951 Gaspra

29 Oct 91 - 951 GASPRA becomes the first asteroid to be encountered by a spacecraft: Galileo passed by at a distance of 16,000 km and showed Gaspra to be 19x12x11 km with a wedge shaped darkish rocky surface potted with craters named after famous spas (Bath has a diameter of 2km). There were indications that pieces had broken off of three areas suggesting Gaspra (S-class) is a survivor from a series of catastrophic collisions. Gaspra's rotation of 7h 2m 21s was obtained from its light curve measured on Earth. Its shape probably indicates a violent break up of a larger differentiated body which left one of the pieces as Gaspra.

243 Ida

28 Aug 93 - 243 IDA becomes the second asteroid ever encountered by a spacecraft: Galileo passed by at just 2,000 km. Ida is an S-type asteroid of 55x24x20 km and images have provided the first conclusive proof that asteroids can have satellites - its 1.6x1.4x1.2 km moon later named Dactyl. There is heavy cratering, about five times that seen on Gaspa, indicating Ida is possibly the older of the two. One crater, Afon, has a diameter of 5.2 km.

253 Mathilde

27 Jun 97 - The NEAR (Near Earth Asteroid Rendezvous) spacecraft's 25 minute, 9.93 km/s, 1212 km (750 miles) flyby of 253 MATHILDE obtained 534 images and was the closest asteroid encounter to date. It was also the first meeting with a C-class asteroid. Mathilde's diameter was found to be 52 km (33 miles), with a slow rotation of 17.4 days. With an albedo of only 3% it is twice as dark as a chunk of charcoal. Such a dark surface is believed to consist of carbon-rich material that has not been altered by the planet-building processes. One surprise was that NEAR's imager found at least five craters larger than 20 km (12 miles) just on the lighted side of the asteroid, this size is very large compared to the diameter of the asteroid. The surface turned out to be uniformly black and colourless, and none of the craters reveal any other rocks. Such uniformity seems to confirm that C-classs are pristine samples of the building blocks of the solar system. A very porous carbonaceous condrite asteroid, objects hitting Mathilde are like hitting a Styrofoam cup, which may have dampened the effects of the impacts. Did you know?: Only two known asteroids rotate slower than Mathilde - 288 Glauke & 1220 Crocus.

Asteroid Numbers

9 Mar 98 - Jet Propulsion Lab. Searches through more than 28,000 Hubble images have provided a sizeable catch of about 100 asteroids. Preliminary analysis SUGGESTS A TOTAL OF 300,000 (1-3 km) bodies orbiting between Mars and Jupiter. At present there are only 8,319 confirmed main-belt asteroids.

Mass Extinctions

1 May 98 - Carnegie Institution of Washington, District of Columbia. A new theory suggests a scenario whereby a collision between 'rubble-pile' asteroids in the asteroid belt may throw out large quantities of dust into interplanetary space as well as asteroid fragments. This shower of dust over millions of years might change the Earth's climate enough to account for GRADUAL MASS EXTINCTIONS. During the dust-induced cold snaps the Earth would be at abnormally high risk from the increased number of Earth-crossing fragments. The debate also includes linking the Earth's 100,000 year climate cycle with the Orbital mechanics of our planet (elliptical to circular). Currently the Earth is accumulating about 30,000 metric tonnes of cosmic dust each year. This dust comes from just three families of asteroids - Eos, Themis and Koronis. Originally these families were just one asteroid which over time has broken up into smaller and smaller fragments. There is now a constant flow of dust from these families which the Earth ploughs through on its yearly orbit. The theory is that, over the extinction period, the Earth could have collected some 10 million metric tonnes of dust per year accounting for the gradual extinctions.

Detecting Hazardous Asteroids

14 Jun 98 - JPL. A new program office to co-ordinate efforts to DETECT, TRACK AND CHARACTERISE potentially hazardous asteroids and comets will be established at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA. NASA's Near-Earth Object Program Office will focus on the goal of locating at least 90 percent of the estimated 2,000 asteroids and comets that approach the Earth and are larger than about 1km (2/3-mile) in diameter, by the end of the next decade.

The Torino Scale

22 Jul 99 - NASA HQ. Planetary scientists have developed a new scale as a means of conveying the risks associated with asteroids and comets that might collide with the Earth. It will assign values to celestial objects moving near Earth running from zero to 10. An object with a value of zero or one will have virtually no chance of causing damage on Earth; a 10 means a certain global climatic catastrophe. The scale was created by Dr. Richard P. Binzel, professor of Earth, Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology (MIT). It is named the TORINO IMPACT HAZARD SCALE after the Italian city in which the scale was initially adopted by the International Astronomical Union (IAU) in June 1999. No asteroid identified to date has ever had a value greater than one, noted Binzel, who has been working on the scale for five years. Several asteroids that had initial hazard scale values of one have been reclassified to zero after additional orbit measurements showed that the chances of impact with the Earth were essentially zero.
http://impact.arc.nasa.gov

9969 Braille

29 Jul 99 - NASA HQ. Deep Space 1 flew within an estimated 26 km (16 miles) of an asteroid today. The spacecraft's infrared sensor confirmed that the small asteroid 9969 BRAILLE IS SIMILAR TO VESTA, which is a rare type of asteroid. "This clear link between Vesta and Braille is an important finding," said Dr. Laurence Soderblom of the U.S. Geological Survey, team leader for Deep Space 1 experiments using the spacecraft's integrated spectrometer and imaging instrument. Scientists are now wrestling with a thorny question: Is the near-Earth asteroid Braille a chip off Vesta's old block, or are the two asteroids siblings which originated elsewhere, perhaps thrown off a larger body that has long since been destroyed? Braille's longest side is now estimated at 2.2 km (1.3 miles) and its shortest side appears to be 1 km (0.6 miles).
www.jpl.nasa.gov/ds1news

1999 JM8

26 Oct 99 - Cornell Univ. 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 EARTH-CROSSING ASTEROID KNOWN AS 1999 JM8 which passed within 5.3 million miles of Earth earlier this month. The radar images reveal a several-mile-wide object with a peculiar shape and an unusually slow and possibly complex spin state. 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 kilometre. "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." Originally, the object was found in 1990 and was dubbed 1990 HD1, but it subsequently went unseen until last spring. On May 13, 1999, the MIT/Lincoln Labs Near-Earth Asteroid (LINEAR) search program re-discovered the object and it became 1999 JM8. In early August images of the asteroid were taken 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. www.news.cornell.edu/releases/Aug99/
AsteroidPix.bpf.html

45 Eugenia

6 Oct 99 - National Science Foundation. Astronomers this week announced their DISCOVERY OF A MOON ORBITING AN ASTEROID, 45 Eugenia, in the first images ever obtained of such an object from Earth. The results are the first from a program to search for satellites around nearly 200 asteroids using ground-based telescopes with adaptive optics, a recent technology that corrects for the distortions caused by the Earth's atmosphere. Eugenia's moon was found with the Canada-France-Hawaii telescope on Mauna Kea, Hawaii. A surprising result of this discovery is the very low density of the primary asteroid - only about 20 percent denser than water. Most asteroids appear dark and were thought to be composed primarily of rock, which is about three times denser than water. "A picture is emerging that some asteroids are real lightweights," said Dr. William Merline, leader of the team. "Either these objects are highly porous rubble-piles of rock, or they are mostly water ice," said Dr. Clark Chapman, another team member. Researchers estimate that the diameter of the satellite is about 13 km. Eugenia's diameter is about 215 km. The researchers have determined that the satellite has a circular orbit about 1,190 km away from Eugenia. It orbits about once every five days, and was probably formed during a collision. Previously, faint and close satellites would have been lost in the glare of the primary asteroid. "It is similar to taking a photo of a candle located 400 km away and then discovering a firefly (that is 300 times fainter) flying within two meters of the flame," said Dr. Laird Close, a participant from the European Southern Observatory. The results are the first from a program to search for satellites around nearly 200 asteroids. www.boulder.swri.edu/~merline/press_release

308 Polyxo

21 Jan 2000 - An imager aboard a NASA F-18 aircraft is being used to observe an asteroid occulting a star. This observation will reveal the size of the asteroid 308 POLYXO, which, like most asteroids, is too small for even the Hubble Space Telescope to resolve.
www.boulder.swri.edu/swuis/swuis.instr.html

2685 Masursky

1 Feb 2000 - JPL. New images taken by the camera onboard the Cassini spacecraft are giving scientists the first size estimates on asteroid 2685 MASURSKY and preliminary evidence that it may have different material properties than previously believed. Cassini's camera took pictures of the asteroid when the spacecraft was 7 hours and 5 1/2 hours before closest approach, at a distance of 1.6 million km (960,000 mi). Since Masursky is too small to be measured from Earth, scientists. So far, the images reveal that the side of Masursky imaged by Cassini is roughly 15 to 20 km (9 to 12 mi) across. www.jpl.nasa.gov/pictures/cassini and iclops.lpl.arizona.edu

216 Kleopatra

9 May 2000 - "With its dog bone shape, KLEOPATRA has the most unusual shape we've seen in the solar system," said Steven Ostro of JPL, who led a team of astronomers observing Kleopatra with the 305-meter (1,000-foot) telescope of the Arecibo Observatory in Puerto Rico. 216 Kleopatra, is a large object in the main asteroid belt; it measures about 217 km (135 mi) long and about 94 km (58 mi) wide. Kleopatra was discovered in 1880, but until now, its shape was unknown. By decoding echoes and transforming them into images, the 'dog bone' shape appeared which has been used to evaluate conditions on its surface---namely, what "local gravity" is (between 3 and 10 milliG), escape velocity (between 40 and 200 m/s depending on where you are on the asteroid), and what the surface "slope" over the asteroid is (less than 40 degrees everywhere), making for a very relaxed surface with no steep cliffs or hillsides. It was also evaluated whether or not the asteroid is really two separate "ends" in orbit about each other - it isn't. Based on these computations, it can be inferred that the asteroid is covered with a loose 'soil' (called regolith) consisting of debris from previous, smaller collisions of Kleopatra with other main belt asteroids. In fact, these new radar images are the first ever made of a main belt asteroid. They were obtained when Kleopatra was about 171 million km (106 million mi) from Earth. Travelling at the speed of light, the transmitted signal took about 19 minutes to make the round trip to Kleopatra and back. "Getting images of Kleopatra from Arecibo was like using a Los Angeles telescope the size of the human eye's lens to image a car in New York," Ostro said. Kleopatra's strong reflection of radar signals indicates it is mostly metal, possibly nickel-iron alloy. www.jpl.nasa.gov/pictures/kleopatra

719 Albert

12 May 2000 - University of Arizona. Spacewatch astronomers at Kitt Peak, Ariz., have REDISCOVERED THE LAST "LOST" NUMBERED MINOR PLANET, 719 Albert. Until this month Albert had long eluded astronomers. It was last seen by direct observation in 1911, the year it was discovered by astronomer Johann Palisa (1848-1925) at the Imperial Observatory in Vienna, a world-class observatory of the pre-World War I Austro-Hungarian empire. Palisa was using the observatory's prize 68-cm (27-inch) telescope when he discovered the new minor planet on Oct. 3, 1911. He observed it again on Oct. 4, as did an astronomer at Copenhagen Observatory, which had been notified of Palisa's find. That was the last direct observation anyone had of 719 Albert, named for a baron who had donated generously to the Vienna Observatory, until last week.
cfa-www.harvard.edu/cfa/ps/pressinfo/
Albert.html

Asteroid Numbers

22 Jun 2000 - JPL. A new study estimates THERE ARE 900 OR SO ASTEROIDS, all a kilometre in diameter or larger, some pass within a few moon distances of Earth every year. The spatial and size distribution of the group has been plotted, together with their sizes which range from mere specks to more than 64 kilometres (40 miles) in diameter. Calculating which, if any, of the 900 asteroids identified in the study could hit the Earth is tricky, says Bottke, one of the report's authors. "The problem is that fewer than half of these Earth-threatening asteroids have been discovered so far. Of those we have found, we can accurately predict whether they will strike the Earth over the next hundred years or so, but we can't project out several thousands of years. The new predictions, say the astronomers, imply that 40 percent of the kilometre-or-larger asteroids near Earth already have been discovered. The remaining 60 percent, however, might be more difficult to find.
neat.jpl.nasa.gov

433 Eros

22 Sep 2000 - John Hopkins Univ. Applied Physics Lab. The NEAR Shoemaker spacecraft in orbit around 433 EROS since Feb 14 has provided enough data for its first detailed summary of the asteroid. Findings confirm that asteroid 433 Eros is a consolidated, primitive sample from the solar system's beginnings. "We can now say that Eros is an undifferentiated asteroid with homogeneous structure, that never separated into a distinct crust, mantle and core," says NEAR Project Scientist Dr. Andrew F. Cheng of the Johns Hopkins Univ. This 33x13x13 km possible 'chip of an old block' is classified as an S-type, the most common classification of asteroid. Eros' largest crater measures 5.5 km (3.4 miles) wide and it sits opposite from an even larger 10 km (6.2-mile) saddle-shaped depression. Eros has a stable rotation of 5h and 16m and an escape velocity that ranges from 3.1 to 17.2 meters per second, which would allow a baseball thrown from its surface to leave forever.
near.jhuapl.edu/

Asteroids in a Spin

09 Sep 2003 - Southwest Research Institute (SwRI) and Charles University (Prague). A new study has found that SUNLIGHT CAN HAVE SURPRISINGLY IMPORTANT EFFECTS ON THE SPINS OF SMALL ASTEROIDS. The study indicates that sunlight may play a more important role in determining asteroid spin rates than collisions, which were previously thought to control asteroid spin rates.the study, which showed that sunlight absorbed and reemitted over millions to billions of years can spin some asteroids so fast they could potentially break apart. In other cases, it can nearly stop them from spinning altogether. The team even noted that the effects of sunlight, combined with the gravitational tugs of the planets, can slowly force asteroid rotation poles to point in the same direction.
www.swri.org/press/koronis.htm

The first asteroid to have a male name was Eros - because of its odd behaviour!

Lots of asteroids have down-to-Earth names like Hilda, Thora, Ida, Doris, Sylvia, Hector and Albert.

Others have more unusual, but excellent names, like Interamnia, Euphrosyne, Arethusa, Loreley, Herculina, Bamberga and Diotima.