Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999baas...31q1584m&link_type=abstract
American Astronomical Society, DPS Meeting #31, late abstracts, #59.04; Bulletin of the American Astronomical Society, Vol. 31,
Astronomy and Astrophysics
Astronomy
1
Scientific paper
The Electron Reflectometer (ER) onboard Mars Global Surveyor measures the energy and angular distributions of 10 eV to 20 keV electrons. During the aerobraking phase, measurements of the Martian ionosphere were made in the northern hemisphere between solar zenith angles (SZAs) of 45 and 115 degrees. The ionopause was crossed at altitudes ranging from 180 km to over 1000 km, with a median of 380 km. The 400-km-altitude polar mapping orbit allows ionospheric observations at SZAs from 25 to 155 in both the northern and southern hemispheres. The near-planet ionosphere/magnetotail structure of the night hemisphere is dominated by the presence of intense crustal magnetic fields, which are located south of the dichotomy boundary. Crustal field strengths in excess of 200 nT are measured at 400 km altitude, which are strong enough to create miniature magnetospheres that exclude solar wind plasma traveling up the magnetotail. When the spacecraft passes through one of these crustal magnetospheres, the ER count rate falls to the instrumental background, representing an electron flux drop of at least two orders of magnitude. A map of these flux drop-outs in longitude and latitude closely resembles a map of the crustal magnetic sources. Away from crustal magnetic fields, ionospheric photoelectrons are typically observed up to SZAs of 125 degrees, and solar wind electrons are seen at larger SZAs.
Acuña Mario Humberto
Cloutier Paul A.
Lin Robert P.
Mitchell David Leroy
Ness Norman F.
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