Ongoing Volcanic Activity on Venus: Insights from Magellan Radar Data

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’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 (Gülcher 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 & 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  change detection algorithms based on the threshold evaluation method described by Kittler & 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 km². 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 km². 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’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).

Acknowledgements

G.M., D.S. and M.M. acknowledge support from the Italian Space Agency (Grant No. 2022-15-HH.0).

References

Ford, J. P. Guide to Magellan Image Interpretation. 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. Science 223, 1072–1074 (1984).

Smrekar, S. E. et al. Recent hotspot volcanism on Venus from VIRTIS emissivity data. Science 328, 605–608 (2010).

Gülcher, A. J. et al. Corona structures driven by plume–lithosphere interactions and evidence for ongoing plume activity on Venus. Nat. Geosci. 13, 547–554 (2020).

Herrick, R. R. & Hensley, S. Surface changes observed on a Venusian volcano during the Magellan mission. Science 379, 1205–1208 (2023).

Lee, J. Y., Jung, S. W., & Hong, S. H. Mapping lava flow from the Kilauea eruption of 2018 in the east rift zone using space-based synthetic aperture radar. GISci. Remote Sens. 60(1), 2176275 (2023).

Saunders, R. et al. Magellan mission summary. J. Geophys. Res.: Planets 97, 13067–13090 (1992).

Kittler, J. & Illingworth, J. Minimum error thresholding. Pattern Recognit. 19, 41–47 (1986).

Ghail, R. C. et al. VenSAR on EnVision: taking Earth observation radar to Venus. Int. J. Appl. Earth Obs. Geoinf. 64, 365–376 (2018).

Smrekar, S. et al. VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy): a discovery mission. In 2022 IEEE Aerospace Conference (AERO) 1–20 (IEEE, 2022).

Whitten, J., Smrekar, S., Hensley, S., Dyar, M., & Nunes, D. (2021, December). VERITAS: Change Detection and Community Involvement in Target Selection. In AGU Fall Meeting Abstracts (Vol. 2021, pp. P34B-05).