07 August 2000

Killer Asteroid Hunt Reaches a Milestone

By Michael Paine

According to NASA scientists, the hunt for large asteroids that might collide with Earth has reached a milestone -- it is estimated that about half of these giant space rocks have now been found.

NASA's goal is to find 90 percent of "Near Earth Asteroids" larger than 1000 yards (1 kilometer) by 2009. In recent years the discovery rate has improved dramatically. In figures just released by NASA, the LINEAR system in New Mexico still dominates the discovery statistics.

Full story.

By Leonard David

17 July 2000

Spacewatch Scans the Heavens for Killer Rocks

TUCSON, ARIZONA -- At any moment, Planet Earth could be menaced by potentially devastating asteroids. Although we may not be able to avoid getting hit, the Spacewatch Project could at least warn of us an approaching asteroid.

Now being built is a 72-inch (1.8-meter) diameter telescope, to be situated near the currently working Spacewatch telescope. "That will make it the largest telescope in the world dedicated full-time to that exclusive purpose," said Robert McMillan, director of the Spacewatch Project here at the University of Arizona's Lunar and Planetary Laboratory.

The new telescope will be used exclusively for asteroid searches, relocating objects that have become, quite literally, lost in space, and for keeping an eye on the whereabouts of newly found objects.

Full story.

BBC News
Dr David Whitehouse

July 10, 2000

Earth-approaching space rock found by accident

A new member of the family of asteroids that can pass close to the Earth has been discovered.

The space rock was found by accident on 2 July by astronomer Leonard Amburgey of Fitchburg, Massachusetts.

He typed in the wrong celestial co-ordinates into his computer-controlled telescope and stumbled across the 3-km (1.8 miles) sized object.

The asteroid has been given the temporary designation 2000 NM by the Minor Planet Center in Cambridge, Massachusetts. It poses no threat to Earth.

Full story.

For images and Web links for these items, visit


The inner solar system is a dangerous place thanks in part to the presence of Earth-threatening asteroids. Now a new study not only predicts the current number of near-Earth asteroids (NEAs) but also estimates their orbital distribution and explores the mechanisms by which they are replenished.

An asteroid is considered an NEA if its closest point to the Sun (perihelion) is less than 1.3 astronomical units and its farthest point from the Sun (aphelion) is greater than 0.983 a.u. Most originate as fragments carved off main-belt asteroids during collisions. The study, by William F. Bottke Jr. in the June 23rd Science, shows how this debris can migrate, via a drag force called the Yarkovsky effect, into dynamically unstable regions of the belt. Once there, their orbits are affected by the gravitational tug of Mars, Jupiter, and Saturn.

Bottke and his team found that this gentle tugging created three so-called intermediate sources for NEAs: those in a 3:1 orbital resonance with Jupiter, asteroids whose orbits are affected by the orbital precessions of Jupiter and Saturn, and those adjacent to the main belt in Mars-crossing orbits. Once an asteroid becomes an NEA, Bottke found that it remains a threat for two to six million years before it is either ejected from the solar system, crashes into the Sun, or collides with a planet.

Finally, Bottke's study predicts that about 910 NEAs with diameters of 1 kilometer or larger are on a potential collision course with Earth. This is roughly half of astronomers' original estimates, but a third higher than a recent study by David L. Rabinowitz (Yale University), appearing in the January 13th Nature, who based his work on discovery statistics from the NEAT (Near-Earth Asteroid Tracking) and Spacewatch search programs.

More information about near-Earth asteroids can be found on the Sky & Telescope Impact Hazards Web page.

Cornell University
Ithaca, NY 14853

'Treasure map' of inner space shows orbits and sizes of 900 large asteroids, some of which could threaten Earth

June 22, 2000

ITHACA, N.Y. -- A new study portrays the paths of asteroids in the inner solar system as a vast Los Angeles-style traffic system crisscrossed with superhighways along which are hurtling huge, rocky projectiles. And in the middle of the highway network, on a possible collision path, is the planet Earth.

The study estimates that an armada of asteroids, 900 strong, all a kilometer in diameter or larger, present a potential hazard to life on Earth. Some pass within a few moon distances of Earth every year. "Sometime in the future, one of these objects could conceivably run into the Earth," warns astronomy researcher William Bottke at Cornell University. "One kilometer (about .6 of a mile) in size is thought to be a magic number, because it has been estimated that these asteroids are capable of wreaking global devastation if they hit the Earth."

Bottke is lead researcher on a U.S.-French team that has discovered the spatial and size distribution of a large group of asteroids called NEAs (for near-Earth asteroids), a vast system of orbiting rocks in inner space, ranging in size from mere specks to more than 64 kilometers (40 miles) in diameter. The astronomers believe the results of their observational and computer-based study will better quantify the likelihood of future catastrophic collisions with Earth. The survey also is expected to help observational astronomers in improving their search for hard-to-find asteroids that might pose a threat to the planet.

The team's report, "Understanding the Distribution of Near-Earth Asteroids," appears in the latest edition (June 23) of the journal Science. The authors, besides Cornell's Bottke, are astronomers with the Spacewatch group at the University of Arizona's Lunar and Planetary Laboratory and at the Observatoire de la Côte d'Azur in Nice, France.

Calculating which, if any, of the 900 asteroids identified in the study could hit the Earth is tricky, says Bottke. "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. So it's possible some of these asteroids eventually will move onto an Earth-collision trajectory. It's a dangerous place out there."

The new predictions for the distribution of NEAs in the inner solar system, say the astronomers, imply that 40 percent of the kilometer-or-larger asteroids near Earth already have been discovered. The remaining 60 percent, however, might be more difficult to find, says Bottke. "Most of these asteroids are too far from Earth to be easily detected or are located in regions of the sky that are challenging for astronomers to survey."

The study's authors refer to their survey as a "NEA treasure map" indicating in which orbits most NEAs spend their time. The researchers say the new estimate of the number of large asteroids is about half of that predicted by similar types of analyses reported in the past decade and is slightly larger than an estimate published recently in the journal Nature.

For many decades there has been good evidence that most of the small chunks of rocky or iron material that slam into the Earth's atmosphere daily are chips off old blocks of asteroids. Most of the asteroids in the solar system revolve around the sun on independent orbits, corralled between Mars and Jupiter in a formation known as the main belt. Occasionally, two of these asteroids -- some of them hundreds of miles in diameter -- slam into each other at great speed, causing chunks of all sizes to be blasted off the surfaces.

Most of this material continues to orbit the sun in the main belt. But sometimes the newly formed asteroids migrate to unstable regions of the asteroid belt known as resonances, areas where the tiny gravitational kicks produced by nearby planets such as Mars, Jupiter or Saturn can significantly change asteroid orbits. In some cases, these changes are enough to swing asteroids into a possible future collision path with the Earth.

To find the location of these potentially threatening and hard-to-find projectiles, the researchers used the results of the Spacewatch group's 10-year search for asteroids in the solar system during which it has discovered about 100 NEAs. The problem is that this tally is only a small fraction of the predicted number of NEAs. Using a statistical technique to compensate for the big gaps, Spacewatch astronomers were able to calculate the total number of NEAs but not their approximate location. To obtain the orbits of the undetected NEAs, Spacewatch astronomers combined their NEA population estimates with theoretical models, produced by the Cornell and Nice researchers, which show how asteroids in the main belt are transported to the near-Earth environment.

Other authors of the study were Robert Jedicke of the University of Arizona and Alessandro Morbidelli, Jean-Marc Petit and Brett Gladman of the Observatoire de la Côte d'Azur. The study was funded by NASA and the European Space Agency.

Related World Wide Web sites: The following sites provide additional information on this news release. Some might not be part of the Cornell University community, and Cornell has no control over their content or availability.

  • University of Arizona, Lunar and Planetary Observatory, Spacewatch Project
  • Near-Earth Object Program, Jet Propulsion Laboratory
  • Asteroid and Comet Impact Hazards, NASA Ames Space Science Division
  • Observatoire de la Côte d'Azur

    U N I V E R S E
      T O D A Y

    Space Exploration News From Around the Internet, Updated Every Weekday. June 23, 2000 - Issue #262


    A new report being prepared for Science Magazine estimates that there are 900 asteroids at least a kilometer in size buzzing around near the Earth - and we've only found 40% of them. The lead researcher, William Bottke from Cornell University, has developed a method to statistically project the number of near-Earth asteroids based on data from Spacewatch, an asteroid tracking program.

    News Stories



    January 12, 2000


    NASA scientists taking a census of large asteroids in our solar system neighborhood have cut their estimate in half.

    The revised calculation comes from data gathered by NASA's Near-Earth Asteroid Tracking System (NEAT) and published in the January 13 issue of the journal Nature.

    "Until now, scientists thought the population of large, near-Earth asteroids was between 1,000 and 2,000, but we've downgraded that figure significantly," said Dr. David Rabinowitz, of Yale University, New Haven, CT, lead author of the article and NEAT co-investigator. "We now believe there are between 500 and 1,000 near-Earth asteroids larger than one kilometer (about 0.6 miles) in diameter.

    "This newer estimate was made possible by the computerized technology of the NEAT camera," Rabinowitz said. The NASA-funded system began tracking near Earth asteroids and comets in 1995 with a charge-coupled device camera mounted on a 1-meter (39- inch) Air Force telescope atop Mount Haleakala on Maui, HI.

    The new figures may represent good news in the quest to achieve NASA's stated goal of finding 90-percent of all large, near-Earth asteroids by 2010, according to Pravdo. "Right now we know of 322 large, near-Earth asteroids," he said. "That was a fairly small fraction of the 2,000 asteroids in our previous estimate. With our new calculations of between 500 and 1,000 such objects, this 322 figure represents a large chunk."

    While stressing that we must learn more about potential hazards from asteroids, Rabinowitz said, "None of the asteroids we've observed will hit Earth anytime in the near future."

    "This new analysis reduces by half the estimated number of these potential hazards to Earth," Pravdo said.

    "In the past, we relied on humans poring over photographic plates of the nighttime sky," Rabinowitz said. "The problem was, they didn't know how many asteroids they were missing, because they couldn't see faint objects. People's eyes also became tired and teary and they overlooked some objects. Machines don't get tired."

    "With this computerized technology, we can find asteroids more easily and count them more accurately," said NEAT project manager Dr. Steven Pravdo of NASA's Jet Propulsion Laboratory, Pasadena, CA, a co-author of the Nature article. "It's important to know your observational limits, and with that information, we can develop models for what we are not able to see. This makes our estimates even more accurate."

    Additional co-authors on the Nature article are Eleanor Helin of JPL, NEAT principal investigator, and Kenneth Lawrence, also of JPL. Helin was also principal investigator of the Palomar Planet-Crossing Asteroid Survey, a photographic search program, conducted for almost 25 years until it was discontinued and replaced by NEAT, the electronic detection program, in 1995. Her efforts were key to the organization of the NEAT program.

    Data gathered by the asteroid tracking system are processed at Haleakala, and then undergo post-processing and analysis at JPL. This latest asteroid estimate is based on data collected between 1995 and 1998.

    The asteroid tracking system has been on hiatus for the past year, but plans are in the works to re-activate the system in February using an upgraded 1.2 meter (48 inch) Air Force telescope on Haleakala. In addition, later this year, NEAT scientists will begin using the 1.2 meter (48 inch) Oschin telescope at Palomar Observatory near San Diego, CA.

    Additional information on the NEAT project is available at Information on near-Earth objects is available at

    The Near Earth Asteroid Tracking System is managed for NASA's Office of Space Science, Washington, D.C. by JPL, a division of the California Institute of Technology, Pasadena, CA.

    Yale University

    January 12, 2000

    Yale Researcher Finds Number of "Near-Earth Asteroids" Are Fewer than Believed

    New Haven, Conn. -- The number of "near-Earth asteroids" that have a chance, though miniscule, of colliding with Earth this century is half what was originally estimated, a Yale researcher says.

    "They are the kind of asteroids you hear about in movies that are about two-thirds of a mile in diameter and could easily obliterate a city because they are coming in at cosmic velocities," said Research Associate David Rabinowitz. "The main thing we want to stress is that none of the known asteroids are in imminent danger of falling to earth and no impacts are predicted in the near future."

    It was previously estimated that there are 1,000 to 2,000 such asteroids in chaotic orbits. Rabinowitz and his fellow researchers estimate that these asteroids actually total half that, or 500 to 1,000. Each has a 0.5 percent chance of colliding with Earth in the next million years, he said in the article published this week in the journal "Nature."

    "The reduced number doesn't make us feel that much safer, but it does allow us to plan more accurately," Rabinowitz said. "The goal is to find the asteroids hundreds to thousands of years before they even come close."

    The other researchers were Eleanor Helin, Kenneth Lawrence, and Steven Pravdo, all of the Jet Propulsion Laboratory at the California Institute of Technology. They made their observations through a U.S. Air Force telescope in Hawaii that was designed to look for artificial satellites.

    Rabinowitz said smaller asteroids the size of a large house or hotel generally burn up or blow up before they hit the ground.

    "But an asteroid the size of a city block is more dangerous because it could punch through the atmosphere and raise a lot of dust, which would change the climate of the Earth," he said. "It would be like a nuclear bomb coming in."

    Efforts are underway around the world to survey this asteroid population because most of the threatening bodies remain undiscovered and their number is uncertain, the researchers said.

    The observations were made using a large-format, charge-coupled device and a one meter aperture telescope based on the summit of Haleakala Crater on the island of Maui. Earlier photographic methods required a trained observer to identify asteroids by visual inspection and the accuracy varied according to the skill of the observer. The automated method is more consistent and provides a record of every detectable asteroid.

    The researchers said that, at the current rate of discovery, about 90 percent of the asteroids probably will be identified in the next 20 years. The goal, however, is to double the current worldwide detection rate to complete the program in 10 years.

    "If we can find the asteroids in 10 years, that's plenty of time," Rabinowitz said. "If you wait 100 or 1,000 years, that's too much time."

    Rabinowitz is currently working with Professor Charles Baltay, chairman of the Yale Physics Department, to develop one of the world's largest electronic cameras. It will be used by Yale astronomers and physicists to study the properties of distant galaxies and supernova, and to study the expansion of the universe. The new camera also will be used in cooperation with astronomers at the Jet Propulsion Lab to continue the survey for near-Earth asteroids.

    BBC News: Taskforce tackles asteroid threat

    January 3, 2000


    On Tuesday 4th January the British National Space centre will announce the establishment of a government task force to investigate the threat posed to the Earth by asteroids and comets.

    The distinguished members of the Task Force, Dr. Harry Atkinson (Chairman), Sir Crispin Tickell and Professor David Williams will consider the threat posed by asteroids and comets, the action that Britain is currently taking to evaluate and reduce the risk, and will make recommendations as to what should be done in the future. Their recommendations will be submitted to Dr David Cope, the Director General of the British national Space Centre, who will report to Lord Sainsbury by 31st May 2000.

    There has already been substantial press interest in this announcement, so keep your eyes on the media. Lord Sainsbury will be on BBC1 between 0800 and 0830 with Austin Atkinson.

    Here we go!

    Jay Tate
    Spaceguard UK

    Department of Trade and Industry
    London, England

    30 December 1999


    A Task Force to look at the potential for risk posed by Near Earth Objects (NEOs) has been announced by Science Minister, Lord Sainsbury.

    The three-strong team will make proposals to the British National Space Centre on the nature of the hazard and the potential levels of risk. It will also consider how the United Kingdom should best contribute to international effort on NEOs.

    The Task Force will be chaired by Dr Harry Atkinson, formerly of the Science and Engineering Research Council (SERC) and past Chairman of the European Space Agency's Council. Two other appointees, Sir Crispin Tickell and Professor David Williams join Dr Atkinson.

    Lord Sainsbury said: "The risk of an asteroid or comet causing substantial damage is extremely remote. This is not something that people should lie awake at night worrying about. But we cannot ignore the risk, however remote, and a case can be made for monitoring the situation on an international basis.

    "I hope that the setting up of this Task Force will help the UK play a full and prominent role in international discussions on this important issue. I am delighted to be able to announce such a well-qualified team of experts and I look forward to receiving their report by the middle of 2000."


    July 22, 1999: New Torino Scale Measures Asteroid Threat

    National Research Council
    Washington, D.C.

    May 13, 1998

    Policies Needed for Reporting Potential Hazards Of Asteroid Collisions with Earth

    Recent news of a possible asteroid collision with Earth in 2028 sparked intense scientific and popular interest worldwide. When further data revealed that the asteroid had virtually no chance of hitting this planet, the episode prompted the astronomy community to re-evaluate how they communicate such information to the public.

    NASA and astronomers should develop protocols for reporting information about asteroids that appear to pose a potential hazard to Earth, says a new report from a National Research Council committee, which began its work before the recent episode. These protocols will be important because several telescope facilities and new instruments now coming into operation will dramatically increase the rate by which scientists are able to discover asteroids and comets whose orbits approach Earth. With the flood of discoveries expected within the next decade also will come the risk of false alarms.

    Some 400 Earth-approaching asteroids and comets larger than one kilometer in diameter have been discovered so far, but only an estimated 10 percent of the objects this size have been identified. Of the thousands that may be discovered, some initially -- for a few days, weeks, or even years -- may seem likely to collide with Earth, until enough data have been collected to determine accurate orbits and interpreted to show otherwise. Policies for handling such potentially important information will be needed. International scientific organizations, such as the International Astronomical Union, could play a role in this task, the report says.

    Most asteroids orbit the sun in a belt between Jupiter and Mars, but thousands have orbits that sometimes take them uncomfortably close to Earth. Geological processes such as erosion tend to erase scars left when asteroids and comets occasionally hit Earth, but there are some notable exceptions, such as Arizona's Meteor Crater. Moreover, there is evidence that an asteroid or comet some five to 10 kilometers in diameter created an enormous crater in Yucatan, Mexico, some 65 million years ago. That event has been implicated in the extinction of dinosaurs and other living organisms. This information, coupled with recent evidence of the collision of Comet Shoemaker-Levy 9 with Jupiter in 1994, has led to increased scientific and public interest in assessing the likelihood that a large object might hit Earth again.

    Although asteroids and comets are potential hazards to Earth, these tiny worlds offer a trove of clues to the solar system's birth and early history, the report says. Exploration of asteroids also may be used as stepping stones toward manned missions to Mars. Comets are frozen chunks of ice and dust thought to be left from the formation of the planets in the solar system. Asteroids are minor planets, some made from almost pure mixtures of nickel and iron like those at the Earth's core or from minerals similar to those found in the Earth's crust, and others from exotic combinations of carbon compounds.

    To better understand the scientific opportunities posed by asteroids and comets, the report recommends that priorities be given to the following areas:

    Telescopic studies. NASA, other government agencies, and private research organizations should further coordinate their programs using ground-based telescopes to search for and study asteroids and comets. Because a typical asteroid or comet is very faint and travels by Earth so quickly, the opportunity to view it may last no more than a few days or a week at most. To conduct the detailed observations that these fleeting objects require, routine or priority access to existing infrared and optical telescopes is needed. Otherwise, telescopes dedicated to characterizing the asteroids and comets discovered by ongoing search programs should be developed.

    Laboratory investigations. More research is needed to increase understanding of extraterrestrial materials, such as meteorites, which are believed to come from asteroids. Laboratory studies can address, for example, the puzzle of how the environment in space changes the surfaces of asteroids to such an extent that the physical characteristics of the most common varieties of asteroids and meteorites do not match. NASA, other government agencies, and private research organizations should support additional laboratory investigations of samples of these space-borne objects. New analytical instruments, such as those necessary to study very small samples of meteorites, also are needed.

    Robotic and manned spacecraft missions. Spacecraft that pass by, rendezvous with, or obtain samples from asteroids orbiting near Earth provide important information on the detailed physical characteristics, composition, and geologic histories of planetary bodies that is otherwise unobtainable. Moreover, Earth-approaching asteroids or comets are among the most accessible objects in the solar system. Indeed, some are easier to reach than the moon. NASA's Galileo missions, for example, provided a wealth of information about asteroids Ida and Gaspra orbiting between Mars and Jupiter. Last year, a NASA spacecraft made detailed observations of another asteroid, Mathilde. The spacecraft is currently en route to a February 1999 rendezvous with Eros, one of the largest Earth-approaching asteroids. NASA should continue such missions and improve spacecraft technology, such as propulsion and navigation systems, to allow additional low-cost rendezvous and sample-return missions.

    Should the United States choose to undertake further manned exploration beyond Earth, a strong case can be made for beginning with missions to Earth-approaching asteroids, the report says. Because missions to these asteroids represent deep-space exploration with moderate technical challenges, they would be the least-expensive next step in human exploration of space and could provide the experience and technology needed for fruitful missions to Mars and beyond. Five percent of Earth-approaching asteroids are readily accessible by relatively short space flights.

    A primary concern would be keeping the length of the mission as short as possible to minimize hazards and risks to which astronauts are exposed, including weightlessness, radiation, meteoroid impact, and equipment failure. Further research should be conducted to study specific technical requirements necessary for a six- to 12-month round-trip expedition. With the anticipated increase in discoveries of Earth-approaching asteroids, there likely will be opportunities for missions to one or more asteroids each year.

    The study was funded by the NASA. The National Research Council is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering. It is a private, non-profit institution that provides science advice under a congressional charter. A committee roster follows.

    Copies of The Exploration of Near-Earth Objects are available from the National Academy Press for $10.00 (prepaid) plus shipping charges of $4.00 for the first copy and $.50 for each additional copy; tel. (202) 334-3313 or 1-800-624-6242. Reporters may obtain a copy from the Office of News and Public Information (contacts listed above).

    Commission on Physical Sciences, Mathematics, and Applications Space Studies Board
    Committee on Planetary and Lunar Exploration
    Ronald Greeley (chair)
    Professor of Geology
    Department of Geology
    Arizona State University
    Jeffrey R. Barnes
    Associate Professor
    College of Oceanic and Atmospheric Sciences
    Oregon State University
    Richard P. Binzel
    Department of Earth, Atmospheric, and Planetary Sciences
    Massachusetts Institute of Technology
    Wendy Calvin
    Astrogeology Team
    U.S. Geological Survey
    Flagstaff, Ariz.
    Russell F. Doolittle*
    Research Professor of Biochemistry
    Center for Molecular Genetics
    University of California
    San Diego
    Heidi Hammel
    Principal Research Scientist
    Department of Earth, Atmospheric, and Planetary Sciences
    Massachusetts Institute of Technology
    Larry A. Haskin
    Professor of Chemistry and Earth and Planetary Sciences
    Department of Earth and Planetary Sciences
    Washington University
    St. Louis
    Bruce Jakosky
    Associate Professor, Atmospheric and Space Physics
    Laboratory for Atmospheric and Space Physics
    University of Colorado
    Kenneth Jezek
    Director, Byrd Polar Research Center, and
    Professor, Department of Geological Sciences
    Ohio State University
    George E. McGill
    Professor Emeritus
    Department of Geosciences
    University of Massachusetts
    Harry Y. McSween Jr.
    Department of Geological Sciences
    University of Tennessee
    Michael Mendillo
    Professor, Department of Astronomy, and
    Professor, Department of Electrical and Computer Engineering
    Boston University
    Gerald Schubert
    Professor of Geophysics and Planetary Physics
    Department of Earth and Space Science
    University of California
    Los Angeles
    Everett Shock
    Associate Professor
    Department of Earth and Planetary Sciences
    Washington University
    St. Louis
    David H. Smith
    Senior Program Officer
    (*) Member, National Academy of Sciences

    The report cited in this release is available online

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