First Evidence of Lava Tubes on Venus

Introduction:

The existence of lava tubes on planetary bodies has long been a subject of interest in planetary geology, with confirmed instances on the Moon, Mars, and Earth [1,2]. These subsurface cavities not only provide insights into volcanic processes but also represent primary targets for the Subsurface Radar Sounder (SRS) instrument planned for the EnVision mission to Venus. The SRS aims to penetrate the planet's surface to depths of several hundred meters, potentially revealing the internal structure of lava tubes and other underground features [3]. However, until now, the presence of lava tubes on Venus has remained speculative due to limitations in observational data [4].

We present the first compelling evidence for the existence of lava tubes on Venus, based on an extensive analysis of pit alignments on Venusian large volcanoes. Our investigation focused on volcanoes larger than 100 km in diameter [5], utilizing radar imagery and topographic data from past Venus missions.

 

Results:

Our survey revealed four distinct instances of sinuous pit chains that do not appear to be associated with tectonic extensional structures. These alignments exhibit characteristics consistent with the collapse features observed above lava tubes on other planetary bodies. Key findings include: (i) morphometry: in plan-view the identified pit alignments display a curvilinear arrangement, typical of collapsed sections of lava tubes. Higher sinuosity has been observed for these instances compared to a sample of pit alignments produced by tectonic collapses; (ii) dimensions: pits’ width and depth cannot exceed those of the underlying lava tube, while pits that form on tectonic structures show a correlation between their diameter and depth; (iii) geological context: all four instances are not only located on the flanks of shield volcanoes, in areas characterized by extensive lava flows which is consistent with the formation environment of lava tubes on other planetary bodies, but they also develop in a direction consistent with the slope of the terrain on which they were observed, thus consistent with the hypothesis that they are the product of lava flowing on an inclined surface. Additionally, the inferred geometry of the cavities matches the crusting-over formation process typically associated with non-inflating lava tube development [6,7]. This process involves the solidification of the upper layer of a lava flow while the underlying molten lava continues to drain, leaving behind a hollow conduit. However, the volumes estimated for the Venusian lava tubes based on the visible extent of the pit alignments and assuming continuity between collapse features, are comparable to those observed on the Moon (fig.1) , implying the presence of cavities larger than those observed on Earth [1].

Figure 1. Collapse width W versus linear volume V₁ expressed in a logarithmic plot, along with power laws trend lines for each planetary body and for the whole dataset (black line) are shown.

 

Conclusions:

This study presents the first observational evidence for the existence of lava tubes on Venus, significantly expanding our understanding of the planet's volcanic processes and geological evolution. The discovery of these structures not only enhances our knowledge of planetary speleogenesis but also has implications for future exploration strategies. The characteristics of the observed Venusian lava tubes, particularly their large scale, suggest that Venus may host some of the most extensive subsurface cavities in the solar system. However, the limitations in current observational data emphasize the need for future high-resolution imaging missions to Venus to fully map and characterize its lava tube systems. As we continue to explore the volcanic landscapes of Venus, these newly discovered lava tubes may help constrain models of the planet's thermal and tectonic evolution, and offer exciting possibilities for understanding the planet's past and present conditions.

 

Acknowledgement: B.D.T. is supported by the European Union – NextGenerationEU and by the 2023 STARS Grants@Unipd programme HECATE.

References: [1] Sauro et al., Earth-Science Reviews 209 (2020): 103288. [2] Carrer et al., Nat. Atro. 8.9 (2024): 1119-1126. [3] Bruzzone et al. EnVision Int. Venus Sci. Works. (2023). [4] Carrer et al., IEEE Tran. on Geos. Rem. Sens. (2024). [5] Hahn and Byrne. JGR: Planets 128.4 (2023): e2023JE007753. [6] Hon et al., Hawaii. Geol. Soc. Am. Bull. 106 (3), 351–370, (1994). [7] Peterson, et al., Hawaii. Bull. Volcanol. 56 (5), 343–360, (1994).