2003 EARTH SCIENCE VIDEOTAPES |
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Tape Title | Record ID | Date Produced | TRT: |
Synopsis |
| CALCULATED RISK: SCIENTISTS ASSESS STELLAR EXPLOSION THREAT TO OZONE | G03-001 | 01/08/03 | 00:05:25 | Hollywood might want to stop production on disaster movies about nearby exploding stars drastically increasing cancer rates on Earth: the very real threat seems less likely than we thought. New research shows 1970s-era estimates of the likelihood of ozone layer damage from a nearby massive star explosion over- estimated the potential. Early numbers predicted explosions within 55 light-years of Earth could destroy 90 percent of the ozone layer for hundreds of years, but new data predict only a supernova within 26 light-years of Earth could wipe out enough protective ozone to double radiation exposure for decades. Such a close explosion happens about once every 670 million years. Ozone shields plants and animals from harmful high- energy radiation.
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TAPE CONTENTS: |
| ITEM (1): Death of a Massive Star - This animation depicts the explosion of supernova 1987A, on which scientists based their revised estimates. A star at least five times as massive as our Sun explodes when its core collapses, heating the star's inner layers to 10 billion degrees Fahrenheit. This triggers a shockwave that rips the star apart and sends debris hurtling into space, the fastest moving up to 18,600 miles per second, 1/10 (one-tenth) the speed of light. Supernovae emit gamma and cosmic rays that produce chemicals in our atmosphere that destroy Earth's ozone layer.
Courtesy: NASA
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| ITEM (2): Antarctic Ozone 'Hole' - NASA researchers use satellites to track the annual depletion of the ozone layer over Antarctica. Each winter, winds circling the South Pole trap cold air over the Pole. This allows the formation of polar stratospheric clouds, a surface for chemical reactions of primarily man-made chloro- fluorocarbons (CFCs) that destroy ozone in Earth's atmosphere. The ozone 'hole' (blue) has generally worsened since the 1970s, as shown in this series of annual maximum sizes. The largest hole on record occurred in September 2000. Data from Total Ozone Mapping Spectrometer on the Earth Probe satellite.
Courtesy: NASA
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ITEM (3): Superstar Explosion - Supernova 1987A (red, with yellow gaseous ring) exploded in 1987, the closest massive star explosion to Earth observed since the advent of the telescope 400 years ago. Scientists used data gathered from this explosion 169,000 light years from Earth to revise their estimates on potential threats to the ozone layer. Images from Hubble Space Telescope.
a) 1990, after initial explosion brightness subsided.
b) 1994, with appearance of mysterious gas rings
Courtesy: NASA
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ITEM (4): What's Left Behind - NASA and Harvard-Smithsonian Center for Astrophysics' Chandra X-Ray Observatory captured these false-color x-ray images of supernova remnants. Taken in August and September 1999, these are some of Chandra's first images.
b) E0102-72 in the Small Magellenic Cloud, constellation Tucana
c) G21.5-0.9 in constellation Scutum
d) PSR 0540-69 in constellation Dorado
Courtesy: NASA
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| ITEM (5): Ozone Destruction - Ozone molecules (O3) generally absorb ultraviolet (UV) radiation, shielding the Earth from the harmful rays. Ozone production occurs at a fairly constant rate. Destruction occurs via reactions with naturally-occurring and human-produced molecules. High-energy cosmic and gamma rays break apart nitrogen molecules in the upper atmosphere. The resulting chemicals destroy ozone in a way similar to ozone breakdown by chlorine from CFCs each winter over Antarctica depicted here. If stratospheric destructive compounds increase, as from CFCs or a supernova, ozone destruction increases, thinning the ozone layer. A nearby supernova might lead to double the damaging radiation reaching Earth.
Courtesy: NASA
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