Using the radar systems at the National Science Foundation's recently upgraded radio/radar telescope at Arecibo, Puerto Rico, and at NASA's Goldstone Solar System Radar in California, astronomers have obtained the most-detailed pictures yet of an asteroid which passed within 5.3 million miles of Earth earlier this month.

The radar images of this Earth orbit-crossing asteroid, known as 1999 JM8, reveal a several-mile-wide object with a peculiar shape and an unusually slow and possibly complex spin state, says Lance Benner, of NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif., who led the team of astronomers.

"The photographs of this asteroid are phenomenal," says Donald Campbell, Cornell University professor of astronomy and associate director of the National Astronomy and Ionosphere Center (NAIC) at Cornell, which manages the Arecibo Observatory, for the National Science Foundation. "This is one of the clear firsts for the telescope and radar upgrade."

Scott Hudson, of Washington State University, an expert in using radar images to determine the shapes of asteroids, added that at this stage of the analysis, the resemblance of 1999 JM8 to Toutatis, a similar sized, slowly rotating object also studied in detail with radar, is striking. Why these asteroids and perhaps others rotate so slowly is not understood. "Although collisions between asteroids are thought to be the primary process that determines asteroid-spin states, we don't know how the slow, complex states come about," he says.

The images show impact craters with diameters as small as 100 meters and a few as large as one kilometer. "The density of craters suggest that the surface is geologically old, and is not simply a 'chip' off of a parent asteroid," said Michael Nolan, a staff scientist at the Arecibo Observatory. "We also see a concavity that is about half as wide as the asteroid itself, although we're not sure yet whether or not it's an impact crater."

The pictures may not have been possible before Arecibo's upgrade, financed by the NSF and the National Aeronautics and Space Administration (NASA). Fitted with a powerful new 1 million-watt radar transmitter, it is now possible for the Arecibo radar system to capture detailed images of these kinds of objects at greater distances than in the past.

Originally, the object was found in 1990 by Eleanor Helene of NASA's Jet Propulsion Laboratory, who used the Palomar Observatory on Palomar Mountain, Calif. It was dubbed 1990 HD1, and subsequently it went unseen until last spring. On May 13, 1999, the Massachusetts Institute of Technology/Lincoln Labs Near-Earth Asteroid (LINEAR) search program re-discovered the object and the Minor Planet Center in Cambridge, Mass., designated it 1999 JM8.

Realizing that 1999 JM8 would make a good radar telescope target, astronomers Lance Benner and Steve Ostro of JPL organized observations and radar data collection with the Arecibo and Goldstone telescopes. Ostro, who has led dozens of asteroid radar experiments, noted that radar has revealed a stunning array of exotically shaped worlds.

In early August, Benner and Arecibo astronomers Nolan and Jean-Luc Margot assisted by observatory staff took images of the asteroid with the Arecibo radar system at a resolution of 15 meters (50 feet). At its 5 million-mile distance it took the radar signal about one minute to travel to the asteroid and back to the earth. Arecibo's huge receiving dish captured the echo and stored the data. In all, about 70 to 100 gigabytes of data were collected requiring many days of computer processing to generate the images.

"This is the first good opportunity for radar imaging an asteroid in a very long time," says Margot. "You don't get these kinds of objects passing near the Earth everyday."

In addition to Benner, Campbell, Hudson, Margot, Nolan and Ostro, the radar team included Jon D. Giorgini, Raymond F. Jurgens, Donald K. Yeomans and Martin A. Slade, who are all from JPL.

The radar observations were supported by NASA's Office of Space Science in Washington. The Arecibo Observatory, in Puerto Rico, is part of the National Astronomy and Ionosphere Center, which is operated by the Cornell University under a cooperative agreement with the National Science Foundation and with support from NASA. The Goldstone Solar System Radar is part of NASA's Deep Space Network. JPL is operated by the California Institute of Technology, Pasadena, Calif.

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Asteroids seem to have lower densities than the rocks scientists believe compose them. This implies that there is quite a bit of empty space inside the typical asteroid or small moon. Lionel Wilson (Lancaster University, UK), Klaus Keil (University of Hawaii), and Stanley Love (astronaut candidate, Johnson Space Center) investigated two possibilities for producing the high percentage of pore space. In one case they calculated that if an asteroid were broken apart and then reassembled, the resulting rubble pile would have a porosity of 20 to 40%, hence a density 20 to 40% lower than it had to begin with. They also calculated how fractures would form on bodies that contained water ice that was heated to steam, concluding that the fractures would be pervasive and, hence, decrease the density of the object.

Astronomers have used the world's two most powerful radar telescopes to make the most detailed images ever obtained for a large asteroid in a potentially Earth-threatening orbit. With an average diameter of about 3.5 kilometers (2 miles), 1999 JM8 is the largest of the so-called potentially hazardous asteroids ever studied in detail. Although this object can pass fairly close to Earth in celestial terms, astronomers concur that an actual encounter with Earth is not of concern in the next few centuries.

As recently as 1995, planetary astronomers believed that there are upward of 2,000 asteroids at least 1 kilometer across capable of striking Earth. But since only a fraction of such large near-Earth objects (NEOs) have been found -- 169 to date -- this census was considered only a rough estimate based on search statistics and on the cratering record of the Moon. Now, thanks to hundreds of NEO discoveries in recent years, there is some good news to report. At a meeting of asteroid specialists last month, David Rabinowitz (Jet Propulsion Laboratory) said that there are likely only 500 to 1,000 Earth-crossers with absolute magnitudes of 18 or brighter, which correspond to objects roughly 1 km across or larger. The revised value is based on nearly 3 years of search data systematically collected by JPL's Near-Earth Asteroid Tracking (NEAT) project. However, even if Rabinowitz and his colleagues are correct, Alan Harris (JPL) warns that we still have a way to go. The discovery rate of 1-km NEOs needs to be doubled if we are to track down 90% of them by the year 2010.

August 6: A sizzling-hot rock, a suspected meteorite, fell from the sky Thursday and sailed right over the heads of two lifeguards sitting on their stand.

The egg-sized rock landed with a loud thump on the wet sand, where it sizzled like a piece of lava, the guards said. It landed near the surf about eight feet in front of their 11th Street stand in this Ocean County community.

NASA's Deep Space 1 experimental spacecraft successfully flew approximately 26 kilometers (16 miles) above the surface of asteroid 9969 Braille at 9:46 p.m. Pacific time Wednesday, July 28 (04:46 Universal Time July 29), using a sophisticated new space autopilot system, exceeding 100 percent of the mission's objectives. An exultant operations team looked on as preliminary data returned to the Deep Space 1 operations control area in historic Building 230, indicating that the AutoNav autopilot system skillfully flew the spacecraft to a face-to-face closeup with asteroid Braille.

This was by far the closest flyby of an asteroid ever attempted and yet one more accomplishment in JPL's long history of encounters with previously unexplored solar system bodies.

"This is a dramatic finale to an amazingly successful mission," said Dr. Marc Rayman, chief mission engineer and deputy mission manager. "The encounter with Braille has allowed us to complete the testing and validation of 12 new technologies and to return some exciting science as a bonus. JPL can be proud that one of its missions has now visited the smallest solar system body ever targeted."

Ten minutes after the flyby, when the spacecraft signals reached Earth after a 10-minute journey, the team burst into spontaneous applause at the news that the spacecraft was turning back to face the asteroid, a clear signal that the flyby had succeeded.

Making the encounter all the more memorable-and serving as a testimonial to the team's quick ability to think on its feet-was the fact that the spacecraft experienced a "safing" event earlier in the day, starting at about 5 a.m. PDT on July 28 and ending at about 11 a.m. PDT. A small software glitch, now fully diagnosed, was detected by Deep Space 1's fault-detection software, which triggered a protective program that causes several events: the spacecraft halts non-critical activity, orients its solar panels toward the Sun, points light- and heat-sensitive instruments away from the Sun and reverts to its low-gain antenna while awaiting new commands.

"This has been by far the most challenging and dramatic day on the project," said Rayman. "The last 16 hours before the flyby were really, really exciting. We had the safing event, we recovered from it and we managed to squeeze in a trajectory correction maneuver to update Deep Space 1's flight path. The entire operations team deserves great praise for its heroic response to an event that otherwise would have eliminated any chance of conducting the encounter," he added.

Science results were downlinked in a series of telemetry sessions through Friday morning, July 30. The results from an infrared sensor within the spacecraft's integrated spectrometer and imaging instrument proved to be startlingly significant, for they showed nearly matching compositional fingerprints between near-Earth Braille and Vesta, a much larger asteroid in the main asteroid belt between Mars and Jupiter.

"This clear link between Vesta and Braille is an important finding," said Dr. Laurence Soderblom, from the U.S. Geological Survey, team leader for Deep Space 1 experiments using the spacecraft's integrated spectrometer and imaging instrument.

Thus the novel spacecraft not only passed a technology milestone by flying itself past Braille, but also it now has scientists pondering a deep-space "family tree" mystery.

Scientists are wrestling with a thorny question: is Braille a chip off the old block, Vesta, or are the two siblings that originated elsewhere, perhaps thrown off a larger body long since destroyed?

The scientists made their finding from three sets of data collected by the spacecraft's infrared spectrometer. Called spectra, a form of data resulting from the instrument breaking light into component colors much like a prism does (usually displayed as graphs), the data sets cover different parts of the asteroid and were taken just after closest approach.

Braille's longest side is now estimated at 1.3 miles (2.2 kilometers) and its shortest side appears to be 1 kilometer (0.6 miles). This elongated asteroid was expected to be irregular, and two black-and-white photographs taken approximately 15 minutes after closest encounter have helped to confirm this.

By contrast, Vesta, discovered in 1807, has a diameter of about 500 kilometers (310 miles). The fourth asteroid ever discovered, Vesta shares with Braille a high visual reflectivity, or albedo. In fact, Vesta is the most reflective of the main-belt asteroids.

Apart from flyby findings, project scientists have determined that Braille is one of the asteroids that drift in and out of Earth's orbit over eons and that it will return to Earth's vicinity within a few thousand years.

Diagnosis of an apparent target-tracking problem that impacted visible imaging (the taking of black-and-white photos) during the flyby continues. Preliminary results suggest that a combination of the asteroid's highly irregular shape, its orientation relative to the Sun and the camera's response under these unusual conditions are responsible.

Launched Oct. 24, 1998, Deep Space 1 is the first mission under NASA's New Millennium Program, which tests new technologies for future space and Earth-observing missions. The technologies that have been tested on Deep Space 1 will help make future science spacecraft smaller, less expensive, more autonomous and capable of more independent decision-making so that they rely less on tracking and intervention by ground controllers.

Of the 12 new technologies on board, all but the spacecraft's autonomous navigation system had been completely tested since launch. With the asteroid encounter, AutoNav finished its last 5 percent of testing. Science return was a bonus for this technology validation mission.

A Deep Space 1 asteroid flyby press kit, along with mission status reports from launch to the present, is available online at

The Deep Space 1 spacecraft, which passed the newly-named asteroid Braille last week, has provided scientists with surprising information about the asteroid's composition, linking the tiny, irregularly-shaped Braille with one of the largest bodies in the asteroid belt, and to meteorites collected on Earth.

Data returned by the Deep Space 1's spectrographic camera shows that Braille is composed of the same elements as the giant asteroid Vesta, which orbits the Sun in the asteroid belt between Mars and Jupiter, project scientists announced today from NASA's Jet Propulsion Laboratory in Pasadena, Calif.

The finding is notable because Braille and Vesta are in completely different orbits, and previously seemed to have no connection to one another. Braille is in an eccentric orbit that passes inside the orbit of Mars. Its own unique chemical composition is shared by about 6 percent of the meteorites found on Earth, leading scientists to conclude that the two asteroids and the meteorites share a common origin.

"This is sort of like winning the triple crown," said Deep Space 1's project scientist Bob Nelson. "It is often said a picture is worth a thousand words, well in this case, a spectrum is worth a thousand pictures."

The spacecraft didn't get any good pictures of Braille. In fact, it almost completely missed the tiny, tumbling rock, because it had trouble finding it. Braille is an oblong asteroid that measures only 1.5 miles (2.2 kilometers) from end to end. Larry Soderblom leader of the camera-spectrometer group for the Deep Space 1 science team compared its shape to an oddly twisted carnival balloon -- the kind used by clowns and magicians.

So small is Braille, that the spacecraft's cameras couldn't even detect it until two days before closest approach. When the spacecraft's computer did find the rock, it was about 250 miles (400 kilometers) away from where it had been calculated to be, Soderblom said. This sent mission controllers scrambling to aim the craft's scientific instruments back at the dim little asteroid. They accomplished this in the nick of time, but only as the craft was speeding away from Braille.

The discovery that Braille and Vesta are composed of such similar material is leading scientists to speculate that Braille, and other similarly-composed asteroids in the asteroid belt, are in fact parts of Vesta. Dan Britt, a geologist at the University of Tennessee at Knoxville who is a member of the Deep Space 1 science team, said in an interview with space.com that it is "pretty certain" that Braille and Vesta share the same origin.

Vesta is a nearly spherical asteroid with a complex geologic history similar to that of the inner planets. Its surface is composed of basaltic rock that scientists believe was flowed from a molten interior.

"Vesta is by far the largest (asteroid) with this particular (chemical) signature," Britt said. "And the others are small enough that they could arguably be fragments of Vesta."

The fragments could have been smashed off Vesta in a violent collision with another asteroid, Britt said. He said it is unlikely that Vesta and Braille each came from some larger parent body because the surface of Vesta has such a consistent composition. If Vesta had been a fragment of some larger body, it would show much greater variation, with large regions of its surface showing signs of having formed under different conditions -- not surface volcanism.

Vesta even wears a scar -- a large impact crater that resulted from a violent collision. That catastrophic crash could have ejected material that millions of years afterward has found its way to earth as meteorites and into the inner solar system where Braille orbits.

The successful analysis of Braille's composition is a noteworthy step toward understanding the history of asteroids and the solar system, Britt said. Out of some 11,000 named asteroids, scientists understand the composition of only about 5 percent, he said.

This scientific work is a big bonus for Deep Space 1. The mission's primary objective was not really to study the asteroid at all, but to test a suite of experimental technology, including ion propulsion and autonomous navigation. Braille was chosen almost at random, Britt said, because the mission needed a target.

Having demonstrated the validity of much of that technology, the spacecraft's primary mission is over, but it may get a second life.

NASA could decide to extend the mission for another two years. Deep Space 1 is already aimed to pass by two comets in 2001. If its mission is extended, the craft will be able to study those comets, one of which may be evolving into an asteroid -- a process which scientists know very little about.