Effects ofSolar Energetic Particle Events

on the Martian Surfaceand Atmosphere

F Leblanc, DA Brain, JG Luhmann, GT Delory, RA Mewaldt, CM Cohen

2004 Fall AGU Meeting - Friday 17 December

Motivation

Record-setting Halloween 2003 Solar Energetic Particle event occurred when Earth and Mars “on same field line”

Protons 1 MeV to 1 GeV

Mars Global Surveyor - Electron Reflectometer Data

Electron instrument at Mars “contaminated” by energetic particles

Motivation

What effect do SEP events have on the Martian surface and atmosphere?

Solar Protons at Mars

http://physics.nist.gov/PhysRefData/Star/Text/contents.html

Solar Protons at Mars

http://physics.nist.gov/PhysRefData/Star/Text/contents.html

g = 3.71 m/s2

P(0) = 6.36 mbarH = 11.1 km

Solar Protons at Mars

http://physics.nist.gov/PhysRefData/Star/Text/contents.html

these primaries reach surface

g = 3.71 m/s2

P(0) = 6.36 mbarH = 11.1 km

Shielding by Martian Atmosphere

protonsalphaselectrons

Martian Atmosphere

October Eventat Surface

The time integrated GOES event spectrum resembles the SIREST SEP/SPE input spectrum

http://sirest.larc.nasa.gov/

Integrated Event Spectrum SIREST Input SPE Spectrum

GCRSEP

InputSpectra

OutputSurface Flux

Surface radiation flux from SEPevent exceeds that from GCRsOctober Event

at Surface

neutrons (up and down)

protons

Do Crustal Fields Matter?

Effects of Crustal Fields

exobase

Magnetic fields deflect low energy (few MeV) particles

Deflection of Primary Protons

small deflection at surface for high energy protons

large deflection for lower energy protons(at higher altitudes)

Effects of Crustal Fields

For low energy particles:Less energy is deposited above crustal sources than in surrounding

areas

Summary

• The surface radiation from a large SPE can be important compared to the surface radiation from GCRs.

• Crustal fields can have a significant effect on atmospheric energy deposition during a SPE. They do not have a strong effect on SEPs reaching the Martian surface.