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An orbital diagram of many known Near Earth objects. Astronomers estimated that about 18% of the reported NEOs were unable to obtain confirmatory observations. Credit: NASA
Near-Earth objects (NEO) are small bodies in the solar system whose orbits sometimes bring them closer to Earth, potentially threatening a collision. NEOs are tracers of composition, dynamics, and environmental conditions across the solar system and the history of our planetary system. Most meteorites come from near-Earth objects, which are therefore one of our main sources of knowledge about the development of the solar system. Because some of them are easier to reach with spacecraft than the Moon or the planets, NEOs are potential targets for NASA missions. The total number of known NEOs exceeds 18,000. The discovery rate has increased rapidly, in part due to the 1998 congressional mandate to identify 90% of NEOs greater than 1 km (at the 2005 Congress , recognizing the danger posed by smaller NEOs, extended the mandate to sizes as small as 140 meters.)
The importance of near-Earth objects for science and security has emphasized the need for accurate statistics of the population – but there is a problem. The discovery process for near-Earth objects requires distinguishing between known and unknown targets, and then tracking previously unknown targets to measure their orbits. The catalog of orbital elements of known NEOs, their size frequency distributions, as well as the telescope-visited sky region, all serve as inputs for the derivation of biased demographic models. But many near-Earth objects are detected and reported, but tracking observations are not made.
CfA astronomers Peter Vereš, Matthew Payne, Matthew Holman, Gareth Williams, Sonia Keys and Ian Boardman (all affiliated with the CfA Minor Planet Center) and a colleague analyzed NEO reports from 2013 to 2016; in this more than 170,000 objects (including comets) have been reported as likely candidates. By following the list of applicants submitted to the Planet Minor Center and using statistical tools, scientists estimate that about 18% of all NEO candidates remain unconfirmed. They point to several reasons, including delays in reporting detection; the object moves and scientists have found that delaying the initial report from two to ten hours results in doubling the number of unconfirmed detections (the delay makes tracking the moving source more difficult). Another problem is that unconfirmed NEOs tend to be much weaker and harder to follow. Scientists conclude that the number of unconfirmed NEO candidates could be significant, by the thousands, and stress the need for investigations to promptly submit detection reports.
Explore further:
Objects near the Earth
More information:
Peter Vereš et al. Unconfirmed objects near the Earth, The astronomical journal (2018). DOI: 10.3847 / 1538-3881 / aac37d
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