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Around 70 scientists from all over the world attended a NASA workshop in Arlington, USA, last week to discuss the next steps in mitigating the threat from asteroids and comets. The Workshop on Scientific Requirements for Mitigation of Hazardous Asteroids and Comets recommended further direct measurements of the surfaces and interiors of asteroids and comets by spacecraft and ongoing search programmes.
Meeting organiser Erik Asphaug of the University of California at Santa Cruz summarised the need for the Workshop by saying “unlike volcanoes or earthquakes, the NEO hazard was only recently identified, and we have just begun to understand its implications. This is the only major natural hazard which can, in principle, be made predictable and even eliminated if we find the dangerous ones and learn how to modify their orbits over time.”
Scientists at the workshop discussed a variety of techniques that could be used to avert an impact threat. The evidence presented suggested that gentle thrusts applied for decades, rather than traditional explosives, are likely to be needed to change their orbital paths. This will require early detection together with knowledge of their geologic properties.
More information about the internal structure of asteroids is needed to decide on the best way to deal with them. Increasing evidence that most asteroids larger than a few hundred meters have complex interiors, for example, suggests they may be loosely bound conglomerates which might resist explosive diversion. Also about a sixth of NEOs are now observed to have moons, which would complicate any effort to change their orbits.
Astronomers have now determined the precise orbits and estimated the sizes of approximately 1,500 Near-Earth Objects (NEOs), according to conference presentations. More than 600 of the estimated 1,000 asteroids larger than one kilometer in diameter have been detected so far. The attendees believe this represents good progress toward the target to discover 90% of these 1 km objects by 2008. While no known asteroid is on collision course with Earth, however, the workshop reinforces the belief that ongoing detection should alert us to serious threats.
More info: NOAO report on the workshop
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