Premium
Why the Viking descent probes found only one ionospheric layer at Mars
Author(s) -
Mayyasi Majd,
Mendillo Michael
Publication year - 2015
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2015gl065575
Subject(s) - ionosphere , sunrise , radio occultation , occultation , sunset , mars exploration program , electron density , physics , ionization , geology , atmosphere of mars , atmospheric sciences , electron , astronomy , martian , ion , quantum mechanics
Radio wave transmissions from satellites revealed that Mars had two relatively distinct layers of ionization: a maximum electron density near 130 km, and a secondary layer near 110 km. When the Viking descent probes—with their in situ observing capabilities—passed through the ionosphere, the peak electron density was found, with no indication of a secondary layer below. Here we use an ionospheric model to show that profiles of electron density versus height have shapes that favor the detection of two layers at local times near dawn and dusk (where many thousands of radio occultation observations have been made), but that the two layers essentially merge into one during midday hours (when Viking measurements were made). The profile shapes are attributed to ionizing geometry of solar photons and to chemical processes that affect the profile shapes in a way that favors secondary peak formation near sunrise and sunset.