The variability of the ionospheres of Mars and Venus derived from Mars Express and Venus Express radio science observations

While the orbital and environmental parameters (e.g. orbit-Sun-distance, planetary mass/diameter, gravity acceleration, rotation rate, surface pressure) of Venus and Mars are very different, their planetary ionospheres show many similarities.

Figures 1 and 2 illustrate the variability of the Venus and Mars dayside ionospheres. Both planetary dayside ionospheres contain a pronounced main peak region (V2/M2) originating mostly from the photoionization of the CO₂ based atmosphere by solar extreme ultraviolet radiation. The region below the main peak (V1/M1) has its origin in the primary and secondary impact ionization of the neutral atmosphere by solar X-ray radiation [2]. The observed shape of the V1/M1 region in radio science observations ranges from a secondary peak (Figure 2b) to a smooth decrease in electron density without a pronounced V1/M1 feature.

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