Nasa: grandes asteroides representam ameaça remota à Terra [+ BÔNUS]
O telescópio espacial de infra-vermelho WISE (Wide-field Infrared Survey Explorer), lançado pela NASA em dezembro de 2009, descobriu mais de 33500 novos asteróides e cometas.
Por ser um telescópio de infra-vermelho, o sensor é resfriado com hidrogênio sólido (- 256 ºC ou 17 K), que quando esquenta e atinge uma certa temperatura, torna o sensor “cego”, pondo fim a missão.
Há menos asteróides gigantes no espaço do que se acreditava, e a maioria dos grandes localizados próximo à Terra já foram localizados, motivo pelo qual há uma ameaça remota de que algum deles atinja o planeta, anunciou a Nasa.
As últimas informações do Wide-Field Infrared Survey Explorer, o telescópio Wise da agência espacial americana, revelam que 93% dos asteroides com 1km de diâmetro ou mais já foram localizados.
Os cientistas pensavam que houvesse mil deles, mas revisaram essa cifra para 981, dos quais 911 foram localizados e estão sendo monitorados.
"O risco de que um asteroide realmente grande atinja a Terra antes de que possamos localizá-lo e dar o alerta caiu consideravelmente", disse Tim Spahr, diretor do Centro Minor Planet do Centro Harvard-Smithsonian de Astrofísica em Cambridge, Massachusetts.
O risco permanece entre os asteroides de tamanho médio, com 100m ou mais. Dados do Wise revelam que existem 19.500 deles, e não 35.000, como se acreditava. Apenas 5.200 são monitorados.
Um asteróide possui uma órbita próxima da Terra quando passa a menos de 195 milhões de quilômetros do Sol.
Amy Mainzer, principal autora da última pesquisa publicada no periódico Astrophysical Journal, disse que o Wise deu aos astrônomos uma ideia mais clara do que há no espaço. "É como um censo, quando se pesquisa um pequeno grupo de pessoas para tirar conclusões do todo."
Nasa: grandes asteroides representam amea
Construction of the WISE telescope was divided between:
• Ball Aerospace & Technologies (spacecraft, operations support)
• SSG Precision Optronics, Inc. (telescope, optics, scan mirror)
• DRS and Rockwell (focal planes)
• Lockheed Martin (cryostat, cooling for the telescope)
• Space Dynamics Laboratory (instruments, electronics, and testing).
The program is managed through the Jet Propulsion Laboratory.
NASA - Wide-Field Infrared Survey Explorer
WISE: Wide-Field Infrared Survey Explorer
Wide-field Infrared Survey Explorer - Wikipedia, the free encyclopedia
This chart shows how data from NASA's Wide-field Infrared Survey Explorer, or WISE, has led to revisions in the estimated population of near-Earth asteroids. The infrared-sensing telescope performed the most accurate survey to date of a slice of this population as part of project called NEOWISE. This allowed the science team to make new estimates of the total numbers of the objects in different size categories. NEOWISE observed more than 500 objects larger than 100-meters (330-feet) wide -- what can be thought of as medium to large-size asteroids. Near-Earth asteroids smaller than this size range were not studied, and near-Earth comets will be analyzed at a later time. Asteroid sizes are not drawn to scale in the chart.
Each asteroid image represents about 100 actual objects. Near-Earth asteroids that have already been found are filled in and appear brown. An entire row of asteroid images through the blue outlines shows how many total objects were thought to exist before the NEOWISE survey. The green outlines show the reduced new estimates based on the NEOWISE data.
As the graphic reveals, only a small difference was observed in the estimated total numbers of the largest asteroids -- the ones with the potential for global consequences should they impact Earth. For the medium-sized asteroids, which could still destroy a metropolitan area, new estimates predict fewer space rocks than previously thought. Details are listed below.
--For the largest asteroids, larger than 1,000 meters (3,300 feet), NEOWISE data revises the total population down to 981 from a prior estimate of about 1,000. While this is not a dramatic difference, the findings show that NASA has met an initial near-Earth asteroid goal agreed to with Congress in 1998, calling for at least 90 percent of the largest objects to be found. There are an estimated 911 objects of this size range known, which means that NASA has found 93 percent. That leaves roughly 70 of these bodies left to find.
--The NEOWISE data reveals an approximately 44 percent decline in the estimated numbers of medium-sized asteroids, which are defined as those objects between 100 meters and 1,000 meters (330 and 3,300 feet). Estimates now indicate about 19,500, where as 35,000 were thought to exist before.
--The study does not apply to objects smaller than 100 meters (330 feet), but it is estimated that there are more than a million in this size range based on previous studies.
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Kim Kardashian
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Originalmente postado por Salim
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