Speaker: Dr. Andrei Runov
Affiliation: Earth, Planetary, and Space Sciences, UCLA
Date: Wednesday, April 15, 2026
Time: 12:00 PM
Abstract
Earth’s only natural satellite, the Moon, orbits our planet at about 239,000 miles (385,000 kilometers, or ~60 Earth radii). Each month, it spends about 3–4 days passing through the nightside of Earth’s magnetosphere — the magnetotail. Far from Earth, the magnetotail has a weak, highly variable magnetic field and strong spatial gradients. This makes it a natural laboratory for studying magnetic fields and charged particle interactions under conditions opposite to those in the dipole-dominated inner magnetosphere. Using observations from two ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun) spacecraft, orbiting the Moon on elongated, near-equatorial (~100 km × 19,000 km) trajectories, we examine the near-Moon magnetic field and plasma properties under varying space weather conditions. We find that during quiet times, the plasma properties in the distant lunar magnetotail are largely controlled by the energy of the solar wind, and high-energy particles are rare. During active periods, however, we observe bursts of very energetic – sometimes even relativistic – ‘killer’ electrons near the Moon. Our results suggest that these electrons were energized within the magnetotail itself, although the exact mechanisms remain unclear.