INVESTIGATING ALTERATION CONDITIONS IN LAVA TUBES: ANALOGUE FOR VENUS SURFACE GEOLOGY

Research of the surface geology of Venus through remote imagery and in situ analysis is limited by obstructing atmospheric conditions and temperatures. Emissivity measurements from Venus Express were limited to ~1 µm wavelength in the Near Infrared spectrum, inhibited by the dense carbon dioxide atmosphere. Despite their limitations both landers and remote spectroscopy suggest a surface composition predominantly composed of subalkaline basalt. An exception to this may be Venus’ tesserae which emit lower emissivity, interpreted to be from a more silicic composition. However, emissivity can also be affected by grain size, surface roughness, surface deposits, and surface weathering. This study aims to investigate how the high temperature and atmospheric conditions of Venus could weather basalts at its surface and alter their surface mineralogy, in effect “masking” their bulk compositions from remote sensing techniques. In artificial environments that simulate Venus-like conditions basaltic surfaces oxidize and form new minerals like hematite.

Terrestrial lava tubes may serve as an appropriate Venus analogue to test the effects of high-temperature oxidation conditions. After forming, lava tubes maintain elevated interior temperatures for months to years, during which their interior surfaces often develop a thin hematite veneer. Samples displaying a hematite veneer were collected from lava tubes sourced from Mauna Loa and Kilauea Volcanoes in Hawai’i. Current and ongoing analytical methods include: XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy), and VNIR (Visible-Near Infrared) spectroscopy. This project aims to test whether these surface veneers formed at high temperatures (early during cooling, potentially relevant to Venus surface conditions) or at lower temperatures (through the action of water vapor, less relevant to Venus). XRD data confirms the presence of hematite in the surface layer, VNIR data have not shown the presence of OH bonds on the surfaces of samples (as would be expected if water were involved), and SEM analysis shows a pattern of element distribution consistent with cation migration between the surface and interior. While data collection is still ongoing, results so far support that a high-temperature process is the main oxidizing agent for at least part of the samples.