Academic Commons

Articles

Detection and characterization of 0.5–8 MeV neutrons near Mercury: Evidence for a solar origin

Lawrence, David J.; Feldman, William C.; Goldsten, John O.; Peplowski, Patrick N.; Rodgers, Douglas J.; Solomon, Sean C.

Data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Neutron Spectrometer (NS) have been used to identify energetic neutrons (0.5–8 MeV energy) associated with solar events that occurred on 4 June 2011. Multiple lines of evidence, including measurements from the NS and the MESSENGER Gamma-Ray Spectrometer, indicate that the detected neutrons have a solar origin. This evidence includes a lack of time-coincident, energetic (>45 MeV) charged particles that could otherwise create local neutrons from nearby spacecraft material and a lack of proton-induced gamma rays that should be seen if energetic protons were present. NS data cannot rule out the presence of lower-energy ions (<30 MeV) that can produce local neutrons. However, the ion spectral shape required to produce the measured neutron count rate locally is softer than any known ion spectral shape. The neutron energy spectrum shows a relative enhancement in the energy range 0.8–3 MeV compared with cosmic-ray-generated neutrons from the spacecraft or Mercury. The spectral shape of the measured neutron fluence spectrum is consistent with a previously modeled fluence spectrum of neutrons that originate at the Sun and are propagated through the MESSENGER spacecraft to the NS. These measurements provide strong evidence for a solar origin of the detected neutrons and suggest that a large number of low-energy threshold ion evaporation reactions were taking place on the Sun during the neutron event.

Geographic Areas

Files

Also Published In

Title
Journal of Geophysical Research: Space Physics
DOI
https://doi.org/10.1002/2013JA019037

More About This Work

Academic Units
Lamont-Doherty Earth Observatory
Publisher
American Geophysical Union
Published Here
October 2, 2015
Academic Commons provides global access to research and scholarship produced at Columbia University, Barnard College, Teachers College, Union Theological Seminary and Jewish Theological Seminary. Academic Commons is managed by the Columbia University Libraries.