Among the most surprising asteroid-related discoveries of the past decade was finding the little moon Dactyl orbiting 243 Ida in 1993 and a satellite around 45 Eugenia last year. Solar-system specialists now suspect that asteroid satellites are hardly rare and may in fact be common.

The evidence to bolster this conclusion is mounting rapidly. Steven J. Ostro (Jet Propulsion Laboratory) has just announced results of radar observations, made by his team on September 22nd and 23rd, which reveal the small near-Earth asteroid 2000 DP107 to be double. "The images show separations of up to at least 1 kilometer between the components, which have different sizes and rotation states," Ostro writes in IAU Circular 7496.

In addition, ground-based astronomers have a growing list of asteroids whose light curves look like eclipsing binaries. The strongest cases involve two other small Earth-crossers, 3671 Dionysus and 1996 FG3. There is also suspicion surrounding 90 Antiope, a sizable (120-km) object in the main belt, and last year Ostro and others used radar to determine that 216 Kleopatra had a 200-km-long dog-bone shape. William F. Bottke (Southwest Research Institute), who studies the mechanic characteristics of asteroids, wonders whether big bodies like Kleopatra and Antiope can be made to spin with so much angular momentum -- via an off-center impact, for example -- that they literally fly apart. Bottke and colleague Daniel Durda hope to simulate such scenarios in the coming months.

NASA's NEAR Shoemaker spacecraft has spotted square-shaped craters on asteroid Eros, a telltale sign of mysterious goings-on in the asteroid belt long ago.

Astronomers in the United States have long dominated the search for asteroids and comets that might someday collide with Earth. But if the recommendations of a just-released study are adopted, Great Britain stands to become a major player as well. On September 18th the Task Force on Potentially Hazardous Near-Earth Objects released its 59-page report, which contains 14 recommendations for accelerating the discovery and characterization of NEOs. The three-member task force was formed in January by Lord Sainsbury, Britain's minister for science, and it drew heavily on experts from around the world.

The most significant recommendation, at least in terms of potential cost, requests that the British government construct a 3-meter telescope in the Southern Hemisphere that will be dedicated to NEO searches. The task force believes such a telescope could track down smaller objects, those less than 500 meters across, which far outnumber their larger kin and thus strike Earth more frequently on average. The cost for such an expensive undertaking could be shared among several European partners, the report says. Another recommendation is to use an existing 1-meter instrument, the Jacobus Kapteyn Telescope on La Palma in the Canary Islands, solely to follow up observations of close-approachers after their discovery. And the report calls for the establishment of a British Center for Near Earth Objects, to coordinate the country's NEO research and to serve as a clearinghouse for information.

Reaction to the report has ranged from favorable to enthusiastic among astronomers who study asteroids and comets. "I am particularly impressed by the internationality of the Report," comments Brian Marsden, director of the IAU's Minor Planet Center. The recommendations are "suitably ambitious," notes Duncan Steel, who coordinated Australia's search effort before its government funding ended in 1996. The proposed 3-m observatory would be especially welcome, since at present only one modest telescope is searching for NEOs from the Southern Hemisphere. Steel says that the task force's plan, if adopted, "would place the UK as the number two nation globally in such activity." If fully implemented, the program would cost the British government about 10 million pounds ($15 million) annually.

Launched in 1996, NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft took the long road to asteroid 433 Eros. But since arriving in orbit there last February, NEAR has had plenty to do. As a suite of papers in this week's issue of *Science* demonstrates, this rocky body is proving to be both simple and mysteriously complex.

A very irregular 33 kilometers long and 11 across, Eros has a surprising surfeit of warehouse-sized blocks on its surface. According to planetary geologist Joseph Veverka (Cornell), NEAR's most detailed pictures show few craters and lots of blocks -- just the opposite of what he expected for an object with such weak gravity. "We simply don't understand why the surface is littered with so many blocks," Veverka says. Maybe the debris from impacts is tossed out at low speeds (contrary to computer simulations), or maybe material is ejected into the same orbit as Eros itself, only to be swept back up later.

Eros turns out to be almost totally devoid of color, much blander overall than asteroids 243 Ida and 951 Gaspra, which were visited by the Galileo spacecraft. Diagnostic X-rays coming off of Eros's surface (triggered, for example, by solar flares) imply a rocky composition overall that has not been subject to wholesale melting. The asteroid has a bulk density of 2.67 grams per cubic centimeter; that value is consistent throughout the interior, ruling out buried, metal-rich chunks or big hollows hidden below the surface rubble. But there's some hint of structural variation, and one end may be covered with a thick blanket of pulverized rock that is largely absent at the other.

Eros does not have much gravity, and at its outermost tips the escape velocity is low enough (3 meters per second) for fleet-footed future astronauts to launch themselves into space. Mission planners may use this gentle giant's weak gravity to advantage next month, when they will bring the spacecraft to within 6 km of the surface. Current plans call for a dramatic end to the mission in February, when NEAR-Shoemaker will slowly drop directly onto the surface.

The spacecraft was renamed NEAR-Shoemaker in March to honor the late Eugene Shoemaker, a renowned planetary geologist who died in 1997.

Eros, the chunky asteroid named after the god of love, is slowly revealing to scientists the mysteries of its size, rotation and other properties.

Eros has been studied by the Near Earth Asteroid Rendezvous (NEAR)-Shoemaker spacecraft since last Valentine's day when a careful maneuver put the spacecraft in orbit around the asteroid to determine its properties. Some of those findings, such as Eros' mass and bulk density, appear in the Sept. 22, 2000 edition of the journal Science in a paper by principal author Dr. Don Yeomans of NASA's Jet Propulsion Laboratory. Yeomans is the radio science team chief for NEAR-Shoemaker. The journal also features three other research reports on Eros.

Scientists have learned that Eros is most likely made of rocky material with a uniform density throughout. The asteroid's bulk density is similar to that of Earth's crust. Like Earth, the surface of Eros is covered with a layer of looser rock and soil.

Though it is about 6,700 trillion kilograms (14,700 trillion pounds) in mass, Eros is a fragment from the breakup of a once larger asteroid. "It's a chip off a larger block from millions of years ago," said Yeomans.

Eros is rotating around its shortest axis, making one revolution every 5 hours and 16 minutes. As though thrown in a tight spiral pass by some cosmic quarterback, Eros' rotation axis appears to remain steady on its journey through space. Because the asteroid is so much smaller with much less gravity than Earth, it wouldn't take an Olympic athlete to jump entirely off the surface into space.

Scientists were able to study Eros' rotation, mass distribution and structure based on a series of observations taken onboard the spacecraft. By photographing the asteroid and measuring infrared light reflected from it, scientists could determine its mass, detect minerals and record its motion. As the craft edged into closer and closer orbits around the asteroid, it took fresh data that helped determine the asteroid's size, shape and mass distribution. These activities were critical for navigating the spacecraft in to tighter orbits about Eros so that close-up images could be taken.

"If we didn't know the precise size, shape and mass distribution of the asteroid ahead of time, it would not have been safe to send the spacecraft to within a few kilometers of the asteroid's surface," said Yeomans.

By the mission's end in February 2001, the total surface of the asteroid will have been imaged and measured.

A chemical analysis of a rare, uncontaminated 4.5 billion-year-old meteorite that fell to Earth earlier this year shows that its composition sets it apart from other meteorites found on Earth, giving scientists a glimpse of the solar system that has not been seen before.

The findings, when added to other studies of the meteorite, may provide new information about the first moments of the solar system's formation.

Purdue University chemist Michael Lipschutz, and his graduate student Jon Friedrich, have analyzed 45 chemical elements in a meteorite that fell to Earth into the wilds of northwestern Canada on January 18.

Chemically speaking, the meteorite, called the Tagish Lake meteorite, falls into a classification called carbonaceous chondrite. The carbonaceous chondrites are very rare and extremely interesting to scientists. These meteorites contain carbon as organic compounds, some of which are the basic building blocks for life, and interstellar material, which comes from exploded stars outside of our solar system.

The Purdue study shows, however, that some compositional and mineralogical features set the Tagish Lake sample apart from other carbonaceous chondrites, placing it into a gap between two subtypes of meteorites in that class.

"This meteorite is unique, and represents a new kind of planetary material," says Lipschutz, a professor of chemistry who has studied meteorites for more than 30 years. "From the chemical composition, it's reasonable to assume it came from parts of the solar system different than the ones that produced other carbonaceous chondrites previously studied."

Lipschutz says the oxygen isotopes in the sample place the Tagish Lake meteorite somewhere between the subtypes called CI and thermally metamorphosed CM, putting the sample in a class by itself.

"Thermally metamorphosed meteorites came from parts of their parent bodies that went through some type of major heating experience that caused some volatile elements to vaporize," he says. "The fact that it's not thermally metamorphosed means that this meteorite is much more closely related to the CI meteorites than to any other kind of meteorite."

CI meteorites are considered a "measuring stick" of sorts in cosmochemistry, Lipschutz says, because they contain a chemical composition similar to the outside surface of the Sun.

"The Tagish Lake meteorite is, in fact, a sample of the pre-solar nebula, out of which the planets formed," he says. "We have never before had a sample of this material."

Purdue is among four research centers worldwide that were selected to perform laboratory analyses of the Tagish Lake meteorite. The studies focused on trace elements -- chemical elements found in parts per million or parts per billion -- which can be used to obtain information about the meteorite's parent body and its history.

The findings, presented Thursday and Friday (8/31 - 9/1) at the Meteoritical Society's annual meeting in Chicago, will be combined with other studies of the meteorite to present a more complete picture of the meteorite's history. While the possibilities have researchers very excited, the meteorite's true significance remains to be fully understood, Lipschutz says.

The studies at Purdue were completed using several analytical tools including an inductively coupled plasma mass spectrometer, or ICPMS. Friedrich, a doctoral candidate working with Lipschutz to chemically analyze meteorites, adapted the ICPMS to study meteorite samples. The ICPMS machine allowed him to complete his studies in a fraction of the time required by standard methods.

The Tagish Lake meteorite fell to Earth in January in a remote area between Atlin, British Columbia and Carcross, Yukon Territory. A week later, nearby resident Jim Brook found the meteorite fragments while driving home. He collected the samples using rubber gloves and kept them frozen to prevent contamination or degradation.

The meteorite is considered one of the best preserved samples from our early solar system, Lipschutz says.

For decades planetary scientists have struggled to learn which asteroids are the source of ordinary-chondrite meteorites, which make up more than 80 percent of all known falls on Earth. The most likely "parents" were thought to be the rocky bodies called S-types that dominate the inner asteroid belt. But there's a compositional mismatch: the S asteroids' slightly red color and weak spectral lines implied that they contained too much metal to be the parent bodies for the chondrites. Even Galileo's flybys of the S asteroids 243 Ida and 951 Gaspra failed to solve the mystery. So some researchers proposed that some kind of "space weathering" was masking the asteroids' true optical properties. Others posited the existence of an entire population of undiscovered asteroids that were peppering Earth with their chondritic castoffs.

The solution, it turns out, had unknowingly been discovered 25 years ago. In 1975, while probing why the lunar regolith becomes darker and redder with time, Bruce Hapke (now at the University of Pittsburgh) and two colleagues proposed that the solar wind slowly evaporated the lunar soil, causing individual grains to be coated with a microscopic film of iron droplets just a few nanometers (billionths of a meter) across. "Our suggestion was completely ignored at the time," recalls Hapke, in part because no one could find any trace of the vapor deposits.

But at this week's meeting of the Meteoritical Society, held in Chicago, meteorite specialists at last convinced themselves that space weathering really does happen, and that "nanophase iron" is primarily responsible for it. "It's a pretty tight case," notes Carle Pieters (Brown University). "Observations, experiments, and theory are now all telling us the same thing." The stage for this consensus was set in 1993, when electron microscopy by NASA-Johnson Space Center researchers Lindsay P. Keller and David S. McKay revealed the tiny iron droplets in lunar samples from the Apollo 16 and 17 landing sites. They theorized that the iron is deposited from the puff of vapor created when micrometeorites slam into the lunar soil.

"I think everyone now agrees that ordinary chondrites come from the S types," observes Beth Clark (Cornell University). She has found evidence of space weathering in detailed spectra of the asteroid 433 Eros gathered by the NEAR-Shoemaker spacecraft. In Chicago Clark reported that Psyche, the largest crater on Eros, exhibits patches of soil that are much brighter and slightly redder than elsewhere. She believes the bright patches were exposed by tiny landslides. Once a fresh surface is exposed to space, suggests Clark Chapman (Southwest Research Institute), the microscopic film of iron begins to accumulate, first reddening then darkening over time.

Despite the newfound optimism, the case for space weathering won't be considered ironclad until the tiny beads can be found in ordinary-chondrite meteorites themselves. And that, Clark and Pieters agree, may prove difficult even with state-of-the-art microscopic tecniques.

September 1, 2000 -- This morning a half-kilometer wide space rock is zooming past Earth barely 12 times farther from our planet than the Moon. In cosmic terms, it's a near miss. But don't bother grabbing your hard hats, scientists say, as there is absolutely no danger of a collision. Instead, the close encounter will afford astronomers a welcome opportunity to study a bright near-Earth asteroid from close range.

Today's hasty cosmic visitor -- known by researchers as 2000 QW7 -- was discovered just last weekend on August 26, 2000, with NASA/JPL's Near Earth Asteroid Tracking system (NEAT). QW7 caught the attention of NEAT project scientists because it was fast-moving and unusually bright. At 13th magnitude, amateur astronomers can easily spot the minor planet through 8-inch or larger telescopes.

According to NEAT principal investigator Eleanor Helin, QW7 offers an exceptional opportunity for Earthbound observers to study a near-Earth asteroid. "This is a very important object," she said. "It's so bright that amateur astronomers can track it now and through the end of this year. We should be able to obtain a precise orbit, as well as colors, a light curve and other physical properties during this discovery apparition."

A group of astronomers led by Jean-Luc Margot of the Arecibo Observatory has already made the first radar detection of the space rock using NASA's Goldstone antenna in the Mojave desert. "Radar measurements, in combination with optical data, can immediately shrink trajectory uncertainties by a factor of 1000 or more for a recently discovered object like 2000 QW7," says Jon Giorgini, a senior engineer in JPL's Solar Systems Dynamics Group.

"An improved orbit from the radar data will help us run the orbit backwards and search for pre-discovery images of the asteroid," added Helin. "It's a bit of a mystery why we haven't seen this one before."

Orbital elements for the asteroid and an observing ephemeris are available from the Minor Planet Center.

Asteroid 2000 QW7 falls into a category of Near-Earth Objects (NEOs) called Potentially Hazardous Asteroids, or PHAs.

"Technically an asteroid is a PHA if it can get within about 0.05 AU of Earth's orbit and if it's larger than a few hundred meters," explains Donald Yeomans, manager of NASA's Near Earth Object Program office at the Jet Propulsion Laboratory. "There are currently 266 known Potentially Hazardous Asteroids -- none of them pose an immediate threat to the Earth." (Editor's Note: 1 AU, or Astronomical Unit, is the average distance between the Sun and Earth. It equals 149 million km)

Although PHAs in their current orbits won't collide with Earth, astronomers monitor them because one day they might become dangerous. Gravitational nudges by Earth, Mars or Jupiter can potentially set such asteroids on a collision course with our planet, says Yeomans. At present, all known PHAs rank zero on the Torino Scale -- a numerical measure of asteroid collision hazards similar to the Richter scale for earthquakes.

Close encounters between the Earth and PHAs happen fairly often. Just last month, four such asteroids flew by Earth at distances ranging from 0.038 to 0.084 AU (or 15 to 33 times the distance between the Earth and Moon). More data are available from the PHA Earth Close Approach Table maintained at JPL's Near Earth Object web site.