Modelling dications in the diurnal ionosphere of Venus

Abstract

Context. Previous studies have shown that doubly-charged positive ions, including molecular ions, can have detectable densities in the ionospheres of Mars, Titan, and the Earth. Aims. In the present paper, we continue our approach by modelling the Venusian ionosphere. The neutral atmosphere of Venus has a similar composition to the ones encountered in the other terrestrial planets, with carbon dioxide (as on Mars), nitrogen (as on Earth and Titan), and atomic oxygen (as on Earth). Methods. We computed the doubly-charged positive ion production through photoionisation (primary production) and electron impact ionisation (secondary production). We computed the densities under the photochemical equilibrium assumption. Results. We predict a CO 2 ++ layer centred around 140 km altitude with a density reaching 30 dications per cm 3 in active solar conditions and a N 2 ++ layer centred around a 140−150 km altitude with density reaching 0.3 cm −3 . We find good agreement between the modelled O ++ densities and Pioneer Venus Orbiter measurements. Finally, we investigate the problem of possible detection of these ions by the European spacecraft Venus Express. Conclusions. Although molecular doubly-charged positive ion densities are low, these ions cannot be considered as negligible compared to other minor ion species. Their detection should be possible in the future through remote sensing or in-situ methods including ion mass spectrometry and UV spectroscopy.

Comprehensive calculation of the energy per ion pair or <I>W</I> values for five major planetary upper atmospheres

“…For Earth's thermosphere, we use the model MSIS-90 (Hedin, 1991) with N 2 , O 2 , O as main three components. For Venus we use VTS3 (Hedin et al, 1983) Gronoff et al (2007). For Mars, we use MTGCM (Bougher et al, 1999) with CO 2 , CO, N 2 , O 2 and O applied to the Viking/Mariner conditions (e.g., Simon et al, 2009).…”

Ionization processes in the atmosphere of Titan

“…It has been adapted to several planets, becoming successively transsolo (Lummerzheim & Lilensten 1994), transcar (Lilensten & Blelly 2002), tran4 ) in the case of Earth, and, for orther planets, transTitan (Lilensten et al 2005a,b), transMars (Witasse et al 2003(Witasse et al , 2002Simon et al 2008), transVenus (Gronoff et al 2007. The transTitan code used here consists of primary production through photoabsorption and secondary production through electron impacts.…”

Modelling the Venusian airglow

“…The Venusian version was described in Gronoff et al (2007). This code was adapted for Mars (Witasse 2000;Witasse et al 2002Witasse et al , 2003, and Titan .…”