Space-based Observation of Lunar Impact Flashes

抄録

When a meteoroid impacts the Moon at several tens of km/s, a brilliant flash, referred to as a lunar impact flash, can be observed at the point of impact by ground-based telescope. Lunar impact flashes observed from the ground are biased due to atmospheric extinction, background illumination of earthshine, and short observation windows, typically a few hours per day during a period of approximately 10 days. NASA's meteoroid impact program took 10 years to detect 400 lunar impact flashes. EQUULEUS will demonstrate low-energy trajectory control techniques, such as multiple lunar flybys, proposed by the University of Tokyo and JAXA, within the Earth-Moon region. The spacecraft will be launched by NASA-SLS in 2019. The DELPHINUS camera system will be placed onboard EQUULEUS to observe lunar impact flashes while the spacecraft stays in halo orbit around an Earth-Moon L2 point. Thus, the lunar distance from the spacecraft is approximately one tenth that from ground-based observation. We estimate that DELPHINUS will detect 1,607, 2,699, and 4,534 lunar impact flashes during its six-month mission phase by assuming the limiting magnitude of its camera to be the 4.5th, 5.0th, and 5.5th magnitudes, respectively. The present study describes the DELPHINUS camera system and the first method for space-based observation of lunar impact flashes.