The importance of identifying volcanically active areas in the future exploration of Venus
The exploration of Venus will go through a new golden era thanks to the recently selected NASA Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy (VERITAS) (Smrekar et al., 2020) and Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) (Garvin et al., 2022) missions, the ESA EnVision mission (Ghail et al., 2020), and the Roscosmos Venera-D mission (Zasova et al., 2019). Moreover, other two missions are currently being evaluated for selection: the ISRO Shukrayaan-1 mission (i.e., Haider et al., 2018; Sundararajan, 2021) and the Chinese VOICE mission (e.g., Wang et al. 2022). These missions will focus on the analysis of the chemical composition of the atmosphere and the geologic features of Venus.
One of the main targets of the future missions to Venus will be the identification of potentially volcanically active areas on Venus. Identifying the locations of possibly active volcanism with its related composition is crucial to estimate energy and volatile budget on Venus, that is of great importance to understand the geodynamic evolution of Venus and the terrestrial planets. Evidence of ongoing volcanism can give us clues in the debate between catastrophic (i.e., Schaber et al., 1992; Basilevsky and Head, 1998; Romeo and Turcotte, 2010) and equilibrium resurfacing (i.e., Phillips et al., 1992; Guest and Stofan, 1999; O’Rourke et al., 2014), indicating how volcanic and tectonic activity is currently evolving on Venus (e.g., Weller and Kiefer 2020). The analysis of recently erupted (chemically unweathered) lava flows will also provide useful information about the volatile content of the mantle of Venus (e.g., Filiberto 2014). We comment here the results of the work by Brossier et al. (2022) (https://doi.org/10.1029/2022GL099765) and the related implications for the future orbiting and in-situ investigations of Venus.
As observed by previous studies (e.g., Pettengill et al., 1992), the presence of high dielectric (ferroelectric) minerals can increase the radar reflectivity and lower the radar emissivity on Venus. It is observed that some minerals (e.g., perovskite, chloroapatite) can lower the emissivity even at anomalously low altitudes. Theoretical studies indicate that the high dielectric minerals can be formed over the time by the interactions between the surface and lower atmosphere, also known as chemical weathering (e.g., Zolotov 2019). In this way, dielectric measurements on Venus can be used as a potential chronometer to constrain the age of surface materials.
Brossier et al. (2022) (https://doi.org/10.1029/2022GL099765) analyze the radar emissivity excursions of seven different sites at Ganis Chasma, four of which already studied by Shalygin et al. (2015) using Venus Monitoring Camera (VMC) data of the Venus Express, while other three sites were selected separately for comparison (Fig. 1). Their results show that for a given (range of) altitude and temperature, the emissivity excursions do not occur uniformly over all the analyzed surface materials (Fig.2). This implies that, in the study area, the observed emissivity excursions are mainly controlled by the presence (or absence) of distinct ferroelectric minerals with high dieletric constant. Based on the magnitude of the observed radar emissivity excursions of the seven different sites, the authors conclude that sites 1, 3, and 4 may be characterized by unweathered and thus extremely young surface materials where high dielectric minerals have not yet been formed.
Similarly, using a holistic approach, other recent studies have combined laboratory results, geologic interpretation, and Venus Express VIRTIS 1 micron surface emissivity data to provide additional lines of evidence for recently or possibly ongoing volcano-tectonic activity at Idunn Mons, the major volcanic structure of Imdr Regio on Venus (D’Incecco et al., 2017, 2021a,b,c; Filiberto et al., 2020., 2021; Cutler et al., 2020; López et al., 2022). Combining this new work with previous studies by Brossier et al., (2020) and Brossier and Gilmore (2021), this demonstrates that the Magellan dataset is able to provide important clues about the materials on the surface, which can be used as a potential chronometer for the surface age of Venus. The results of this manuscript are extremely relevant to our understanding of how volcanic processes are currently acting on Venus. Further, these models can be tested with the upcoming fleet of missions expected to arrive at Venus in the next decade.