Tesserae on Venus may preserve evidence of fluvial erosion

The study investigates whether Venus’s oldest and most tectonically complex terrains—tesserae—record evidence of fluvial erosion, challenging the prevailing view that high present-day surface temperature (~450 °C) and pressure (~9 MPa) preclude significant surface erosion. Using Magellan mission SAR imagery and limited-resolution topography, the authors explore whether valley systems exist within tesserae that resemble terrestrial fluvial drainage networks. Motivated by climate modeling that suggests Venus could have sustained Earth-like, temperate conditions with liquid water for much of its early history prior to a runaway greenhouse event, the research aims to assess tessera morphology for signatures consistent with past fluvial processes and thereby test hypotheses about early Venusian climate.

Prior work established tesserae as stratigraphically oldest, high-standing, tectonically complex units (~8% of Venus’s surface) embayed by younger volcanic plains (e.g., Ivanov & Head, Hansen & Willis, Ghail, Gilmore & Head). The prevailing interpretation of Venus’s surface emphasizes minimal erosion due to current extreme conditions, supported by pristine volcanic morphologies, wrinkle ridges, graben-fissure systems, and lava channels (canali and sinuous rilles), with fluvial origins for canali generally rejected. Impact craters on plains are mostly pristine except where resurfaced by volcanism, reinforcing limited erosion. Global resurfacing models propose either catastrophic resurfacing or steady-state processes with mean surface ages ~150–750 Ma. Climate modeling (Way et al.; Ingersoll) suggests early Venus may have had Earth-like conditions, potentially allowing fluvial erosion before greenhouse-driven water loss. Magellan altimetry (50–100 m vertical; 10–20 km horizontal) and SAR (∼100 m/pixel; 98% coverage) provide the best available data; stereo topography offers 1–2 km horizontal resolution for ~20% of the planet (Herrick et al.).

• Study areas: Eight tessera regions located within Venus quadrangles V-33, V-34, V-12, and V-4.
• Core proxy approach: Identify paleo-valleys indirectly where younger plains lavas flood and embay tessera margins. The lava surface serves as an approximate horizontal datum, highlighting pre-existing lows (valleys) versus highs (tessera inliers). Even with later local uplift affecting both tessera and lava, the lava-flooding pattern preserves valley geometry.
• Data sources: Magellan Cycle 1 left-looking SAR images (~100 m/pixel, 98% surface coverage) and Magellan altimetry (∼50–100 m vertical resolution; ∼10–20 km horizontal). Where available, stereo-derived topography (Herrick et al.) with improved ~1–2 km horizontal resolution was used.
• Image processing and visualization: SAR images were draped over Magellan altimetry and stereo-topography using ArcGIS ArcScene to generate elevated oblique 3-D views (vertical exaggeration ~20×; viewing elevation ~20°). These views aided interpretation of topographic relationships between tessera highs and lava-filled lows.
• Mapping and comparison: Paleo-valley patterns inferred from lava-flooded geometries were mapped along tessera margins. Interpreted patterns were compared to terrestrial stream drainage types (trellis, radial, parallel, rectangular, dendritic, annular) following Howard (1967) and Bridge & Demicco (2008) to assess morphological similarity and infer possible geological controls.
• Geological interpretation framework: For each site, both tectonic-only and erosion-only scenarios were considered. The preferred model integrates initial tectonic deformation (e.g., folding, faulting) followed by fluvial erosion that widened and modified valleys; wind erosion is considered subordinate.
• Limitations acknowledged: The proxy preferentially reveals major valleys near tessera margins and may underrepresent interior/upslope networks; topographic resolution and SAR data gaps limit precision; vertical exaggeration can mislead apparent dips, necessitating cautious interpretation.

• Multiple tessera margins exhibit lava-embayment patterns that outline valley networks morphologically analogous to terrestrial stream drainage systems, consistent with fluvial erosion superimposed on earlier tectonic topography.
• Across eight study regions, mapped paleo-valley patterns match five of the six canonical terrestrial drainage types: trellis, radial, parallel, rectangular, and (more speculatively) dendritic; annular was not recognized.
• A representative case in southern Salus tessera fits a model of a plunging syncline (NNE–SSW) subsequently widened by erosion, with tessera inliers within a lava-flooded valley; lineament sets suggest inward-dipping surfaces consistent with layered sequences and erosion rather than purely tectonic or purely erosional models.
• A tear-drop-shaped kipuka within a lava-flooded tessera valley suggests flow directionality (west-to-east), consistent with erosive fluid flow.
• Interpreted drainage patterns imply controls by local geology: homogeneous materials and slopes (radial, parallel, dendritic) and orthogonal fractures or dipping stratigraphy/flows with differential erodibility (trellis, rectangular).
• Relevant contextual data: tesserae occupy ~8% of Venus; Magellan SAR resolution ~100 m/pixel with 98% coverage; Magellan altimetry resolution ~50–100 m vertical and ~10–20 km horizontal; stereo topography improves horizontal resolution to ~1–2 km where available.

The identification of valley networks in tesserae that resemble terrestrial drainage patterns directly addresses the central question of whether fluvial processes acted on Venus. The results support a scenario in which tessera topography formed through initial tectonic deformation (folding and faulting) and was subsequently modified by fluvial erosion, implying the presence of liquid water prior to the runaway greenhouse transition. This interpretation aligns with climate models positing extended periods of temperate, potentially habitable conditions on early Venus. The drainage patterns also offer insights into subsurface geology and structural controls (e.g., dipping stratigraphy, fracture orthogonality, differential erodibility), broadening interpretations of tessera lineaments to include layered volcano-sedimentary packages and variably eroded flood basalts or layered intrusions. Furthermore, recognizing erosional modification helps reconcile the apparent age similarity between tesserae and younger volcanic plains derived from crater counts: sustained erosion in tessera time could preferentially remove craters, making these terrains appear younger than their true, potentially much older, ages once erosion ceased with climate change.

This work introduces an indirect yet robust method to infer paleo-valleys in Venusian tesserae using lava-flooding patterns, revealing drainage geometries analogous to terrestrial systems and supporting the hypothesis that fluvial erosion acted on Venus’s oldest terrains. These findings bolster models of an early, cooler, wetter Venus and suggest tesserae may record protracted geological histories. The approach also provides a reconnaissance tool to relate drainage patterns to underlying geology and reinterpret tessera lineaments and intra-tessera plains. Future research should employ higher-resolution radar and topography from upcoming Venus missions to directly map valley networks, quantify drainage metrics, test for sedimentary deposits, and refine stratigraphic and tectonic histories across more tessera regions.

• Data resolution constraints: Magellan altimetry has coarse horizontal resolution (∼10–20 km) and limited vertical precision (∼50–100 m); stereo-derived topography covers only ~20% of the planet at ~1–2 km resolution. SAR data contain gaps and variable look directions.
• Proxy bias: Lava flooding preferentially fills major valleys near tessera margins, potentially underrepresenting interior/upslope networks and finer-scale drainage.
• Interpretational ambiguity: Alternative tectonic-only scenarios cannot be entirely excluded with current data; vertical exaggeration in visualizations can mislead apparent dips without careful correction.
• Limited geographic sampling: Only eight tessera regions were analyzed; broader coverage is needed to generalize findings.