On October 26th, the Near Earth Asteroid Rendezvous (NEAR) spacecraft made its closest approach yet to the asteroid 433 Eros, gliding only 5 kilometers (3 miles) above its surface. At that height -- lower than the cruising altitude of many commercial airplanes above the Earth -- cameras aboard NEAR-Shoemaker will resolves features as small as 0.7 meter (2 feet) across.

Among the many remaining mysteries astronomers hope to solve with these ultra-detailed views are the asteroid's numerous boulders and missing craters. Eros appears to be relatively devoid of small impacts. Yet there's an overwhelmingly large number of boulders. In fact, at sizes of 20 m and smaller, there are more boulders than craters on the surface of Eros. Speaking Monday at a meeting of planetary scientists in Pasadena, California, Clark Chapman (Southwest Research Institute) pointed out that there are approximately one million boulders, 8 meters or larger, on the 32-km long object.

One possible reason for the absence of the small craters was suggested by asteroid expert, William F. Bottke (Southwest Research Institute). He proposes that unlike the Moon, when an impactor hits Eros, it shakes the entire body. This smoothes out the surface much the same way shaking a box of sand would remove any patterns. However, the abundant boulders are more perplexing. It is unclear whether they are the result of ejecta deposits from impacts or if meteorite collisions with Eros exhumed the rocks. Scientists working with Eros are hoping the close flyby with provide the answers.

Andrew F. Cheng (Applied Physics Laboratory) pointed out that Eros is crisscrossed with an extensive network of ridges and grooves, some of which run from one end of the asteroid to the other. Such structures indicate that Eros is not a rubble pile but instead has a coherent, rocky interior. Eros's strongly elongated shape and the extent of the fracturing argues that the asteroid was cleaved from a larger body in the distant past.

A Massachusetts Institute of Technology researcher said today that the number of near-Earth asteroids (NEAs) may be higher than recent estimates.

Research presented by MIT graduate student Scott Stuart at a meeting of the American Astronomical Society's Division of Planetary Science showed that because the inclinations -- angles of orbit in relation to the plane of the Earth's orbit around the sun -- of known NEAs are not representative of the entire population, there may be more undetected NEAs out there.

NEAs with low inclinations are easier to find than highly inclined NEAs, Stuart noted. Thus, the known NEAs tend to have low inclinations rather than being representative of the population.

With the new determination of higher inclinations for the NEA population, researchers at MIT Lincoln Laboratory now estimate that there is a mean total of more than 1,100 near-Earth asteroids bigger than 1 kilometer (0.6 miles) in diameter. Recent estimates had ranged from 750 to 900. Those prior estimates used a small number of asteroid detections and assumed that the NEAs have lower inclinations than suggested by Lincoln Near-Earth Asteroid Research (LINEAR) Project data.

This new number is consistent with earlier estimates of the population made by the late astrogeologist Eugene Shoemaker, who based his analysis on the number of asteroid impact craters on the moon.

NEAs are objects within our solar system whose orbits may bring them close to the Earth. While no currently known NEAs are now on a collision course with the Earth, many NEAs remain undetected.

The amount of damage that would be caused by an asteroid depends on its size. Asteroids bigger than 1 kilometer are thought to be capable of causing extensive damage on a global scale.

Astronomers find and catalog asteroids by imaging large swaths of sky with telescopes and searching for objects that move against the background of fixed stars. By tracking an asteroid's location over several months, astronomers can calculate the orbit that the asteroid follows and determine whether it could pose a hazard to the Earth.

LINEAR has been scanning the skies to discover and catalog NEAs and to provide advance warning if any are bound for Earth. Since March 1998, LINEAR has found 70 percent of all near-Earth asteroids discovered worldwide. It is a major contributor toward NASA's goal of cataloging 90 percent of NEAs larger than 1 kilometer within the next 10 years.

No one yet knows exactly how many NEAs are out there. However, it is possible to make estimates of the number remaining to be discovered based on the number already found and the amount of searching that has been done to discover them.

LINEAR has detected more than 400 different near-Earth asteroids. This ten-fold increase in detections has allowed researchers to investigate more accurately the inclination distribution of NEAs.

Stuart is a participant in the MIT Lincoln Laboratory Scholars program, an employee education program, working with Richard Binzel, professor of Earth, Atmospheric and Planetary Sciences at MIT, and a member of the LINEAR project team. Principal investigator of the LINEAR project at Lincoln Laboratory is Grant Stokes, assistant division head.

The Moon is heading for a close encounter with a Leonid debris stream on Nov. 17, 2000.

For most stargazers, this year's quarter Moon during the Leonid meteor shower will be a blazing nuisance. Bright moonlight will overpower many faint shooting stars as the Earth passes through the outskirts of three cometary debris streams during a 36-hour period spanning Nov. 17 and 18, 2000.

But for some astronomers, the Moon itself will be the main event if a Leonid meteor storm erupts.

"On Nov. 17 [around 0500 UT] the Moon will pass approximately four Earth-diameters from the center of a dust trail left behind by comet Tempel-Tuttle in 1932," says David Asher of the Armagh Observatory, an expert on Leonid debris filaments. "The Moon will be considerably closer to the trail than Earth," raising the possibility of vigorous Leonid activity there.

When Leonid meteoroids rain down on the airless Moon, they won't cause "shooting stars" as they do on our planet. There's no atmosphere on the Moon where cosmic debris particles can incinerate as fiery streaks of light. Lunar Leonids will simply hit the ground with a head-spinning velocity of nearly 140,000 mph.

Prior to 1999, no one had ever recorded natural impacts of any sort on the Moon. But last year surprised Moon-watchers captured video footage of at least six exploding Leonid meteorites while the Moon passed through another debris stream from comet Tempel-Tuttle. The impact flashes were relatively faint -- 3rd magnitude at most -- but they were clearly visible in videos recorded by astronomer David Dunham and others.

Although the Moon will pass nearly as close to a debris stream in 2000 as it did in 1999, meteor watchers won't be able to spot the telltale flashes of lunar Leonids. This year the Moon will plunge into the stream farside first. All of the meteoroids that hit the Moon will land on terrain that's hidden from direct view.

Nevertheless, say scientists, there may be a way to monitor this year's activity indirectly.

"When a Leonid meteoroid hits the Moon it vaporizes some dust and rock," explains Jody Wilson of the Boston University Imaging Science Team. "Some of those vapors will contain sodium (a constituent of Moon rocks) which does a good job scattering sunlight. If any of the impact vapors drift over the lunar limb, we may be able to see them by means of resonant scattering. They will glow like a faint low-pressure sodium street lamp."

Even when there are no ongoing meteor showers, the Moon is surrounded by a gaseous halo called the lunar "exosphere," says Wilson. Consisting of a just a few hundred atoms per cubic centimeter, the exosphere is barely more than a vacuum. The solar wind blows it into a long tail much like a comet's. It points away from the Sun and extends for hundreds of thousands of kilometers. The giant tail is so rarefied that it's completely invisible to the unaided eye even when the Earth passes through it once a month around the time of the New Moon.

Wilson and his colleagues at Boston University, led by Prof. Michael Mendillo, routinely monitor the Moon's tail. They use extraordinarily sensitive cameras that can detect sunlight scattered from as few as 5 sodium atoms per cubic centimeter. For comparison, the density of Earth's atmosphere at sea level is 3 x 1019 molecules/cm3.

"The primary goal of our research is to figure out what process is most responsible for producing the Moon's atmosphere," says Wilson. "Is it solar radiation, the solar wind, meteoroid impacts, or some combination? We're still not sure."

"Two years ago the density of the Moon's sodium tail tripled just after the 1998 Leonid fireball shower," he continued. "The meteoroids in '98 were larger than usual and they were really slamming the Moon when they hit. There's no doubt that the primary source of the exosphere at that time was the Leonids."

Mendillo's group was monitoring the Moon again in 1999 when a full-fledged Leonid meteor storm burst over Western Europe. "We know that the Moon was close to a debris trail in '99 because of all the impact flashes people saw," noted Wilson, "but the sodium concentration didn't seem to be much greater than normal."

It may be that 1998 was simply special. Leonid particles that hit the Moon (and the Earth) that year were relatively large ones (like marbles rather than snowflakes) that had accumulated into a coherent dust filament as the result of an orbital resonance with Jupiter. "I suspect the enhanced sodium tail in 1998 was related to the total mass of the impacting meteoroids rather than to their number," says Rob McNaught (Australian National University) who studies Leonid debris trails in collaboration with David Asher. "Of all the recent years we've studied, 1998 would probably have the greatest mass hitting the Moon and thus the greatest sodium production."

"I think we'll look back years from now and realize that 1998 was very special," agrees Wilson. "The fireballs on Earth were unique and we've never detected another meteor-related enhancement of the Moon's tail. That includes 1999 when the sheer number of Leonids hitting the Moon was probably much higher than the year before. Even in '98, when the sodium density tripled two days after the shower (that's how long it takes for sodium to travel down the tail the length of the Moon's orbit), the enhancement didn't last long. The sodium tail faded back to normal within 24 hours.

"All this could add up to solar processes, not meteoroid impacts, as the dominant day-to-day producers of lunar exospheric gas. But we need more data to be sure."

A better year for spotting lunar Leonids directly is just around the corner, say meteor experts. On Nov. 18, 2001, the Moon will be just 2 days past New when a furious Leonid storm is likely to erupt. David Asher and Rob McNaught predict as many as 10,000 meteors per hour on Earth and similar numbers of impacts on the Moon. (Leonid rates in 2000 are likely to be 100 times lower.)

Unlike this year, the 2001 "sub-Leonid point" (the spot where Leonids crash directly down onto lunar terrain) will be favorably positioned on the darkened nearside of the Moon, which will appear as a super-thin crescent. Camcorder shots of detonating Leonids may be possible for careful photographers filming just after the Sun sets on Nov. 18th next year.

Until then, Leonid impacts will be hidden from direct view. Moon-watchers must rely on ghostly vapors from the far side of the Moon, and not their own senses, to tell the tale of the Lunar Leonids 2000.

Large telescopes with deformable optics are allowing astronomers to study distant asteroids with unprecedented clarity -- leading to the discovery of new shapes and configurations and presenting scientists with new puzzles to solve.

An international team of astronomers led by Dr. William Merline of the Boulder office of Southwest Research Institute (SwRI) released today the first-ever images of a large, double asteroid. Each asteroid in the pair is the size of a large city (about 50 miles across), separated by about 100 miles, mutually orbiting the vacant point of interplanetary space that lies midway between them. The discovery was made using the W.M. Keck Observatory atop Mauna Kea, the tallest mountain in Hawaii. The asteroid pair was once assumed to be a single body, called Antiope, orbiting the sun in the outer parts of the asteroid belt between the orbits of Mars and Jupiter.

The team also released a picture of a small moon orbiting the large asteroid Pulcova. This moon was discovered in February 2000 using the Canada-France-Hawaii Telescope (CFHT), also on Mauna Kea. It is only the third asteroid discovered to have a small moon. Asteroid-moon pairs had not been seen until 1993, when the Galileo spacecraft imaged the one-mile-wide moonlet Dactyl, as it rushed past the 19-mile-diameter asteroid Ida. The Merline team reported the second asteroidal moonlet a year ago, circling the 135-mile-sized asteroid Eugenia. The team named the companion Petit-Prince, officially accepted by the International Astronomical Union in August.

"It's getting to be kind of bewildering," says Dr. Christophe Dumas of the Jet Propulsion Laboratory (JPL), a team astronomer. "Asteroids were once thought to be single, mountain-like chunks of material, perhaps smashed into 'flying rubble piles' by occasional collisions among themselves."

Astronomers expect strange new configurations to provide still more surprises as the survey continues. "Every new asteroidal companion we discover seems to bring new configurations and new mysteries," says team member Dr. Clark R. Chapman, also of the SwRI Boulder office.

The team's approach uses a new technology, called adaptive optics, which enables telescopes to see asteroids and other small points of light in the heavens with the same clarity as the Hubble Space Telescope. Until recently, ground-based telescopes were hindered by distortions caused by Earth's atmosphere, in much the same way water distorts the view of an underwater object. The new technique passes light from the telescope through a specialized "correction box" to instantaneously analyze the distorted light and compute the amount of correction necessary to remove the blurring of the atmosphere. The correction information is then fed to deformable mirrors in the box that remove the distortion, providing a sharper image.

A fascinating demonstration of the new telescope technology is in a movie of the asteroid Kleopatra, also released today, observed during a seven-hour period. Earlier this year, Steve Ostro of JPL published reconstructions of Kleopatra's shape based on radar reflections obtained when that asteroid was fairly close to the Earth in November 1999. During the same month, team member Dr. Francois Menard, currently a visiting scientist at CFHT, obtained adaptive optics images. "Excellent agreement of both optical and radar pictures of Kleopatra's 'dog-bone' shape provides added confidence in the reliability of adaptive optics images," says Menard.

"Radar works well for asteroids near the Earth, but adaptive optics is much more powerful for studying asteroids in the middle of the asteroid belt and beyond," says Dr. Laird Close of the European Southern Observatory and the University of Arizona.

This week, Merline and his colleagues reported to an annual meeting of international scientists specializing in solar system studies on two years of asteroid surveys conducted at three observatories equipped with the new adaptive optics systems.

"In fact, large asteroidal satellites and twin companions are rather rare," Merline told attendees of the 32nd annual meeting of the American Astronomical Society's Division for Planetary Sciences, convened this week in Pasadena, California. "Preliminary study of about 200 asteroids has turned up only two asteroids with moons (Eugenia and Pulcova) and just one double (Antiope)," he explains. "It is possible that a few more moonlets might emerge from more sophisticated analysis of the data we have collected."

Pulcova is an asteroid about 90 miles in diameter. Its small satellite, roughly a 10th its size, orbits Pulcova every four days at a distance of about 500 miles.

Asteroidal companions provide vital information about asteroids that has been difficult to obtain. Until now, the best measurements of asteroid masses -- their bulk densities, such as whether they are "light" like ice, "dense" like metal, or in between like rocks -- came from deflections of spacecraft flying past an asteroid. Such spacecraft encounters are rare, and deflections of more distant objects (other asteroids or planets) by an asteroid's gravity are weak and difficult to measure. But an asteroidal satellite, or twin, is a body whose trajectory is so mightily deflected by the asteroid's gravity that it is actually forced to orbit around it. The revolution time provides a measure of the body's mass, hence density. Using such techniques, Merline's team find that Eugenia, Pulcova, and Antiope are all rather light bodies. They are much less dense than familiar rocks, more like ice, but their surfaces appear very dark, like rock. Interesting differences in the densities motivate further research on asteroids with satellites.

NASA and the National Science Foundation are funding this research. Observations are being conducted at the Keck Observatory and the CFHT (operated by the National Research Council of Canada, the French Centre National de la Recherche Scientifique, and the University of Hawaii). Other team members are Dr. J. Chris Shelton (Mt. Wilson Observatory) and Dr. David Slater (SwRI, San Antonio).

SwRI is an independent, nonprofit, applied research and development organization based in San Antonio, Texas, with more than 2,700 employees and an annual research volume of more than $300 million.

University of Arizona Spacewatch Project founders just realized a 20-year dream.

Spacewatch astronomers led by Tom Gehrels and Robert McMillan have used a 36-inch (0.9-meter) UA telescope on Kitt Peak to electronically scan the skies for asteroids throughout the solar system since 1984. Before Spacewatch, astronomers used photographic plates to hunt asteroids.

Spacewatch has been a striking technological and scientific success. But Gehrels' and McMillan's original hope in 1980 was to use a 72-inch (1.8-meter) telescope in their electronic asteroid survey.

Two weeks ago, perseverance and hard work paid off. The new 72-inch Spacewatch telescope captured its first light from an asteroid, asteroid 2000 RD 53, on Sept. 14. The Spacewatch team took first digital data with the telescope on the same very fast moving near-Earth object on Sept. 19.

Last Thursday, Sept. 28, the Spacewatch team made its most interesting observations yet. Telescope-drive software tracked the fast-moving asteroid 2000 SM10 for more than three hours.

Like happy new parents, Spacewatchers provide information, images and video of the newborn and its accomplishments on the web.

"I think the 1.8-meter will be the biggest telescope in the world dedicated full time to asteroid discovery and astrometry," McMillan, Spacewatch director, said. (Astrometry is a branch of astronomy that measures the positions and movements of celestial bodies.)

Astronomers refer to brightness in terms of "magnitude," with larger magnitudes corresponding to dimmer objects. The unaided human eye when dark-adapted under clear, dark sky sees objects at about six-and-half magnitude brightness. The 36-inch telescope detects objects down to 21.7 magnitude. (That's roughly equivalent to photographic film rated at ASA one million, McMillan noted.)

The 72-inch will detect objects down to 22.7 magnitude, or two-and-a-half times fainter than the 36-inch can detect. The bigger telescope will discover twice as many asteroids as the smaller telescope now finds, McMillan said.

Plans are to upgrade -- not retire -- the 36-inch telescope. McMillan said. Now that the 72-inch telescope is coming on line, the 36-inch can be temporarily shut down late next year so new detectors can be installed. The new detectors are 10 times larger than the detector that has been used in the telescope since 1989. "That upgrade alone will boost our discovery rate by a factor of 6 to 10, depending on how we use it."

"The telescopes will be complementary. The smaller telescope, when upgraded, will get a much wider field of view, or cover 10 times as much sky. The 1.8-meter will concentrate on finding the very faint objects," McMillan said. Faint targets for the new telescope include the small Near-Earth Asteroids, some of the bigger and brighter Trans-Neptunian Objects in the Kuiper Belt, and Near-Earth Asteroids that have previously flown by Earth as these objects usually appear fainter on successive swings by the planet, he added.

The 72-inch telescope looks radically different from its white, single- barreled 36-inch elder sibling.

UA originally acquired the 72-inch, f/2.7 fused silica mirror blank from the military for an asteroid telescope, but the mirror blank was loaned to the Multiple-Mirror Telescope on Mount Hopkins, Ariz., until 1993, Gehrels noted. The mirror is mounted in altitude-azimuth type mount in a mirror- support cell contributed by the UA/Smithsonian MMT Observatory.

The telescope itself was built at the UA's University Research Instrumentation Center. Telescope designers used "folded prime focus" rather than a straight prime-focus for a more compact telescope that could be housed in a smaller, less expensive dome. The telescope support structure is painted black to reduce light scattering, prompting engineers and astronomers to dub it the "Stealth" telescope.

Contributions from foundations, corporations and private individual donors, and grants from NASA and the U.S. Air Force Office of Scientific Research paid for the roughly $5 million telescope.

The venerable 36-inch Spacewatch telescope, which was originally sited on the UA campus in 1921, moved to Kitt Peak in 1962. Among its distinguished accomplishments:

• First to use CCD scanning routinely in astronomy
• First to use CCDs to survey the sky for comets and asteroids
• First near-Earth asteroid detected with a CCD (1989 UP)
• First astronomical group to develop automated, real-time software for moving-object detection
• First to discover a near-Earth asteroid by software (1990 SS)
• First automatic discovery of a comet (C/1992 J 1)
• Detected smallest known asteroid (1993 KA2, about 4 - 9 meters diameter)
• Detected closest known approach of an asteroid to the Earth (1994 XM1, at 105,000 km)
• Identified two new asteroid populations -- small near-Earth asteroids and distant Centaurs (objects in unstable orbits between Jupiter and Neptune)
• Discovered fastest rotating and most accessible asteroid at time of discovery (1998 KY 26)
• Continues to detect 20 to 30 near-Earth asteroids annually
• Smallest telescope in the world for Trans-Neptunian Object discoveries. (Trans-Neptunian Objects, or TNOs, are primordial objects orbiting the sun beyond Neptune.)

Researchers at The University of Western Ontario (Western) and the University of Calgary (U of C) -- working with colleagues from Canada, the United States and the United Kingdom -- have found that meteorites recovered in northern British Columbia may be one of the most primitive solar system materials ever examined.

Peter Brown, a professor in Western's Department of Physics and Astronomy, and Alan Hildebrand, a professor in the Department of Geology and Geophysics at U of C, are the lead authors of the report featured on the cover of the Oct. 13, 2000 issue of the international journal Science.

The meteorites, recovered by B.C. resident Jim Brook in late January, and scientists at Western and the U of C during April and May, were found on Tagish Lake, B.C. It was the largest meteorite fall in Canadian history.

"We can now say that this may be the 'crown jewel' of meteorite finds," says Brown. "This discovery will aid scientists in the reconstruction of the early solar system."

"The standard composition of the solar system is partly defined by the most primitive meteorite in existence," says Neil MacRae, earth sciences professor at Western and a co-author on the Science paper. "If our results are proven correct, this new discovery will ultimately change that definition."

The Tagish Lake Meteorite is a new type of carbonaceous chondrite -- a rare, organically rich, charcoal-like class of meteorites. Carbonaceous chondrite meteorites make up about three per cent of meteorite finds in the world. The chemical class most closely resembling this meteorite constitutes less than 0.1 per cent of all meteorites recovered to date, though the Science paper suggests the Tagish Lake Meteorite to be even more primitive and therefore may represent a new class.

The first recovered pieces of the Tagish Lake Meteorite have been kept frozen, which will allow researchers to identify the full range of compounds in a primitive, carbon-rich meteorite for the first time. These organic materials may help scientists better understand chemical processing in the outer part of the solar nebula. The meteorite is also rich in interstellar grains. Coupled with the limited aqueous alteration on the parent asteroid of the Tagish Lake Meteorite, this may mean that new things will be learned about the nuclear furnaces of stars.

"The most significant and exciting things to be discovered in this meteorite may not yet be known," says Hildebrand. "We, together with Jim Brook, are supplying material to dozens of researchers located around the world for their studies. It is a delightful and somewhat rare situation for scientists when we can't predict what may be learned."

Other members of the research team include Michael Mazur, Tina Rubak-Mazur, Michael Glatiotis, and J. Andrew Bird at U of C; Michael Zolensky at NASA Johnson Space Center; Monica Grady at the Natural History Museum in England; Robert Clayton and Toshiko Mayeda at the University of Chicago; Edward Tagliaferri at ET Space Systems in California; Richard Spalding of Sandia National Laboratories in New Mexico; Margaret Campbell, Robert Carpenter, Heather Gingerich, Erika Greiner, Phil McCausland and Howard Plotkin at Western; Eric Hoffman at Activation Laboratories Ltd. in Ancaster, Ontario; David Mittlefehldt at Lockheed Engineering and Science Co. in Houston; and John Wacker at the Pacific Northwest National Laboratory, Richland, Washington.

In 1984, University of Arizona astronomers began using a 0.9-meter (36-inch) telescope to hunt for near-Earth asteroids and comets -- some of which pose an impact hazard to our planet. Since then, the Spacewatch Project has taken more than 300,000 images, discovering more than 200 near-Earth asteroids and 14 comets. Very soon these astronomers will be using a more powerful eye to scan the skies. A 1.8-m reflector is now complete and is currently undergoing testing. Built at a cost of $5 million, the Spacewatch instrument employs a fused-silica primary mirror acquired from the U.S. military that had been on loan to the Multiple-Mirror Telescope on nearby Mount Hopkins. The new telescope can detect much fainter objects than its predecessor, down to magnitude 22.7. It viewed its first asteroid -- designated 2000 RD53 -- on September 14th. The 36-inch telescope will be upgraded then returned to service, exploiting its wider field of view for follow-up observations of new discoveries.