Thursday, June 17, 2004

NASA Spacecraft Reveals Surprising Anatomy Of A Comet 06.17.04 Findings from a historic encounter between NASA's Stardust spacecraft and a comet have revealed a much stranger world than previously believed. The comet's rigid surface, dotted with towering pinnacles, plunging craters, steep cliffs, and dozens of jets spewing violently, has surprised scientists. Image above: This image and diagram show the comet Wild 2, which NASA's Stardust spacecraft flew by on Jan. 2, 2004. The picture on the left is the closest short exposure of the comet. The listed names on the right are those used by the Stardust team to identify features. "Basin" does not imply an impact origin. + Click for full image. Image credit: NASA/JPL-Caltech. Animation: This movie strings together a series of still images of comet Wild 2 taken during Stardust's historic flyby of the comet. + Click for animation. Animation credit: NASA/JPL-Caltech. "We thought Comet Wild 2 would be like a dirty, black, fluffy snowball," said Stardust Principal Investigator Dr. Donald Brownlee of the University of Washington, Seattle. "Instead, it was mind-boggling to see the diverse landscape in the first pictures from Stardust, including spires, pits and craters, which must be supported by a cohesive surface." Stardust gathered the images on Jan. 2, 2004, when it flew 236 kilometers (about 147 miles) from Wild 2. The flyby yielded the most detailed, high-resolution comet images ever. "We know Wild 2 has features sculpted by many processes. It may turn out to be typical of other comets, but it is unlike any other type of solar system body," Brownlee said. He is lead author of one of four Stardust papers appearing in the Fri., June 18, issue of Science. "We're fortunate that nature gave us such a rich object to study." Stardust images show pinnacles 100 meters tall (328 feet), and craters more than 150 meters deep (492 feet). Some craters have a round central pit surrounded by ragged, ejected material, while others have a flat floor and straight sides. The diameter of one large crater, called Left Foot, is one fifth of the surface of the comet. Left Foot is one kilometer (.62 miles) across, while the entire comet is only five kilometers (3.1 miles) across. Image left: This is an artist's concept depicting a view of comet Wild 2 as seen from NASA's Stardust spacecraft during its flyby on Jan. 2, 2004. + Click for full image. Image credit: NASA/JPL-Caltech. "Another big surprise was the abundance and behavior of jets of particles shooting up from the comet's surface. We expected a couple of jets, but saw more than two dozen in the brief flyby," said Dr. Benton Clark, chief scientist of space exploration systems, Lockheed Martin Space Systems, Denver. The team predicted the jets would shoot up for a short distance, and then be dispersed into a halo around Wild 2. Instead, some super-speedy jets remained intact, like blasts of water from a powerful garden hose. This phenomenon created quite a wild ride for Stardust during the encounter. "Stardust was absolutely pummeled. It flew through three huge jets that bombarded the spacecraft with about a million particles per second," said Thomas Duxbury, Stardust project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. Twelve particles, some larger than a bullet, penetrated the top layer of the spacecraft's protective shield. The violent jets may form when the Sun shines on icy areas near or just below the comet's surface. The solid ice becomes a gas without going through a liquid phase. Escaping into the vacuum of space, the jets blast out at hundreds of kilometers per hour. The Stardust team theorizes sublimation and object hits may have created the comet's distinct features. Some features may have formed billions of years ago, when life began on Earth, Brownlee said. Particles collected by Stardust during the Wild 2 encounter may help unscramble the secrets of how the solar system formed. Stardust was launched in 1999. It is zooming back to Earth with thousands of captured particles tucked inside a capsule. The capsule will make a soft landing in the Utah desert in January 2006. The samples will be analyzed at the planetary material curatorial facility at NASA's Johnson Space Center, Houston. Comets have been objects of fascination through the ages. Many scientists believe they delivered carbon and water, life's building blocks, to Earth. Yet their destructive potential is illustrated by the widely held theory that a comet or asteroid wiped out the dinosaurs. 7:56:05 PM    comment []

Canned heat   Question When my father was undergoing military service in the desert, his medical officer told him that should he ever become separated from his unit and stranded in the dunes the best course of action would be to drink his water supply ­ a 2-pint (1.1-litre) flask ­ over the first couple of hours rather than trying to eke it out for days. Is this true? Would either course of action be more likely to help him survive? And why? Thomas Hutchinson , St Ives, Cornwall, UK   Answers An old US army training film described a soldier's water supply as the total in his canteen and in his body, suggesting he should keep the water inside himself instead of outside. It featured a cartoon of a foolish soldier who refused to drink his ration, and got so thirsty and dehydrated that he became irrational. He went out in the midday sun looking for water. By the time he drank from his canteen, the reservoir in his body had all evaporated in sweat, and he soon perished. A wiser soldier topped up his internal reservoir from his canteen, kept his mind in order, stayed in the shade until evening, and hiked to safety. That said, if you drink up all your supply at the start you might urinate a lot of it right back out. You can help your body to conserve water by not drinking until you are fairly thirsty. Your urine will be scanty and darker than normal ­ which is acceptable in such an emergency, though unhealthy in the long run. But at all times you must drink enough to stay mentally alert and avoid heat exhaustion. Spencer Weart , College Park, Maryland, US     The advice to drink the 2 pints of water in the first few hours rather than eke it out is sound for a number of reasons. First, dehydration is rapidly accompanied by irritability and mental confusion, which is then followed by physical dysfunction. Such symptoms do not make for good decision making nor efficient action. Trials on military personnel in Australia have shown that maintaining adequate hydration is essential for efficient mental and physical activity and gives you a far greater chance of survival than trying to stretch out a limited water supply. The actual survival time differs little, as the graphs of performance show that those who maintain adequate hydration can operate very efficiently until the water runs out, at which point they begin to deteriorate rapidly. Those who eke out their supplies decline almost immediately although at a slower rate. As gruesome confirmation of this, several people have been found dead of dehydration while still carrying water. Secondly, if you take small sips of water, much of it merely moistens the membranes of the mouth and evaporates. You should swallow at least a cup of water at each drink, so most of it reaches the stomach and is absorbed. And if you do become lost with only limited water, it is important not to eat because digestion uses up water. You can live and function reasonably well for weeks without food, but in hot conditions one or two days without water can kill. Eric Wheatley , Bridgetown, Western Australia 7:50:34 PM    comment []

The lesson of the 1981 "supply-side" tax cuts When President Reagan took office in 1981, he quickly succeeded in passing substantial "supply-side" cuts in both individual and corporate income taxes.  He predicted that the 1981 tax cuts would “pay for themselves” through higher investment and faster growth in productivity and incomes.  Once enacted, the 1981 tax cuts opened up wide budget deficits (6% of gross domestic product, the largest peacetime deficit in history), leading Congress and the president to agree to substantially increase taxes on corporations in 1982 and on payrolls in 1983.  Although those measures helped to narrow the budget deficit, large deficits persisted and further major tax hikes were adopted in 1990 and 1993.  By the time that the tax increases of 1993 took effect, any supply-side effects of the 1981 tax cuts had been largely eliminated. Contrary to the predictions of supply-side proponents, the 1981 tax cuts did not lead to better economic performance.  Economists generally measure performance from one business cycle peak to the next.  The last three peaks occurred in 1979, 1989, and 2000.  It is instructive to compare the performance of investment, productivity, and output in the 1979-89 cycle, which was influenced by the 1981 tax cuts, with the 1989-2000 cycle, which was little affected by those cuts. The boost to investment from the 1981 tax cuts that supply-siders had predicted never materialized.  In fact, investment grew much faster during the 1990s than the 1980s—5.9% versus 2.5%.  Productivity also grew much faster in the 1990s.  Although total output, or GDP, grew slightly faster in the 1990s (3.2% versus 3.1%), the promised increase in federal revenue was a bust.  Revenues rose at only a 2.5% rate in the 1980s compared to 4.1% in the 1990s. Proponents of the tax cuts of 2001, 2002, and 2003 again used supply-side arguments about improved economic performance and claims that the tax cuts would "pay for themselves." The economic experience of the 1980s and 1990s does not support those arguments. This Snapshot was written by EPI Research Director Lee Price. 7:48:23 PM    comment []