But what would be considered as “ground truth” on a planet where the ground is not visible by the cameras? On Venus, geometry is getting the strongest case: chains of curves, the finesse of radar variations, model calculations indicate that the crust might contain open voids by far bigger margins than many scientists previously thought.
Venus is still a concealment study. The surface lies at temperatures of approximately 465C under pressures of approximately 90 times that of the Earth and clouds composed of sulfuric acid, making the study of planetary geology only possible with radar, gravity and limited number of atmospheric windows. but still the plains of the planet and the vast shield volcanoes still speak an outlines volcanic history, sinuous channels, extensive lava flows, and circular edifices that are volcanic basaltic provinces with stricter physical conditions.
Lava tubes have filled that gap of observation between hypothetical footnote and operating hypothesis with engineering implications. A test of capability of structures under load, known as finite element limit analysis has been applied to Venusian conditions to determine the size of voids that might be left stable. The findings put reasonable tube widths in the range of a “few hundred meters,” and, given good values of rock strength and roof thickness, push maximum widths to around one kilometer. The modeling paper stated in its language that, given the width of the “lava tubes, lavalas of a few hundred meters in width can become stable,” which is significant in light of the fact that the distance of the channel-like structures are already observable in orbit.
That hypothetical celling takes off where Venus offers surface clues of demise. Radar imagery and topography work has recognized curving chains of pits at the sides of large shield volcanoes with a form that runs down slope as expected of ancient lava transport instead of running straight down the slope along tectonic forces. When those pit chains are skylights in filled conductors, they provide an uncommon indirect method of mapping underground architecture without the need to drill: conduits formerly used to take heat and melt over kilometers may now be documented as holes in the roofline.
Another body of evidence also narrows the story: Venus does not seem to be complete. Examinations of Magellan radar data, which is the most recent worldwide, high-resolution survey of Venus, have been employed to assert that surface characteristics have altered amid a repeat survey in the early 1990s. One team reported radar backscatter movement that was linked to new lava flows at Sif Mons and in western Niobe Planitia with approximate flow thicknesses of 3 to 20 meters. In a complementary finding concerned with Maat Mons, time-lapse comparisons of radar images identified the variations of a volcanic vent in the changes of moving molten rock, which strengthened the notion that some, no less than some of the volcanoes of Venus have been working in the geologically recent past.
The systems of underground tunnels and surface change are identical: magma, pressure, and heat transport systems. The presence of tubes at the larger end of the range of stability would suggest extensive, high-volume emplacement of lava that would be able to construct roofs resistant to collapse even in a setting where temperature, chemistry and rock mechanics are no longer typical of Earth basaltic. They also direct to the types of measurements which are relevant next: surface manifestations like pit chains, skylights, and minor mass deficits which manifest themselves as anomalies of gravities.
And there mission design cannot be separated with geology. Orbital radar and gravity mapping can bridge gaps that older datasets failed to bridge: whether pits are over buried conduits, whether the so-called fields of flow are compositionally young, and whether the volcanic plumbing of the planet is concentrated or diffuse. To a world in secret, the reward will not be a single dramatic image but the map of a consistent underground picture the surface of Venus being the thin, flawed lid of some deeper, still running engine.
