Planetary analog sites in the Indian subcontinent and the Indian Ocean: underexplored environments suited for astrobiological and space research

Astrobiology seeks to understand the origin, evolution, distribution, and future of life in the Universe, focusing on habitability beyond Earth. Due to the high cost and complexity of space missions, studying planetary analog sites on Earth is essential for supporting and de-risking future exploration. These analog sites are extreme terrestrial environments that mirror environmental, geological, geochemical, or biological conditions on other planetary bodies. Investigating how life persists in these settings advances knowledge of extraterrestrial habitability and enables realistic testing of life-detection instruments. This review presents the first comprehensive synthesis of more than 50 planetary analog field sites across the Indian subcontinent and Indian Ocean region. We identify 2 geological regions with active astrobiological research, 4 requiring targeted geochemical and geomicrobiological surveys, and 5 with high planetary relevance but minimal study. We assess how these sites fill gaps in global astrobiological research and evaluate their readiness for future investigations. The sites include high-altitude cryospheric settings such as Himalayan glaciers and permafrost, analogues to Martian and lunar environments; saline-alkaline lakes like Sambhar Lake, comparable to Martian paleolakes; intrabasaltic bole beds in the Deccan Traps, relevant to phyllosilicate formation on Mars; subsurface caves and mines, analogous to lunar lava tubes; and hydrothermal vent systems along the Central and Southwest Indian Ridges, relevant to icy ocean worlds. Comparing these sites to global analogues reveals that, although most are not yet fully characterized, several offer unique environmental combinations. As deep-space missions prepare to search for life beyond Earth, a geographically broader set of analog sites is critical. Highlighting the diversity and scientific value of these under-characterized regions in South Asia and their marine periphery, this review provides a foundation for characterizing previously overlooked planetary analog sites. These sites expand the global analogue parameter space and offer underutilized natural laboratories for planetary habitability and biosignature research.

1 Introduction

Astrobiology explores fundamental questions about the origin, evolution, distribution, and future of life on Earth and beyond (Chyba and Hand, 2005; Marais and Walter, 1999). The search for life outside Earth begins with identifying and characterizing potentially habitable environments. These include Solar System bodies such as Mars, Europa, and Enceladus, as well as on exoplanets orbiting distant stars (McKay, 2022; Kane et al., 2021). Our understanding of how life first emerged and evolved on Earth informs this search. Early life thrived in environments we now call “extreme,” is a designation that reflects an anthropocentric perspective, since these conditions represent physiologically normal habitats for the microorganisms that inhabit them (Merino et al., 2019; Rothschild and Mancinelli, 2001). In extreme environments, microbes can tap into redox active elements (e.g., H, S, Fe, and Mn) for energy, in absence of sunlight and underscoring the possibility of life in dark subsurface habitats beyond Earth (Canfield et al., 2006). They exploit a wide range of electron donors and acceptors, enabling diverse metabolic pathways, allowing them to thrive across a wide range of environmental conditions (Froelich et al., 1979).

Physicochemical extremes, including high radiation, hypersalinity, pressure variations, and nutrient-poor terrains, persist on Earth, defining the boundaries of habitability (Merino et al., 2019; Coleine and Delgado-Baquerizo, 2022). These environments act as planetary analogues, providing natural laboratories to study microbial survival, biosignature preservation, and the potential for life on other planetary enviornments. They are also essential in developing and validating life-detection instruments, refining scientific methods and aiding mission planning through terrain and environmental simulations (Léveillé, 2009; Martins et al., 2017). Recently, the concept of planetary analogues broadened beyond “geological analogues” to include “functional analogues”, which may be natural sites or engineered platforms chosen for their scientific or operational goals, such as petrology, mineralogy, biological processes, or engineering needs (Foucher et al., 2021). This broader view allows for a more strategic integration of analogue environments across mission phases, from instrumentation development to in situ exploration and data interpretation.

International space agencies have identified various terrestrial field sites as astrobiological analogues for planetary bodies like Mars, Venus, the Moon, and icy ocean worlds such as Europa and Enceladus (Supplementary Table 1). Hyperarid deserts and volcanic terrains provide key parallels for Mars and other rocky planets. The Atacama Desert (Chile) is a leading analogue for the UV-intense, arid Martian surface and is widely used to study microbial survival and biosignature preservation (Azua-Bustos et al., 2022; Lebre et al., 2017; Visscher et al., 2020). Similar Mars-like extremes exist in the McMurdo Dry Valleys (Salvatore and Joseph, 2021) and the Tibetan Plateau (Liu et al., 2022; Sun et al., 2018), which combine aridity, cold, and low pressure. Volcanic and hydrothermal systems, such as the Iberian Pyritic Belt (Amils et al., 2007; 2014; Gómez et al., 2011) and Icelandic basaltic terrains (Voigt et al., 2025; Fagents and Thorvaldur, 2007) act as analogues for acidic, mineral-rich environments linked to past Martian hydrothermal activity and Venusian volcanism. Impact structures, like Manicouagan crater (Canada) provide insights into impact-generated habitats relevant to Mars and icy ocean worlds (Spray et al., 2010; Cloutis et al., 2015). For icy ocean worlds, subglacial and deep-sea hydrothermal systems are particularly informative. Antarctic subglacial lakes (e.g., Lake Vostok) (Cassaro et al., 2021) and seafloor hydrothermal systems such as Lost City (Amador et al., 2017) and Gakkel Ridge (Ramirez-Llodra et al., 2023) capture water–rock interaction, chemical energy availability, and isolation expected in subsurface oceans. Despite advances in analogue research, geologically diverse regions in the Indian subcontinent and surrounding ocean remain underexplored. The Indian plate, shaped by complex tectonics and unique extremes (Valdiya, 2016), represents a promising yet overlooked additions to the planetary analogue inventory. Including these sites would broaden the global scope of astrobiology, expand analogue functions, and deepen our understanding of habitability across a wider spectrum of planetary environments.

The Indian subcontinent and the adjoining Indian Ocean offer diverse geological settings ideal for testing hypotheses about the origin and resilience of life in extraterrestrial environments (Figures 1, 2). Despite numerous extreme habitats, these regions are underexplored in astrobiological research due to limited integration of regional geology with planetary science, fragmented collaborations, and practical challenges. Many sites are hard to access, while sustained research is hampered by limited funding. In some geological sites, anthropogenic activity and contamination hinder the preservation of pristine conditions for analogue studies. Nevertheless, these sites remain highly relevant, as their tectonic, mineralogical, and geochemical features preserve natural extremes that parallel planetary environments (Supplementary Tables 2–4; Figures 1, 2). The tectonic collision between the Indian and Eurasian Plates, around 50 Ma (Molnar and Tapponnier, 1977; Jain, 2014; Wu et al., 2023), formed the Himalayas and exposed stratigraphic sequences from the Archean era (4 Ga), including some of Earth’s oldest continental crusts in the Dharwar and Singhbhum cratons (Dey and Jean-François, 2020) and ophiolitic sequences (Bhat et al., 2022). These retain early Earth-like conditions, such as ultramafic rocks, reduced geochemical environments, and minimally metamorphosed sediments. Together, these features make them ideal for studying the emergence of life and the early development of Earth’s atmosphere, oceans, and crust. Geological sites in the Indian subcontinent and nearby ocean relevant to astrobiology include hyperarid zones, evaporitic basins, fluvial channels, volcanic basins, high-altitude ecosystems, geothermal springs, and deep-sea ecosystems. This review foregrounds these underexplored field sites by systematically evaluating their planetary and functional relevance. We emphasize their potential for biosignature detection, expanding habitability regimes, and supporting mission technology development. Recognizing the Indian subcontinent and Indian Ocean as key planetary analogues will broaden astrobiology’s scope and enrich its experimental and operational dimensions.

Figure 1

Figure 1. Planetary analog environments across the Indian subcontinent and the Indian ocean basins that represent planetary bodies of astrobiological interest. Sites are classified according to their research readiness for astrobiological investigations using an asterisk-based scheme: *** denotes well-characterized sites with integrated environmental datasets that enable targeted studies of habitability and biosignatures; ** indicates sites where geological characterization is robust but baseline geomicrobiological surveys are still required to fully establish astrobiological relevance; and * identifies exploratory targets, where preliminary geological or geomorphological evidence suggests planetary relevance but comprehensive characterization is currently lacking.

Figure 2

Figure 2. Schematic representation of extreme environments across the Indian subcontinent and the Indian Ocean that serve as planetary analogues. Terrestrial ecosystems include mud volcanoes, saline habitats, desert sandstorms, glaciers, ophiolites, geothermal springs, high-altitude lakes, and natural caves and mines. Marine ecosystems of the Indian Ocean remain relatively underexplored, with documented sites including deep-sea hydrothermal vents, hydrocarbon seeps, and subsurface trenches. This figure is adapted and inspired by Merino et al. (2019). Sites are classified according to their research readiness for astrobiological investigations using an asterisk-based scheme: *** denotes well-characterized sites with integrated environmental datasets that enable targeted studies of habitability and biosignatures; ** indicates sites where geological characterization is robust but baseline geomicrobiological surveys are still required to fully establish astrobiological relevance; and * identifies exploratory targets, where preliminary geological or geomorphological evidence suggests planetary relevance but comprehensive characterization is currently lacking.

2 Extreme environments as planetary analogues for habitability

Life requires fundamental physicochemical conditions that support metabolism, growth, and reproduction (Falkowski et al., 2008). These requirements are largely derived from Earth, where microbial life is the earliest and most adaptable lifeform (Nealson and Conrad, 1999). While extraterrestrial life may have different chemistry, it is expected to follow universal principles (Benner, 2010; Cockell et al., 2016; Hoehler, 2007; McKay, 2022; Méndez et al., 2021). The most critical requirement is a solvent. On Earth, water’s unique properties, including polarity, heat capacity, and its ability to dissolve diverse compounds, make it indispensable for sustaining life. Thus, planetary bodies and exoplanets that host liquid water, even transiently, are considered prime targets for exoplanet research (Kite and Ford, 2018; Goldblatt, 2015). Another essential requirement is the availability of key elements, carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (CHNOPS), which form the backbone of biomolecules (Rossetto and Mansy, 2022). Microorganisms acquire energy and essential elements from their geochemical environment through redox-active compounds that exist in chemical disequilibrium (Hoehler, 2007). Therefore, planetary bodies with active water-rock interactions can provide the chemical energy needed to sustain life in environments.

Earth’s extreme environments demonstrate how life can persist in harsh conditions. Microorganisms in deserts, deep rocks, hypersaline lakes, and hydrothermal systems (Figure 2) use chemical energy from iron, sulfur, and hydrogen. Their survival under intense radiation, desiccation, or pressure shows that life can exist in dark subsurface habitats on early Earth, Mars, and icy ocean worlds like Europa and Enceladus. These adaptations expand the concept of habitability and provide models for biosignature preservation in energy-limited environments. Microbial strategies are also vital for space exploration. Analogue studies guide planetary protection and inform life-detection instrument design. They show how biology can support long-duration missions. Microorganisms that extract metals from regolith, produce oxygen, or recycle resources enable in situ resource utilization (ISRU) on the Moon, Mars, and beyond (Santomartino et al., 2023; Koehle et al., 2023; Cockell et al., 2024a). Testing these processes under analogue conditions on Earth develops robust bioengineering strategies for off-world survival. Integrating biology-geology systems into exploration is essential for advancing astrobiology and tackling the challenges of human spaceflight.

3 The Indian Plate

The Indian Plate, comprising Archean cratons, Proterozoic mobile belts, Phanerozoic sedimentary basins, large igneous provinces, and tectonically active regions like the Himalayas, preserves a geological record that spans from the Archean to the present (Chaudhuri et al., 2018), hosting extreme environments (Supplementary Table 2; Figures 3, 4). The Archean cratons (3.6–2.5 Ga), including the Dharwar, Singhbhum, Bastar, Aravalli, and Bundelkhand cratons, contain some of Earth’s earliest continental crust and provide key insights into early Earth processes. Stromatolites and banded iron formations in these cratons (Beukes et al., 2008; Mukhopadhyay et al., 2025; Dey and Jean-François, 2020) preserve evidence of microbial activity in an anoxic world, as seen in structures in Venezuela’s orthoquartzite caves (Sauro et al., 2018). The younger Proterozoic mobile belts (2.5–0.5 Ga), include the Aravalli-Delhi Belt, the Eastern Ghats Mobile Belt, and the Central Indian Tectonic Zone, record ocean closures, continental collisions, crustal reworking, Great Oxidation Event (2.4 Ga), and the Neoproterozoic Oxygenation Event (0.5 billion years ago) (Kaiho et al., 2024; Olejarz et al., 2021; Chen et al., 2022). Glaciogenic deposits in these belts show microbial survival during Snowball Earth episodes Precambrian alluvial successions in the Indian plate (Chakraborty et al., 2022), formed before land plants, retain microbial textures and mineral signatures that illuminate early surface processes and serve as extraterrestrial analogs. Astrobiologically, these Precambrian records are valuable for their biosignatures (Barge et al., 2022; Bosak et al., 2021; Chan et al., 2019; Brocks and Summons, 2003), e.g., microfossils, of microbial ecosystems under low-oxygen conditions that have guided the modern search for past life on Earth (Schopf et al., 2017) and to evaluate any evidences of extinct or extant life on Mars (Hurowitz et al., 2025) and icy ocean worlds, e.g., Europa, Enceladus, and Titan.

Figure 3

Figure 3. Geographic distribution of extreme environments, that can serve as planetary analogues, overlaid on a hypsometric map of the Indian subcontinent and adjoining Indian Ocean. The left panel illustrates the regional distribution of terrestrial and marine sites across diverse ecosystems, while the right panel provides a detailed view of the Himalaya and Tibetan Plateau, highlighting clusters of high-altitude and glacial environments. The underlying topography and bathymetry emphasize the environmental gradients that shape the diversity of analogue sites. Geological base map compiled from GEBCO Compilation Group (2025).

Figure 4

Figure 4. Geographic distribution of extreme environments, that can serve as planetary analogues, overlaid on a generalized geological map of the bed rock of the Indian subcontinent. The underlying geological framework (Cenozoic, Mesozoic, Paleozoic, and Precambrian units) highlights the lithological diversity associated with these analogue sites. Geological base map compiled from Wandrey, C.J., 1998, Geologic map of South Asia (geo8ag).

The Phanerozoic era (about 0.5 Ga-present) brought extensive sedimentation in Gondwana basins. From the Late Carboniferous and Jurassic era, these basins preserve fluvial sandstones, coal beds, and fossil-rich strata that track ecosystem evolution during Gondwana’s breakup (Chakraborty et al., 2019). Along the plate’s northern margin, the Tethyan Himalayan Basin accumulated marine sediments from the Cambrian to the Eocene, recording the Tethys Ocean’s history (Liu and Einsele, 1994; Jiang et al., 2016). Phanerozoic strata also record redox changes, from anoxic to sulfidic to oxic conditions, that shape biosignature preservation (Sperling et al., 2021). Lacustrine, fluvial, deltaic, and evaporitic systems in this strata serve as a planetary analogs for Martian sedimentary processes (Lewis and Aharonson, 2014; Grotzinger et al., 2011) during climate transitions (Kite and Susan, 2024), including ancient lake basins (Michalski et al., 2022), fluvial valley networks (Cardenas et al., 2022; Dickson et al., 2020), deltaic fan complexes (Tebolt and Goudge, 2022; De Toffoli et al., 2021; Di Achille and Hynek, 2010), and carbonate-bearing rocks (Wray et al., 2016). While Phanerozoic basins refine biosignature detection methods in post-vegetation ecosystems, Precambrian records remain the best terrestrial analogs for other rocky planetary bodies.

The Deccan Traps, emplaced around 66 Ma during the Cenozoic, form one of Earth’s largest flood basalt provinces and are tied to mantle plume activity and the end-Cretaceous mass extinction (Sen et al., 2009; Beane et al., 1986; Mishra et al., 2024). Deccan basalts, with their basaltic stratigraphy, alteration patterns, and mineralogy, closely parallel Martian terrains like Mawrth Vallis (Craig et al., 2017; Bhattacharya et al., 2016; Greenberger et al., 2012). This analogy is strengthened by the fact that Mars possesses a predominantly basaltic, mafic crust rich in olivine, low- and high-Ca pyroxenes, and plagioclase, overlain by extensive secondary alteration minerals such as Fe/Mg smectites, sulfates, carbonates, chlorides, and perchlorates, assemblages that reflect diverse water-rock interactions across Martian history (Ehlmann and Edwards, 2014). Intrabasaltic bole beds (paleosols) in the Deccan preserve layered phyllosilicates, mirroring those on Mars (Craig et al., 2017). The mafic mineralogy and alteration textures of Deccan basalts and bole beds together provide a strong Earth analog for Mars’s mineral evolution. Deccan’s porous, fractured flows also support diverse iron- and sulfur-based endolithic microbes (Dutta et al., 2019; 2018; Jungbluth et al., 2016), offering direct insights into potential Martian subsurface habitats where mafic weathering and redox gradients could sustain life.

Altogether, the Indian Plate encompasses extreme environments shaped by tectonics, climate, and deep time. From Archean cratons and Proterozoic belts to Phanerozoic basins and Cenozoic basalts, these natural laboratories preserve biosignatures, record planetary transitions, and serve as Earth analogs for extraterrestrial settings, from early Mars to the subsurface oceans of icy ocean worlds such as Europa and Enceladus. Studying biosignatures in these terrestrial settings will constrain type of biosignatures and their survivability, or potential to degrade in Martian equivalents, particularly in clay-rich (Bishop et al., 2018; Gainey et al., 2017; Ehlmann et al., 2008) or iron-rich sediments (Kizovski et al., 2025; Ehlmann and Edwards, 2014).

3.1 Soda and hypersaline lakes

Soda lakes, with high concentrations of sodium, carbonate, and bicarbonate ions, maintain persistently high-pH, alkaline waters. Most occur in endorheic basins, where salts accumulate over geological timescales, creating some of Earth’s most stable extreme environments (Boros and Kolpakova, 2018; Kempe and Kazmierczak, 2011). These lakes supports diverse microbial communities adapted to extreme alkalinity (Zorz et al., 2019; Sorokin et al., 2015; 2014; Jones et al., 1998; Sorokin and Kuenen, 2005). Their high-pH, carbonate-rich chemistry mirrors Archean alkaline basins, making soda lakes strong analogs for early Earth, where similar geochemical gradients and water-rock interactions shaped early metabolisms and prebiotic chemistry (Cohen et al., 2024). These alkaline features also parallel high-pH environments on early Mars (Hurowitz et al., 2023) making soda lakes valuable for evaluating geochemical stability, carbon cycling, and microbial strategies relevant to life on early Earth and other rocky planets. Notable soda lakes include Lake Magadi and Lake Natron (East Africa) (Deocampo and Renaut, 2016), Big Soda and Mono Lake (California, USA) (Cloern et al., 1983; Honke et al., 2019; Kharaka et al., 1984), the Kulunda Steppe lakes (Russia) (Meyer et al., 2008), and lakes of the Cariboo plateau (Canada) (Renaut, 1990). They support dense populations of alkaliphilic and halophilic microbes, including cyanobacteria, sulfur-oxidizing bacteria, and alkaliphilic archaea (Jeilu et al., 2022; Cloern et al., 1983; Humayoun et al., 2003; Rojas et al., 2018; Foti et al., 2008; Sorokin et al., 2014; Zorz et al., 2019). Many of these microbes thrive on anaerobic metabolisms such as fermentation, methanogenesis, denitrification, metal respiration, as observed in the saline lake Sonachi (East Africa) (Fazi et al., 2021). Microbial metabolisms from these analog sites remain viable under Mars-simulated conditions, reinforcing their astrobiological relevance. Laboratory experiments show methanogenic archaea can survive and produce methane under simulated Martian regolith (Kral et al., 2002), pH, pressure, and temperature (Sinha et al., 2017). These findings highlight the significance metabolisms thriving in soda lakes and the potential for similar pathways to persist in Martian subsurface or microhabitat.

Soda lakes in the Indian subcontinent remain underexplored compared to global studies. Key sites include Lonar Crater Lake (1.2 km diameter, 0.14 km depth), formed by a meteorite impact around 37 Ka from a chondritic impactor (Fredriksson et al., 1973; Chandran et al., 2023), is hosted in the basaltic Deccan plane. It hosts microbial communities adapted to high alkaline and saline conditions, including cyanobacteria, purple sulfur bacteria, and archaea (Paul et al., 2016; Paul Antony et al., 2013). The combination of high pH, basaltic geology, and impact-driven hydrology makes Lonar Lake a key planetary analog for Mars (Pandey et al., 2019), where alkaline brines and volcanic terrains occur. Impact craters on Mars provide local habitable environments (Cockell et al., 2024b), capable of sustaining water, supporting microbial metabolisms, and preserving biosignatures. Most notable examples include Gale Crater and Jezero Crater explored by Curiosity and Perseverance. Another significant analogue site is Sambhar Lake in Rajasthan, which is India’s largest inland saline lake and exhibits moderate alkalinity (Sinha and Raymahashay, 2004). Although well known for its salt production and avian biodiversity, Sambhar’s seasonally fluctuating hydrology, episodic flooding and desiccation cycles, and extensive evaporite crusts create steep gradients in salinity, pH, redox state, and water activity, conditions highly relevant to understanding microbial survival strategies in extreme environments. Moreover, unlike Mono Lake’s permanent stratification, Sambhar’s monsoon-driven wet-dry cycling and evaporitic mineral formation provide insights into episodic lacustrine activity relevant to Mars paleolake environments. The documented microbial communities adapted to alkaline conditions (pH 9–10) and seasonal desiccation (Sahay et al., 2012; Pal et al., 2020) enable biosignature preservation studies under carbonate-precipitating conditions. These characteristics also make Sambhar Lake, a valuable analog for Martian evaporitic basins and liquid brine environments (Chevrier and Slank, 2024), where fluctuating water availability, salt concentration, and pH shifts may have constrained habitability and influenced biosignature preservation. Taken together, both these lakes provide a complimentary setting for exploring alkaline geochemistry, microbial adaptation, prebiotic chemistry, and biosignature preservation in extreme saline-alkaline settings.

3.2 Dust storms of arid desert

The hot, arid regions of the Thar and Cholistan Deserts serve as valuable terrestrial analogues for planetary research, particularly for understanding Martian surface processes, including dust storms (Wang and Richardson, 2015; Leovy et al., 1973). These deserts, characterized by intense solar radiation, extreme temperature fluctuations, and low water availability, experience frequent mineral dust storms that reduce visibility, alter sediment textures, and drive significant aeolian transport (Middleton et al., 1986; Jain et al., 2025). Airborne dust influences planetary climate, habitability, and the remote detection of biosignatures (Boutle et al., 2020). Dust storms offer a means to evaluate how dust loading, particle composition, and scattering affect remote sensing signals, improving biosignatures detection strategies for Mars and other rocky planetary surfaces. Although the fluid dynamics of dust storms are similar on Earth and Mars, the mineralogical and chemical composition of dust differs. Thar desert dust contains up to ∼10% iron oxides (Mishra and Tripathi, 2008), while Martian dust is nearly twice as iron-rich (Berger et al., 2016), reflecting the iron-rich Martian basaltic regolith. Terrestrial dust storms transport microbial cells, as shown by Asian dust reaching Japan (Yamaguchi et al., 2012), Saharan dust plumes (González-Toril et al., 2020), and dust carried across the United States (Barberán et al., 2015). These findings raise questions about microbial survival during atmospheric transit and the possibility of long-range intraplanetary dispersal (Amato et al., 2023). Understanding dust-driven microbial dispersal on Mars is essential for assessing habitability and managing planetary protection risks.

Airborne microbial communities in the Thar and Cholistan deserts remain unstudied; most research focuses on soils, dunes, and rock surfaces (Rao et al., 2016; Parihar et al., 2022; Fatima et al., 2019). To address this gap, predictive models and automated samplers deployed before dust events or used to collect post-storm dust are needed. Microbial communities in the Thar and Cholistan exhibit adaptations such as spore formation, DNA repair mechanisms, and metabolic flexibility, which enable survival under nutrient-poor and water-limited conditions. These traits, along with the preservation of organic compounds in dry sediments, make the region a natural laboratory for refining relevant life-detection strategies. Finally, the geomorphology of the Thar and Cholistan, characterized by active dune fields, evaporite crusts, and silicate-rich sediments, provides an ideal test bed for assessing rover mobility, autonomous navigation, and remote-sensing technologies intended for surface operations on the Moon, Mars, and potentially Titan, where dune morphologies have been observed by Cassini (Radebaugh et al., 2008).

3.3 Natural caves and unused mines

Caves and lava tubes on Mars and the Moon protect against intense radiation, temperature extremes, and surface hazards. The Martian surface is exposed to strong cosmic and solar radiation (Matthiä et al., 2016), wide temperature swings, and frequent dust storms that alter surface chemistry and hide biosignatures (Dartnell et al., 2007). The lunar surface is even harsher, lacking atmosphere and experiencing severe temperature changes, constant micrometeorite impacts, and abrasive regolith (Benaroya, 2017). Caves provide stable microenvironments where ice, hydrated minerals, and volatiles persist, shielding organic molecules and biosignatures from radiation. These protected settings are ideal for deploying life-detection instruments, recovering well-preserved samples, and assessing habitability on Mars, the Moon, and other rocky bodiess (Blank, 2018; Boston et al., 2001; Léveillé and Datta, 2010). Extensive cave networks, including lava tubes and pit craters, have been identified on Mars and the Moon; some lunar caves maintain stable temperatures suitable for habitation (Sauro et al., 2020). Earth-based caves thus serve as planetary analogues, enabling studies of biosignature preservation, microbial-mineral interactions, and the effect of long-term darkness. Karst caves on Earth form as groundwater dissolves soluble rocks such as limestone, dolomite, and gypsum (Waele and Gutiérrez, 2022), host diverse extremophilic microorganisms, many relying on chemolithoautotrophy and adapted to low-nutrient condition (Gabriel and Northup, 2013; Zhu et al., 2022; Turrini et al., 2024). Lava tubes are also key sites for testing robotic exploration technologies (Morrell et al., 2024). Globally, several caves have astrobiological significance. The Movile Cave in Romania, an oxygen-poor ecosystem, sustains microbial communities based on sulfur chemolithotrophy as well as methanogenesis, methanotrophy, and methylotrophy (Hutchens et al., 2004; Chen et al., 2009; Wischer et al., 2015). Lechuguilla Cave in New Mexico harbors antibiotic-resistant microbes preserved in pristine conditions, providing insights into the evolution of the deep biosphere (Cunningham et al., 1995). The Frasassi Caves in Italy support sulfur-cycling microbial mats that exemplify metabolisms relevant to extreme environments (Macalady et al., 2006; 2007). In the Indian subcontinent, Borra Caves, Krem Phyllut, Mawsmai, and Kotumsar Cave (Chhattisgarh) are predominantly karstic limestone systems formed through carbonate dissolution.(Baskar and Ramanathan, 2022; Baskar et al., 2011; 2009), are promising analogue sites. They feature speleothems, subterranean drainage, and redox-stratified microenvironments. Their microbial communities rely on chemoorganotrophy from external organic inputs and chemolithotrophy, including sulfur oxidation and iron cycling, supported by water-rock interactions. Borra Caves and Kotumsar Cave experience strong monsoon-driven fluctuations in redox, hydration, and sedimentation. These dynamic settings offer a unique opportunity to assess whether mineral-bound organics, isotopic signatures, and textural biosignatures persist under repeated disturbance rather than requiring long-term stability. Mars likely saw similar intermittent subsurface habitability driven by obliquity shifts, transient melting, or episodic brine activity. Indian cave systems thus serve as valuable analogues for evaluating biosignature preservation after non-continuous habitable phases on Mars.

Beyond natural caves, unused and decommissioned mines provide valuable subsurface laboratories for astrobiology by granting engineered access to depths that mimic Martian subsurface conditions, such as elevated pressure, low nutrient availability, and limited radiation. These settings serve as analogues for studying how microbial communities survive, metabolize, and interact with minerals under planetary subsurface conditions. Globally, several mines have been repurposed for science: the Sanford Underground Research Facility (formerly Homestake gold mine, USA) hosts laboratory for subsurface research (Rowe et al., 2021; Osburn et al., 2019; Jangir et al., 2019; Heise, 2015); the Boulby Underground Laboratory (UK) supports planetary science and microbiology research in a potash mine (Wadsworth et al., 2020; Cockell et al., 2019; Payler et al., 2019); the Canadian Underground Research Laboratory revealed biofilm-associated minerals in granite (Brown et al., 1994); the Soudan mine (USA) has yielded diverse iron-oxidizing and -reducing microbes (Hsu et al., 2024; Badalamenti et al., 2016; Edwards et al., 2006); and deep mines in South Africa have produced groundbreaking discoveries of microbial taxa thriving in high-pressure conditions (Gihring et al., 2006; Onstott et al., 1997). Similar opportunities also exist in Indian subcontinent. The Kolar Gold Fields in the Dharwar Archean craton (Siddaiah and Rajamani, 1989; Reddy et al., 2017), sections of the Paleoproterozoic regions hosted in Jaduguda uranium mines in the Singhbhum shear zone (Pal et al., 2011), the Zawar zinc mines in Rajasthan, and the Malanjkhand copper mine in Madhya Pradesh (Pandey et al., 2007; Equeenuddin et al., 2017; Sikka, 1989) expose diverse lithologies and complex geochemical settings. These environments are ideal for investigating extremophile microbial communities, biogeochemical cycling, and biosignature preservation. Repurposing such sites as underground laboratories would enable studies of water-rock interactions hosting microbial life, radiation shielding strategies, and life-support simulations.

3.4 Terrestrial mud volcanoes

Mud volcanoes (MVs) are dynamic features found in compressional tectonic settings, both marine (Napoli et al., 2025) and terrestrial (Milkov, 2000). They vent fluids and fine-grained sediments rich in CO_2, CH₄, and other hydrocarbons (Mazzini and Etiope, 2017), forming morphologies from low mud flows to steep cones (Kopf, 2002; Dimitrov, 2002). By transporting clay-rich sediments, rock fragments, and deep subsurface microorganisms, MV’s offer unique opportunities to study extremophiles and their metabolic networks in fluid- and mineral-rich habitats (Ijiri et al., 2018; Lee et al., 2018; Rajendran et al., 2025). Marine MVs have been well studied, revealing essential syntrophic interactions for microbial survival between anaerobic methanotrophs (ANMEs) and sulfate-reducing bacteria, reminiscent of Early Earth ecosystems (Orphan et al., 2001; Lösekann et al., 2007; Pachiadaki et al., 2011; Lee et al., 2018; Omoregie et al., 2008; Ruff et al., 2019; Niemann et al., 2006). Terrestrial MV’s, now gaining attention (Miyake et al., 2023; Merkel et al., 2021; Tu et al., 2017), are more accessible sites providing critical information regarding the limits of Earth’s deep biosphere. They can also be employed for interpreting methane emissions and mud-like morphologies on Mars (Krýza et al., 2025; Komatsu et al., 2016; Skinner and Adriano, 2009; Hosein et al., 2014). Pitted cone (‘mud-volcano like’) features, on Mars, are extensively mapped (Mills et al., 2024), suggesting sites where past subsurface volatile or sediment mobilization may have supported extreme microbiomes.

Prominent terrestrial MVs are found in the Makran accretionary prism, including the Hingol complex, Gwadar, Ormara, and Lasbela, where large cones like Chandragup I (∼90 m) periodically discharge methane-rich fluids and fine sediments In the northern Andaman forearc basin, regional compression, overpressured shales, and mass-transport deposits drive MV formation (Ankush and Sriram, 2024; Ray et al., 2013; Kumar et al., 2021; Chaudhuri et al., 2012). Andaman Island MVs emit methane-rich gases, water, and mud breccia, sometimes erupting after seismic events. Microbial studies in the Andaman and Nicobar MVs have identified broad bacterial and heterotrophic communities (Amaresan et al., 2018; Meena et al., 2023; Manna et al., 2021), but targeted enrichment of extremophiles native to reduced, methane- and hydrocarbon-rich environments remains limited.

4 The Himalayan range

The Himalayan and adjoining mountain ranges, the Third Pole, are the highest terrain on Earth (altitude: 4 km, area: ∼595,000 km²), and host extreme environments including glaciers, natural caves, geothermal springs, saline ecosystems, and ophiolites (Supplementary Table 3; Figures 3, 4). The origin of the Himalayan range lies in the ongoing collision between the Indian and Eurasian plates, which began around 50 Ma ago, uplifting the Tethys Ocean floor and producing the world’s tallest mountains. The Himalayan range hosts ophiolites, glaciers, permafrost, and geothermal systems, forming a diverse natural laboratory. These environments allow investigation of water-rock reactions, carbon fluxes, microbial adaptations, and biosignature preservation under extreme conditions, offering analogues highly relevant to early Earth and potentially habitable planetary settings.

4.1 Ophiolites

The Himalayan tectonic setting preserves fragments of ancient oceanic lithosphere in the form of ophiolites, which are emplaced sections of oceanic crust and mantle typically found within suture zones (Kelemen et al., 2023; Coleman, 1977; Dickinson, 1971). Ophiolites are frequently composed of peridotite, gabbro, and basalt, displaying evidence of alteration by seawater. Serpentinization of ultramafic rocks in ophiolites, results in generation of hydrogen, methane, and other reduced compounds that provide chemical energy for microbial life (Klein et al., 2013; McCollom and Bach, 2009; Moody, 1976). These processes are central to understanding how water-rock interactions sustained early life on Earth (Schwander et al., 2023) and how biosignatures might be preserved in mineralized fractures, offering analogues for habitable environments on Mars (Emran et al., 2025; Schulte et al., 2006; Oze and Sharma, 2005) and seafloor environments of icy ocean worlds such as Europa and Enceladus (Ramkissoon et al., 2025; Melwani Daswani et al., 2021; Taubner et al., 2018; Holm et al., 2015; Guo and Eiler, 2007). On Mars, serpentinization and fracture-hosted fluid circulation are predicted to occur in the ancient crust, where subsurface water-rock reactions could have generated hydrogen and methane, and established redox gradients capable of supporting chemolithotrophic life. Similarly, Europa and Enceladus are thought to harbor global subsurface oceans in contact with ultramafic seafloors; here, ongoing hydrothermal alteration, fluid circulation, and potential venting may create energy-rich environments conducive to microbial metabolism. In both planetary settings, mineralized fractures and precipitates may trap chemical or isotopic signatures, making ophiolite systems powerful Earth analogues for assessing where and how such biosignatures might be preserved.

The well-preserved Oman (Semail) Ophiolite remains the most complete section of oceanic lithosphere exposed on land, making it a global benchmark for studying oceanic crust formation, alteration, and serpentinite-hosted microbial ecosystems (Rempfert et al., 2023; 2017; Lima-Zaloumis et al., 2022; Fones et al., 2019). Across South Asia, ophiolite remnants of the Neo-Tethys Ocean occur along the Indus Suture Zone in Ladakh and Pakistan, the Indo-Myanmar ranges, the Indus-Tsangpo belt in Tibet, and the Andaman Islands (Villalobos-Orchard et al., 2025; Bhat et al., 2022; Ullah et al., 2020; 2023; Jalil et al., 2023; Pedersen et al., 2010). Methane was associated with lamellar clinoenstatites, as determined by Raman spectroscopy, included in the orthoenstatites of ultra-high-pressure peridotite of Nidar Ophiolites (Indus Suture Zone) (Das et al., 2017; Sachan et al., 2007). This association strongly implicates serpentinization-related processes as a source of reduced carbon and H₂, two key energy carriers that can sustain chemolithoautotrophic life in the absence of sunlight. Such geochemical conditions closely parallel those inferred for subsurface hydrothermal systems on early Mars and for the rock-water interfaces at the seafloors of Europa and Enceladus, where serpentinization is thought to generate H₂- and CH₄-rich fluids. Despite this promise, biosignature investigations within South Asian ophiolites, including Nidar, remain extremely limited, particularly with respect to microbial community structure, metabolic pathways, and mineralogical preservation of biological or abiotic methane signatures. Systematic geomicrobiological studies integrating mineralogy, isotopic analyses, organic geochemistry, and microbiology at Nidar could therefore provide critical constraints on the biogenic versus abiogenic origins of methane, the habitability of ultramafic systems, and the detectability of biosignatures in serpentinized crust. As such, the Nidar ophiolite represents a strategically important but underexplored planetary analogue site for evaluating methane-based habitability and rock-powered life beyond Earth.

4.2 Cryosphere

The Himalayan cryosphere holds the largest ice volume outside the polar regions (Bolch et al., 2012), encompassing valley and cirque glaciers, ice caps, glacial lakes, permafrost zones, and alpine wetlands. Glacier-fed lakes and streams are major carbon sources, emitting up to 1746 ± 139 mg C m⁻² d⁻¹ and 1960 ± 176 mg C m⁻² d^-1, primarily through dissolved inorganic carbon fluxes (Shukla et al., 2023). As glacial lakes expand, they become prime sites to study microbial survival, metabolism, and biosignature preservation in cold, carbon-rich, UV-exposed settings analogous to early Earth and icy ocean world, like Titan. Glaciers, permafrost, and subglacial zones are considered as planetary analogues to icy habitats on Mars, Europa, and Enceladus (Garcia-Lopez and Cid, 2017). Terrestrial glaciers mimic Europa’s ice shell with low temperatures, limited liquid water, strong UV exposure, and increasing radiation shielding with depth. Permafrost resembles the frozen near-surface layers of Mars, where cold, arid, and oligotrophic conditions favor long-term microbial and organic molecule preservation. Subglacial ecosystems, sustained by chemolithotrophy in the absence of sunlight, model potential habitable zones beneath Europa’s and Enceladus’s ice-covered oceans, where water–rock interactions may generate redox gradients supporting life. Microorganisms here are polyextremophiles, tolerating low temperatures (Margesin and Miteva, 2011; Cavicchioli, 2016), high radiation (Zhang et al., 2023), desiccation (Marks et al., 2025), nutrient limitation. Many rely on chemolithotrophic metabolisms, such as sulfur, methane, and iron oxidation or reduction, for sustenance or growth under subglacial conditions where sunlight is absent (Anesio et al., 2017; Bourquin et al., 2022). Himalayan glaciers (Stres et al., 2013; Venkatachalam et al., 2015; Rafiq et al., 2017; Kumar et al., 2019; Dhakar and Pandey, 2020; Singh et al., 2024) and rivers (Paudel Adhikari et al., 2019; Suyal et al., 2022) host rich assemblages of such psychrophilic and oligotrophic taxa, including organisms capable of degrading complex organic substrates and accessing energy from recalcitrant carbon pools (Sanyal et al., 2018; Ali et al., 2025). These adaptations closely parallel those proposed for life on icy planetary bodies, making Himalayan extremophiles valuable models for studying biosignature production, metabolic flexibility, and prebiotic chemistry under cryogenic, high-radiation, and energy-limited conditions.

4.3 Geothermal systems

Geothermal systems (hot springs) further expand the Himalayan analogue landscape by providing environments shaped by hydrothermal circulation, water-rock interactions, and chemically enriched fluids-conditions analogous to early Mars and ocean-world hydrothermal systems. These hot springs, characterized by elevated temperatures, variable alkalinity, and carbonate- or silica-rich fluids, support thermophilic and chemotrophic microbial communities and are plausible sites for prebiotic chemistry, as they generate redox gradients and concentrate organic precursors. Terrestrial geothermal (hot) springs with natural wet-dry cycling are also thought to be more conducive to prebiotic polymerization and protocell formation than deep-sea hydrothermal vents, making them strong analogues for early Earth and Mars environments (Westall et al., 2018; Des Marais and Malcolm, 2019; Deamer and Georgiou, 2015). On Mars, mineral evidence of carbonates, phyllosilicates, and opaline silica suggests past alkaline hydrothermal fluids interaction with the crust (Hurowitz et al., 2023), highlighting terrestrial geothermal (hot) springs as planetary analogues for understanding habitability and biosignature formation on ancient Mars. In the Himalayan region, geothermal systems such as the Puga (Roy et al., 2020a; Roy, et al., 2020b; Mondal et al., 2022), Chumathang (Anu et al., 2024), Panamik (Mondal et al., 2022; Choudhary et al., 2024) hot springs host diverse phototrophs and chemotrophs thriving on sulfur-, iron-, and hydrogen-based metabolisms (Ansari et al., 2025). Their mineral precipitates, including silica sinters and carbonate deposits, provide promising substrates for biosignature entombment and preservation, analogous to hydrothermal deposits targeted by Mars rover missions. Beyond hot springs, the Himalayan region also hosts alkaline and saline lakes such as Tso Kar, Kyagar Tso, and Tso Moriri, influenced by geothermal inputs and experience strong seasonal and climatic variability. These lakes offer complementary opportunities to investigate biosignature preservation in brine-rich systems, including the stability of organic compounds and microbial textures under fluctuating salinity and redox conditions (Pandey et al., 2020). Collectively, Himalayan geothermal systems and associated alkaline lakes constitute an underexplored but highly valuable natural laboratory for studying hydrothermal habitability, prebiotic chemistry, and biosignature formation and preservation, with direct relevance to ancient Mars.

5 The Indian Ocean

The Indian Ocean formed during the breakup of Gondwana in the Mesozoic, with seafloor spreading initiating along the Carlsberg and Central Indian ridges around 140–120 Ma (Gaina et al., 2007; 2015), hosts many deep-sea vents, hydrocarbon seeps, and, trenches for exploration (Supplementary Table 4; Figure 3). Its rock record preserves key tectonic and magmatic features, including slow- to ultra-slow spreading ridges, fracture zones, seamount chains, and thick sedimentary sequences influenced by the Himalaya and monsoonal systems. Together, these archives document the evolution of oceanic lithosphere, plate reorganization, and paleoceanographic change across the Cenozoic. Within the Indian Ocean, oxygen-depleted habitats, including hadal trenches, hydrothermal systems, and cold seeps, provide valuable analogues for extraterrestrial environments.

5.1 Deep-sea hydrothermal vents

Deep-sea hydrothermal vents found along mid-ocean ridges allow seawater to circulate through fractured crust and interact with hot rocks heated by underlying magma, forming a hydrothermal system (Le Bris et al., 2019). These environments replicate extreme conditions expected on icy ocean worlds such as Europa and Enceladus, including persistently low temperatures, high pressures, shielding from surface radiation, and chemical disequilibrium generated via water-rock interactions (McClain et al., 2022; Aguzzi et al., 2024). They also mirror the chemical energy sources anticipated on these worlds, such as hydrogen, methane, and reduced metals generated through water-rock interactions, making them valuable analogues for evaluating potential habitability and biosignature preservation in deep, radiation-protected icy environments. These systems function as natural laboratories for developing and testing strategies for biosignature production and life detection in extraterrestrial oceans (George, 2020; German et al., 2022) as they sustain microbial communities reliant on chemosynthesis rather than photosynthesis (Ricci and Greening, 2024; Sogin et al., 2020; Dick, 2019). Evidence for hydrothermal activity within the subsurface oceans of icy ocean worlds (Porco et al., 2006; Zimmer et al., 2000) comes primarily from plume analyses and geochemical signatures. On Enceladus, the detection of silica nanoparticles and salts in plume material (Sekine et al., 2015; Hsu et al., 2015) strongly suggests ongoing water-rock interactions at hydrothermal temperatures. For Europa, observations of surface chlorides and inferred ocean-rock exchange processes provide indirect support for similar interactions within its subsurface ocean (Trumbo et al., 2019; Lowell and Myesha, 2005; Barrett and Lutz, 2025). Moreover, the detection of water together with trace amounts of CO₂, H₂, CO, N₂, and complex hydrocarbons in Enceladus’s plume provides key geochemical evidence for water-rock interactions capable of supporting methanogenic reactions (Taubner et al., 2018). These findings collectively indicate that conditions conducive to chemolithotrophic metabolisms, including methanogenesis (Holden and Harita, 2023; Lyu et al., 2018), may exist on both moons. The ongoing Europa Clipper mission aims to further constrain Europa’s subsurface composition, chemistry and ocean-seafloor interactions (Pappalardo et al., 2024).

Deep-sea hydrothermal vents on Earth span a broad thermal range, from low-temperature diffuse flows (<50 °C) to high-temperature “black smokers” (>350 °C). In contrast, hydrothermal systems on icy ocean worlds are expected to operate at more moderate temperatures. Some models allow for transient magmatic heating on Europa that could briefly generate high-temperature fluids (>150 °C) (Běhounková et al., 2021), while others suggest fluids at ca. 100 °C (Travis et al., 2012; Trinh et al., 2023). On Enceladus, plume chemistry indicates water-rock interactions at similarly moderate temperatures (ca 90 °C), sufficient to drive serpentinization and hydrogen production (Choblet et al., 2017; Sekine et al., 2015). The Indian Ocean Ridge System, subdivided into the Central (CIR), Southwest (SWIR), and Southeast Indian Ridge (SEIR), is a slow- to ultra-slow spreading system hosting diverse vent fields. On the Central Indian Ridge (CIR), notable sites include Kairei and Edmond (Van Dover et al., 2001), Solitaire, Dodo (Nakamura et al., 2012), and Onnuri (Lim et al., 2022). Along the Southwest Indian Ridge (SWIR), key fields include Mount Jourdanne (Münch et al., 2001), Longqi (Tao et al., 2012), Duanqiao (Yang et al., 2017), Tiancheng (Zhou et al., 2018), Old City (Lecoeuvre et al., 2021), and Carlsberg ridge (Qiu et al., 2021; Liang et al., 2023; Cai et al., 2024). The Southeast Indian Ridge (SEIR) hosts the Pelagia vent field (Han et al., 2018). These fields exhibit variable geology, from basaltic to ultramafic hosts, supporting rich mineral formations including massive sulfides, iron-oxyhydroxides, barite, and talc (Perez et al., 2021; van der Most et al., 2023; Thomas et al., 2024; Ta et al., 2024). Microbial studies using isolations, 16S rRNA sequencing, and metagenomics reveal assemblages adapted to vent-specific gradients in fluids, chimneys, and plumes (Li et al., 2016; Huang et al., 2023; Adam-Beyer et al., 2023; Namirimu et al., 2022; Wee et al., 2021; Bai et al., 2021; Han et al., 2018; Ding et al., 2017; La Duc et al., 2007). Thermophiles and chemolithoautotrophs drive sulfur, iron, and methane cycling (Zhong et al., 2022; Cao et al., 2014; Surya Prakash et al., 2025; Wee et al., 2021). These ecosystems highlight metabolic diversity relevant to potential chemolithotrophic life on icy ocean worlds. Unlike the extensively studied Mid-Atlantic Ridge and East Pacific Rise, vent fields along the Central, Southwest, and Carlsberg Ridges occur across a wide range of spreading rates and mantle source compositions, potentially generating hydrothermal fluids with different redox states. These differences are relevant to models of ocean-rock interaction on icy ocean worlds, where variability in mantle composition, heat flux, and fluid circulation is expected. However, despite being active vent systems on a major global ridge network, Indian Ocean vents remain comparatively less explored relative to other ocean basins. Targeted investigation of Indian Ocean vent systems can therefore refine interpretations of chemical and potential biological signals expected from the subsurface oceans of Europa, Enceladus, and other icy ocean worlds.

5.2 Hydrocarbon seeps

Hydrocarbon seeps occur where deeply derived geofluids migrate upward and discharge on the seafloor. In contrast to hydrothermal vent systems, the fluids released at seep sites could range from 2 to 30 °C and circumneutral pH conditions (∼7), Hydrocarbon seeps host life can thrive on chemical energy derived from methane, hydrocarbons, and associated redox gradients (Joye, 2020). These metabolic strategies are directly applicable to several planetary bodies where hydrocarbons or methane-rich fluids are expected to occur, including Titan, with its extensive organic lakes (Hayes, 2016; Stofan et al., 2007); Enceladus and Ganymede, where plume analyses indicate hydrocarbons and potential serpentinization-derived gases (Taubner et al., 2018; Sekine et al., 2015; Tosi et al., 2024); and Europa’s subsurface oceans could host hydrocarbon-bearing or reducing environments (Mishra et al., 2025) capable of supporting similar biochemical pathways. Globally, hydrocarbon seep systems are actively studied as analogues for these extraterrestrial settings, particularly those in the Gulf of Mexico (Bernard et al., 1976) and the Black Sea (Schmale et al., 2005), where methane seepage, gas hydrates, and chemosynthetic communities provide insights into carbon cycling, energy availability, and biosignatures preserved in authigenic carbonates, sulfide minerals, and barite. These well-characterized sites form key reference points for interpreting the habitability of hydrocarbon-rich planetary bodies.

Hydrocarbon seeps in the Indian Ocean, including Krishna-Godavari Basin, Mahanadi Basin, Kerala-Konkan basin (Pillutla et al., 2024; Kumar et al., 2014) and recently discovered sites in the Mannar region (Singh and Srinivasa Rao, 2021; Ghosh et al., 2025), represent an important and expanding set of analogue environments. These seep systems, with a methane flux ranging below 5 mM (Ghosh et al., 2025), span hydrate-bearing sediments, and fault-mediated fluid conduits, and may support microbial consortia adapted to anaerobic methane oxidation and sulfur cycling. Their geological diversity, active hydrocarbon fluxes, and microbially mediated mineralization processes offer valuable opportunities for examining hydrocarbon-based life and organic preservation mechanisms. These Indian Ocean seep systems therefore offer opportunities to address how sustained but low-temperature methane fluxes structure microbial ecosystems, which mineral phases best preserve methane-derived biosignatures, and how biosignature formation and preservation differ between hydrate-associated and fault-controlled seep environments. Compared to the extensively characterized Gulf of Mexico seeps, Indian Ocean systems remain comparatively underexplored, underscoring their value as complementary analogue sites for testing the robustness and context-dependence of methane-based habitability models.

5.3 Deep-sea trenches

Deep-sea trenches are the deepest depressions on Earth’s seafloor. Hadal trenches (Jamieson, 2020; Jamieson et al., 2010), at depths greater than 6,000 m, offer additional insights into microbial survival under extreme hydrostatic pressure, low temperature, and limited nutrients (Tyler, 2003; Jørgensen and Boetius, 2007). Redox stratification within trench sediments produces distinct oxic, nitrogenous, and ferruginous zones (Luo et al., 2018; Schauberger et al., 2021), and pressure effects may even induce anaerobic metabolism in otherwise oxic conditions (Yang et al., 2024). Until today, the Mariana Trench remains the most studied hadal site, with work on geomorphology, geochemistry, microbial adaptations, and autonomous sampling technologies revealing that nearly 89% of recovered microbial taxa remain unclassified (Dietrich et al., 1978; Kato et al., 1998; Tarn et al., 2016; Nunoura et al., 2018; Liu et al., 2019; Li et al., 2021; Xiao et al., 2025). Other key trenches include the Japan, Izu-Ogasawara (Hiraoka et al., 2020; Arakawa et al., 2005), and Kermadec systems (Zhang et al., 2024). Recent discoveries in the Kuril-Kamchatka and Aleutian Trenches revealed chemosynthetic communities spanning 2,500 km at depths exceeding 9 km (Peng et al., 2025). The Indian Ocean hosts the Sunda (Java) Trench, that reaches hadal depths and has remained largely unsampled for decades (Jamieson, 2020). A 2019 expedition using a full-depth submersible revealed diverse habitats and microbial-associated features, including putative chemolithoautotrophic bacterial mats, underscoring the urgent need for targeted exploration of this trench to understand extreme microbial ecosystems better (Jamieson et al., 2022).

To maximize the astrobiological relevance of deep-sea research, Earth-based studies must be explicitly linked with models of extraterrestrial hydrothermal environments. Laboratory pressure reactors simulating icy ocean world conditions allow controlled investigations of microbial survival, metabolism, and biosignature production. Observations of plume chemistry and dynamics at Earth’s vents may also refine strategies for remote sensing of plumes on icy ocean worlds. Expanded exploration of Indian Ocean environments with autonomous submersibles and robotic platforms will not only deepen understanding of microbial survival strategies and biogeochemical processes but also provide critical test beds for technologies being developed for space missions (Feng et al., 2022; O’Neill, 2021; Li et al., 2021).

6 Scientific gaps within the astrobiology community

The planetary environments compiled in Supplementary Table 5 encompass a diverse set of environmental conditions across the Solar System and demonstrates how geological sites in the Indian subcontinent and Indian Ocean can provide a robust framework for comparative astrobiology. Each analogue system represents only a subset of environmental variables relevant to its extraterrestrial counterpart and must be interpreted within those limits. For example, hyper-arid deserts like the Atacama and Thar simulate Martian desiccation and dust-driven sediment transport, but their temperature ranges (−6 °C–50 °C) are much warmer than those on Mars (−130 °C–20 °C) (Atri et al., 2023). The Deccan Traps offer mineralogical and textural parallels to lunar lava tubes but lack the vacuum, micrometeoroid impacts, and space-weathering of airless bodies. Deep karst systems in Meghalaya or Deccan cavities can mimic the stable microclimates of lunar lava tubes but do not reproduce low gravity or vacuum. Hydrocarbon seeps in the Indian Ocean give insight into methane-driven microbial metabolisms relevant to icy ocean worlds such as Titan (Mastrogiuseppe et al., 2019; Hayes, 2016), but no terrestrial site matches Titan’s cryogenic methane-ethane lakes. Himalayan cryospheric zones simulate freeze-thaw and subsurface ice dynamics but cannot replicate the atmospheric pressure, radiation, or CO₂-rich climate of Martian mid-latitudes. These examples show that planetary analogues are necessarily partial models, selected to isolate specific geological, geochemical, astrobiological, functional, atmospheric, or remote-sensing processes. Terrestrial sites do not fully recreate planetary environments; they provide structured starting points for further research. A key goal is to build a systematic framework that maps analogue categories to specific extraterrestrial habitats with greater quantitative rigor. A recent study (Butturini et al., 2025), combined constraints from terrestrial methanogen habitats—deep fractures, hypersaline lakes, and subglacial waters—with models of Martian subsurface thermal structure, ice and water distribution, and radiogenic heat. This analysis identified a candidate methanogenic habitat at 4.3–8.8 km depth beneath Acidalia Planitia, suitable for methanogenic families such as Methanosarcinaceae and Methanomicrobiaceae. This integrative approach shows how analogue research can generate explicit predictions of habitable zones on other worlds. While this work establishes a structured, multi-type analogue framework, these categories can serve as a foundation for future quantitative, habitat-focused studies.

While global analogue sites have greatly advanced our understanding of planetary environments, the unique geological and environmental diversity of Indian sites offers complementary perspectives that enrich astrobiological and planetary studies (Supplementary Table 5). To prioritize the proposed analogue sites for astrobiological investigation, we adopt a research-readiness framework that evaluates the extent of existing characterization, degree of anthropogenic influence, and relevance to specific planetary environments (Supplementary Table 6). This framework classifies analogue sites into three categories: (1) well-characterized, research-ready sites with integrated environmental datasets; (2) sites with well-constrained geological context but limited geochemical and geomicrobiological data; and (3) exploratory targets with high planetary relevance but minimal investigation. Organizing analogue sites along this continuum highlights key knowledge gaps and provides a structured roadmap for future astrobiological research.

6.1 Research-ready sites

Several analogue environments in the Indian subcontinent are sufficiently characterised to support hypothesis-driven astrobiological investigations. Among these, Lonar Crater Lake and Sambhar Lake offer distinct but complementary insights. Lonar Crater Lake, a benchmark for Martian basaltic impact craters and alkaline paleolakes, provides robust geochemical, mineralogical, and microbiological datasets for studying impact-driven alteration, biosignature formation, and preservation. (Chandran et al., 2023; Pandey et al., 2019; Paul et al., 2016). In contrast, Sambhar Lake, a hypersaline-alkaline evaporitic system, parallels Martian evaporitic basins and facilitates examination of how monsoon-driven drying and rewetting cycles affect biosignature retention compared to more climatically stable terrestrial analogues (Pal et al., 2020). Both these sites, also, allow investigations to distinguish natural biosignatures from anthropogenic overprints, a challenge for Martian sample analysis. On the other hand, the Himalayan geothermal systems (Bakreswar, Manikaran, Puga, Chumathang, Panamik) further expand the analogue suite by combining hydrothermal activity, high altitude, high UV flux, and tectonic variability (Ansari et al., 2025; Verma et al., 2022; Pandey et al., 2020). Several of these sites, particularly Puga, experience comparatively minimal anthropogenic influence relative to Sambhar Lake and Lonar Crater, enhancing their value for biosignature studies. Although their biochemical characterization remains less comprehensive compared to microbiological data, these geothermal systems provide complementary settings for investigating Early-Earth life along with habitability and biosignature preservation on Mars.

6.2 Geologically characterized

The second tier of analogue sites is characterised by robust geological and geochemical frameworks but lacks systematic geomicrobiological investigation. First, the Deccan Traps basaltic terrains closely resemble Martian flood basalts (Craig et al., 2017; Bhattacharya et al., 2016), with well-constrained geological and geochemical parameters. However, the patterns of microbial colonisation, metabolic strategies, and biosignature expression within basalt interiors are insufficiently characterised. Archaean microbial communities have been detected in Deccan basalts (Dutta et al., 2019). Based on this, further key research questions include the potential for sustained microbial activity under energy-limited conditions and the influence of basalt mineralogy on biosignature preservation. Anthropogenic impact across the Deccan province varies spatially and can be minimised through strategic site selection. In contrast, ophiolite belts along the Indus Suture Zone, including the Nidar belt, serve as compelling analogues for hydrothermal systems on Mars and icy ocean worlds. Structural geology and petrology highlight the presence of methane signatures in the pyroxenes (Das et al., 2017; Sachan et al., 2007). Anthropogenic disturbance in the Ladakh region is generally low, making it ideal for geomicrobiological studies, which remain unexplored. These sites provide insights into the minimum water-rock interaction rates required to sustain life in ultramafic crust and whether serpentinized systems generate biosignatures distinct from those in basalt-hosted environments. Moreover, carbonate caves and deep mines, such as Borra, Kotumsar, Krem Phyllut, Mawsmai, Kolar Gold Fields, Jaduguda, and Zawar, represent radiation-shielded subsurface environments analogous to Martian caves and lunar lava tubes. Their geological structures and mineral assemblages are well characterised, while biological investigations are limited to caves (Baskar and Ramanathan, 2022) and minimal in mine environments. Moderate anthropogenic influence in certain mined settings necessitates careful differentiation between indigenous and introduced microbial communities. Similarly, high-altitude cryospheric environments in Changthang, Siachen, Khumbu, Zanskar, and Spiti function as analogues for the Icy ocean world cryosphere and lunar cold traps. While extensive physical and climatic datasets are available and anthropogenic influence is generally low, targeted biological studies are needed to elucidate how microorganisms survive repeated freeze-thaw cycles, intense ultraviolet radiation, hypoxia, and low atmospheric pressure. This combination of stressors is not fully represented by polar analogues. Finally, saline-alkaline lake systems in the Rann of Kutch and the Tibetan-Himalayan region present unique intersections of salinity, alkalinity, altitude, and ultraviolet exposure, serving as relevant analogues for Martian paleolakes and evaporitic basins. Although their geochemistry is well constrained, microbial diversity, metabolic functions, and pathways for biosignature preservation remain underexplored. Anthropogenic influence is higher in the Rann of Kutch than in the Tibetan-Himalayan region. These systems are well-suited for investigating the upper salinity and alkalinity limits of life and for identifying which evaporite mineral phases most effectively preserve biosignatures under variable hydrological regimes.

6.3 Exploratory targets

This third category includes exploration sites that are important for science but have had little limited systematic investigation across geological, geochemical, and geomicrobiological dimensions. These places differ in their levels of human impact, which future research should specifically consider. While the shapes of mud volcanoes in the Andaman region are well known, their geomicrobiology remains poorly understood capturing only the heterophs (Meena et al., 2023; Manna et al., 2021). These sites provide access to deep sediments and raise key questions about how differences in mineral composition and fluid-sediment interactions underground affect small habitats, energy availability, and microbial survival. In another context, arid desert systems, including the Thar Desert, possess well-characterized geomorphology but remain poorly constrained microbiologically. These regions experience low to moderate anthropogenic disturbance from agriculture, settlements, and transport corridors. Such environments provide a natural context for quantifying microbial aerosolization during dust storms, assessing the viability and metabolic state of transported cells, and identifying taxa that serve as potential forward-contamination candidates capable of withstanding desiccation, radiation, and extended atmospheric transport. In addition, the Thar Desert offers a valuable functional testbed for the development, calibration, and validation of dust-storm detection and monitoring technologies. Similarly, in contrast to terrestrial systems, Indian Ocean hydrothermal vent fields are among the least explored vents, particularly with respect to geochemical and geomicrobiological characterization, compared to well-studied Atlantic and Pacific systems (Van Dover et al., 2001; Dick, 2019). This deficiency constrains understanding of how unique features of the Indian Ocean, including mantle composition, spreading rate, and trace-metal availability, influence chemosynthetic metabolism, microbial community structure, and biosignature expression, compared with the more extensively studied Atlantic and Pacific systems. Subduction zones and hadal trench environments, including Sunda (Java) trench, is largely unexplored and requires systematic exploration (Jamieson et al., 2022). Finally, methane-rich sedimentary basins and hydrocarbon seep system, as Mannar basin, will be subject to moderate anthropogenic influence from hydrocarbon exploration and fishing activities (Ghosh et al., 2025; Singh and Srinivasa Rao, 2021). Nevertheless, these environments are essential for investigating the operation of methane- and hydrocarbon-driven metabolisms in warm, dynamic continental shelf settings, as well as the rates at which seep-associated biosignatures are altered or degraded by oxygenation, bioturbation, and sediment reworking.

7 Challenges in studying analogue sites hosted in the Indian subcontinent and Indian Ocean

Geomicrobiological research in planetary analogue sites faces several challenges that affect both sampling, including accessibility and logistical constraints, and data interpretation. High-altitude regions such as Ladakh and remote geothermal zones in the Himalayas often require specialized transport, acclimatization, and multiple administrative permissions. These limitations reduce the frequency and duration of field campaigns, restricting the resolution of temporal and spatial microbial assessments. Environmental heterogeneity and seasonal variability further complicate the identification of representative sampling windows. A hybrid strategy that combines targeted seasonal expeditions with autonomous in situ monitoring could help overcome these limitations. Portable analytical tools, remote sensing platforms, and sentinel sensor networks can extend temporal coverage, while standardized low-impact sampling protocols preserve site integrity and ensure reproducibility. Long-term collaborations with local institutions and authorities are also essential to streamline permitting and enable sustained access.

Key research gaps arise from methodological limitations. Most studies rely on isolated sampling campaigns and culture-based approaches, offering only a partial view of microbial diversity. The limited use of advanced molecular techniques such as metagenomics, metatranscriptomics, and metabolomics restricts our understanding of functional capabilities and ecological dynamics (Clark et al., 2023; Jansson and Baker, 2016; Krassowski et al., 2020). Without long-term monitoring, the response of microbial communities to seasonal or episodic environmental fluctuations also remains unresolved (Nguyen et al., 2021; Gunnigle et al., 2017; Whitaker and Banfield, 2005). Another critical gap lies in the study of biosignature preservation. While pigments, lipids, isotopic signals, and biominerals provide promising biosignatures, determining their preservation potential requires understanding how these markers persist across a wide range of chemical and physical conditions, including the geologically diverse and extreme environments found in India. Such assessments are essential for evaluating which biosignatures are most likely to survive in analogue settings and, by extension, on other planetary bodies (Barge et al., 2022; Campbell et al., 2015; Hays et al., 2017; Moore et al., 2022; Summons et al., 2011). Preservation of these geological sites is equally critical. Many analogue sites, in and around Indian subcontinent and the Indian ocean, are increasingly threatened by unregulated geotourism, microbial contamination, and anthropogenic alteration of fragile mineralogical and geochemical gradients (Dowling, 2010; Santos and José, 2023). Extreme environments, as sensitive indicators of environmental change, respond rapidly to shifts in temperature, precipitation, and chemical fluxes. Protecting their integrity is therefore essential not only for advancing astrobiology but also for sustaining long-term ecological and climate monitoring. Linking planetary exploration with Earth’s analogue sites underscores a dual responsibility: advancing scientific discovery while safeguarding irreplaceable natural heritage from irreversible human impact. Realizing the full potential of these environments requires coordinated interdisciplinary research that integrates geomicrobiology, geochemistry, planetary science, and remote sensing. Establishing long-term observatories, deploying in situ analytical tools, and fostering regional and international collaborations will be vital for building a robust framework for analogue research. Beyond their astrobiological value, these sites serve as natural laboratories for studying early Earth conditions and biogeochemical cycling of carbon, sulfur, and nitrogen under natural constraints, thereby informing both planetary exploration and climate science.

Addressing these concerns requires strict contamination control, including not only sterile or UV-sterilized tools but also comprehensive use of field blanks and negative controls. Establishing restricted-access research zones can further reduce human disturbance, while multi-seasonal monitoring of physicochemical parameters (pH, salinity, redox, mineral composition) coupled with high-resolution molecular profiling (e.g., shotgun metagenomics, amplicon sequencing) will help establish reliable baselines. Incorporating computational decontamination pipelines (Murray et al., 2015; Schmieder and Edwards, 2011; Lu and Salzberg, 2018) can then separate indigenous microbial populations from transient contaminants. Closely related to this challenge is the lack of standardized procedures for aseptic sampling, in situ preservation, and metadata reporting, which limits reproducibility and cross-site comparisons. Developing unified protocols aligned with international standards such as MIxS (Field et al., 2011) and Darwin Core (Wieczorek et al., 2012) is therefore critical. This can be achieved through interdisciplinary workshops that bring together planetary scientists, geomicrobiologists, and geochemists to co-design context-specific methods, followed by pilot testing across diverse analogue sites. Publishing the resulting framework as an open-access, modular protocol, with training modules and field-ready checklists, would promote consistency, enhance data comparability, and support long-term multi-site analysis. Finally, the establishment of dedicated infrastructure near key analogue sites, such as field stations, environmental monitoring platforms, and sample repositories, would strengthen the research ecosystem. Policy support is needed to designate protected analogue research zones, ensuring both long-term access and preservation of site integrity. Together, these measures would allow planetary analogue environments to be studied with the rigor required for astrobiological relevance, positioning them as critical contributors to global efforts in understanding habitability, biosignature preservation, and planetary exploration.

8 Future perspectives

The Indian subcontinent and its adjacent oceans encompass a wide array of extreme environments, including high-altitude cold deserts, geothermal springs in the Himalayas, hypersaline lagoons, deep caves, submarine hydrothermal systems, and cold seeps along the Indian Ocean ridges. These geological settings represent valuable planetary analogues, providing critical insights into early Earth life, planetary habitability, and the preservation of biosignatures beyond Earth. To fully realise this potential, the Indian Space Research Organisation (ISRO), in collaboration with international space agencies, should prioritise the systematic identification and formal designation of analogue sites throughout the region.

Progress in astrobiological analogue research in India depends on implementing strategic, sustainable, and collaborative approaches to fieldwork and data collection. The diversity and ecological sensitivity of terrestrial and marine analogue environments, from high-altitude glaciers to deep-sea hydrothermal vents, require careful planning to balance scientific goals with environmental stewardship. Expedition-style field campaigns, modelled after successful initiatives such as the International Ocean Discovery Program (IODP), provide an effective framework. These coordinated efforts unite interdisciplinary teams, enable systematic, minimally invasive sampling, and promote responsible research practices and long-term environmental conservation. Establishing dedicated planetary analogue observatories at key sites is essential for integrating in situ measurements, autonomous sensor networks, and remote-sensing platforms to generate comprehensive, multi-scale environmental datasets. The integration of emerging technologies, such as portable genomic sequencers, autonomous loggers, underwater drones, and satellite-linked sensor arrays, can significantly expand monitoring capabilities. Combining these technological advancements with ISRO’s Earth-observation systems will further improve spatial and temporal mapping of extreme habitats in the region. Establishing robust interdisciplinary collaborations among microbiologists, geochemists, planetary scientists, oceanographers, and engineers is essential for advancing the study of analogue environments. These partnerships are critical for developing the expertise required to address the complexity of these systems and to innovate methodologies for biosignature detection and habitability assessment. Effective institutional coordination among universities, research institutes, government agencies, and space organisations can streamline field operations, facilitate resource sharing, and sustain long-term research initiatives. Integrating these activities into open-access, standardised data systems will enhance the global visibility and impact of Indian analogue research, while ensuring responsible preservation and sharing of data from sensitive environments. This comprehensive and forward-looking strategy positions India as a leader in planetary analogue science, supporting both national and international objectives in astrobiology and planetary exploration.

In the long term, the Indian subcontinent and Indian Ocean will emerge as a global hub for planetary analogue science, directly supporting exploration of the Moon, Mars, and icy ocean worlds. We systematically assess these analogues to prioritise future investigation. Two regions, alkaline ecosystems and geothermal springs, are already under active study. Four more, Deccan Traps, Nidar ophiolite belts, Karst caves, and the Ladakh cryosphere, have strong geological rationale but require further survey. Five additional regions, mud volcanoes, desert ecosystems, hydrocarbon seeps, deep-sea vents, and hadal trenches, are highly relevant but remain minimally explored. Overall, these findings highlight a globally significant, underutilised suite of analogue environments in this region, supporting technology, biosignature research, and astrobiological studies. This foundational reference guides coordinated national and international efforts, ensuring lasting contributions to planetary exploration and responsible stewardship of planetary analogues.

Author contributions

YJ: Conceptualization, Data curation, Formal Analysis, Investigation, Supervision, Validation, Visualization, Writing – original draft, Writing – review and editing. SD: Data curation, Formal Analysis, Investigation, Validation, Visualization, Writing – original draft.

Funding

The author(s) declared that financial support was not received for this work and/or its publication.

Acknowledgements

We are grateful to Tarushi Srivastava for her efforts in the initial data compilation and to Kritika Awasthi for her thoughtful figure design. We also thank the Mohit Daswani and reviewers for their constructive comments and suggestions, which greatly improved the clarity and quality of this manuscript. Discussions during the Space Instrumentation and Payload Development (SIPD) workshop at IIT Kanpur (2024) and the Space Science Roadmap Formulation (SSRF) meeting at URSC (2024) helped shape the scope of this work and highlighted the current lack of a unified astrobiological framework within the Indian Space Research Organization.

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fspas.2025.1712191/full#supplementary-material

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