X-ray craft sees Venus in whole new light. (Science News of the week).Astronomers Famous astronomers and astrophysicists include: Directory: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A
U.S. X-ray space telescope. It was named after astrophysicist Subrahmanyan Chandrasekhar and was launched into orbit in 1999. Its mirror, with an aperture of 1.2 m (4 ft) and a focal length of 10 m (33 ft), produces unprecedented resolution. and released last week, may provide new information about the atmosphere of the cloud-covered planet. Venus doesn't have its own source of X rays. Rather, X rays from the sun induce the Venusian emissions when they bombard bom·bard tr.v. bom·bard·ed, bom·bard·ing, bom·bards 1. To attack with bombs, shells, or missiles. 2. To assail persistently, as with requests. See Synonyms at attack, barrage2. 3. the planet's upper atmosphere and are absorbed by ionized i·on·ize tr. & intr.v. i·on·ized, i·on·iz·ing, i·on·iz·es To convert or be converted totally or partially into ions. i atoms. The atoms reemit the incoming radiation at a lower X-ray energy, a process known as fluorescence. The X-ray--emitting atoms reside high in the atmosphere, 120 to 140 kilometers above the surface of Venus. In contrast, visible light from Venus, which is the result of sunlight reflected from the planet's clouds, comes from a region just 50 to 70 km from the surface. The X rays reveal details about a region of the planet's atmosphere never before studied by an orbiting spacecraft, notes study collaborator Konrad Dennerl of the Max Plank Institute for Extraterrestrial Physics in Garching, Germany. His team reported the findings at an X-ray astronomy X-ray astronomy, study of celestial objects by means of the X rays they emit, in the wavelength range from 0.01 to 10 nanometers. X-ray astronomy dates to 1949 with the discovery that the sun emits X rays. meeting in Noorwidjk, the Netherlands. Previous X-ray detectors in Earth orbit couldn't image Venus because the planet lies too close to the sun for sensitive electronic detectors to safely point directly at it. Chandra can peer at Venus without risk during only two brief intervals every 548 days, Dennerl notes. X-ray spectra from the spacecraft reveal that ionized oxygen and carbon atoms emit most of the radiation. The X-ray intensity varied minute to minute, which may result from variations in incoming solar radiation solar radiation, n the emission and diffusion of actinic rays from the sun. Overexposure may result in sunburn, keratosis, skin cancer, or lesions associated with photosensitivity. , Dennerl suggests. His team had hoped to detect another source of X rays, this one from the interaction between the solar wind--charged particles blowing from the sun--and neutral atoms in Venus' atmosphere. Researchers recently discovered that the solar wind solar wind, stream of ionized hydrogen—protons and electrons—with an 8% component of helium ions and trace amounts of heavier ions that radiates outward from the sun at high speeds. causes comets near the sun to emit X rays (SN: 6/1/96, p. 346). Venus also lies near the sun and has several features in common with comets, including a carbon dioxide--rich atmosphere. But the weak emissions expected from this solar wind mechanism would have required observations 10 times longer than the 6.5 hours his team had available, Dennerl says. |
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