Der Asteroid von Bahnstation 6 29APR09

Meteoriten © 2009 NASA / Peter Jenniskens
Der Asteroid von Bahnstation 6
(lifepr) Heidelberg, 28.04.2009 -
http://www.lifepr.de/pressemeldungen/spektrum-der-wissenschaft-verlagsgesellschaft-mbh/boxid-103016.html

In den Morgenstunden des 7. Oktobers 2008 trat der rund vier Meter große Asteroid 2008TC3 in die Erdatmosphäre ein. Bruchstücke stürzten in die nubische Wüste im nördlichen Sudan. Damit wurde er vom Asteroiden zum Meteoriten. Erstmals wurde ein Himmelskörper mit Kollisionskurs auf die Erde beobachtet und bis zu seinem Aufprall verfolgt. Wissenschaftler fanden zwei Monate später Bruchstücke von 2008TC3 nahe einer Eisenbahnlinie, welche die beiden nordsudanesischen Städte Wadi Halfa und Abu Hamad verbindet. Untersuchungen zeigten nun, dass die Gesteinsbrocken einzigartig sind.

2008TC3 gehört zu den so genannten Achondriten, einer seltenen Klasse von Steinmeteoriten, die nur rund acht Prozent aller Meteoriten ausmacht, die auf die Erde fallen. Innerhalb dieser Klasse gehört er wiederum einer Unterart an, von der bisher nur ein einziges Exemplar auf der Erde gefunden wurde. Wissenschaftler suchten nach dem möglichen Herkunftsort von 2008TC3 und fanden einen rund drei Kilometer großen, erdnahen Asteroiden der Klasse F. Noch nie wurden Bruchstücke dieser seltenen Art im Labor untersucht.

Almahata Sitta - Bahnstation 6 Im Dezember 2008 suchte der NASA-Astronom und Meteoritenexperte Peter Jenniskens mit 45 anderen Personen in der sudanesischen Wüste nach Überbleibsel des Meteoriten. Nahe der ägyptischen Grenze, bei der Bahnstation Nummer 6 der Eisenbahnlinie zwischen Wadi Halfa und Abu Hamad wurden sie fündig. Insgesamt sammelten sie rund vier Kilogramm Gestein. Der Meteorit trägt nun den Namen seines Fundgebietes. Almahata Sitta, arabisch für Bahnstation 6.

Chronologie der Ereignisse
Ein Programm zur automatischen Himmelsüberwachung entdeckte 2008TC3 am 6. Oktober 2008. Rund dreizehn Stunden vor dem Aufprall errechneten Wissenschaftler seine Bahn. Aufgrund der geringen Größe des Himmelskörpers, erwarteten Experten, dass er vollständig in der Erdatmosphäre verglühen würde. Wenn nicht, würde er um 4:45 Uhr MESZ im nördlichen Sudan niedergehen. Mit einer Geschwindigkeit von mehr als zwölf Kilometern pro Sekunde raste 2008TC3 durch die irdische Lufthülle, leuchtete hell auf und explodierte in einer Höhe von rund 37 Kilometern. Übrig blieb eine Staubspur, die von Satelliten und vom Erdboden aus fotografiert wurde. 2008TC3 wog zwischen sechzig und hundert Tonnen und setzte eine Energie von etwa einem Zehntel der Hiroshima-Bombe frei, wie die Fachzeitschrift Sterne und Weltraum in ihrer Mai-Ausgabe feststellt.

Über Sterne und Weltraum
"Sterne und Weltraum", die 1962 gegründete Zeitschrift für Astronomie, berichtet umfassend, anschaulich und informativ über alle Bereiche der Astronomie, der Weltraumforschung und der Amateurastronomie. Fachleute präsentieren allgemeinverständlich die aktuellen Ergebnisse ihrer astronomischen Forschung und beschreiben die Entwicklung neuartiger Instrumente, Observatorien und Messverfahren. Amateurastronomen geben Tipps zum Beobachten interessanter Himmelsobjekte und -phänomene, testen Teleskope und deren reichhaltiges Zubehör und geben dem Sternfreund fundierte Anleitungen zur eigenständigen Erkundung des Sternenhimmels, zur Astrofotografie sowie zum Auswerten ihrer Beobachtungen. Produkte für die Amateurastronomie werden ebenso vorgestellt wie die schönsten Fotos von Galaxien, Sternhaufen und farbenprächtigen Nebeln. Beiträge aus der Astronomiegeschichte und zu Fragen des naturwissenschaftlichen Weltbildes runden das Themenspektrum ab.

Quellenangabe: Sterne und Weltraum, 5/2009

2008 TC3, Almahata Sitta meteorite came from F-class asteroid 26MAR09

http://www.sciam.com/article.cfm?id=asteroid-meteorite-sudan-fireball

Rock Science: First Meteorites Recovered on Earth from an Asteroid Tracked in Space Fragments in the Sudanese desert make up an "asteroid trifecta":
discovery, prediction and recovery By John Matson Scientific American March 25, 2009

Last October, asteroid monitors at the Catalina Sky Survey at the University of Arizona in Tucson picked up a small object on an immediate collision course with Earth. The asteroid was too small to present a real threat - just a few meters across, it stood little chance of penetrating the atmosphere intact. Indeed, it exploded in astratospheric fireball over northern Sudan less than 24 hours later - anevent witnessed by people on the ground as well as the pilots of a KLM airliner- conforming well to astronomer's predictions for its trajectory. But the asteroid, dubbed 2008 TC3, was nonetheless a momentous discovery: Among the countless small objects that strike Earth's atmosphere every year, none had ever been detected and tracked before it impacted. Now the Sudan bolide has yielded yet another first:

Researchers report in Nature today
<http://www.nature.com/nature/journal/v458/n7237/full/nature07920.html>that they have recovered 47 meteorites from the object in the Nubian Desert. And lead author Peter Jenniskens, a meteor astronomer at the SETI Institute in Mountain View, Calif., says that another search completed earlier this month, after the paper was submitted, has upped the meteorite count to about 280.
Astronomer Donald Yeomans, manager of NASA's Near-Earth Object Programoffice <http://neo.jpl.nasa.gov/> at the Jet Propulsion Laboratory inPasadena, Calif., calls 2008 TC3 "a perfect asteroid trifecta,"referring to "pre-impact discovery, successful impact prediction, and successful sample return." (Yeomans did not contribute to the recovery research, but his office played a leading role in tracking the asteroid's entry <http://www.cfa.harvard.edu/mpec/K08/K08T50.html>.)

The find allows astronomers to connect the chemical composition of the meteorite to its orbit and reflectance in the sky during tracking. "The holy grail of asteroid science is to uniquely link a specific meteorite and its detailed composition to a specific asteroid type," Yeomans says."And that has now been done without an expensive sample-return mission. "This object, which the study's authors call Almahata Sitta (Arabic for Station Six, a train station in the desert where eyewitnesses saw the fireball and that served as the researchers' base camp), appears to belong to a rare class of bodies called F-class asteroids, which constitute just 1.3 percent of all asteroids. Chemically speaking, Almahata Sitta is a meteorite whose specific composition is unique among meteorite collections. It is a fragile, porous ureilite (a relatively rare kind of olivine- and pyroxene-bearing meteorite)containing graphite and nanodiamonds, among other materials. Its fragility, Jenniskens says, helps explain why it broke apart so high in the atmosphere. With the benefit of the object's rarity as an F-class body and its orbit, tracked backward through time, the researchers established a possible link to a larger F-class asteroid, the 1.6-mile-(2.6-kilometer-) diameter 1998 KU2, which may have originated from the same parent body as Almahata Sitta."The orbit of the asteroid, by just tracking it for 20 hours, is 10,000times better than anything you can get from just observing a fireball Jenniskens says. "What's neat about this is that the big asteroid allows you to extend back in time the evolutionary history." He notes that scientists might be able to pinpoint the specific region of the asteroid belt that 2008 TC3 came from with more F-class asteroids from the same parent body. Even the brief amount of time 2008 TC3 was tracked provided an excellent lead on where to look- and the desert surface provided an ideal surface for turning up the dark fragments. "The entry trajectory was very precisely known," Jenniskens says. The first samples were found in early December by a 45-person search team from the University of Khartoum. (Three scientists from that university and one from the University of Juba in Sudan are among the co-authors of the study.) "We had many eyes and hands," Jenniskens says, trying "to find these."

NASA-- Sudan Meteorite Recovery Teleconference to be held 25MAR09

MEDIA ADVISORY : M09-044

NASA Sets Teleconference To Discuss Recovered Meteorites

WASHINGTON -- NASA will hold a media teleconference on Wednesday, March 25, at 2 p.m. EDT (1800 UT) to reveal science findings from recently discovered meteorites.

The meteorites originate from a small asteroid that entered Earth's atmosphere over the Nubian Desert of northern Sudan on Oct. 7, 2008. The discovery presents scientists with an unprecedented opportunity to understand these nomads of the solar system better.

The briefing participants are:

- Peter Jenniskens, meteor astronomer at NASA's Ames Research Center, Moffett Field, Calif., and the SETI Institute in Mountain View, Calif.

- Steve Chesley, scientist in NASA's Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

- Michael Zolensky, cosmic mineralogist at NASA's Johnson Space Center in Houston

- Lucy McFadden, professor of astronomy at the University of Maryland in College Park

Reporters who would like to participate in the call should submit requests for dial-in instructions to Steve Cole at stephen.e.cole@nasa.gov.

A replay of the teleconference will be available until May 1 by dialing 888-403-4660.

Supporting visuals will be available online at the start of the event at: http://www.nasa.gov/topics/earth/tc3

Audio of the teleconference will be streamed live on NASA's Web site at: http://www.nasa.gov/newsaudio

First Tracked Rock Recovered in Sudan (Asteroid 2008 TC3) 21FEB09

http://www.newscientist.com/article/dn16635-first-tracked-space-rock-recovered-after-impact
First tracked space rock recovered after impact-0246 GMT on 7 October-Sudan (Asteroid 2008 TC3)
by David Shiga
New Scientist
February 19, 2009
The discovery of meteorites from an asteroid that exploded over Sudan in October completes an astronomical trifecta. For the first time, scientists have detected a space rock ahead of a collision with Earth, watched it streak through the atmosphere, and then recovered pieces of it. Analysis of the meteorites could shed light on conditions in the early solar system more than 4 billion years ago. When the asteroid, called 2008 TC3, was discovered on 6 October last year, it was just 20 hours away from hitting Earth. Though the warning period was short, it was the first time a space rock had been found before it impacted the planet. Orbital calculations predicted the object would plunge into the atmosphere above Sudan at 0246 GMT on 7 October, and it arrived right ontime. Observations suggested it was no more than 5 metres across, too small to survive intact all the way to the ground and cause damage. The brilliant fireball it made as it descended through the atmosphere was seen far in the distance by the crew of a KLM airliner, and was observed by various satellites, including a weather satellite called Meteosat-8. Now, a team of meteorite hunters has found fragments of the object. The meteorites are a unique group in that they come from an object seen hurtling through space before its plunge into Earth's atmosphere.

Numerous fragments
Students from the University of Khartoum, led by Dr Muawia Shaddad, found the first fragments using data provided by NASA to home in onwhere fragments were likely to be found. Scientists involved with the discovery, including Peter Jenniskens ofthe SETI Institute in Mountain View, California, have reportedly submitted a study about the find to a scientific journal, and have not responded to interview requests. But Lindley Johnson, head of NASA's Near-Earth Object Program office atthe agency's headquarters in Washington, DC, reported the find on Mondayin Vienna, at a United Nations meeting discussing near-Earth object (NEO) impacts. <http://www.oosa.unvienna.org/oosa/en/COPUOS/stsc/2009/index.html>

An image of the first fragment found is included in the slides from Johnson's presentation (pdf) <http://www.oosa.unvienna.org/pdf/pres/stsc2009/tech-25.pdf> (see slide 19).
Donald Yeomans, who manages NASA's efforts to find and track NEOs at the Jet Propulsion Laboratory (JPL) in Pasadena, California, confirmed that"quite a few" fragments have been found but declined to discuss them further.

Weak material?
Before the fragments were found, meteorite expert Peter Brown of the University of Western Ontario in Canada said the asteroid was likely made of relatively weak material, given that 2008 TC3 broke up unusually quickly once it hit the atmosphere, exploding about 37 kilometres above ground. Another object known to have broken up at about this height scattered fragments over Tagish Lake in Canada in 2000. The Tagish Lake meteorites turned out to be made of a very crumbly material, and fall into a class of meteorites called carbonaceous chondrites, which have been modified little by heat or other processes since the solar system formed more than 4.5 billion years ago. "I would caution making direct compositional comparisons [with the Tagish Lake meteorites], but it does certainly underscore the global weakness of [2008 TC3]," Brown said in comments posted on the JPL website in November. He added that observations of the rock's quick breakup "all but rule out" a composition rich in iron. <http://neo.jpl.nasa.gov/news/2008tc3.html>

Point of origin
When the analysis of these rock fragments does come out, what is it likely to tell us? Meteorites in general provide a valuable record of conditions in the early solar system, such as temperature and chemical composition. And the 2008 TC3 meteorites could be especially illuminating because the parent object was observed in space before the breakup, allowing scientists to calculate its former orbit around the Sun. This provides precious information connecting the meteorites to their place of origin in the solar system. For most other meteorites, such calculations involve a lot of guesswork. Meteorites had previously been recovered after about 10 "fireball" events, where parent space rocks were observed streaking through the sky. But in those cases, scientists had to try to reconstruct the object's orbit based on its path through the atmosphere. "It's often very difficult to get from a streak in the sky to what theorbit was," says Allan Treiman of the Lunar and Planetary Institute in Tucson, Arizona. "But if they've got its location before it hit the atmosphere, they're far better off - that's really wonderful."