Future human space exploration of the Moon and Mars could lead to the study of processes on the surface and subsurface of these planetary bodies in more detail. Nowadays, analogue space missions on Earth are used to prepare humanity for the challenges that will need to be overcome in order to settle on the Moon or Mars. The Hawaii - Space Exploration Analog and Simulation (HI-SEAS) habitat, is one of the places where these types of missions are performed. The habitat is located on the volcano Mauna Loa (Hawaii). Currently, operations of simulated missions at HI-SEAS are coordinated by the International MoonBase Alliance (IMA), an organization dedicated to building a Moon base prototype in Hawaii and ultimately a real settlement on the Moon. During the EMMIHS-1 campaign, a two week analog mission to the Moon was performed from the 20th of February till the 6th of March 2019. EMMIHS-1 was the first of a series of analogue Moon missions at the HI-SEAS habitat, as part of the EuroMoonMars program. Results of the simulated missions contribute to the understanding of how to properly build a Moon base on the lunar surface in the near future and what research still needs to be performed in order for humans to return to the Moon. Part of the lunar simulation was focused on how to do geological fieldwork despite the limitations of the analog spacesuits. This included the field research of secondary mineralization inside lava tubes and the hydrous alteration of lava flows. The research was conducted wearing analog spacesuits during extra vehicular activities (EVAs) with basic geological equipment and a drone. Infrared spectroscopy was applied on all collected samples, as an easy and quick tool for mineral identification. Furthermore, lab-measurements will deliver a better characterization of the mineralogical and elemental content of the samples. Another type of geological research that was performed during the mission was the study of the alteration of the lava flows on Mauna Loa, which can be used as an analogue for the hydrous alteration of basaltic rocks on Mars. Its goal was to help understand the surface processes on the red planet. Furthermore, the samples collected from within the lava tubes can help determine the impact of biogeological activity on secondary mineralization within those environments. As lava tubes mimic subsurface conditions of other planetary bodies, the results can be used to help find microbial extraterrestrial life on other planets.@en

Over the past decades, due to an increasing number of successful orbiter and lander space missions, interest in planet Mars experienced an enormous growth. To complement Mars missions, studies using samples from Earth as analogue for Mars contribute to the increasing knowledge about Mars. This study is the first to use basaltic rock samples from the shield volcano Mauna Loa (Hawaii) as Martian analogue for a hydrous alteration study.

First, samples from differently aged lava flows were collected during the EMMIHS-I simulated Moon mission at the HI-SEAS habitat. The HISEAS habitat is situated on the north-eastern flank of the shield volcano Mauna Loa (Big Island, Hawaii). In order to obtain the most representative samples, only the top 10 cm of horizontally emplaced pahoehoe lava flows were sampled in a radius of 6 km around the HISEAS habitat. From the samples, thin sections were analysed using petrographic microscopy, SEM-EDS and SWIR hyperspectral imagery. Combining the datasets from these three methods made it possible to estimate the chemical composition of the present hydrated minerals. Additionally, XRF was used to study the elemental changes along the depth profiles through the samples and calculate geochemical weathering indices. The Hawaiian rocks were then compared to datasets from Mars. The Hawaiian XRF dataset was compared with calibrated APXS data from the Mars Exploration Rovers (MER). Hawaiian mineral spectra obtained using SWIR hyperspectral imagery were compared with remote sensing data from Mars Orbital spacecrafts.

In the field, hydrous alteration can be recognized by the removal of metallic surface layers, presence of brown horizontal surface layers and horizons enriched in ferric iron. The main detected alteration products include Fe,Mg-smectites, hydrated silica, Al-silicates, Al-hydroxide and palagonite. These products formed due to the interaction between meteoric water and basaltic rocks. The calculated geochemical weathering indices indicate alteration and weathering processes acting on the top 2-3 cm of the rock samples from lava flows with ages >400 years. The values indicate the alteration products formed in an arid to semi-arid environment at cold to moderate temperatures.

Comparisons between the Hawaiian datasets and the Martian datasets mentioned in the Methods section [5,6,7,8], show that the alteration products on Mars are similar to the hydrous alteration products found on Mauna Loa. When calculating the already mentioned geochemical weathering indices for the MER datasets, the Martian values indicate a low degree of weathering and alteration processes, similar to the values of the Hawaiian rocks. This suggests that the Martian alteration products formed in a similar environment as the Hawaiian alteration products. These observations are consistent with the assumption of a present active hydrosphere on an early Mars.

This study shows analogies between rock samples from the Hawaiian shield volcano Mauna Loa and Martian datasets in terms of mineralogy and alteration environments. The study suggests the same type of clay minerals as identified on Mauna Loa have formed in an arid to semi-arid environment at cold to moderate temperatures on an early Mars. These findings add to the assumption that Mars once had a more Earth-like climate with an active hydrosphere and relatively thick atmosphere.@en