Observation of Auroral-like Peaked Electron Distributions at Mars D.A. Brain, J.S. Halekas, M.O. Fillingim, R.J. Lillis, L.M. Peticolas, R.P. Lin, J.G. Luhmann, D.L. Mitchell, G.T. Delory, S.W. Bougher, M.H. Acuna, H. Reme UC Berkeley Space Sciences Lab SA53B-1166

30-second Summary Auroral emission was recently observed at Mars! We observe electrons responsible for auroral emission We see ~13,000 peaked electron energy spectra (very similar to terrestrial auroral electrons) Spectra associated with open and closed crustal field lines A few spectra can produce previously observed UV emission Most energetic spectra may be associated with SEP events Controlled by Mars orientation, IMF direction, SW pressure

Aurora Discovered at Mars! Bertaux et al., Nature, 2005 Mars Express SPICAM (UV) instrument Observed at 129 km, ~120°SZA, ~19:00 LT Wavelengths associated with CO, CO 2 +, O Associated with likely magnetic cusp Intensity difficult to explain Only one reported emission event Is Martian auroral emission commonplace?

Martian Crustal Fields |B|Elevation Angle Radial Field Topology ‘Up’ ‘Down’ Closed Open Draped

Martian Field Topology “Closed” field lines“Open” field lines Electrons carry information about the topology of magnetic field lines observed at S/C altitudes

Tools: MGS MAG/ER Data MGS Orbit circular, 400 km, polar, 2am 6 years of data ER Electron Angular Distributions used to identify cusps/closed field lines Angular resolution = 14°  22.5° data every 2-8 s IMF Direction and SW Pressure Determined indirectly from dayside MAG data, once per orbit ER Electron Energy Spectra used to identify plasma population 10 eV - 20 keV,  E/E ~ 25%, s, FOV = 14°  360°

Auroral Electron Spectra EarthMars FASTMGS Data courtesy C. Carlson

A Martian Auroral Electron Event ABCE Auroral-like peaked electron energy spectra D currents

A Martian Auroral Electron Event ABCDE SN A, E - Open field lines (‘cusps’) B, D - Closed field lines, contain trapped electrons C - Closed field lines, devoid of electrons Auroral electrons observed MGS orbit

Acceleration Mechanism vv v  vv vv  Terrestrial aurorae typically associated with charged particles accelerated by a potential. Are the isotropic Martian electron distributions consistent with this paradigm? 1. Source Electrons initially isotropic T e (sheath) ≈ 40 eV 2. Acceleration Potential boosts v  V ≈ 200 eV (sample event)   ≈ 24   electrons field-aligned 3. Isotropization As B increases, v   v   B observed / B source ≈ 6  source could be sheath; waves may also contribute Yes, if source is high temperature region and potential drop large, or waves contribute

Another Event BeamedEvidence for waves, field rotation Secondary eletrons from atmosphere?

Still Another Event Closed field lines?

Global Distribution  - MEX observation  - MGS event ~13,000 identified spectra fluxes  higher than typical nightside spectra

Emission and Energy Deposition Emission estimated using electron transport model Peaked SpectrumTail Spectrum Downward energy flux ergs/cm 2 /s 5.8   Column emission (289.7 nm) 4 R0.3 R Column emission (1304 nm) 1.5 R0.3 R Column emission (1356 nm) 0.6 R0.1 R Peak emission altitude145 km151 km Mars Express: 71±42R at 129 km for nm Our peaked spectrum 17  too small Options: Require more intense spectrum Need to integrate horizontally

Emission and Energy Deposition Some auroral-like spectra 17  more intense than our example  MGS has observed electron distributions capable of producing the emission intensities observed by Mars Express Example spectrum Distribution of downward energy flux of peaked electron spectra Energy flux organized by location

SEP Event during MEX Observation ER instrument background countrate SW Pressure proxyMEX Event Did the SEP event contribute to the MEX observation? Are SEP events prerequisites for intense auroral emission? keV electrons Energy Count Rate  ER 10’s MeV ions  Energy Count Rate

SEP Correlation at MGS? Background Count Rate ~50% of most energetic peaked spectra occur during SEP events

External Control Season IMF DirectionUpstream Pressure  E,  S everywhere else duskward dawnward summer winter high P low P

Future Directions Better identify and characterize peaked electron spectra Correlate intensity with external conditions Organize by cusp location/polarity Investigate correlation with waves, field rotations Determine role of SEPs in creating emission Add converging magnetic fields to emission calculations ( see Poster #SA51B-1142 by M. Fillingim et al. - today! ) Compare to Mars Express ASPERA-3 and SPICAM observations Goals: Identify source region Identify source mechanism and role of reconnection Fully characterize resulting emission Compare to other planetary aurorae