Radio Sounding of the Mars Ionosphere over a full Solar Cycle by the Mars Express Radio Science Experiment (MaRS)
Abstract
The Mars Express Radio Science experiment MaRS sounds the ionosphere of Mars since 2004. It started during the declining phase of the past solar cycle in 2004, went through a pronounced deep and long solar minimum in 2008 and 2009 and covers most of the current solar cycle through its solar maximum. The great advantage of the MaRS experiment compared to other radio sounding experiments at Mars performed at only a single frequency is the dual-frequency radio sounding at X-band simultaneously at S-band. This helps to identify the true electron density distribution and to separate true ionospheric features, in particular in the topside, from contributions caused by the spacecraft.The large-scale daytime ionosphere shows a two-layer structure of a main layer M2 and a lower layer M1 formed by mostly solar EUV and solar X-ray and secondary ionization, respectively. The base is typically identified at 90 km. Sometimes additional electron density may be found below the M1 layer which is suspected to be caused by short solar X-rays interacting with the neutral atmosphere (see presentation by K. Peter et al.). The topside is defined by a transport region with varying plasma scale heights. The ionopause is rarely seen, mostly when the general electron density noise background is low which coincides with observations during planetary opposition.The M1 and M2 peak densities are clearly under solar control and follow the solar zenith angle and the solar cycle. The altitudes of both layers change also with the solar zenith angle. Variations in altitude for a given solar zenith angle may be caused by atmospheric waves propagating through ionospheric altitudes (see presentation by Tellmann et al.).The vertical electron content follows also the solar zenith angle and is dominated by the M2 layer which contains at least 50% of the total.This presentation reviews the MaRS ionospheric soundings over 13 years and a full solar cycle.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E2546P