http://www2.keck.hawaii.edu/news/asteroid.html<br /><br />High-Resolution Images of Asteroid (511) Davida<br />W.M. Keck Observatory<br />September 4, 2003<br /><br />Davida Image<br />Davida Asteroid Rotation Animation<br /><br />Image Credit: W.M. Keck Observatory<br />A sequence of images of asteroid (511)<br />Davida, spanning slightly more than one<br />hour, as it rotates on Dec. 26, 2002. In this<br />view, the asteroid is seen from above its<br />north pole, as it spins counter-clockwise,<br />left to right. The features on the edges,<br />such as the flat facets, show that the<br />asteroid has rotated about one-quarter<br />turn.<br /><br /><br />MONTEREY, Calif. -- A team of scientists from the W.M. Keck Observatory and<br />several other research institutions have made the first full-rotational,<br />ground-based observations of asteroid (511) Davida, a large, main-belt<br />asteroid that measures 320 km (200 miles) in diameter. These observations<br />are among the first high-resolution, ground-based pictures of large<br />asteroids, made possible only through the use of adaptive optics on large<br />telescopes. This research will help improve understanding of how asteroids<br />were formed and provide information about their compositions and structures.<br />Because the asteroids were formed and shaped by collisions, a process that<br />also affected the Earth, Moon, and planets, these studies will also help<br />astronomers understand the history and evolution of the solar system.<br /><br />" Asteroid Davida was discovered 100 years ago, but this is the first time<br />anyone has been able to see this level of detail on this object," said Dr.<br />Al Conrad, scientist at the W.M. Keck Observatory. "With adaptive optics,<br />we're finally able to transform asteroids like Davida from a single, faint<br />point-source into an object of true geological study."<br /><br />Ground-based observations of large, main-belt asteroids are made possible<br />only through a powerful astronomical technique called adaptive optics, which<br />removes the blurring caused by Earth's atmosphere. Without adaptive optics,<br />critical surface information and details about the asteroid's shape are<br />lost. The techniques used at the W.M. Keck Observatory allow astronomers to<br />measure the distortion of light caused by the atmosphere and rapidly make<br />corrections, restoring the light to near-perfect quality. Such corrections<br />are most easily made to infrared light. In many cases, infrared observations<br />made with Keck adaptive optics are better than those obtained with<br />space-based telescopes.<br /><br />The observations of asteroid (511) Davida were made with the 10-meter<br />(400-inch) Keck II telescope on December 26, 2002. Images were taken over a<br />full rotation period of about 5.1 hours, just a few days before its closest<br />approach to Earth. At that time, Davida's angular diameter was less than<br />one-ten-thousandth of a degree, about the size of a quarter as seen from a<br />distance of 18 kilometers (11 miles). The high angular resolution allowed<br />astronomers to see surface details as small as 46 kilometers (30 miles),<br />about the size of the San Francisco Bay area. The next time Davida comes<br />this close to Earth will be in the year 2030.<br /><br />At the time of the observations, Davida's north pole faced Earth. While<br />scientists could see the asteroid spinning, only the northern hemisphere was<br />visible. Yet the profile of the asteroid is far from circular: At least two<br />flat facets can be seen on its surface. Although scientists knew previously<br />from light variations that Davida must have an oblong shape, details of that<br />shape were not available until now. Initial evaluation of the images reveal<br />some dark features, and scientists are still working to understand to what<br />extent these are surface markings, topographical features, or artifacts of<br />the image processing.<br /><br />" Adaptive optics on large telescopes is allowing us to make detailed<br />studies from the ground that were previously impossible or prohibitively<br />expensive," said Dr. William Merline, principal scientist with the Southwest<br />Research Institute, and a participant in this research. "We can now make<br />observations that once required either the scarce resources of space<br />telescopes or spacecraft missions to asteroids. While these space telescopes<br />and space missions are still needed for complete study of the asteroids,<br />ground-based observations such as these will help tremendously in planning<br />the mission observations and focusing the resources where they will be most<br />effective."<br /><br />Asteroids are the collection of rocky objects orbiting between Mars and<br />Jupiter. They were likely prevented from forming into a planet, partly due<br />to Jupiter's massive gravitational influence.<br /><br />" Although the asteroids began their lives colliding gently, in a way that<br />would lead them eventually to form a planet, Jupiter's gravity eventually<br />stirred up their orbits, and they began to collide at higher speeds," added<br />participant Dr. Christophe Dumas, planetary astronomer with the Jet<br />Propulsion Laboratory. "These collisions tended to cause them to break up<br />rather than gently stick together. The resulting fragments, numbering in the<br />hundreds of thousands, are the asteroids we see today. They collide with<br />each other and have impacted the Earth, Moon, and planets over time. One<br />need only look at the scarred surface of our Moon to see the cumulative<br />result. Study of the asteroid's shape, size, and surface features helps us<br />understand how these collisions operate and thus how our planet was, and<br />still is, being affected by these impacts."<br /><br />Observations of the shapes of asteroids, such as those released today, can<br />tell us about the types and severity of impacts that occurred, and possibly<br />also give clues into the overall structure of an asteroid --- for example,<br />whether it may be solid rock, or a jumble of smaller rocks. Surface features<br />can reveal a history of large impacts or variations in the composition that<br />should, in turn, further help us understand the asteroid's history.<br /><br />Asteroid (511) Davida was discovered by R. S. Dugan in 1903 in Heidelberg,<br />Germany. The (511) in Davida's name means it was the 511th asteroid to be<br />discovered and included in the list of asteroids maintained by the<br />International Astronomical Union.<br /><br />Team members responsible for the observations are Al Conrad, David Le<br />Mignant, Randy Campbell, Fred Chaffee, Robert Goodrich, Shui Kwok of the<br />W.M. Keck Observatory; Christophe Dumas, Jet Propulsion Laboratory; William<br />Merline, Southwest Research Institute; Heidi Hammel, Space Science<br />Institute; and Thierry Fusco, Onera, France.<br /><br />The W.M. Keck Observatory is operated by the California Association for<br />Research in Astronomy, a scientific partnership of the California Institute<br />of Technology, the University of California, and the National Aeronautics<br />and Space Administration.<br /><br /># # #<br /><br />Dr. William J. Merline, Southwest Research Institute, Boulder, CO; 303-546-9670<br />Dr. Christophe Dumas, Jet Propulsion Laboratory, Pasadena, CA; 818-393-5327<br />Dr. Albert R. Conrad, W.M. Keck Observatory, Kamuela, HI; 808-881-3812<br /><br /> <br />Media Contact:<br /><br />Laura K. Kraft <br />W.M. Keck Observatory <br />65-1120 Mamalahoa Hwy. <br />Kamuela, HI96743 <br />(808) 885-7887 <br />lkraft@keck.hawaii.edu