May 18, 1998 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 have been discovered so far, but only an estimated 10 percent of the objects 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 arm 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.
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