Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....109..401h&link_type=abstract
The Astronomical Journal (ISSN 0004-6256), vol. 109, no. 1669, p. 401-417
Astronomy and Astrophysics
Astronomy
5
Asteroids, Impact Prediction, Parallax, Radial Velocity, Solar Orbits, Charge Coupled Devices, Monte Carlo Method, Telescopes
Scientific paper
We have determined the observational and dynamical properties of Earth-crossing asteriods in the final weeks before their impacts with Earth. An asteroid that is within a few weeks of either Earth impact or of a very close approach to Earth has a large parallax and a small proper motion. The proper motion of such an asteroid has a maximum value of only a few minutes of arc per day, and it vanishes for some approach directions. An asteroid that is 10 days from impact has a parallax of several minutes of arc when viewed from two positions on Earth having a projected separation of 1 R (solar halo). Wide-field cameras can easily detect this parallax. Impacting asteroids greater than 100 m in diameter, which is near the minimum size that produces significant local damage, appear as stars of at least visual magnitude 18 during their final 10 days to impact unless they approach Earth from the vicinity of the Sun in the sky. They are detectable with relatively small telescopes equipped with CCDs. A typical proposed station for detecting them may have 20 telescopes with apertures between 5 and 16 in. and 1 telescope with an aperture of 36 in. (0.9 m). The largest telescope would only be used to search for objects near the sun (near dusk and dawn), and it would be available during the remainder of the night to improve the orbits and physical characterization of objects that may pass near or hit Earth. While the apertures of the required telescopes are relatively modest, such a systematic search for Earth-approaching asteroids will be a computer intensive task and it will require the correlation of the positions of anomalous objects between two or more sites in near real time to determine whether or not they have a measurable parallax. Thermal infrared emission may provide a complementary way of detecting impacting asteroids especially if they approach Earth from near the direction of the Sun.
Hills Jack G.
Leonard Peter J. T.
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