Meteoroid Orbits: Implications for Near‐Earth Object Search Programs

Abstract

ABSTRACT: The available orbital database on macroscopic potential impactors of our planet (asteroids and comets, collectively near‐Earth objects or NEOs) numbers less than one thousand, whereas there have been some hundreds of thousands of orbits of Earth‐impacting meteoroids determined in various surveys, mostly using meteor radars. If one assumes that NEOs have orbital characteristics broadly similar to meteoroids, then the orbits of the latter can give important indications concerning the conduct of search programs designed to discover large NEOs well ahead of any catastrophic impact, allowing ameliorative action to be taken. For smaller NEOs that cannot be telescopically detected until the day or so before impact, the radiant distribution of observed meteors shows the regions of the sky from which impactors are most likely to emanate. It is shown that the vast majority of meteoroids striking the Earth have geocentric (apparent) radiants within two near‐ecliptic regions a few tens of degrees wide and centered on longitudes ±90° from the apex of the Earth's way (the so‐called helion and antihelion sources). These are bodies with low inclinations, large eccentricities (e= 0.7 – 0.9) and quite small semimajor axes (mostly a= 1.3 – 2.5 AU). After allowing for the terrestrial motion about the Sun (conversion to the true radiant), the longitudes are around ±120° from the apex. For a ground‐based search on the nightside, the best search region is that within ∼20° of the arc joining the geocentric and true radiants (longitudes 90° and 120°). On the dayside, proximity to the solar direction argues for a space‐based surveillance program, if small NEOs are to be found just prior to impact.