Contact: Judith H Moore j.h.moore@imperial.ac.uk 44-0-20-7594 6702 Imperial College of Science, Technology and Medicine July 16, 2003 Fewer Earthbound asteroids will hit home Scientists say pancake model of asteroid impact won't stick Scientists report in Nature today that significantly fewer asteroids could hit the Earth's surface than previously reckoned. Researchers from Imperial College London and the Russian Academy of Sciences have built a computer simulation that predicts whether asteroids with a diameter up to one kilometre (km) will explode in the atmosphere or hit the surface. The results indicate that asteroids with a diameter greater than 200 metres (the length of two football pitches) will hit the surface approximately once every 160,000 years - way down on previous estimates of impacts every 2,500 years. The findings also predict that many more asteroids blow up in the atmosphere than previous estimates, which means the hazard posed by impact-generated tidal waves or tsunamis is lower than previous predictions. The researchers suggest that proposals to extend monitoring of Near Earth Objects (NEO) to include much smaller objects should be reviewed. Dr Phil Bland of Imperial's Department of Earth Science and Engineering and a Royal Society University Research Fellow, said: "There is overwhelming evidence that impacts from space have caused catastrophes for life on Earth in the past, and will do so again. "On the Moon it's easier to track the number, frequency and size of collisions because there is no atmosphere, so everything hits the surface. On Earth the atmosphere acts like a screen and geological activity erodes many craters too. "Massive impacts of the type thought to have wiped out the dinosaurs leave an indelible print on the Earth but we have not been able to accurately document the effect of smaller impacts. Now, we have a handle on the size of 'rock' we really need to worry about and how well the Earth's atmosphere protects us." When small asteroids hit the atmosphere the two forces collide like two objects smashing together, which often breaks the asteroid into fragments. Until now, scientists have relied on the 'pancake' model of asteroid impact to calculate whether the asteroid will explode in the atmosphere. This treats the cascade of fragments as a single continuous liquid that spreads out over a larger area - to form a 'pancake'. But a new model known as the 'separate fragment' (SF) model, which was developed by co-author of the study, Dr Natalya Artemieva of the Russian Academy of Science, has challenged this approach. "While the pancake model can accurately predict the height from the Earth's surface at which the asteroid will break up, it doesn't give an accurate picture of how the asteroid will impact," explains Dr Bland. "The SF model tracks the individual forces acting on each fragment as it descends through the atmosphere." To create a more accurate model of how asteroids interact with the atmosphere the researchers ran more than 1,000 simulations using both models. Objects made of either iron or stone, known as 'impactors', were used to reflect the composition of asteroids and experiments were run with varying diameters up to 1 km. The researchers found the number of impacts for iron impactors were comparable using both models. For stone the pancake model significantly overestimated the survivability rate across the range used. The SF simulations also allowed the researchers to define the different styles of fragmentation and impact rates for iron and stone, which correspond closely with crater records and meteorite data. "Our data show that over most of the size range we investigated stony asteroids need to be 1,000 times bigger than the iron ones to make a similar sized crater. Much larger objects are disrupted in the atmosphere than previously thought. "But we are not out of the woods yet," added Dr Bland "asteroids that fragment in the atmosphere still pose a significant threat to human life." Dr Phil Bland is a member of the Meteorite and Impact Group that includes scientists from Imperial College London and the Natural History Museum. ### Notes to editors Publication: Nature (17 July 2003) Title: "Efficient disruption of small steroids by Earth's atmosphere" Authors: P.A Bland (1) and N.A Artemieva (2) (1) Department of Earth Science and Engineering, Exhibition Road, Imperial College London, SW7 2AZ, Uk (2) Institute for Dynamics of Geospheres, Russian Academy of Sciences, Leninsky Prospect 38/6 Moscow, 117939 Russia. About Imperial College London Consistently rated in the top three UK university institutions, Imperial College London is a world leading science-based university whose reputation for excellence in teaching and research attracts students (10,000) and staff (5,000) of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and management and delivers practical solutions, which enhance the quality of life and the environment - underpinned by a dynamic enterprise culture. Website: http://www.imperial.ac.uk ---------------------------------------------------------------------------- MEDIA RELATIONS OFFICE JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011 http://www.jpl.nasa.gov DC Agle (818) 393-9011 NEWS RELEASE: 2003-099 July 15, 2003 Asteroid Hunters Discover Near-Earth Object with New Camera NASA astronomers in pursuit of near-Earth asteroids have already made a discovery with the newly installed Quasar Equatorial Survey, or 'Quest,' camera mounted in mid-April on Palomar Mountain's 1.2-meter (48-inch) Oschin telescope. "The Quest camera is still undergoing commissioning trials," said Dr. Steven Pravdo, project manager for the Near-Earth Asteroid Tracking Project at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "But that doesn't mean we can't do some real science in the meantime. What we found was a near-Earth asteroid, estimated to be about 250 meters (820 feet) in size." The detection of the near-Earth object, 2003 NL7, occurred on the evening of July 8. It has been confirmed by follow-up measurements from three other observatories and subsequently certified by the official clearinghouse of the solar system's smaller inhabitants, the Minor Planet Center. While 2003 NL7 has been labeled a near-Earth asteroid, it is considered non-hazardous, with a 2.97-year orbit of the Sun in which its closest approach to Earth's orbit is about 25.1 million kilometers (15.6 million miles). The Quest camera is being developed as a multi-purpose instrument by Yale and Indiana universities with Dr. Charles Baltay, chairman of Yale's physics department, as the principal investigator. It is designed for use in detecting and characterizing quasars, near-Earth asteroids, trans-Neptunian objects, supernovas, and a large variety of other astrophysical phenomena, by scientists from Yale, JPL and the California Institute of Technology in Pasadena. The complex camera consists of 112 electronic chips known as charged coupled devices (CCDs) arranged over the Oschin telescope's focal plane. This gives the Quest camera 161-megapixel capability. By comparison, a good store-bought digital camera would probably be in the four-megapixel range. "When Quest becomes operational, it will be a significant advancement for the Near-Earth Asteroid Tracking team," said Dr. Raymond Bambery, the Near-Earth Asteroid Tracking Project's principal investigator. "We expect the new camera to increase the efficiency of detection of near-Earth asteroids by some 3 to 4 times that of the camera it replaced. This will make a major contribution to NASA's goal of discovering more than 90 percent of near-Earth objects that are greater that 1 kilometer (.62 mile) in diameter by 2008." The Near-Earth Asteroid Tracking System is managed by JPL for NASA's Office of Space Science, Washington, D.C. JPL is a division of Caltech. More information on the Near-Earth Asteroid Tracking Program is available at http://neat.jpl.nasa.gov/ . -end-