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.