Astronomie - Forscher entdecken Asteroid 2018 LA, bevor er die Erde erreichte

4.06.2018

Gefährlich war er nicht, aber ein Erfolg: Nasa-Wissenschaftler haben einen kleinen Asteroiden frühzeitig entdeckt und seine Bahn in Richtung Erde verfolgt. Sie konnten trotz geringer Datenmenge einen Korridor vorausberechnen, in dem er in die Erdatmosphäre eintrat.

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Kleiner Asteroid (Symbolbild): Die Modelle zur Vorhersage eines Einschlags sind angemessen.
 

Am vergangenen Samstag haben Forscher einen kleinen Asteroiden auf Kollisionskurs zur Erde entdeckt und seinen Einschlagort vorausberechnen können. Der Asteroid 2018 LA hatte einen Durchmesser von etwa zwei Metern - Objekte dieser Größe verglühen normalerweise in der Erdatmosphäre und richten keinen Schaden an. Dieser wurde vom Catalina-Teleskop in Arizona entdeckt, als er noch etwa so weit entfernt war wie die Mondumlaufbahn. Er erschien als Streifen auf Bildern, die von dem Teleskop aufgenommen wurden.

Die Bilder wurden an das Minor Planet Center in Cambridge im US-Bundesstaat Massachusetts weitergeleitet. Dort berechneten Mitarbeiter eine Bahn und einen möglichen Einschlagort, was aufgrund der wenigen verfügbaren Daten nur ungenau möglich war. Demnach sollte der Asteroid irgendwo zwischen dem südlichen Afrika, dem Indischen Ozean und Neuguinea auf die Erde treffen.

Die Berechnungen erwiesen sich als zutreffend: Der Himmelskörper trat um 18:44 Uhr über Botswana in die Erdatmosphäre ein und verglühte in einem Feuerball. Eine Warnung hatte das Planetary Defense Coordination Office der US-Raumfahrtbehörde National Aeronautics And Space Administration (Nasa) wegen der Größe von 2018 LA nicht ausgegeben.

Es kommt nicht oft vor, dass Himmelskörper, die auf die Erde zufliegen, frühzeitig entdeckt und verfolgt werden. "Der Asteroid 2018 LA war erst der dritte Asteroid, der auf einem Kollisionskurs entdeckt wurde", sagt Paul Chodas, Leiter des Center for Near-Earth Object Studies (CNEOS) am Jet Propulsion Laboratory der Nasa. "Es ist auch erst das zweite Mal, dass die hohe Wahrscheinlichkeit eines Aufpralls weit vor dem Ereignis selbst vorhergesagt wurde."

Quelle: golem.de

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A Tiny Asteroid Just Hit Earth, Sparking a Fireball Over South Africa (Video)

Scientists discovered the asteroid, called 2018 LA, early Saturday. After a closer look at the space rock's trajectory, it "was determined to be on a collision course with Earth, with impact just hours away," NASA officials said in a statement. The asteroid hit Earth's atmosphere over the southern African nation of Botswana at 12:44 p.m. EDT (1644 GMT) while hurtling down at a whopping 38,000 mph (61,155 km/h). That's 10 miles (or 17 kilometers) every second! 

Astronomers with the Catalina Sky Survey near Tucson, Arizona, were the first to discover the asteroid. The space rock was very faint, with observations suggesting it was just 6 feet (2 meters) across — small enough to burn up completely during its fiery plunge through the atmosphere, NASA officials said. [Asteroid Threat: Potentially Dangerous Space Rocks in Pictures]

"The discovery of asteroid 2018 LA is only the third time that an asteroid has been discovered to be on an impact trajectory," Paul Chodas, manager of the Center for Near-Earth Object Studies (CNEOS) at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, said in the statement. "It is also only the second time that the high probability of an impact was predicted well ahead of the event itself."

The asteroid's fiery demise was caught on camera by spectators, who later posted their footage to YouTube. In one video, from a farm between Ottosdal and Hartebeesfontein in South Africa, the asteroid appears as a brilliant streak that flares up into a spectacular fireball on the horizon. 

Asteroid 2018 LA was nearly as far away as the moon (which is typically about 239,000 miles, or 384,600 km, from Earth) when it was discovered on Saturday, NASA officials said. It looked like little more than a streak in long-exposure images by the Catalina telescope. 

These images show the discovery of asteroid 2018 LA by the Catalina Sky Survey on June 2, 2018. The asteroid hit Earth 8 hours after these images were taken, burning up in Earth's upper atmosphere over Botswana, Africa.
These images show the discovery of asteroid 2018 LA by the Catalina Sky Survey on June 2, 2018. The asteroid hit Earth 8 hours after these images were taken, burning up in Earth's upper atmosphere over Botswana, Africa.
Credit: NASA/JPL-Caltech/CSS-Univ. of Arizona

"This was a much smaller object than we are tasked to detect and warn about," Lindley Johnson, NASA's planetary defense officer, said in the statement. "However, this real-world event allows us to exercise our capabilities and gives some confidence our impact prediction models are adequate to respond to the potential impact of a larger object."

Catalina Sky Survey astronomers reported the asteroid finding to the Minor Planet Center in Cambridge, Massachusetts, which managed to calculate a preliminary trajectory for the asteroid. That trajectory plot was the first hint that 2018 LA could hit Earth.

The Minor Planet Center then reported the asteroid to CNEOS. JPL's automated Scout system, which tracks asteroids, confirmed 2018 LA was on a collision course with Earth and sent observation alerts out to asteroid observers to try spotting it. 

While this isn't the first time a small asteroid has been spotted just before it hit Earth, it certainly isn't that common. Only two other instances come to mind, according to JPL. 

On Oct. 7, 2008, the 13-foot (4 m) asteroid 2008 TC3 hit Earth over northern Sudan. That asteroid was spotted 19 hours before impact, enough time for scientists to plot a precise trajectory for the falling space rock. Later expeditions used that trajectory to find meteorite fragments of 2008 TC3.

The second event occurred Jan. 1, 2014, when the asteroid 2014 AA was spotted just a few hours before it fell over the Atlantic Ocean.

All three asteroids were discovered by the Catalina Sky Survey while astronomer Richard Kowalski was overseeing observations, NASA officials said. NASA scientists and astronomers around the world regularly observe the sky for any signs of potentially dangerous asteroids that could pose an impact threat to Earth.

Neither asteroid 2018 LA nor its two predecessors were large enough to cause the type of damage seen in 2013, when an asteroid about 56 feet (17 m) wide exploded over the Russian city of Chelyabinsk. The fireball shattered windows and damaged thousands of buildings, leaving more than 1,200 people injured. 

Quelle: SC

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