Lunar gamma ray emission seen during the first year by Fermi

TL;DR

This paper reports the first year detection of lunar gamma-ray emission by Fermi-LAT, revealing cosmic ray interactions with the lunar surface during solar minimum, and discusses related planetary gamma-ray searches.

Contribution

First detection of lunar gamma-ray emission during Fermi-LAT's initial year, demonstrating the instrument's capability to monitor cosmic ray interactions on the Moon.

Findings

Lunar gamma-ray flux peaked during solar minimum.

Fermi-LAT successfully detected lunar gamma-ray emission with high confidence.

Ongoing search for gamma-ray emission from planets and asteroids.

Abstract

We report the detection of the lunar gamma-ray emission during the first year of Fermi-LAT observations. Such emission is produced by cosmic ray nuclei interacting with the lunar surface. Thanks to the solar minimum conditions and the reduced effects of heliospheric modulation, the lunar flux was at its maximum due to the increased flux of Galactic cosmic rays hitting the lunar surface. Fermi-LAT instrument has a superior sensitivity, angular resolution, and observes the whole sky every two orbits. It is the only gamma-ray mission capable of detecting the lunar emission with high confidence and to monitor it over the full 24th solar cycle. We also report the status of a search of the gamma-ray emission from major planets and asteroid populations in the ecliptic plane.