A team of researchers has identified what appears to be a massive underground lava tube on Venus, roughly 1 kilometer wide, hidden beneath the western flank of a shield volcano called Nyx Mons. The finding, drawn from a fresh analysis of decades-old radar data, adds to a growing body of evidence that Venus is far more geologically active than scientists once believed. If confirmed, the structure would be the first subsurface conduit ever detected on another planet, with implications for how we understand volcanic plumbing systems beyond Earth.
Old Radar, New Discovery on Nyx Mons
The detection did not come from a shiny new spacecraft. Instead, researchers led by Lorenzo Bruzzone at the Università di Trento went back to images captured by NASA’s Magellan orbiter, which mapped Venus with Synthetic Aperture Radar between 1990 and 1994. By reanalyzing those SAR images with modern processing techniques, the team identified a skylight and pit feature on Nyx Mons that corresponds to an open subsurface conduit roughly 1 km in diameter. The study, published in Nature Communications, provides quantitative estimates for the tube’s width, roof thickness, and void depth, painting a picture of a structure large enough to fit several city blocks inside.
What makes this result credible rather than speculative is the quality of the underlying data. The Magellan mission produced Full Resolution Radar Maps, or FMAPs, derived from full-resolution Basic Image Data Records at approximately 75 m/pixel resolution. That is the sharpest radar imagery ever collected of Venus’s surface, and the raw data remain publicly archived through NASA’s Planetary Data System. Bruzzone’s team used these archival products to measure radar shadows and backscatter anomalies around the pit, building a geometric model of the void below. The approach is indirect, relying on how radar waves interact with surface openings rather than direct imaging of the cave interior, but it follows established methods used to study lava tubes on the Moon and Mars.
Why a Lava Tube Fits Venus’s Volcanic Story
For decades, Venus was treated as a geologically inert world, its surface assumed to have been resurfaced in a single catastrophic event hundreds of millions of years ago and then frozen in place. That view has eroded steadily. Earlier NASA-funded research, drawing on observations from ESA’s Venus Express mission and cross-referencing them with Magellan topography, found evidence of relatively recent volcanism on the planet. Lava flows in certain regions appeared younger than the surrounding terrain, suggesting that Venus’s interior still generates enough heat to drive eruptions, and that its volcanic history may be far more episodic and ongoing than a single resurfacing event would imply.
A lava tube near Nyx Mons fits neatly into that revised understanding. On Earth, lava tubes form when the outer surface of a flowing lava stream cools and solidifies while molten rock continues to drain through the interior, leaving behind a hollow conduit. The process requires active, sustained volcanism. Finding such a structure on Venus implies that the planet’s volcanic systems were not only active in the geologically recent past but were vigorous enough to sustain the kind of prolonged lava flow needed to carve out a tube of this scale. The research team has also hypothesized that the conduit may extend far beyond the portion directly mapped by the radar data, according to a summary from the university. If true, Venus could harbor an extensive network of subsurface channels that have never been observed.
The Limits of Radar Shadows
The most important caveat here is one the researchers themselves acknowledge: Magellan’s SAR was designed to map surface features, not to peer underground. The evidence for the lava tube comes from interpreting how radar signals bounce off and around the skylight opening, not from direct subsurface penetration. That means the geometric model of the void, including its estimated depth and roof thickness, is an inference built on assumptions about how the radar interacts with specific rock geometries. Alternative explanations, such as a deep collapse pit without an extended tube, cannot be fully ruled out with the available data, and the team treats the lava-tube interpretation as strongly favored but not definitive.
The resolution ceiling also matters. At 75 m/pixel, the FMAPs represent the best Venus radar imagery in existence, but they still cannot resolve fine structural details inside a cave opening. Smaller collapses, branching passages, or partial blockages within the conduit would be invisible at that scale, and subtle textural differences on the pit floor are smeared together in a single radar pixel. The full-resolution mosaics and related Magellan products in NASA’s archive are open for independent verification, which is a strength of the study’s methodology. But confirmation will likely require a different kind of instrument altogether, one capable of sending radar pulses through the surface and directly sampling echoes from underground layers and voids.
EnVision Could Settle the Debate
That instrument may already be in development. ESA’s EnVision mission, currently in preparation for Venus orbit, will carry a Subsurface Radar Sounder, or SRS, capable of probing to approximately 1 km below the surface. Unlike Magellan’s SAR, which mainly recorded echoes from the top layer, the SRS is specifically designed to detect subsurface structures by sending lower-frequency radar pulses that can penetrate rock and regolith. In principle, a 1 km detection depth would allow EnVision to sense a Nyx Mons conduit of the size inferred from the Magellan data, either by catching direct reflections from the void or by mapping the layering of surrounding lava flows that would betray its presence.
In practice, the outcome will depend on local conditions at Nyx Mons: rock composition, porosity, the presence of fractures, and the thickness of any weathered surface layer that might scatter or absorb the radar signal. Even a negative result—no clear echo from a tube—would sharpen the picture by constraining how large or continuous the void can be. If EnVision does detect a distinct subsurface reflector where Bruzzone’s team predicts the tube, it would mark the first time a planetary radar sounder has confirmed a specific underground volcanic structure on another world. That, in turn, would validate the use of legacy SAR datasets like Magellan’s for hunting lava tubes and other conduits across Venus, potentially transforming a three-decade-old archive into a map of hidden volcanic plumbing.
Why Subsurface Conduits Matter for Venus Science
The stakes go beyond a single tube. Subsurface conduits are crucial to how volcanism shapes a planet’s atmosphere and climate over time. On Earth, lava tubes and dike systems can transport magma tens of kilometers from a source vent, distributing eruptions across wide areas and modulating the rate at which gases like carbon dioxide and sulfur dioxide reach the air. If Venus hosts similar networks, they could help explain how the planet sustained intense volcanic outgassing long enough to build its dense, greenhouse-dominated atmosphere. Mapping where those conduits occur, and how they relate to surface flows and volcanic edifices like Nyx Mons, would give modelers new constraints on the timing and intensity of past eruptions.
Subsurface voids also offer rare windows into the mechanical behavior of Venusian crust. The dimensions of a tube—its width, roof thickness, and collapse patterns—encode information about lava viscosity, eruption duration, and the strength of the overlying rock. A 1 km-wide conduit with a stable roof suggests either very low-density lava capable of flowing for long distances, exceptionally strong crustal materials, or both. Comparing the Nyx Mons structure to lava tubes on Earth, the Moon, and Mars could reveal whether Venus’s near-surface rocks are more prone to forming large, coherent roofs or whether similar processes operate across rocky worlds despite their different temperatures and atmospheric pressures. With EnVision and other planned missions poised to revisit the planet, the Nyx Mons lava tube candidate offers a concrete target for turning those broad questions into testable hypotheses.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
