Characteristic Features of V 0 Layer in the Venus Ionosphere as Observed by the Akatsuki Orbiter: Evidence for Its Presence During the Local Noon and Post‐Sunset Conditions

• Published in: Geophysical research letters Vol. 49; no. 7
• Main Authors: Tripathi, Keshav R., Choudhary, R. K., Ambili, K. M., Imamura, T., Ando, H.
• Format: Journal Article
• Language: English
• Published: 16.04.2022
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL097824

Abstract Characteristic features of the Venus ionosphere below the V 1 base, named as V 0 layer, have been studied using the Radio Science payload onboard Akatsuki orbiter. An ionospheric layer below the V 1 base is known to be present in the Venus ionosphere but found to be geographically localized, seen mostly during the daytime between 55 and 90° solar zenith angle (SZA). We, for the first time, show its presence at different latitudes and SZA, including near the equator during the local noon and post‐sunset hours. The maximum density of this layer was ∼4 × 10 10  m −3 at the altitude range of 110 ± 4 km. In the absence of in‐situ measurements, it's difficult to comment on the origin but the presence of such layers during post‐sunset hours suggests their meteoric origin as the observed altitudes are consistent with the height range predicted by the meteor models. Other possible sources of such layers are also discussed. Plain Language Summary Akatsuki orbiter has been conducting radio occultation (RO) measurements since 2016 to study the atmosphere and ionosphere of Venus using an onboard Radio Science experiment. A total of 34 electron density profiles have been obtained so far, among which 25 are from the dayside. There are six profiles that show an enhancement in the electron density below 120 km altitude, the base of V 1 layer. We report the presence of such layers near the equatorial region, both during the day and night time. We have named it the V 0 layer because they are no longer geographically localized phenomena, earlier believed to be. A most probable explanation for the presence of this layer is the ionization of metallic molecules associated with meteor showers. As photo‐ionization is a main source of ions in the Venus ionosphere, its presence during the post‐sunset hours supports the idea of their meteoric origin as the night side of Venus receives no solar radiation. However, to confirm V 0 as a sporadic or consistent layer, we need to investigate with in situ measurements supported by more frequent RO experiments. Key Points First observations of V 0 layer in the Venus ionosphere near the subsolar point at solar zenith angle (SZA) ∼5°, and well past the solar terminator at SZA ∼108° First observation of V 0 layer at the equator during the local noon Akatsuki radio science measurements, for the first time, show that such layers are not SZA dependant