IMPACT DETECTIONS OF TEMPORARILY CAPTURED NATURAL SATELLITES

Temporarily captured orbiters (TCOs) are near-Earth objects (NEOs) that make a few orbits of Earth before returning to heliocentric orbits. Only one TCO has been observed to date, 2006 RH120, captured by Earth for one year before escaping. Detailed modeling predicts that capture should occur from the NEO population predominantly through the Sun–Earth L1 and L2 points, with 1% of TCOs impacting Earth and approximately 0.1% of meteoroids being TCOs. Although thousands of meteoroid orbits have been measured, none until now have conclusively exhibited TCO behavior, largely due to difficulties in measuring initial meteoroid speed with sufficient precision. We report on a precise meteor observation of 2014 January 13 with a new generation of all-sky fireball digital camera systems operated in the Czech Republic as part of the European Fireball Network, providing the lowest natural object entry speed observed in decades-long monitoring by networks worldwide. Modeling atmospheric deceleration and fragmentation yields an initial mass of ~5 kg and diameter of 15 cm, with a maximum Earth-relative velocity just over 11.0 km s−1. Spectral observations prove its natural origin. Back integration across observational uncertainties yields a 92%–98% probability of TCO behavior, with close lunar dynamical interaction. The capture duration varies across observational uncertainties from 48 days to 5+ years. We also report on two low-speed impacts recorded by US Government sensors, and we examine Prairie Network event PN39078 from 1965 with an extremely low entry speed of 10.9 km s−1. In these cases uncertainties in measurement and origin make TCO designation uncertain.