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The horizontal wind velocity vectors at the lower cloud layer were retrieved by tracking the displacement of cloud features using the 1.74 µm images of the full Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS-M) dataset. This layer was found to be in a superrotation mode with a westward mean speed of 60–63 m s−1 in the latitude range of 0–60° S, with a 1–5 m s−1 westward deceleration across the nightside. Meridional motion is significantly weaker, at 0–2 m s−1; it is equatorward at latitudes higher than 20° S, and changes its direction to poleward in the equatorial region with a simultaneous increase of wind speed. It was assumed that higher levels of the atmosphere are traced in the equatorial region and a fragment of the poleward branch of the direct lower cloud Hadley cell is observed. The fragment of the equatorward branch reveals itself in the middle latitudes. A diurnal variation of the meridional wind speed was found, as east of 21 h local time, the direction changes from equatorward to poleward in latitudes lower than 20° S. Significant correlation with surface topography was not found, except for a slight decrease of zonal wind speed, which was connected to the volcanic area of Imdr Regio. [ABSTRACT FROM AUTHOR]

We present joint analysis of the UV (365 nm) images captured by the cameras on board ESA's Venus Express and JAXA's Akatsuki spacecraft. These observations enabled almost continuous characterization of the cloud top circulation over the longest period of time so far (2006–2021). More than 46,000 wind vectors were derived from tracking the UV cloud features and revealed changes in the atmospheric circulation with the period of 12.5 ± 0.5 years. The zonal wind component is characterized by an annual mean of −98.6 ± 1.3 m/s and an amplitude of 10.0 ± 1.6 m/s. The mean meridional wind velocity is −2.3 ± 0.2 m/s and has an amplitude of 3.4 ± 0.3 m/s. Plausible physical explanations of the periodicity include both internal processes and external forcing. Both missions observed periodical changes in the UV albedo correlated with the circulation variability. This could result in acceleration or deceleration of the winds due to modulation of the deposition of the radiative energy in the clouds. The circulation can be also affected by the solar cycle that has a period of approximately 11 years with a large degree of deviation from the mean. The solar cycle correlated with the wind observations can probably influence both the radiative balance and chemistry of the mesosphere. The discovered periodicity in the cloud top circulation of Venus, and especially its similarity with the solar cycle, is strongly relevant to the study of exoplanets in systems with variable "suns". [ABSTRACT FROM AUTHOR]

A problem of determining attainable landing sites on the surface of Venus is an essential part of the Venera-D project aimed to explore the planet using a lander. This problem appears due to the inability for the descent module to land at any point on the surface of Venus because of the short duration of the launch window (about 2 weeks from the optimal launch date), as well as restrictions on the maximum permissible overload. An additional factor affecting the reduction of attainable landing sites is the low angular velocity of Venus' own rotation. This study proposes a new approach to expand the attainable landing areas. The approach is based on the use of the gravitational field of Venus to transfer the spacecraft to an orbit resonant to the Venusian one with a ratio of periods of 1:1. All the simulations were performed at the patched conic approximation. As an example, we considered a flight to Venus at launch in 2029 or 2031. For both cases maps of attainable landing areas on the Venus surface were plotted. It has been demonstrated that there is always at least one launch date within the launch window allowing the spacecraft to reach almost any point on the surface of Venus. It is shown that the application of the proposed approach makes it possible to achieve a significant expansion of the attainable landing areas (over 70% of the surface) and, in some cases, provide access to any point on the surface of Venus. However, the price of this advantage is an increase in the flight duration by one Venusian year. • The method of expanding attainable areas on the Venus surface has been developed. • The landing areas on the Venus surface are calculated for launch in 2029 and 2031. • The use of gravity assist of Venus is proposed for expansion of landing areas. [ABSTRACT FROM AUTHOR]

The baseline Venera-D mission, proposed to be launched after 2026, consists of an orbiter and a landing module, which includes a lander and a small long-lived station. In this work, we present the possibility of augmenting the mission with one or two micro-spacecraft in Lagrange point orbits to significantly enhance the science return. Both L 1 and L 2 collinear points, situated at about 1 million km from Venus, are considered for scientific objectives. The paper focuses on trajectory design for the micro-spacecraft to be deployed by the Venera-D mission. The transfer scenario we propose performs the insertion of micro-spacecraft into Lagrange point orbit by making use of the main orbiter's propulsion, while the propulsion on board micro-spacecraft is used only for trajectory correction and station-keeping manoeuvres. This scenario allows the Venera-D mission to add one or two micro-spacecraft of mass about 50 kg with only a total Δ V budget 30 m/s over 3 years on orbit. [ABSTRACT FROM AUTHOR]