A Dangerous Class of Asteroids that is Nearly Invisible

Near Earth Asteroids (NEAs) that have high angular velocities are harder to detect than those that move across the sky more slowly. Even when detected, fast-moving objects often are not recovered: their ephemeris uncertainty grows very rapidly, making follow-up observations so difficult that many observers do not attempt them. Because of this, global ability to discover NEAs declines dramatically with increasing angular velocity - causing a strong bias against discovery of asteroids with high inclination and/or high eccentricity. Such objects never encounter Earth at low relative velocity, and their angular velocities can be low only with improbable viewing geometries. Hence, global NEA discovery capability remains almost blind to highly inclined/eccentric NEAs - especially at small yet still dangerous sizes in the 20-140 meter range. The bias against detecting such objects is already severe in regimes of moderate inclination and eccentricity that are known to be well-populated by larger NEAs. Hence, the abundance of small NEAs in these orbits is uncertain and hard to measure - yet their high velocities make their impacts especially damaging. We quantify the bias against these objects and suggest strategies to mitigate it.