Ongoing Volcanic Activity on Venus: Insights from Magellan Radar Data
Authors: Sulcanese Davide , Mitri Giuseppe , Mastrogiuseppe Marco 
Published: July 2024

Detecting ongoing volcanic activity on Venus presents significant challenges due to the planet's dense atmosphere, which hinders direct observation of the surface via satellite optical imagery. The most comprehensive data on Venus&#8217;s surface morphology to date have been provided by radar images acquired by the Magellan spacecraft, which orbited the planet from 1990 to 1994 (Ford, 1993).Evidence of geologically recent volcanic activity, on the scale of millions of years, has been supported by indirect markers such as variations in atmospheric SO2 levels (Esposito, 1984), changes in surface thermal emissivity (Smrekar et al., 2010), and detailed morphological analyses of volcanic-related features (G&#252;lcher et al., 2020). Furthermore, the direct observation of a volcanic vent deforming between successive Magellan observations has been interpreted as indicative of active volcanic processes (Herrick &amp; Hensley, 2023). However, until now, clear evidence of active lava flows on the Venusian surface has not yet been found.To address this, we processed and coregistered Magellan images and applied a change detection technique similar to those used for radar data acquired on Earth (Lee et al., 2023). Specifically, we utilized mosaics generated from Full-Resolution Basic Image Data Records (F-BIDRs), having a spatial resolution of 75 m/px (Saunders et al., 1992). The regions of Venus observed by Magellan were specifically chosen where images from at least during Cycle 1 (mid-September 1990 to mid-May 1991) and Cycle 3 (mid-January to mid-September 1992) were available. This ensured consistent comparisons as both cycles employed a leftward-looking radar-viewing geometry, minimizing discrepancies caused by different viewing direction. Our processing involved more precise image realignment using tie points identified with ArcGIS pro georeferencing tools, speckle noise removal using dedicated despeckling techniques, and&#160; change detection algorithms based on the threshold evaluation method described by Kittler &amp; Illingworth (1986).The analysis revealed evident changes in radar backscatter in two specific regions: the western flank of Sif Mons and the western part of Niobe Planitia. The western flank of Sif Mons, a broad shield volcano located in Eistla Regio, showed a notable increase in radar backscattering in correspondence of lava flows, covering approximately 30 km&#178;. This intensification in Cycle 3 images, superimposed on the darker flows from Cycle 1, strongly indicates ongoing volcanic activity. Similarly, in the western Niobe Planitia, a volcanic plain characterized by the presence of numerous small shield volcanoes, new, bright, sinuous lineations were observed extending northeastward, covering about 45 km&#178;. These features, visible only in Cycle 3 data, also suggest the deposition of new lava during the Magellan mission.With the upcoming VERITAS and EnVision missions from NASA and ESA respectively, which will acquire new radar images of Venus&#8217;s surface with significantly improved spatial resolutions compared to the Magellan probe (Ghail et al., 2018; Smrekar et al., 2022), further change detection analyses will become feasible. These advancements will not only enhance image quality but also enable comparisons between historical Magellan data and new mission images, providing a more comprehensive understanding of the planet's geological changes over time (Whitten et al., 2021).AcknowledgementsG.M., D.S. and M.M. acknowledge support from the Italian Space Agency (Grant No. 2022-15-HH.0).ReferencesFord, J. P.&#160;Guide to Magellan Image Interpretation.&#160;National Aeronautics and Space Administration, Jet Propulsion Laboratory, California Institute of Technology (1993).Esposito, L. W. Sulfur dioxide: episodic injection shows evidence for active Venus volcanism.&#160;Science&#160;223, 1072&#8211;1074 (1984).Smrekar, S. E. et al. Recent hotspot volcanism on Venus from VIRTIS emissivity data.&#160;Science&#160;328, 605&#8211;608 (2010).G&#252;lcher, A. J. et al. Corona structures driven by plume&#8211;lithosphere interactions and evidence for ongoing plume activity on Venus.&#160;Nat. 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