Chemical Gardens Under Mars Conditions: Imaging Chemical Garden Growth In Situ in an Environmental Scanning Electron Microscope

Abstract

Although we now know that there are no canals on Mars, nonetheless the picture painted by that dramatic illusion of nineteenth-century astronomy and twentieth-century science fiction turns out to be broadly correct: Mars is a desert planet that has gradually lost its water (Kass & Yung, 1995). It is possible that life may no longer be extant on Mars but may have evolved there in earlier geological periods in which liquid water was common on the surface of the planet (Bibring et al., 2006), and it is also possible that there may still exist life on Mars in environments where liquid water persists (Davila & Schulze-Makuch, 2016). These hypotheses underlie the current search for signs of life, either extant or fossil, on Mars (Knoll & Grotzinger, 2006).In the recent past, and even today, morphology has been and is taken as a good indicator for life (Javaux, 2019). It goes without question that if one digs up a dinosaur fossil, that is a reliable indicator that such an organism once lived. But for smaller, particularly for single-celled organisms, morphology is an increasingly unreliable indicator of a biotic origin, because there exist abiotic processes that produce extremely lifelike forms (Livage, 2009). Chemical gardens, so called from their resemblance to biological structures, are one such system (McMahon, 2019) that has been known since the beginnings of chemistry (Glauber, 1646). They are today of interest both because they demonstrate how one might make progress with the nascent technology of non-equilibrium self-assembled materials (Barge et al., 2015), and also because geological chemical gardens found in alkaline hydrothermal vents on Earth may have been the places where life on Earth got started (

Dark-induced vertical growth of chemobrionic architectures in silver-based precipitating chemical gardens

“…Chemical gardens is a term often used to describe inorganic precipitates that resemble plant like growth, and these structures grow within minutes or hours of plunging metal ion salts into anionic solutions. [1][2][3][4][5][6][7][8][9][10][11][12] Though the chemical gardens are entirely composed of inorganic moieties, they have a biologically imitative look arising from their non-equilibrium architectures. The plant like or tube-like precipitation in the chemical gardens is a consequence of the diffusive translocation of ionic species upon osmotic imbalance arising in the reaction mixture.…”

False biosignatures on Mars: anticipating ambiguity

“…This expertise now needs to be translated into a geological and astrobiological context by focusing on the minerals, fluids and pressure-temperature conditions present on Mars today and in the geological past (e.g. Sainz-Díaz et al 2021). Some important theoretical foundations have been laid (e.g.…”

“…Natural chemical gardens could plausibly have formed as a consequence of chemical weathering on Mars (García-Ruiz 2000; García-Ruiz et al 2020;Sainz-Díaz et al 2021). Soluble Fe and Mg sulfate salts have been identified at various martian localities (Johnson et al 2007;Bishop et al 2009;Ojha et al 2015).…”

“…More generally, the copious production of silica-rich fluids on early Mars is attested by the widespread occurrence of hydrated silica deposits in fluviolacustrine and groundwater-influenced settings(Pan et al 2021). It has been shown experimentally that chemical gardens can form even at temperatures and pressures characteristic of Amazonian and present-day Mars, close to the H 2 O triple point(Sainz-Díaz et al 2021).…”

Downward fingering accompanies upward tube growth in a chemical garden grown in a vertical confined geometry

“…17,18 The role of chemical gardens as potential environments to develop life has also been explored for astrobiological applications. [19][20][21][22][23][24][25][26] Chemical gardens have been shown to produce a wide range of precipitate structures, including lobes, spirals, hairs, filaments, worms, flowers, bulbs, plumes, tubes, and fingers. [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] Precipitate colour depends on both the oxidation state of the metal cation and the coordination of water molecules around the precipitate structures.…”