Binzel, professor of earth, atmospheric and planetary sciences (EAPS), and operates in collaboration with the University of Hawaii, the Space Science Institute in Boulder, Colo., and the Deutschen Zentrum fï¿½ï¿½r Luft- und Raumfahrt in Berlin and others. Keck Observatory is used to obtain thermal flux measurements to estimate reflectivity. Near-infrared spectroscopy is collected at the NASA Infrared Telescope Facility. The visible spectroscopy is collected at Kitt Peak National Observatory and Palomar Observatory, and on the Magellan I Telescope at Las Campanas Observatory. This program comprises visible spectroscopy, near-infrared spectroscopy and thermal infrared flux measurements. To determine the percentage of sunlight that is reflected from NEAs, MIT researchers used results from the Small Main-belt Asteroid Spectroscopic Survey (SMASS), a multi-wavelength observing program that studies the surface properties of NEAs and other asteroids.

This means that NEAs are slightly smaller than previously assumed, so the number of NEAs that are larger than 1 kilometer is somewhat lower than previously estimated. Through new observations and modeling of the reflective properties of the NEAs, MIT researchers have found that on average, NEAs actually reflect about 14 percent of the sunlight that hits them. To estimate their diameters, astronomers assumed that NEAs reflect about 11 percent of the sunlight that hits them. When NEAs are first discovered, the only data available are their locations in the solar system and their brightness. Over long time spans, we might expect such events to occur every 2,000 to 3,000 years on average, Stuart said. Likewise, events similar to the Tunguska impact are not evenly spaced. This figure comes from looking at time spans of millions of years. The energy of the impact was about 40 megaton, or more than 600 times the energy of the Hiroshima bomb.Įven if impacts of large NEAs occur only once every 600,000 years, this does not mean that they occur at regularly spaced intervals. The NEA in the Tunguska event was relatively small, with a diameter of 50 to 75 meters (150-250 feet). Impacts of asteroids bigger than 1 kilometer are thought to be capable of causing long-term climate damage on a global scale. The amount of damage that would be caused by an asteroid depends on its size.

Stokes, has found 70 percent of all near-Earth asteroids discovered worldwide and is a major contributor to the NASA goal of cataloguing 90 percent of NEAs larger than 1 kilometer (0.6 miles) in diameter. Since March 1998, LINEAR, whose principal investigator is Lincoln Lab associate division head Grant H. The Lincoln Near-Earth Asteroid Research (LINEAR) Project has been scanning the skies to discover and catalog NEAs and to provide advance warning of any that are bound for Earth. While all currently known NEAs are in safe orbits that will not cause them to collide with the Earth in the foreseeable future, many NEAs remain undetected and could be on a collision course with Earth, Stuart said. Near-Earth asteroids are small solar system objects whose orbits around the sun may bring them close to Earth. Events of this magnitude occur, on average, once every 2,000 to 3,000 years. 5.īy combining discovery statistics with new observations of the surfaces of near-Earth asteroids (NEAs), Stuart also determined that impacts similar to the Tunguska event-in which an asteroid destroyed more than 2,000 square kilometers of forest in a remote part of Siberia in 1908-are much less frequent than previously thought. Scott Stuart reported at the 35th annual meeting of the American Astronomical Society Division of Planetary Science on Sept. Of the approximately 1,000 near-Earth asteroids larger than 1 kilometer in diameter, one strikes the Earth on average once every 600,000 years, MIT Lincoln Laboratory researcher J.

One kilometer