Facing tight budgets for its space-science activities, last week NASA abruptly decided to end its funding of radar research at Arecibo Observatory (about $550,000 annually), effective January 1, 2002. Thomas H. Morgan of NASA Headquarters sent a formal notice of the termination to Donald B. Campbell (Cornell University), who heads Arecibo's planetary-radar group.

On Thursday the space agency did an equally abrupt about face, opting to provide $400,000 through the end of fiscal 2002. "We made a mistake," said Edward J. Weiler, who directs NASA's space-science efforts, "and we've fixed it."

The central issue revolves around the fact that the Arecibo program has become part of NASA's effort to find and catalog potentially hazardous near-Earth objects, or NEOs. (Congress has mandated that NASA track down 90 percent of all 1-km-wide asteroids in Earth-crossing orbits by 2008.) But the Arecibo facility doesn't find asteroids -- astronomers use it to make follow-up observations of the ones spotted first by telescopic surveys. Morgan, who manages NASA's NEO program, wants to maximize the discovery rate, and to do so more of his $3.55 million budget must go to the four observing teams that are actively searching for NEOs.

The cancellation decision created a shock wave of disbelief among asteroid researchers and triggered several calls for reconsideration from astronomical organizations. Arecibo has been at the forefront of radar studies since 1960, and astronomers routinely direct its powerful megawatt transmitter toward the Moon, Venus, Mercury, and Jupiter's Galilean satellites. NASA also conducts some radar work using its 70-meter-wide tracking antenna near Goldstone, California. But Arecibo's dish boasts a more powerful transmitter and is at least 10 times better at picking up faint radar echoes.

Researchers were thus fearful of losing their single best ground-based tool for studying asteroidal surfaces and for refining their orbits. These characteristics are of more than purely scientific interest: should astronomers discover an asteroid on a collision course with Earth, knowing its makeup and exact trajectory would be crucial to mounting a defense strategy. Arecibo is the "premier astronomical research facility in the world" for this work, notes theorist Eric Asphaug (University of California, Santa Cruz), because it targets a wide spectrum of asteroids and comets, whereas spacecraft have visited few of these bodies.

Although the Arecibo program has secure (if diminished) fiscal footing for 2002, it still faces funding challenges in the years ahead. For one thing, Weiler has demanded that future research proposals utilizing the Arecibo radar system undergo peer review. Ultimately, he would like to see responsibility for Campbell's group transferred to the National Science Foundation, which already provides $9.5 million each year for Arecibo's general operation.

NASA has notified Don Campbell, Associate Director of the National Astronomy and Ionosphere Center at Arecibo and Head of the Radar Astronomy Group, that all funding for Arecibo radar studies will be terminated on January 1. The large Arecibo dish is used to characterize the surface properties and shapes of asteroids having orbits that bring them close to Earth. It has recently discovered a satellite around one of them, which provides information about the asteroid's interior structure. Arecibo radar measurements provide the most precise orbits for these objects, from which the best assessment of their hazard to the Earth can be made. The research is part of NASA's program to identify, by 2008, all objects larger than 1 km with near-Earth orbits and to characterize a portion of them. The U.S. Congress mandated this program several years ago.

NASA currently funds a number of search and follow-up programs to find these near-Earth objects and to determine their orbits. With no additional funding to meet the Congressional mandate, NASA has carved $3.55M out of other portions of its planetary astronomy research and analysis program in FY2002. The Arecibo program is unique in the precision of its measurements and its ability to characterize these targets, but pressure from increasing costs in the search and recovery programs required to meet the 2008 deadline, with no increase in funding for the program to do the job, has caused NASA to cannibalize other programs. Arecibo is the latest victim.

NASA has invested $11M in the Arecibo facility to upgrade it for carrying out radar studies of solar system objects as distant as the moons of Saturn (in support of the Cassini mission), but now has no funding to make the observations. NASA research programs have been level-funded over the past decade while costs have increased and new research programs have been inserted. The agency has recently committed to increase funds for its research programs at the rate of inflation and provide some new funding for astrobiology. In such a constrained fiscal environment, NASA says that asteroid characterization "may have to take a back seat" to NEO search and recovery because it "can no longer do everything it is supposed to do". In the meantime, the rest of NASA's observational astronomy program and mission support suffer and a substantial investment in a national facility is abandoned.

The Division for Planetary Sciences of the American Astronomical Society believes that the Arecibo program should not be terminated to meet an arbitrary deadline. The Congressional language says that these goals should be achieved "to the extent practicable" not at all costs. The NASA NEO search program is already making excellent progress. In the long term we call on the Administration to work with the Congress to increase the resources for non-astrobiology research programs in NASA Space Science as they provide the knowledge base on which our solar system exploration efforts rely.

The DPS is the world's largest professional organization dedicated to the exploration of the solar system.

Two decades ago, after carefully analyzing the Moon's cratered face, the late Eugene Shoemaker estimated that nearly 2,000 asteroids at least 1 kilometer across must have some chance of striking Earth. Lately there's been a growing consensus that Shoemaker overestimated the impact threat. Recent studies have put the count of 1-km-wide near-Earth asteroids (NEAs) under 1,000, with one research team suggesting that it could be as low as 700.

However, a new assessment, published in the November 23rd issue of Science, has racheted the population estimate back up to near 1,250. The higher count comes from J. Scott Stuart (MIT Lincoln Laboratory), who analyzed nearly three years of NEA discoveries from the prolific LINEAR telescope near Socorro, New Mexico. His computer simulations explored possible orbital characteristics for NEAs and determined which of those orbits would have led to a discovery by LINEAR (an acronym for Lincoln Near-Earth Asteroid Research). Besides yielding a large population of 1-km NEAs, the resulting statistics argue that many of them have orbits with inclinations near 23°. This sizable tilt is shared by hundreds of objects belonging to the Phocaea and Hungaria "families" in the inner asteroid belt.

Because LINEAR has found so many more NEAs (727 to date) than any other search effort, asteroid specialists will likely consider Stuart's results the most definitive -- *if* they hold up to closer scrutiny. Dynamicist Alan W. Harris (Jet Propulsion Laboratory) finds the new, higher value very plausible, in part because NEAs continue to be discovered at a fast clip. "I think it's interesting stuff," comments William Bottke (Southwest Research Institute), whose has modeled the NEA population theoretically. Bottke's results track Stuart's in most respects but don't yield so many high-inclination objects, a key discrepancy.

In 1992 a NASA-sponsored report backed a plan to locate 90 percent of all kilometer-size NEAs within a decade. After a slow start, that search is well under way, with about 550 of these large Earth-crossers now catalogued. But if the total population is above 1,200, as Stuart suggests, then most of them await discovery. Reaching the 90-percent threshold could take LINEAR another 40 years, he estimates, because of diminishing returns over time. Harris thinks that's overly pessimistic, but he agrees that asteroid-hunters have decades of work yet ahead of them.

There are asteroids and there are asteroids. Most were once part of larger "parent bodies" and some supply meteorites that plunge to Earth.

But how do you trace the family line of asteroids? Scientists compare mineralogy of asteroids by analyzing their near-infrared spectra. They also compare asteroids' orbits around the sun. And recently they found a perfect match -- "uniting" in a scientific sense, mother and daughter asteroids.

"We determined the mineralogy of asteroid 1929 Kollaa and found that it was once part of a larger asteroid called 4 Vesta. I was inspired to observe these objects because they belong to the rare V-class of asteroids, and they have orbits about the Sun that are very similar," explained Michael Kelley from NASA's Johnson Space Center. "Vesta is the asteroid for which the V-class was established. Until now, no mineralogical analysis had ever been done on another V-type. In that sense, Vesta was unique until our recent work was done. We found not only that this second V-class asteroid, 1929 Kollaa, was once part of Vesta, but that it is also related to a very specific group of meteorites."

Kelley will present this new discovery on Thursday, November 8, at the Geological Society of America's annual meeting in Boston.

Most planetary scientists believe that 4 Vesta is the source of howardite, eucrite, and diogenite meteorites (HED) found on Earth, but Kelley points out that it is not a direct process. "Vesta is located in a part of the main asteroid belt that makes it almost impossible for it to deliver meteorites directly to Earth. So there are probably intermediate asteroids, which were once part of Vesta, located in more favorable orbits that provide delivery."

One of the ramifications of this discovery is that it will help scientists build a geologic map of the asteroid belt and understand what forces have acted on asteroids in the past. This information, along with asteroids' mineralogy, would be crucial if there was ever a need to prevent an asteroid from striking the Earth and causing a major disaster.

The odds of earth suffering a catastrophic collision with an asteroid over the next century are about one in 5,000, which is less likely than previously believed, according to research published this month.

Astronomers using data from the Sloan Digital Sky Survey found that the solar system contains about 700,000 asteroids big enough to destroy civilization. That figure is about one-third the size of earlier estimates, which had put the number at around two million and the odds of collision at roughly one in 1,500 over a one hundred-year period.

"Our estimate for the chance of a big impact contains some of the same uncertainties as previous estimates, but it is clear that we should feel somewhat safer than we did before we had the Sloan survey data," said lead researcher Zeljko Ivezic of Princeton University.

The results were published in the November issue of the Astronomical Journal.

The new estimate draws on observations of many more asteroids, particularly small faint ones, than were available in previous impact risk estimates, said Ivezic. The ability to detect faint objects in large numbers is a hallmark of the Sloan survey, a multi-institutional collaboration that is mapping one-quarter of the sky. While its main purpose is to look at objects outside our galaxy, the survey also records images of closer objects that cross the view of its telescope, which is located at the Apache Point Observatory in New Mexico.

The survey data also allowed the astronomers to gauge the size of asteroids with improved accuracy, which required categorizing the objects by their composition. Asteroids with a surface of carbon -- looking like giant lumps of coal -- are darker than those made of rock. A small rocky asteroid therefore looks just as bright as a much larger one made of carbon.

"You don't know precisely the size of an object you are looking at unless you know what type it is," Ivezic said, noting that the Sloan survey provides information about the color of objects, which allows astronomers to distinguish between carbon and rock.

Based on observations of 10,000 asteroids, the researchers estimated that the asteroid belt contains about 700,000 that are bigger than one kilometer (six-tenths of a mile) in diameter, which is the minimum size thought to pose a catastrophic risk to humans and other species. The asteroid belt is the source for a smaller group of asteroids called "near- earth objects," which have broken from the belt and have the potential to collide with earth. Although they did not specifically observe near earth objects, the researchers believe that their census of main belt asteroids reveals the likelihood of collisions with similarly sized near-earth asteroids.

Ivezic noted that the new impact risk estimate, like most previous ones, relies on assumptions about a single event 65 million years ago when a 10-kilometer asteroid collided with earth and killed the dinosaurs. The researchers assumed that such impacts occur on roughly 100 million-year intervals and used that statistic to calculate the impact odds for the more common asteroids of smaller sizes. This calculation required knowing how much more common one-kilometer asteroids are than 10-kilometer ones, which was hard to measure before the Sloan data was available.

"There is a lot of uncertainty when you have a sample of only one event," Ivezic said, referring to the dinosaur-killing impact. "But this is the best information we have."

Previous studies could detect only asteroids five kilometers or larger, so astronomers had to extrapolate to estimate the number of smaller ones, said Ivezic. The Sloan researchers found that this approach produced high estimates. When they could actually observe them, the small asteroids were not as plentiful as had been expected from observations of large ones.

The reason for this reduced number of smaller asteroids is an open question, which, if answered, may offer important clues about the history of the solar system and the factors that shaped the asteroid belts, said team member Serge Tabachnik of Princeton.

Another valuable piece of information for scientists is the observation that the rock and carbon asteroids are separated into two bands, said co-author Tom Quinn of the University of Washington. The heart of the rocky asteroid belt is 260 million miles from the sun, while the other is 300 million miles from the sun. The sun and earth, by comparison, are 93 million miles apart.

The astronomers attribute much of the success of the study to software that automatically identifies asteroids from among the millions of images observed by the Sloan survey. Independent tests by Mario Juric from the University of Zagreb, Croatia, have shown that the Sloan software finds at least nine of every ten asteroids.

"We have only five minutes to follow the motion of an asteroid as it passes in front of the telescope," said Robert Lupton, a Princeton researcher who developed the software for automatic detection of asteroids. "But we have found that we detect them very efficiently and reliably." Lupton said the team benefited greatly from software for finding the positions and relative movements of objects, developed by Jeff Pier, Jeff Munn, Robert Hindsley and Greg Hennessy of the U.S. Naval Observatory.

"The Sloan study is a major advance in our understanding of the gross asteroid belt structure," said Robert Jedicke, an asteroid expert at the University of Arizona. "Their determination of the Earth impact rate for killer asteroids agrees with soon-to-be-published results based on data from the Spacewatch Project at the University of Arizona." The Arizona team based its risk estimate on a study of near-earth objects, rather than main belt asteroids.

The total of known or suspected binary asteroids grew to 18 on September 22nd when William J. Merline (Southwest Research Institute) and his colleagues discovered that the Trojan asteroid 617 Patroclus is a pair of bodies nearly identical in diameter (105 and 95 kilometers). Merline was using the 8.1-meter Gemini North telescope equipped with an adaptive-optics system.

Trojans follow Jupiter around the Sun in a 1:1 orbital resonance. Many have settled near the gravitationally stable Lagrangian points 60 deg. ahead of and behind the planet along its orbit. Patroclus's orbit is inclined 22 deg. to the plane of the solar system, but it matches Jupiter's period. These bodies, likely leftovers from Jupiter's formation, are thought to be as numerous as main-belt asteroids. Thus finding a binary Trojan is not surprising.

What comes as a shock is the nearly identical size of Patroclus's partners. Asteroidal collisions happen at high velocities and leave behind small rubbly remains. Thus Patroclus has probably been a binary since primordial times. "It's unlikely an asteroid that big would have experienced a collision in the past billion years," says Stuart J. Weidenschilling (Planetary Science Institute). "It was most likely [formed from] a glancing blow during accretion."

Following the terrorist attacks on the United States last month, the committee of the International Astronomical Union responsible for naming asteroids has announced the following, in the October 2nd Minor Planet Circular:

"The terrible events three weeks ago today have prompted several correspondents to propose that minor planets be named to honor the victims. Deeply sympathetic to this desire, but as an independent action, the IAU Committee for Small-Body Nomenclature has unanimously agreed to name three minor planets for concepts that represent some of the most basic and universal human values. The resulting names and citations, on MPC 43684, for the consecutively numbered minor planets (8990), (8991), and (8992), which discovered at observatories on three continents, are intended as a positive statement abhorring the tragedy that occurred on a fourth."

"(8990) Compassion = 1980 DN
Discovered 1980 Feb. 19 at the Klet Observatory.
Named by the Committee for Small-Body Nomenclature to honor the compassion of people around the world for the friends and families of the of disasters, exemplified by the terrorist attacks on New York and Washington on 2001 Sept. 11.

"(8991) Solidarity = 1980 PV1
Discovered 1980 Aug. 6 at the European Southern Observatory.
Named by the Committee for Small-Body Nomenclature to honor the solidarity of people around the world with both victims and survivors of terrorist attacks like those on New York and Washington on 2001 Sept. 11, in the goal of terrorism from the world.

"(8992) Magnanimity = 1980 TE7
Discovered 1980 Oct. 14 at the Purple Mountain Observatory.
Named by the Committee for Small-Body Nomenclature to honor the magnanimity of people around the world in dealing with terrorist attacks like those on New York and Washington on 2001 Sept. 11, in the hope that terrorism will be countered with justice for all, not with revenge."

When Guiseppe Piazzi discovered Ceres on January 1, 1801, he believed he'd found the planet hypothesized to orbit between Mars and Jupiter. Although Ceres is no planet, it turned out to be the largest body in the asteroid belt. And now, two centuries later, astronomers finally have a crude idea of what its surface looks like.

Thanks to the optical prowess of the Hubble Space Telescope, a team of observers led by Joel W. Parker (Southwest Research Institute) captured several images of Ceres on June 25, 1995, in ultraviolet light (at which HST affords the best resolution). Previous ground-based observations had resolved Ceres' disk, but only crudely, using adaptive optics; by contrast, Hubble's images reveal details as small as 50 kilometers across. Apparently the side of Ceres recorded by HST is rather bland, except for one dusky dark marking about 250 km across. As Parker and his colleagues describe in the forthcoming January 2002 issue of the Astronomical Journal, it's unclear whether this spot is a crater, a dark area, or something else. But they believe it's a real feature, enough so to propose that it be named Piazzi.

The 5-hour HST run was not long enough to follow Ceres through an entire 9.1-hour rotation, but the pictorial coverage suggests a mean diameter of 950 ± 8 km. From that, as well as previous mass estimates, the team determined that Ceres' mean density is roughly 2.6 g/cm^3 -- a reasonable match to the rocky, carbon-enriched composition suggested by the asteroid's spectrum. Ceres occupies a roughly circular orbit that averages 2.8 astronomical units (414 million km) from the Sun.

In November 1999, when the Deep Space 1 (DS1) spacecraft was flying blind after losing its navigation camera, Marc Rayman and his engineering team surely despaired that their craft would never make its date with Comet Borrelly nearly two years later. But survive it did, and on the night of September 22nd the struggling spacecraft swept just 2,170 kilometers (1,350 miles) from the comet's icy heart. "I have to tell you that the encounter didn't go as anticipated," Rayman deadpanned at a press conference today. "In fact, it went perfectly."

The results, seen here and on the mission's Web site, are the most detailed images yet of a cometary nucleus, surpassing views of Halley's Comet taken 15 years ago by the Giotto spacecraft. Measuring about 8 km long, Borrelly's nucleus has an elongated bowling-pin shape, and its jumbled surface displays a surprising range of light and dark markings, which in reality are dark and extremely black. Cosmochemists believe the nucleus is likely coated with a patchy veneer of carbon- and organic-rich slag. "These pictures have told us that comet nuclei are far more complex than we ever imagined," says Laurence Soderblom, who heads DS1's camera team. "They have rugged terrain, smooth rolling plains, deep fractures, and very, very dark material." Another team member more pointedly likened the nucleus to "a Dove Bar the size of Mount Everest."

Images from the spacecraft (and from the 5-meter telescope on Palomar Mountain as well) reveal that this interplanetary iceberg sports a narrow, Sunward-pointing jet of vaporized ice and dust that looks like it was shot from a trio of side-by-side cannons. And, in fact, one cometary model suggests that over time such ice-fueled jets should eat their way down into the nucleus, hollowing out "wells" from which gas and dust escape. However, Soderblom notes that the main jet-producing region appears to be a flat, relatively bright "plain."

Known officially as 19P (for "periodic"), Borrelly circles the Sun every 6.8 years and is thought to have formed in a different part of the primordial solar nebula (and thus have a different composition) than Halley, which has a 76-year orbit. However, aside from the obvious signature of water in DS1's ion data, and a second feature that suggests carbon monoxide, Borrelly's composition remains uncertain. "We've only scratched the surface," notes project scientist Robert M. Nelson. Luckily, the nucleus passed directly through the entrance slit of the craft's infrared spectrometer, and these observations may show what coats the icy surface.

Another surprise was found in the cloud of ionized gases streaming away from the nucleus. This million-degree plasma wasn't concentrated directly in front of the nucleus, as had been expected, but was instead offset from it by some 2,000 km. "This is just like a jet fighter flying along with its shock wave off to one side," explains experimenter David Young. "It's in the wrong place, period, and we have to figure out why that is." Young, Soderblom, and the rest of Deep Space 1's science team hope to present much more detailed findings at a scientific meeting in late November. However, observes comet expert Donald Yeomans, what's been learned from DS1's results in the last few days already represents "a giant step forward in our understanding of the cometary nucleus."

By the time the NEAR-Shoemaker mission ended last February, the spacecraft had photographed asteroid 433 Eros from virtually every angle. Since then geologists have been poring over thousands of images of this 33-kilometer-long rock, and they've come to appreciate that its surface is anything but simple. Besides the usual assortment of craters, Eros sports two features never before encountered on an asteroidal surface: thousands of boulders and hundreds of flat-topped "ponds." In yesterday's issue of the journal Nature, mission scientists describe their efforts to unravel these enigmatic discoveries.

The boulders are scattered over the entire surface. A census of the 6,760 biggest ones (those at least 15 meters across) reveals that they are concentrated along the asteroid's equator and, in particular, in and around a large crater provisionally named Shoemaker. According to Peter C. Thomas (Cornell University) and three colleagues, this clustering is probably not a coincidence. They suspect that perhaps a billion years ago, when the 8-km-wide crater was blasted into Eros, blocky debris from the impact rained back onto the surface. The boulders nearest Shoemaker had relatively brief flights, whereas those farthest away took an hour or two before returning to the surface. The boulders likely created small depressions when they landed, but Thomas thinks that since then loose material on the surface has stirred and shifted enough to fill them in.

The existence of all this rough rubble contradicts preexisting notions about asteroidal surfaces. It's been thought that these bodies have too little gravity to retain much impact debris. If the largest boulders really came from a single, recent crater, observes dynamicist Erik Asphaug (University of California, Santa Cruz), then Eros represents "an impact modeler's delight" because only a specific combination of impactor size, speed, and target properties will make an 8-km crater and the observed distribution of boulders.

Meanwhile, Mark S. Robinson (Northwestern University) has led an effort to understand the hundreds of strange, smooth-topped "ponds" found on Eros. There's little question that they are sedimentary deposits of fine-grain dust that became compacted over time, but where did the dust come from? Robinson suggests that sunlight may be giving the very smallest dust grains an electrostatic charge strong enough to levitate them above the surface. These "free floaters" could then migrate into low spots. He notes that a similar phenomenon has been observed on the Moon during lunar sunrise and sunset. Like the boulders, the pond-filled depressions cluster near Eros's equator -- a hint that they too may be related to the formation of Shoemaker.

A satellite roughly 35 kilometers across has been found circling the large, main-belt asteroid 22 Kalliope by two teams of astronomers working just hundreds of yards apart on the summit of Mauna Kea in Hawaii. William J. Merline (Southwest Research Institute) and Francois Menard (Grenoble Observatory) first noticed the satellite in infrared images taken on the morning of September 3rd with the Canada-France-Hawaii Telescope. Meanwhile, another team had already come to the same realization. Jean-Luc Margot and Michael E. Brown (Caltech) had been following the asteroid since the morning of August 30th using an infrared adaptive-optics system on the Keck II telescope.

At the time the companion was about 1,000 km from Kalliope and 4.9 magnitudes (90 times) fainter. Kalliope itself, about 180 km across, has an M-type spectrum. That means that its composition is dominated either by the metals iron and nickel, or by a metal-poor silicate mineral called enstatite. Fortunately, the new satellite -- which is officially designated "S/2001 (22) 1" -- will be a powerful tool for deciding between these possibilities. Determining its orbit will yield Kalliope's mass and, in turn, its bulk density.

The count of double asteroids is growing steadily, with 12 known and another five suspected. Observers have found three paired systems this year alone.

When Robert L. Millis (Lowell Observatory) and his Deep Ecliptic Survey team recorded a distant, 20th-magnitude body in the head of Scorpius last May, they realized that it was circling the Sun beyond Neptune among a swarm of similar bodies collectively called the Kuiper Belt. They also suspected that their discovery, designated 2001 KX76, might rival 1 Ceres for the title of largest asteroid. But at the time, the new object's orbit was too uncertain to know its precise distance from Earth. Lacking that, the team could only guesstimate a size based on its apparent brightness.

Now a fresh round of observations has allowed European astronomers to pin down the orbit and, in turn, the object's diameter. Team leader Gerhard Hahn (German Aerospace Center) believes that 2001 KX76 is at least 1,200 km across, assuming that its surface has an albedo (reflectivity) of 7 percent -- and 1,400 is not out of the question. Determining the size more accurately will have to await measurements at far-infrared wavelengths, which have not yet been made.

Pinning down the orbit required some sleuthing and a bit of luck. First, members of Hahn's team used a 2.2-meter telescope in Chile to update the object's position. Then they traced the motion of 2001 KX76 back in time using Astrovirtel, an electronic image archive. Luckily, the object turned up in several images dating back to 1982. Armed with two decades of data, Arno Gnaedig (a German amateur astronomer) calculated that 2001 KX76 is currently 43.2 astronomical units (6.5 billion kilometers) from Earth. Its orbit is similar to that of Pluto, locked in a dynamical resonance with Neptune that keeps it an average of 39.9 a.u. from the Sun.

Millis has yet to propose a name for 2001 KX76. Brian G. Marsden, who coordinates minor-planet observations for the International Astronomical Union, says that by convention such "Plutinos" are given names for figures associated with the underworld. "Hades" might be a good choice, Marsden hints, because of its prominence in Greek mythology.