Low-energy Suprathermal Electrons in Mercury’s Magnetosphere George C. Ho , Richard D. Starr, Jon D. Vandegriff, Stamatios M. Krimigis, Robert E. Gold, David Schriver, Pavel Travnicek, Haje Korth, Ralph L. McNutt, Jr., and Sean C. Solomon The Johns Hopkins University Applied Physics Laboratory, Maryland, U.S.A.
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Low-energy Suprathermal Electrons in Mercury’s Magnetosphere George C. Ho, Richard D. Starr, Jon D. Vandegriff, Stamatios M. Krimigis, Robert E. Gold,
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Low-energy Suprathermal
Electrons in Mercury’s Magnetosphere
George C. Ho, Richard D. Starr, Jon D. Vandegriff, Stamatios M.
Krimigis, Robert E. Gold, David Schriver, Pavel Travnicek, Haje
Korth,
Ralph L. McNutt, Jr., and Sean C. Solomon
The Johns Hopkins University Applied Physics Laboratory,
Maryland, U.S.A.
MSO X
MS
O Z
M
SO
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Energetic Electrons at Mercury
• Energetic electrons with E>30 keV are regularly detected in MESSENGER’s orbit about Mercury.– Duration: seconds to hours,– Latitude: equator to pole,– Energy range: ≤ 300 keV,– Most intense close to the planet,– Intensity: 3 orders of magnitudes above background– Also being detected by XRS and GRNS Ho et al., Science, 2011
Low Energy Electrons Measurement• During all three Mercury flybys,
XRS observed electron-induced fluorescence
• Extensive modeling indicates they are caused by suprathermal electrons (>1 keV) interacting with the XRS detector material
P38B-04Ho et al., PSS, 2011
• Once MSRG entered orbit around Mercury, these events are routinely observed by XRS at periapsis
• The XRS dataset of these electron provide us a unique and reliable way to catalog these events
XRS
EPS
Fall AGU 2012
Algorithm to Select XRS-E Event • Developing an algorithm to select electron event using XRS
GPC data• The algorithm select event based on:
– Orbital location– Duration of an event– Intensity and Intensity difference on filtered data– Spectral slope
• Criteria were chosen to filter out:– Genuine X-ray fluorescence event– Astronomical event– Solar particle event– Electron induced planetary X-ray event (Starr et al., JGR, 2012)
Preliminary Results• 1265 events were
identified between Apr 2011 to Feb 2013 (~1700 orbits)
• Majority of the events are on the nightside
• The distribution have a peak at the dawn sector
• Majority of the events have a narrow latitudal distribution between 0° and ~40°N
• At local noon, there is a narrow band of events between 40°N to 50°N
Preliminary Results• 1265 events were
identified between Apr 2011 to Feb 2013 (~1700 orbits)
• Majority of the events are on the nightside
• The distribution have a peak at the dawn sector
• Majority of the events have a narrow latitudal distribution between 0° and ~40°N
• At local noon, there is a narrow band of events between 40°N to 50°N
Electron Energy Profiles (Schriver et al., Fall AGU 2012)Y
(Rm
)
E(keV) E(keV)
Electron energies:• bulk energies about 1-10 keV in the inner magnetosphere (XRS range)• small fraction up to ~ 50-100 keV (EPS range)
Energization due mainly to non-adiabatic motion near low magnetic field (reconnection) regions
• 1265 events were identified between Apr 2011 to Feb 2013 (~1700 orbits)
• Majority of the events are on the nightside
• The distribution have a peak at the dawn sector
• Majority of the events have a narrow latitudal distribution between 0° and ~40°N
• At local noon, there is a narrow band of events between 40°N to 50°N