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X-Rays Reveal 250000 Tonnes Of Water Released By Deep Impact
Leicester, UK (SPX) Mar 31, 2006 Observations by the Swift spacecraft of the collision last July 4 between Comet Tempel 1 and a probe released by NASA's Deep Impact mission showed the comet grew brighter and brighter in X-ray light, in an outburst that lasted 12 days and released about 250,000 tons of water. "The Swift observations reveal that far more water was liberated and over a longer period than previously claimed," said research team leader Dick Willingale of the University of Leicester. Swift's primary mission is to study objects in the distant universe, but its agility allows it to observe many objects per orbit. Willingale and colleagues used Swift to monitor X-ray emissions from Tempel 1 before and after its collision with the 300-pound impactor. Speaking at a meeting of the Royal Astronomical Society, Willingdale explained that the X-rays provide a direct measurement of how much material was kicked up after the collision. The X-rays were created by the newly liberated water lifted into the comet's thin atmosphere and illuminated by the high-energy solar wind from the Sun. "The more material liberated, the more X-rays are produced," said team member Paul O'Brien. The X-ray power output depends on both the water production rate from the comet and the flux of subatomic particles streaming out of the Sun as the solar wind. Using data from NASA's Advanced Composition Explorer satellite, which constantly monitors the solar wind, the researchers could calculate the solar wind flux at the comet during the X-ray outburst � which enabled them to determine what part of the collision was responsible for the X-ray emissions. Tempel 1 usually is a dim weak comet with a water production rate of about 16,000 ton per day. After Deep Impact's probe hit the comet, however, the rate increased to 40,000 tons per day over the period of five to 10 days after impact. Over the duration of the outburst, the team calculated, the mass of water released by the impact totaled 250,000 tons. One Deep Impact mission objective was to determine what causes cometary outbursts. A simple hypothesis suggests such outbursts are caused by meteorites hitting the comet nucleus. If so, Deep Impact should have initiated an outburst. Although the impact was observed across the electromagnetic spectrum, most of what astronomers saw was directly attributable to the impact. After five days, optical observations showed the comet grew indistinguishable from its state prior to the collision � while the X-ray observations provided a stark contrast. The collision instigated an extended X-ray outburst largely because the amount of water produced by the comet had increased. "A collision such as Deep Impact can cause an outburst, but apparently omething rather different from the norm can also happen," Willingale said. "Most of the water seen in X-rays came out slowly, possibly in the form of ice-covered dust grains." Related Links RAS National Astronomy Meeting Swift NASA Deep Impact
ESA Awards Contracts For Don Quijote Asteroid Impact Mission Designs
Paris France (SPX) Apr 3, 2006ESA has awarded contracts to three industrial teams to carry out initial design studies for the agency's proposed mission to attempt to deflect the path of an asteroid. The mission, called Don Quijote, will comprise a primary spacecraft called Hildago, and an impactor called Sancho. |
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