VLT NACO Instrument Helps Discover First Triple Asteroid:

One of the thousands of minor planets orbiting the Sun has been found to have its own mini planetary system. Astronomer Franck Marchis (University of California, Berkeley, USA) and his colleagues at the Observatoire de Paris (France) [1] have discovered the first triple asteroid system – two small asteroids orbiting a larger one known since 1866 as 87 Sylvia [2].

"Since double asteroids seem to be common, people have been looking for multiple asteroid systems for a long time,” said Marchis. “I couldn't believe we found one."

The discovery was made with Yepun, one of ESO's 8.2-m telescopes of the Very Large Telescope Array at Cerro Paranal (Chile), using the outstanding image’ sharpness provided by the adaptive optics NACO instrument. Via the observatory's proven "Service Observing Mode", Marchis and his colleagues were able to obtain sky images of many asteroids over a six-month period without actually having to travel to Chile.

One of these asteroids was 87 Sylvia, which was known to be double since 2001, from observations made by Mike Brown and Jean-Luc Margot with the Keck telescope. The astronomers used NACO to observe Sylvia on 27 occasions, over a two-month period. On each of the images, the known small companion was seen, allowing Marchis and his French colleagues to precisely compute its orbit. But on 12 of the images, the astronomers also found a closer and smaller companion. 87 Sylvia is thus not double but triple!

Because 87 Sylvia was named after Rhea Sylvia, the mythical mother of the founders of Rome, Marchis proposed naming the twin moons after those founders: Romulus and Remus. The International Astronomical Union approved the names.

Sylvia's moons are considerably smaller, orbiting in nearly circular orbits and in the same plane and direction. The closest and newly discovered moonlet, orbiting about 710 km from Sylvia, is Remus, a body only 7 km across and circling Sylvia every 33 hours. The second, Romulus, orbits at about 1360 km in 87.6 hours and measures about 18 km across.

The asteroid 87 Sylvia is one of the largest known from the asteroid main belt, and is located about 3.5 times further away from the Sun than the Earth, between the orbits of Mars and Jupiter. The wealth of details provided by the NACO images show that 87 Sylvia is shaped like a lumpy potato, measuring 380 x 260 x 230 km and spinning at a rapid rate, once every 5 hours and 11 minutes.

The observations of the moonlets' orbits allow the astronomers to precisely calculate the mass and density of Sylvia. With a density only 20% higher than the density of water, it is likely composed of water ice and rubble from a primordial asteroid. "It could be up to 60 percent empty space," said co-discoverer Daniel Hestroffer (Observatoire de Paris, France).

“It is most probably a "rubble-pile" asteroid”, Marchis added. These asteroids are loose aggregations of rock, presumably the result of a collision. Two asteroids smacked into each other and got disrupted. “The new rubble-pile asteroid formed later by accumulation of large fragments while the moonlets are probably debris left over from the collision that were captured by the newly formed asteroid and eventually settled into orbits around it. Because of the way they form, we expect to see more multiple asteroid systems like this.”

Marchis and his colleagues will report their discovery in the August 11 issue of the journal Nature, simultaneously with an announcement that day at the Asteroid Comet Meteor conference in Armação dos Búzios, Rio de Janeiro state, Brazil.

More information:

Only four observers, all using video recorders, saw asteroid 302 Clarissa pass in front of a 10th-magnitude star on the night of June 24th. But that was enough to reveal at least two surprises, reports David Dunham, head of the International Occultation Timing Association. His preliminary assessment suggests that Clarissa is about 64 kilometers long -- nearly twice its assumed diameter of 38 km. More importantly, Phil Dombrowski (Glastonbury, Connecticut) recorded a 0.25-second-long disappearance hundreds of kilometers from Clarissa's center. Instead, Dunham thinks it's likely due to a companion satellite perhaps 5 or 6 km across. He notes that Brad Timerton, watching closer to the occultation's centerline from Newark, New York, recorded a miss, indicating a gap between the two bodies. Of the 27 confirmed binary asteroids, none have been discovered during an occultation; Dombrowski's observation, if it holds up, would become the first.

From IAUC #8354

Further to IAUC 8265 and 8292, R. Behrend writes (on behalf of fourteen others) that photometric observations of (4492) obtained during 2002 Oct. 30-Dec. 4 and 2004 Mar. 18-May 18 show a regularly shaped lightcurve with period 1.108 day and amplitude 0.5 mag, with sharp attenuations characteristic of mutual eclipse/occultation events observed at minima of the regular lightcurve having depth about 0.6 mag and duration about 2.5 hr -- suggesting that this is probably a binary system, with properties similar to those of (1089) and (1313).

M. C. Nolan, E. S. Howell, and A. A. Hine, National Astronomy and Ionosphere Center

Arecibo radar delay-Doppler images (2380 MHz, 12.6 cm) obtained on 2004 May 1-3 show that 2003 YT_1 is a binary system. Preliminary estimates of average diameters, based on range extents at 15-m and 30-m resolution, are 1000 and 180m. The primary has an irregular shape, and has a rotation period no longer than 2.6h. The orbit appears to be eccentric, with a period near 30h. The secondary has a rotation period no longer than 6h, inconsistent with synchronous rotation.

(From IAU Circular 8227)

1937 UB (HERMES)
J. L. Margot, University of California, Los Angeles; M. C. Nolan, V. Negron, A. A. Hine, D. B. Campbell, and E. S. Howell, National Astronomy and Ionosphere Center; L. A. M. Benner, S. J. Ostro, and J. D. Giorgini, Jet Propulsion Laboratory; and B. G. Marsden, Minor Planet Center, write: "Arecibo (2380-MHz, 12.6-cm) radar observations on Oct. 18 and 20 UT show that the recently rediscovered (IAUC 8223) near-earth-object 1937 UB has a strongly bifurcated appearance. Our images show two separate components of roughly equal sizes, consistent with an orbiting binary pair. The range-Doppler separation between components was 150 m at 1.5 Hz on Oct. 18.2 and 600 m at 0.7 Hz on Oct. 20.1. The Doppler broadening of each component was 0.8 Hz on Oct. 18 and 0.6 Hz on Oct. 20. Preliminary estimates of the diameters, based on visible range extents, are 300-450 m. Upper limits to the spin period of each component are 13-21 hr for the above size range. Additional data are needed to provide an unambiguous orbital solution and to verify whether the system is in a doubly synchronous configuration. Radar and lightcurve observations throughout this apparition would be extremely valuable."

(From IAU Circular 8216)

P. Pravec, P. Kusnirak, and L. Sarounova, Ondrejov Observatory; P. Brown and G. Esquerdo, University of Western Ontario (UWO); D. Pray, Greene, RI, U.S.A.; L. A. M. Benner, Jet Propulsion Laboratory (JPL); M. C. Nolan, National Astronomy and Ionosphere Center; J. D. Giorgini and S. J. Ostro, JPL; and J.-L. Margot, California Institute of Technology, report that photometric observations -- obtained during 2003 Sept. 16-27 at Ondrejov, at UWO, and by Pray -- show the near-earth object (66063) to be a binary system with orbital period 14.53 hr. The primary rotates with a period of 2.492 hr, its low lightcurve amplitude indicative of a nearly spheroidal shape. The lightcurves suggest that the secondary has an aspect ratio of about 1.5 and a rotation synchronous with its orbital period. Mutual eclipse/occultation events indicate a secondary-to-primary mean diameter ratio of >/= 0.5. Arecibo (2380-MHz, 13-cm) delay-Doppler radar observations, obtained during Sept. 29-Oct. 4, show a spheroidal primary and an elongated secondary with separations at least as large as 600 m.

At its July 2003 meeting in Sydney the IAU Committee on Small Bodies Nomenclature (CSBN) adopted the name "Linus" for the satellite of asteroid (22) Kalliope (cf. IAUC 7703). The CSBN also confirmed the name, adopted three years ago by the IAU Working Group on Planetary System Nomenclature, of "Petit Prince" for the satellite of (45) Eugenia (cf. IAUC 7129).

In some Greek legends Linus, a famous musician, is said to be the son of Kalliope. In one version of the legend he was killed by Apollo because he rivalled the god in his musical skill.

Petit Prince comes from the Antoine de Saint-Exupery character the Little Prince. It is thought that Saint-Exupery based the character on Eugene Louis Jean Joseph (1856-79), Prince Imperial, son on the Empress Eugenie, wife of Napoleon III. Asteroid Eugenia was named after the Empress.

W.J. Merline and a large team using the 10-m Keck telescope and working in the infra-red with adaptive optics found a satellite by asteroid (283) Emma. On July 14.6 UT the satellite was at separation 0".26 (projected separation 370 km) and position angle 218 degrees. The satellite was also observed by the same team with the European Southern Observatory 8-m Very Large Telescope UT4/YEPUN (+ NAOS/CONICA adaptive optics system) on July 15.3, 15.4, and 16.4. The H-band brightness difference is about 5.5 mag, giving an estimated diameter of the satellite of about 12 km. (IAUC 8165)

On August 14.6 Jean-Luc Margot, California Institute of Technology, Discovered a satellite by (379) Huenna (V = 12.9) again with the Keck II telescope and adaptive optics on Mauna Kea. The satellite was observed to follow the primary at the non-sidereal rate of roughly 10"/hour for a period exceeding 2 hours. At discovery the companion was at a separation of 0".89 (projected separation 1200 km) in p.a. 34 deg from the primary. The primary to secondary flux ratio in H band is about 165, giving a diameter ratio of about 13. (IAUC 8182)

On the next night the team led by Merline, also using Keck II, discovered a satellite of (130) Elektra. On Aug. 15.6 the satellite was at separation 0".72 (projected separation 1170 km) and position angle 70 deg.

They confirmed the satellite on Aug. 17.6. The K'-band brightness difference is about 8.5 mag, giving an estimated diameter of the satellite of about 4 km. (IAUC 8183)

Repeated observations over many weeks or months will be needed to determine the orbits of the satellites. From this comes a measure of the asteroid's mass and hence, from its size, an estimate of its density. This gives clues to the asteroid's structure. The remarkably low density of some asteroids supports the idea that many are loosely aggregated 'rubble piles'.

William J. Merline (Southwest Research Institute) found a companion to asteroid 121 Hermione on September 28th. The object, discovered with the 10-meter Keck II telescope in Mauna Kea, Hawaii, appears to be about 13 kilometers across and has a projected separation from Hermione of 630 km. With this find, close to two dozen objects are now confirmed or suspected to be binary asteroids. Merline's discovery also appeared on IAU Circular 7980.

Binary asteroids -- two rocky objects orbiting about one another -- appear to be common in Earth-crossing orbits, astronomers using the world's two most powerful astronomical radar telescopes report. And it is probable, they say, that these double asteroid systems have been formed as a result of gravitational effects during close encounters with at least two of the inner planets, including Earth.

Writing in a report published by the journalScience on its Science Express web site (April 11, 2002), the researchers estimate that about 16 percent of so-called near-Earth asteroids (NEAs) larger than 200 meters (219 yards) in diameter are likely to be binary systems, with about a three-to-one relative size of the two encircling bodies. To date, five such binary systems have been identified by radar, says lead researcher Jean-Luc Margot, an O.K. Earl postdoctoral fellow in the Division of Geological and Planetary Sciences at the California Institute of Technology.

Margot, who at the time of the observations was a research associate in the planetary studies/radar group at the National Science Foundation's (NSF) Arecibo Observatory in Puerto Rico (managed at Cornell University), says that theoretical and modeling results show the binary asteroids appear to be formed extremely close to Earth -- within a distance equal to a few times the planet's radius (6,378 kilometers or 3,963 miles). "The fact that one out of every six large NEAs is a binary and that they typically survive on the order of 10 million years, implies that these close encounters must happen frequently compared to the lifetime of the binary asteroids," says Margot.

The Science article, "Binary Asteroids in the Near-Earth Object Population," is coauthored by Michael Nolan, research associate at Arecibo; Lance Benner, Steven Ostro, Raymond Jurgens, Jon Giorgini and Martin Slade at the Jet Propulsion Laboratory (JPL); and Donald Campbell, professor of astronomy at Cornell. The observations were made at the 70-meter Goldstone NASA tracking telescope in California and at Arecibo Observatory.

NEAs are formed in the asteroid belt, between the orbits of Mars and Jupiter, and nudged by the gravitational attraction of nearby planets, largely Jupiter, into orbits that allow them to enter the Earth's neighborhood. Most of the asteroids are the remnants of the initial agglomeration of the inner planets.

Astronomers have long speculated about the existence of binary NEAs, based in part on impact craters on Earth. Of about 28 known terrestrial impact craters with diameters greater than 20 kilometers, at least three are double craters formed by impacts of objects about the same size as the newly discovered binaries. Astronomers also have noted the changes in brightness of reflected sunlight for some NEAs, indicating a double system was causing an eclipse or occultation of one by the other.

In 2000, Margot and his co-researchers, using measurements from the Goldstone radar, found that a small, roughly 800-meter-diameter (half-a-mile) asteroid, 2000 DP107 (discovered only months before by a team from the Massachusetts Institute of Technology), was a binary system. Observations over eight days last October with the much more sensitive Arecibo telescope clearly established the physical characteristics of DP107's two asteroids as well as their orbit about each other. The smaller object called the secondary, it was found, is about 300 meters (1,000 feet) in diameter and is orbiting the larger asteroid, the primary, every 42 hours at a distance of 2.6 kilometers (1.6 miles). The two asteroids appear to be locked in synchronous rotation, with the smaller always with the same face oriented to the larger.

Since that observation, says Margot, four more binary NEAs have been discovered, all in Earth-crossing orbits and each with a main asteroid significantly larger than the smaller body. "The primary is rotating much faster than most NEAs in all five binaries that have been discovered," says Cornell's Campbell. The Science Express article speculates that the most likely way the binaries are created is by close encounters of asteroids with the inner planets Earth or Mars. Of the five binary NEAs discovered to date, none has an orbit that brings it as close to the sun as Venus or Mercury.

NEAs, basically piles of rubble held together by gravity, are on trajectories that bring them within a few thousand miles of the planets, where tidal forces ---- essentially the pull of gravity -- can increase the spin rate of the asteroid, causing it to fly apart. The ejected rubble then reforms in orbit around the larger asteroid.

"The asteroid is already rotating very quickly as it approaches the planet. A little extra boost from tidal forces can be enough to exceed its breakup limits, and it sheds mass. This mass can end up forming another object in orbit around the asteroid. Right now this seems the most likely explanation," says Margot.

There is an important reason for studying binary asteroids, says JPL's Ostro: their potential for colliding with Earth. Knowing the density of so-called PHAs (for potentially hazardous asteroids), he observes, "is an extremely important input to any mitigation plans." He says, "Getting NEA densities from radar is dirt cheap compared with getting a density with a spacecraft. Of course, the most important thing to know about any PHA is whether it is two objects or one, and this is why we want to observe these binaries with radar whenever possible."

Margot notes, "Radar gives us very precise measurements of the size of the objects and their shape. The radar measurements of the distance and velocity of each component allows us to obtain precise information on their orbits. From this we can obtain the mass of each of the objects allowing, for the Þrst time, measurements of NEA densities, a very important indicator of their composition and internal structure."

Arecibo Observatory is operated by the National Astronomy and Ionosphere Center at Cornell under a cooperative agreement with the NSF. The research was supported by the NSF, with NASA providing additional support for the planetary radar program at Arecibo.

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."

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.

A small asteroid now passing near Earth has revealed one of its secrets: it's actually two asteroids. A team of six radar astronomers led by Lance A. M. Benner and Steven J. Ostro (JPL) has found that 1999 KW4 is a double body whose components are separated by at least 2 km. Based on their observations from May 21-23, announced yesterday on IAU Circular 7632, one half is at least three times the size of the other. But neither piece is thought to be more than 2 or 3 km across.

The swarm of objects beyond Neptune known as the Kuiper Belt just keeps getting curiouser and curiouser. Last December, while checking up on 1998 WW31, an object that had been discovered out there two years earlier, Christian Veillet and two colleagues realized that it sometimes appeared elongated while other times as a double blip. News of the binary's discovery was announced this week on IAU Circular 7610.

Veillet's team recorded 1998 WW31 with the 3.6-meter Canada-France-Hawaii Telescope in Hawaii and the facility's new 100-megapixel camera. Even so, at 23rd magnitude and 6.9 billion kilometers away, 1998 WW31 did not divulge much about itself. Fortunately, a series of observations taken nearly a year earlier also showed doubling and elongation, clinching its status as a binary. Veillet says the two components orbit at least 40,000 km apart, and that one is about 0.4 magnitude brighter than the other. This would make the bodies roughly 150 and 200 km across.

For the second time this year and the fifth in the last 13 months, astronomers have identified an asteroid encircled by a satellite. Alex Storrs and the Hubble Space Telescope Asteroid Team found a companion orbiting 107 Camilla, a main-belt asteroid about 220 kilometers across. The discovery was made in a quick succession of HST images taken on March 1st. Although the satellite was seen 1,000 km from Camilla, more observations will be needed before its orbit can be calculated. Storr's team has another HST run scheduled for March 27th. Details appear in IAU Circular 7599.

The discovery of Camilla's companion brings the count of confirmed binary asteroids to seven; another eight or nine are suspected of duplicity, most of which are small near-Earth objects with unusual light curves.

On February 18th, Michael Brown and Jean-Luc Margot (Caltech) went on an asteroid hunt. While observing with the 10-meter Keck II telescope atop Hawaii's Mauna Kea, Brown and Margot took a look at the 130-kilometer-wide asteroid 87 Sylvia. The minor planet, discovered in 1866, is one of the largest asteroids in the solar system.

Using Keck's adaptive-optics system, the two astronomers resolved a small moon orbiting Sylvia. They report that separation between the two bodies appears to be approximately 1,200 km, and based on initial observations, the companion is only 7 km wide.

The discovery is very encouraging for Brown and Margot. "Based on small-number statistics -- finding one in one night -- there might be a lot more out there," says Brown. "Suffice to say we're not done [looking]."

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.

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.

A team of European astronomers claims to have taken an unusual direct photograph of an object that may be a member of a class of strange space objects -- asteroid pairs that closely orbit one another.

Asteroid (216) Kleopatra, first discovered in 1880, previously was thought to be a solo dumbbell-shaped object, but it now appears in infrared images taken using the European Southern Observatory's 3.6-meter telescope at La Silla Observatory in Chile to be a pair of bright objects closely circling one another, separated by a thin space of unknown size.

Franck Marchis, Daniel Hestroffer and their colleagues used adapted optics on the telescope on Oct. 25 to look directly at Kleopatra, a Main Belt body with an elongated orbit that passes between Mars and Jupiter. They say the session showed that Kleopatra is comprised of two similarly sized lobes, neither of which is small enough to be called a moon.

An international team of astronomers using a ground-based telescope has discovered a moon orbiting the asteroid (45)Eugenia. The pictures are the first of an asteroidal satellite taken from Earth, and the second ever taken; the Galileo spacecraft previously discovered a moon around the asteroid Ida.

Details about the satellite (first announced in March on IAU Circular 7129) have been published in Nature by William J. Merline (Southwest Research Institute) and his colleagues. They explain how they found the moon by using an adaptive-optics system on the Canada-France-Hawaii telescope. The satellite -- designated S/1998 (45) 1 -- is about 13 kilometers in diameter and orbits Eugenia in 4.7 days at a distance of 1,190 km. Eugenia itself is about 215 km in diameter. Taking these values, the astronomers determined that Eugenia has a density of 1.2 grams per cubic centimeter, suggesting that the body may be a "rubble pile" or having an interior consisting mostly of water ice.