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'McMurdo' Panorama from Spirit's 'Winter Haven'. Credit: NASA/JPL/Cornell
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Primary Mission Aim

LifeSpringsMars aims to retrieve samples of digitate, nodular hot spring silica structures discovered by NASA’s Spirit Rover in the Columbia Hills, which represent humanity’s best chance to find signs of past life on Mars. 

Have we seen a biosignature on Mars?

In 2007, NASA’s Spirit Rover discovered unusual nodular deposits of opaline silica on Mars which were later found to strongly resemble nodular opaline silica deposits found in hot springs in the most Mars-like environment on Earth, in the Atacama Desert at El Tatio and Tuja, Chile. Both have digitate, or finger-like, protrusions around the outside of the nodular structures and granular-textured, porous bases to at least some nodules.  

Nodular opaline silica deposits: Columbia Hills
Nodular opaline silica deposits: El Tatio

On Earth, it has been demonstrated that these unusual nodular deposits form in the presence of microbes, which become entombed within the silica layers. The digitate structures preserve this type of evidence for primitive microbial life throughout the entire geological record, back to 3.5 billion years ago, in the Pilbara region of Western Australia, where microbially-deposited hot spring deposits have recently been discovered (Djokic et al., 2017, 2021). 

Left: Pancam false-colour image of nodular opaline silica deposits taken by the Spirit Rover at the Columbia Hills, Mars (from Ruff et al., 2011). Right: Nodular opaline silica deposits from Tuja, Chile (from Ruff and Farmer, 2016).

El Tatio digitate silica structures. Credit: Ruff & Farmer, 2016

Microscopic views of El Tatio digitate silica structures. (a) SEM image from a broken off digitate structure, with alternating non-porous and filamentous concentric laminae with porosity. Inset highlights webs of silica-encrusted microbial filaments within porous laminae. Scale bar = 1 mm. (b) SEM image of a surface biofilm community showing silica-encrusted microbial filaments and sheaths, and spindle-shaped diatoms (arrows). Scale bar = 20 mm. (c) Photomicrograph of a transverse petrographic thin section through a digitate structure from El Tatio. Note the palisade fabrics formed by silicified populations of filamentous cyanobacteria (green). Scale bar = 500 µm. (d) Enlarged view from boxed area in c) showing silicified cyanobacteria oriented roughly perpendicular to laminae overlain by laminae containing silica encrusted fine filaments with orientations roughly parallel to laminae. Scale bar = 50 µ m. (From Figure 6 of Ruff and Farmer, 2016)

Leading experts who study these ancient signs of life believe that these hot spring deposits on Columbia Hills are the best target in the search for signs of life on Mars (Ruff and Farmer, 2016; Cady et al., 2018). However, are the digitate features on the opaline silica hot spring deposits on Mars truly microbially mediated, or could they have formed through other processes, such as erosion by water, acidic fluids, or wind-driven sandblasting? 

Our research team is pursuing a more detailed  understanding of these structures, but the only way to confirm a potentially biological origin for the textures of the Home Plate opaline silica deposits is to retrieve these samples from Mars and bring them back to Earth for analysis with the most advanced analytical techniques: this is the primary aim of the LifeSpringsMars mission. 

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