Inanna: Decoding the Role of Space in Venus’ Atmospheric Evolution Through Time

Why did Venus, once likely similar to Earth, evolve into a scorching world with a dense, toxic atmosphere? In the coming decade, Venus will be in the spotlight, with a new generation of missions descending through its clouds or probing its surface to explore its geologic past in search of answers. However, one critical part of the puzzle remains: How has the long-term influence of the space environment affected the evolution of Venus’ atmosphere?

Inanna, a new mission proposed to the European Space Agency’s M8 call, is designed to address this missing piece of the puzzle. It is the first mission fully dedicated to comprehensively investigate how the interplay between the solar wind and the Venusian ionosphere, the ionised uppermost part of the atmosphere, has driven atmospheric escape over time. Inanna is a two-spacecraft mission: the main Venus Orbiter, carrying instruments for in situ measurements of ions, neutrals, and electromagnetic fields, and the Solar Wind Monitor, which will spend most of its time in the solar wind to continuously characterize the solar wind and interplanetary magnetic field. This unique configuration will finally provide us with the means to disentangle the temporal variations in solar forcing from spatial structures in Venus’ induced magnetosphere, and give us solid evidence for how the Venusian atmosphere has evolved via interactions with outside forces through time.

By capturing both the drivers and the planetary response, Inanna will characterize the dynamic processes that accelerate and remove particles from Venus’ upper atmosphere. Deep dip campaigns of the Venus Orbiter, reaching down to or below the ionospheric peak at ~150 km, will show how energy and momentum from the solar wind couple into the atmosphere, and how atmospheric escape varies with region, composition and solar conditions. In addition, instruments to measure winds, temperature, and composition in the upper mesosphere, thermosphere, and ionosphere will help assess how energy and momentum may propagate upward from lower atmospheric layers.

While other upcoming missions focus on the history of Venus’ interior and lower atmosphere, Inanna complements and extends them by offering crucial insight into what has been lost to space and how that loss has occurred. Understanding this is essential to piecing together the full story of Venus’ transformation through time. In this presentation we will highlight the Inanna mission concept, its scientific goals, and how we plan to achieve them.