Venusian Ionosphere During Deep Solar Minima: Some New Insights Using Akatsuki Radio Science Experiment

Abstract

The characteristic features of different layers in the Venus ionosphere during the deep solar minimum of the solar cycle 24 have been studied using a radio science experiment onboard the Akatsuki spacecraft. Radio signals from the spacecraft were tracked at the Indian deep space network, Bangalore; Usuda Deep Space Center, Japan; and DLR Ground station, Weilheim, Germany. The orbital geometry of the spacecraft provides rare opportunities to probe the Venusian ionosphere and atmosphere in the equatorial region at low solar zenith angles (SZAs). The height of the peak plasma density of the V₂ layer (∼141 km) was seen to remain almost constant for the SZA ≤ 90° while the peak density was the least among the published results. Features of the V₁ layer (∼125 km) agree well with the Venus Express radio occultation measurements. All three types of V₁ layers were observed in Akatsuki observations. The V₀ layer (∼110 km) was observed in about 15% of cases and was seen to occur irrespective of SZA and geographical constraints. Nighttime occurrence of the ionosphere was very limited despite regular observations.