quarta-feira, 20 de agosto de 2014

76. How Does One Find a Meteorite?



Space rocks1 often2 enter the Earth’s atmosphere.  But they usually3 explode and burn4 before falling to the ground5About 70 percent of our planet is covered with7 water.  As a result8, most meteorites falling from the sky disappear9 on the oceans’ floor10.  We would not know about them if it was not for an international agency.

Reporters gather around11 a piece of a meteorite, which according to12 local authorities and scientists, was lifted from13 the bottom14 of the Chebarkul Lake15 in Chelyabinsk, Russia, Oct. 18, 2013.
You may16 remember the meteorite that exploded last year 23 kilometers above17 Chelyabinsk, in Russia.  
Scientists estimate it was about 18 meters long18 before it fell to Earth19.  They also think it had a mass20 of about 10,000 tons. 
Many people would have died21 if the meteorite fell in a populated area.  Luckily22, it did not.  Instead23 it broke apart mid-air24 and most of the pieces fell into Lake Chebarkul.  But that is a little too close25 for some people.

The Comprehensive26 Nuclear-Test-Ban Treaty27 Preparatory Commission is a group based in Vienna, Austria.  It says the Earth is visited by meteorites more often than we know.  
The group records28 explosions made by meteorites that enter Earth’s atmosphere.  Pierrick Mialle works for the commission, also known as29 the CTBTO.  He is an acoustics expert30, specializing in the study of sounds. He says since31 meteorites are sometimes32 entering the atmosphere, they are creating loud air bursts33.

The commission controls sensors and other equipment that watch34 for possible violations of the Nuclear Test ban treaty.  Some of the devices35 are seismic, meaning36 they measure37 the movement of the Earth.  Others are hydrostatic, meaning they measure the movement of the Earth’s water.  The Commission also uses ultrasound and radioactivity sensors.

Between38 2000 and 2013, the CTBTO recorded 26 powerful39 explosions of large meteorites entering the atmosphere. The B612 Foundation also studies meteorite impacts.  This group estimates at least40 four of those 26 explosions were stronger than41 the nuclear bomb that destroyed Hiroshima.

In addition to42 loud noise43, explosions create low frequency44 infrasound.  Sound waves45 can travel very long distances at such46 low frequencies.  But human beings47 are unable to hear them48. CTBTO stations as far away as49 the Antarctica recorded the explosion of the Chelyabinsk meteorite.

Mr. Mialle says listening stations50 operate anywhere from51 four to 15 high-technology sensors.  He says that the sensors work like large microphones. “They are called micro barometer because they measure micro fluctuations of the atmosphere.  It’s like a large microphone except52 there’s no membrane53.”

He adds that54 some of the explosions are hard to identify55 immediately after56 they are recorded. “For instance57, the first time we had this, what was later called the Super Bolide of North Pacific, in the first few weeks all that was known was a large event in the middle of the Pacific.  But we didn’t know what it was.”

The commission keeps contact58 with other agencies, such as59 the American space agency, that follow60 meteorites.  Space agency officials later confirmed that the mysterious explosion was caused by a meteorite.
When complete, the CTBTO system will have 337 stations worldwide61.  And these stations will be listening for nuclear explosions and other loud sounds in the atmosphere. I’m Anna Matteo.

Vocabulary

  1. Space rocks = rochas espaciais
  2. often = frequentemente
  3. usually = normalmente
  4. burn = queimar
  5. before falling to the ground = antes de cair no chão
  6. About = aproximadamente
  7. covered with = coberto com
  8. As a result = como resultado
  9. disappear = disaparecem
  10. oceans’ floor = fundo do oceano
  11. gather around = reunem-se ao redor de
  12. according to = de acordo com
  13. was lifted from = foi erguido do
  14. bottom = fundo
  15. Lake = lago
  16. may = pode (possibilidade)
  17. above = sobre
  18. long = de comprimento
  19. fell to Earth = caiu na Terra
  20. mass = massa
  21. would have died = teriam morrido
  22. Luckily = por sorte, felizmente
  23. Instead = ao invés disso
  24. broke apart mid-air = partiu-se no meio do ar
  25. too close = perto demais
  26. Comprehensive = abrangente
  27. Nuclear-Test-Ban Treaty = tratado de proibição de testes nucleares
  28. records = registra
  29. also known as = também conhecido como
  30. acoustics expert = especialista em acústica
  31. since = uma vez que
  32. sometimes = as vezes
  33. loud air bursts = explosões de ar altas
  34. watch = observam
  35. devices = dispositivo
  36. meaning = significando
  37. measure = medir
  38. Between = entre (duas coisas)
  39. powerful = poderoso(a)
  40. at least = pelo menos
  41. were stronger than = foram mais fortes do que
  42. In addition to = além de
  43. noise = barulho
  44. low frequency = baixa frequencia
  45. Sound waves = ondas sonoras
  46. such = tais
  47. human beings = seres humanos
  48. unable to hear them = são incapazes de ouvi-las
  49. as far away as = tão distantes quanto
  50. listening stations = estações de escuta
  51. anywhere = algo em torno de (aproximadamente)
  52. except = exceto
  53. there’s no membrane = não há nenhuma membrana
  54. adds that = acrescenta que
  55. hard to identify = dificil de identificar
  56. immediately after = imediatamente após
  57. For instance = por exemplo
  58. keeps contact = mantém contato
  59. such as = tais como
  60. follow = seguir
  61. worldwide = mundialmente