast aus dem Weltraum nicht radiaktiv ist. Dmitri fährt fort:
„Das nehmen wir uns sehr zu Herzen. Beispielsweise habe ich in diesem Jahr eben aus diesem Grunde nur einmal im See gebadet. Es kann ja allerhand Unangenehmes geben, die Strahlung, die Mutation von Fischen. Wir befürchten es dennoch. Dies umso mehr, als man uns gar nichts sagt.“
 Am 15. Februar war am Himmel über dem Gebiet Tscheljabinsk ein Meteorit explodiert. In der Metropole des Südurals hat die Explosionsdruckwelle Fensterscheiben in Wohnhäusern, Werkhallen und in anderen Industrie- und Sozialobjekte herausgeschlagen. Mehr als 1.500 Personen wurden verletzt. Der Schaden durch dieses Vorkommnis hat rund eine Milliarde Rubel betragen.
Quelle: Stimme Russlands

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Update: 16.10.2013 

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Fast 600 Kilo schweres Bruchstück von Tscheljabinsk-Meteorite vom Seegrund geborgen

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Vom Grund des Tschebarkul-Sees im Gebiet Tscheljabinsk ist am Mittwoch der mit rund 570 Kilogramm größte Splitter des Tscheljabinsk-Meteoriten geborgen worden.
Das riesige Bruchstück zersplitterte in mindestens drei Teile. Das genaue Gewicht konnte nicht gemessen werden, da die Waage kaputtging.
Russische Wissenschaftler haben bestätigt, dass dieses Fragment ein Meteorit ist.
 "Nach den für Steinmeteoriten charakteristischen Merkmalen kann man sagen, dass dieser Splitter ein Fragment des Tscheljabinsk-Meteoriten ist. Er hat eine starke Schmelzkruste, deutlich sichtbaren Rost und zahlreiche Dellen“, sagten Experten.
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Quelle: STIMME RUSSLANDS
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Russische Wissenschaftler haben womöglich Überreste eines Meteoriten gefunden, dessen Explosion im Ural vor acht Monaten schwere Schäden anrichtete und 1200 Menschen verletzte. Der etwa 1,5 Meter lange Gesteinsbrocken wurde aus einem See gehievt.
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Russische Wissenschaftler haben womöglich Überreste eines Meteoriten gefunden, dessen Explosion im Ural vor acht Monaten schwere Schäden angerichtet und rund 1200 Menschen verletzt hatte. Der Einsatz im Tschebarkul-See wurde im russischen Fernsehen übertragen. Auf Live-Bildern war zu sehen, wie der etwa 1,5 Meter lange Gesteinsbrocken aus dem See gehievt wurde.
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Als der Stein mit Hilfe von Seilen auf eine Waage befördert werden sollte, zerbrach er in mindestens drei Teile. Auch die Waage ging zu Bruch, als sie 570 Kilogramm anzeigte. "Wir glauben, dass das ganze Teil mehr als 600 Kilo wiegt", sagte einer der beteiligten Forscher der Internetseite "lifenews.ru".
Der Meteorit war Mitte Februar über der mehr als eine Million Einwohner zählenden Stadt Tscheljabinsk und der gleichnamigen Region mit einem grellen Blitz und einer Druckwelle explodiert. Zahlreiche Gebäude wurden beschädigt und etwa 1200 Menschen verletzt. Der Meteorit zerbrach bei seinem Eintritt in die Atmosphäre in mehrere Teile, die größtenteils auf dem Grund des Tschebarkul-Sees vermutet werden.
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Nach Einschätzung von Experten dauert es noch eine Weile, bis zweifelsfrei feststeht, ob es sich bei dem geborgenen Felsbrocken tatsächlich um ein Fragment des Meteoriten handelt. Laut dem Fernsehsender Westi 24 haben Taucher bereits zwölf vermeintliche Bruchstücke aus dem See geholt. Nur in vier Fällen stammte das Gestein tatsächlich aus dem All.
Quelle: donaukurier

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Update: 17.10.2013

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Quelle+Frams von DW-Video

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Update: 22.10.2013 

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Tscheljabinsk-Meteorit: Satelliten waren Zeuge
Forscher ermitteln die genaue Flugbahn aus zufällig entstandenen Satellitenaufnahmen

Infrarotaufnahme des Wettersatelliten Meteosat-9 von der Spur des Tscheljabinsk-Meteoriten

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Tscheljabinsk-Meteorit: Satelliten waren Zeuge
Forscher ermitteln die genaue Flugbahn aus zufällig entstandenen Satellitenaufnahmen
Als am 15. Februar 2013 der Tscheljabinsk-Meteorit über Russland raste und explodierte, machten auch einige Wettersatelliten zufällig Aufnahmen davon. Das Problem dabei: Ihre Daten zur Flugbahn weichen stark voneinander ab. US-Forscher haben nun geklärt, warum das so ist und wie sich trotzdem aus solchen Daten die genaue Flugbahn errechnen lässt. Wichtig ist dies vor allem für die Fälle, in denen Videos oder Beobachtungsdaten vom Boden aus fehlen, so die Forscher im Fachmagazin "Proceedings of the National Academy of Science".
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Als ein Meteorit am 15. Februar 2013 über der russischen Stadt Tscheljabinsk explodierte, waren die Folgen dramatisch. Es wurde die Energie von 100 bis 500 Kilotonnen TNT freigesetzt, Gesteinstrümmer regneten auf die Stadt und Umgebung hinab, zerstörten Gebäude und verletzten hunderte von Menschen. "In seiner Wirkung erinnerte der Meteorit an das Tunguska-Ereignis im Juni 1908", erklären Steven Miller von der Colorado State University und seine Kollegen. Der aus Gestein bestehende 50-Meter-Brocken explodierte ebenfalls in der Luft und löste dabei eine Schockwelle aus, die 2.200 Quadratkilometer Wald der sibirischen Taiga umfegte. 
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Zufall machte auch Satelliten zu Zeugen
Solche Ereignisse waren zwar in der menschlichen Geschichte bisher selten, sie erinnern aber daran, dass die Gefahr eines kosmischen Treffers durchaus real ist, wie die Forscher erklären. Deshalb sei es wichtig, möglichst genau zu wissen, welche Flugbahn ein solcher Bolide hatte und wo er herkam. Denn das helfe dabei, die Wahrscheinlichkeit künftiger Einschläge abzuschätzen. Im Falle des Tscheljabinsk-Meteoriten ließ sich aus Videoaufnahmen vom Boden aus rekonstruieren, dass der Brocken in einem flachen Winkel in die Atmosphäre eintrat und mit rund 18 Kilometern pro Sekunde in Richtung Westen raste.
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Scheinbare Flugbahnen, beobachtet von zwei Satelliten, und tatsächliche Bahn des Meteoriten.
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Auch einige Fernerkundungs-Satelliten zeichneten die Gas- und Staubspur des Meteoriten auf, darunter einige geostationäre Wettersatelliten verschiedener Länder, aber auch ein in einer Bahn über die Pole kreisender militärischer Wettersatellit der USA. Durch einen glücklichen Zufall machte er nur wenige Minuten nach der Explosion des Meteors eine Aufnahme, auf der der Staubschweif des Boliden zu erkennen war. Diese Satellitenbilder liefern wertvolle Zusatzinformationen über die Flugbahn eines solchen Objekts, weil sie ihn von oben oder schräg von der Seite sehen, nicht von unten wie irdische Beobachter. Zudem tasten sie ihr Gesichtsfeld meist in mehr als nur den sichtbaren Wellenlängen des Lichts ab. 
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Extreme Abweichungen
Doch für die Flugbahn des Tscheljabinsk-Meteoriten sorgten ihre Daten bisher mehr für Verwirrung als für Aufklärung: Denn die in ihren Aufnahmen aufgezeichneten Flugbahnen wichen extrem voneinander ab. Unter allen Satellitenaufzeichnungen gab es keine zwei, die in punkto Position, Höhe oder Flugbahn übereinstimmten. "Die Abweichung ist teilweise so groß, dass die Bahnen von unterschiedlichen Ereignissen zu kommen scheinen", berichten die Forscher.
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In ihrer Studie nahmen sich Miller und seine Kollegen diese Satellitenaufnahmen noch einmal vor und untersuchten, wie diese Abweichungen zustande kommen. Dabei prüften sie auch, ob und wie sich aus der Kombination aller Aufnahmen vielleicht doch die tatsächliche Bahn des Meteoriten ermitteln lässt. Wie sich zeigte, liegt der Uneinigkeit der Satelliten ein simpler optischer Effekt zugrunde: "Wenn Objekte vor einem weiter hinten liegenden Hintergrund aus einer schrägen Perspektive angeschaut werden, erscheinen sie versetzt", erklären die Forscher.
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Fotografie der Meteoritenspur vom Boden aus und Satellitenaufnahme
Parallaxen-Effekt ist schuld
Dieser sogenannte Parallaxen-Effekt lässt sich auf einfache Weise nachvollziehen: Hält man seinen Daumen vor das Gesicht und kneift dann erst eines, dann das andere Auge zu, scheint der Daumen vor dem Hintergrund hin und her zu springen. Genau dieser Effekt beeinträchtigt auch die Lagebestimmung der Meteoritenflugbahn durch die Satelliten. Doch das lässt sich korrigieren, wenn man die genaue Höhe, Position und den Blickwinkel der verschiedenen Satelliten kennt.
Die Wissenschaftler nutzten diese Informationen, um den verzerrenden Parallaxen-Effekt aus den Daten herauszurechnen. Dadurch konnten sie die tatsächliche Flugbahn des Tscheljabinsk-Meteoriten ermitteln. Er durchquerte die Erdatmosphäre demnach mit einer Neigung von 18,5° und mit einem Azimut von 287,7° - das entspricht in etwa einer Flugrichtung nach West-Nordwest. Wie die Forscher feststellten, raste der Meteorit dabei aber nicht in einer linearen Bahn zur Erde, sondern eher in einer langsamer werdenden Parabel. 
Diese Ergebnisse stimmen gut mit den Beobachtungen vom Boden aus überein. Noch wichtiger aber: "Sie zeigen, dass Erdbeobachtungs-Satelliten grundsätzlich wertvolle Informationen über die Flugbahn von Meteoren und Meteoriten liefern können - auch dann, wenn es keine oder nur sehr spärliche Beobachtungen vom Boden aus gibt", so Miller und seine Kollegen. Dadurch lassen sich auch solche Ereignisse verfolgen und erforschen, die über unbewohntem Gebiet stattfinden. (Proceedings of the National Academy of Sciences, 2013;
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Quelle: SCINEXX
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Update: 23.10.2013 - Das war die Flugbahn des Meteoriten

Es war der grösste Brocken aus dem All seit Jahrzehnten, der im Februar über dem russischen Tscheljabinsk explodierte. Forscher haben nun die Flugbahn des Meteoriten rekonstruiert.

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Das aus dem Tschebarkulsee geborgene Bruchstück des Meteoriten wiegt rund 570 Kilogramm.
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Seit 1947 war vermutlich kein grösserer Gesteinsbrocken aus dem Weltall in die Erdatmosphäre eingedrungen. Der Meteorit von Tscheljabinsk dürfte nach Berechnungen der Astronomen einen Durchmesser von 20 Metern und eine Masse von 10'000 Tonnen gehabt haben.
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Dieser Superbolide trat mit einer Geschwindigkeit von etwa 18 Kilometern pro Sekunde in die Atmosphäre ein und leuchtete kurzzeitig heller als die Sonne, bevor er über der westsibirischen Stadt Tscheljabinsk explodierte. Eine enorme Druckwelle liess zahlreiche Fensterscheiben in der Region bersten; knapp 1500 Personen wurden verletzt.
Ein grosses Bruchstück des Gesteinsgiganten ging in den Tschebarkulsee etwa 80 Kilometer südwestlich von Tscheljabinsk nieder. Erst am 16. Oktober konnten Taucher das enorme Fragment des Himmelskörpers aus dem See bergen. Es wog rund 570 Kilogramm.
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Satellitenbilder genutzt
Obwohl im Februar zahlreiche Videos und Fotos die Flugbahn der Meteoritentrümmer festhielten, liess sich diese nicht exakt bestimmen. Erst jetzt haben Forscher Bilder von Wettersatelliten mit den Aufnahmen von Augenzeugen kombiniert und so die Flugbahn rekonstruiert. Das Team um Steven Miller von der Colorado State University verwendete dabei Aufnahmen von geostationären Wettersatelliten und Fotos eines amerikanischen militärischen Wettersatelliten. Ihre Ergebnisse veröffentlichten sie im Fachmagazin «Proceedings of the National Academy of Science» (PNAS).
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Die Astronomen betonen, die Berechnung der Meteoriten-Flugbahn sei wichtig, um die Wahrscheinlichkeit künftiger Einschläge abzuschätzen. «Meteoriteneinschläge sind ernüchternde Zeugnisse für die Verletzbarkeit der Zivilisation», mahnen die Forscher.
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Das Gesteinsfragment liegt nun im Museum von Tscheljabinsk.
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Der Meteorit war am 15. Februar 2013 mit einer Geschwindigkeit von etwa 18 Kilometern pro Sekunde in die Atmosphäre eingetreten und leuchtete kurzzeitig heller als die Sonne, bevor er über Tscheljabinsk explodierte. Eine enorme Druckwelle liess zahlreiche Fensterscheiben in der Region bersten; knapp 1500 Personen wurden verletzt.
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Vergleich der Satellitenaufnahmen: aus Nordwesten Satellit DMSP F-16 (58.54°N, 45.65°E; 833 km), ...
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... aus Südwesten Meteosat-9 (0.19°N, 9.41°E; 35,786 km). Klein im Bild eine Aufnahme des Schweifs.
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Der Meteorit kam von Nordwesten, wie die Satellitenaufnahme (Bild im Bild) zeigt.
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Zwei Aufnahmen von Meteosat-9: Der Schweif des Meteoriten in nahem Inrarot (NIR) und ...
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... in einer thermischen Infrarot-Aufnahme. Sie zeigt, dass der Schweif nicht heiss ist.
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Aufnahmen des geostationären Satelliten MTSAT zeigen die Entwicklung des Schweifs über drei Stunden hinweg.
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Video: http://www.youtube.com/watch?v=VdoKEFsemvw
Quelle: 20minuten
Siehe auch hier auf dem Blog umfangreiche Beiträge zu Tscheljabinsk-Meteorit:
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14.03.2013 - Astronomie - Bilanz des Meteoriten-Einschlag im Ural - Update
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29.04.2013 - Astronomie - Meteoriten-Einschlag im Ural - Update

 


Tags: Tscheljabinsk-Meteor-Bergung 

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Mittwoch, 23. Oktober 2013 - 13:00 Uhr

Raumfahrt - SpaceX (VTVL) Grasshopper erreicht 2.440 Fuß (744 m) Höhe

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13.10.2013

SpaceX has released spectacular video of the latest test of its vertical take-off and vertical landing (VTVL) Grasshopper which reached 2,440 feet (744 m) altitude – the highest flight yet – on Oct 7. Like some of the latest ‘hops’ the Grasshopper was filmed from a single camera hexacopter which appears to have been hovering at around 2,000 feet. The video shows the Merlin 1D-powered Falcon 9 first stage tank passing by the hexacopter before getting much closer to the camera during the descent. The final phases of the flight also show significant amounts of flame burning alongside the vehicle and through the legs attached to the support structure, in addition to the normal exhaust plume from the vehicle’s single rocket engine.
As with previous tests the latest flight was conducted in McGregor, Texas. Up until now the demonstrator had flown to a height of 820 feet and included a lateral transfer of some 330 feet. In coming months SpaceX  is expected  to move onto tests of a larger version of the Grasshopper also dubbed by SpaceX founder Elon Musk as Falcon 9R (re-usable). Instead of a single Merlin 1D, the v1.1 successor will have nine -1Ds. Testing will be conducted at a specially constructed site at Spaceport America in New Mexico. The VTVL is designed to test the technologies needed to return a rocket back to Earth intact instead of burning up on atmospheric re-entry. The recent Falcon 9 Heavy flight from Vandenberg AFB, Calif, also included a first attempt at slowing the first stage.

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Quelle: SpaceX

Update: 23.10.2013 

A SpaceX Grasshopper rocket launched 744 meters, or 2,440 feet, into the air and landed perfectly intact on Oct. 7, 2013. This is no small feat, considering the rocket in question is the same height as a 10-story building.

 

The SpaceX Grasshopper Vertical Takeoff Vertical Landing (VTVL) vehicle is designed to test the technology required to return a rocket back to Earth in one piece. The largest VTVL ever launched, the Grasshopper features a Falcon 9 first stage, a single Merlin 1D engine, four steel landing legs with hydraulic dampers, and a steel support structure. As the name implies, the goal of the Vertical Takeoff Vertical Landing vehicle is to return a rocket to the pad it launched from, unscathed and ready to be used again.

 

One of the goals of SpaceX is to make rockets reusable, which will cut costs for space travel and, in turn, allow for the exploration of space not to be limited solely to astronauts. In addition, this reusability will revolutionize manned space travel and allow for human habitation of other planets.

 

“If one can figure out how to effectively reuse rockets just like airplanes, the cost of access to space will be reduced by as much as a factor of a hundred,” said Elon Musk, CEO and Chief Designer of SpaceX. “A fully reusable vehicle has never been done before. That really is the fundamental breakthrough needed to revolutionize access to space.”

 

To break down what the cost of space travel in a reusable vehicle would amount to, here are some numbers. The Falcon 9, the rocket inside of the Grasshopper, has a list price of $54 million. The cost of fuel for each flight, however, is only about $200,000 — approximately 0.4 percent of the total. Since the reusable rocket only needs to be built once, most of that list price is already paid for once production is completed. As stated by Musk, SpaceX is inspired by the reusability of the commercial airline model. A typical commercial airliner costs about the same amount of money to produce as a Falcon 9 and can make several trips per day, and thousands of trips over its lifetime. This reusability is what SpaceX hopes to achieve with its rockets.

 

The test launch done recently with the Grasshopper VTVL is a monumental step towards achieving this goal. The test, conducted at SpaceX’s Rocket Development Facility in McGregor, Texas, lasted 78.8 seconds and marks the highest point a rocket has been launched and successfully landed. SpaceX has future tests planned for the Grasshopper VTVL, with a goal height of 1,000 meters, or 3,280 feet.

 

The idea of reusable rockets makes the dream of space travel for the everyday person seem within reach. If this program cuts costs of space exploration by a hundredfold, perhaps the colonization of Mars really will happen during our lifetime. As SpaceX continues to develop and test this technology, we can only wonder if we will someday join the astronauts in the stars.
Quelle: UC Santa Barbara

 

 

 

 


Tags: VTVL Grashopper Merlin 1D SpaceX 

3299 Views

Mittwoch, 23. Oktober 2013 - 09:47 Uhr

Planet Erde - Kleine Drohnen erstellen neue, sehr detaillierte Kartierung von Matterhorn

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Studie: 'BioBots' kann dazu beitragen Karten zu erstellen von verborgenen, gefährlichen Umgebungen.

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Study: 'Biobots' may help map hidden, dangerous environments
Raleigh, A swarm of insect cyborgs, or "biobots," may one day allow the mapping of unknown and dangerous environments such as collapsed buildings, U.S. researchers say.
Researchers from North Carolina State University say they have have developed software that could track a swarm of biobots, such as remotely controlled cockroaches, equipped with electronic sensors and released into a collapsed building or other hard-to-reach area.
"We focused on how to map areas where you have little or no precise information on where each biobot is, such as a collapsed building where you can't use GPS technology," electrical and computer engineering Professor Edgar Lobaton said.
Because the biobots couldn't be tracked by GPS, their precise locations would be unknown, but the sensors would signal researchers via radio waves whenever biobots got close to each other.
The researchers would send a signal commanding the biobots to keep moving until they encounter a wall or other unbroken surface, then keep moving along it, a technique called "wall following."
Repeating cycles of random movement and "wall following" would eventually allow the creation of a map of the unknown environment, they said.
"This would give first responders a good idea of the layout in a previously unmapped area," Lobaton said.
The researchers report they've tested the software using computer simulations and robots and have plans to test the program with biobots.
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The Swiss Alps' iconic Matterhorn has been has been mapped in detail never possible before by a fleet of autonomous, fixed-wing drones, researchers say.
The Matterhorn, dominating the skyline of the Swiss/Italian border at 14,692 feet, has challenged climbers since it was first scaled in 1865.
The new mapping, conducted by unmanned aerial vehicle company SenseFly and aerial photography company Pix4D, was introduced at the Drones and Aerial Robotics Conference in New York City this past weekend, NewScientist.com reported.
Three drones were launched from the peak of the Matterhorn, flying down the mountain just 100 yards from the face while capturing data points just 8 inches apart.
When they reached the bottom of the mountain a second team of researchers recovered the drones and then relaunched them for additional mapping.
"Such a combination of high altitudes, steep rocky terrain and sheer size of data set has simply not been done before with drones, we wanted to show that it was possible," SenseFly's Adam Klaptocz said.
Tiny drone aircraft yielding detailed maps of coral reef ecosystems
Palo Alto, Calif. (UPI) Oct 17, 2013 - Camera-equipped flying robots can yield insights into climate change effects on important ecosystems like coral reefs, researchers in California say.
Many centuries-old living coral reefs remain unmapped and unmeasured, scientists at Stanford University said, and a shoebox-sized flying drone could help unlock mysteries of these marine ecosystems.
Stanford aeronautics graduate student Ved Chirayath has developed a four-rotor remote-controlled drone outfitted with cameras that can film coral reefs from up to 200 feet in the air.
In an initial study, Chirayath and follow Stanford researcher Stephen Palumbi used the drone to precisely map, measure and study shallow-water reefs off Ofu Island in American Samoa.
"Until now the challenges have been too high for flying platforms like planes, balloons and kites," Palumbi said. "Now send in the drones."
Just as surveys and maps of rainforests have resulted in new understanding of the vital role these ecosystems play in sustaining the biosphere, detailed maps of coral reefs oral maps could do the same for marine environments, the researchers said.
The low-level drones provide better maps that other technologies, they said; satellite imagery through water tends to be distorted by wave movement, radar can't penetrate the water's surface, and sonar doesn't work well in the shallow water where most corals reside.
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Quelle:Spacedaily

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