In-Depth PIB Analysis3 Items Core TopicImportantConcise Economy & InfrastructureGS Paper III 01Geothermal Energy: National Policy 2025 & the Puga Valley Wells Science & TechnologyGS Paper III 02Ultraluminous X-ray Source NGC 4490 ULX-8 Environment & EcologyGS Paper III 03Biosphere Reserves in India & the MAB Programme Economy & Infrastructure — EnergyGeneral Studies Paper III 01 Geothermal Energy in India: The National Policy (2025) and the First Geothermal Wells at Puga Valley, Ladakh Core TopicGS-III · Infrastructure — Energy, Renewable EnergyGS-I · Geography — Interior of the EarthPrelims + MainsPIB · Ministry of New & Renewable Energy · PIB Backgrounder, 2 Nov 2026 India is attempting to move geothermal energy from a mapped resource to a field-tested one: after the National Policy on Geothermal Energy was notified in September 2025, the ONGC Energy Centre commissioned the country’s first two geothermal wells at Puga Valley, Ladakh, in July 2026. ◈ The Basics — Where Geothermal Heat Comes From Geothermal energy is the heat stored within the Earth’s interior. It has two sources: primordial (residual) heat left over from the planet’s formation about 4.6 billion years ago, and heat released continuously by the radioactive decay of isotopes of uranium, thorium and potassium. Layers of the Earth: a rigid crust; the mantle, solid rock that deforms and convects slowly over geological time (its upper weak zone, the asthenosphere, is partially molten); a liquid outer core; and a solid inner core. Temperatures: the backgrounder places the core–mantle boundary at roughly 3,700 °C and the core at 5,000–6,000 °C. Geothermal gradient: temperature rises with depth, on average about 25–30 °C per km in continental crust, and far more steeply in tectonically active zones. Mantle convection drives plate tectonics — earthquakes, volcanism and mountain building. Along faults, fractures, rifts and collision zones, heat rises close enough to the surface to be tapped. Reservoir formation: groundwater percolating down is heated and trapped in permeable, fractured rock beneath an impermeable cap rock; where it escapes it appears as hot springs, fumaroles and geysers. From Underground Heat to Electricity Wells bring hot water and steam to the surface, the steam spins a turbine coupled to a generator, and the cooled fluid is reinjected to sustain reservoir pressure. The cycle resembles a thermal power plant, with natural heat replacing fuel combustion. Figure 1 — How a hydrothermal geothermal power system works Separatorsteam | brineTurbine +GeneratorCondenser /CoolingPower to grid →Production well(hot fluid up)Injection well(fluid returned)Overlying rock — well depths typically 1–3 km(Puga test wells: 1,000 m each)Impermeable cap rock — traps heat and fluidReservoir: hot water & steam in fractured, permeable rockHot basement rock — heat conducted up from depthHeat source: radioactive decay (U, Th, K) + primordial heat ↑ Reinjected fluid is reheated as it moves through the reservoir back towards the production well — which is why a well-managed field behaves as a renewable source. Legacy IAS schematic; not to scale. Figure 2 — The geothermal power chain: hot water → turbine → generator → cooling → transmission The sequence of the power chain is the takeaway here. One correction for answer-writing: wells tap reservoirs in the crust, typically 1–3 km deep — not the mantle, which begins tens of kilometres below the surface. Image courtesy PIB (AI-generated illustration); reproduced with credit for educational use. Plant Types and Uses — The Prelims Vocabulary Dry steam plants: steam from the reservoir drives the turbine directly. Geothermal electricity was first generated at Larderello, Italy, in 1904. Flash steam plants: high-pressure, high-temperature water is depressurised (“flashed”) into steam — the most common design worldwide. Binary cycle plants: moderate-temperature water heats a second, low-boiling-point working fluid in a closed loop (an Organic Rankine Cycle). This suits the low-to-medium enthalpy resources that dominate India. Direct use: district and space heating, greenhouses, aquaculture, crop drying and desalination, without converting heat into electricity. Ground Source Heat Pumps (GSHPs): use the stable temperature of shallow ground for building heating and cooling; usable almost anywhere, not only in hot-spring zones. Enhanced Geothermal Systems (EGS): create artificial permeability in hot, dry rock by hydraulic stimulation. Advanced Geothermal Systems (AGS) circulate fluid through sealed, closed-loop wells. India’s Resource Base The Geological Survey of India (GSI) — established in 1851, under the Ministry of Mines — has mapped 381 hot springs across 10 geothermal provinces. It puts India’s theoretical potential at about 10.6 GW (10,600 MW) and identifies 42 sites as promising for power and direct use. 381Hot springs mapped (GSI) 10Geothermal provinces ~10.6 GWTheoretical potential 42Promising sites 15.67 GWGlobal installed, end-2025 The 10 provinces: Himalayan, Naga–Lusai, Andaman & Nicobar Islands, Son–Narmada–Tapi (SONATA), West Coast, Cambay Graben, Aravalli, Mahanadi, Godavari and the South Indian Cratonic region. Why these places: the Himalayan collision zone and the Andaman volcanic arc carry high heat flow. Rift and graben basins such as SONATA, Cambay, Mahanadi and Godavari have deep faults that channel heat upward. Sites to remember: Puga, Chumathang (Ladakh); Manikaran, Tattapani (Himachal Pradesh); Tapoban (Uttarakhand); Tattapani (Chhattisgarh); Unhavare (Maharashtra); Tuwa (Gujarat); Bakreshwar (West Bengal); Surajkund (Jharkhand); Manuguru (Telangana). Figure 3 — GSI-identified geothermal sites across India Sites cluster along the Himalayan arc and the central Indian rift belts — note the two separate Tattapanis, in Himachal Pradesh and Chhattisgarh. Image courtesy PIB (source: MNRE); reproduced with credit for educational use. ◈ Place in News — Puga Valley Location: the Changthang region of eastern Ladakh, at over 14,000 ft (about 4,270 m); part of the Himalayan geothermal province. Features: hot springs, steam vents and surface deposits of borax and sulphur; long regarded as India’s most promising high-temperature field. 2026 milestone: two wells, each 1,000 m deep, commissioned by the ONGC Energy Centre (ONGC’s research arm for non-conventional energy) for reservoir evaluation. Next step: a planned 1 MW demonstration power project (stated plan) — which would be India’s first geothermal electricity generation. ▤ Policy at a Glance — National Policy on Geothermal Energy, 2025 Instrument: National Policy on Geothermal Energy, notified by the Union Government in September 2025. Nodal Ministry: Ministry of New and Renewable Energy (MNRE). Outlay: no dedicated outlay is stated in the release; R&D is routed through MNRE’s Renewable Energy Research and Technology Development (RE-RTD) programme. Scope: exploration, drilling, reservoir management, power generation and direct-use applications (heating, cooling, agriculture, desalination), including GSHPs. Key provisions: repurposing abandoned oil and gas wells; geo-solar hybrids; support for EGS and AGS; a national geothermal data repository; pilot projects; Centres of Excellence. Participation: a regulatory framework for public and private players, joint ventures, and partnerships with oil & gas companies, States and global geothermal bodies. R&D pipeline: five projects sanctioned by MNRE between July and August 2025, covering resource assessment, indigenous technology and field demonstration. International cooperation: geothermal identified as a focus area with Australia and Iceland, and in an MoU with Saudi Arabia. Linked goals: Net Zero by 2070 and India’s renewable energy targets (policy objective). Figure 4 — Key highlights of the National Policy on Geothermal Energy (2025) The policy’s distinctive features are reuse of oil-and-gas infrastructure, hybrid and next-generation technologies, and a public–private ecosystem. Image courtesy PIB (source: MNRE); reproduced with credit for educational use. Lineage — What Has Changed Then: the GSI began systematic surveys of hot springs such as Puga, Manikaran and Tattapani in the 1970s. For five decades, pilot proposals did not reach commercial generation, and geothermal stayed outside India’s capacity targets, which centred on solar and wind. Now: a dedicated national policy, a nodal ministry, a public-sector oil-and-gas company with deep-drilling capability, and the first deep wells drilled for reservoir testing. Global context: installed capacity reached 15.67 GW by end-2025. Indonesia, the US, the Philippines, Türkiye and New Zealand together hold about 67%. Iceland and Kenya (Olkaria, in the East African Rift) show how geology-rich countries build a significant share of their energy on geothermal. Why It Matters Firm, round-the-clock clean power: output is weather-independent, with high capacity factors. It complements variable solar and wind and reduces the need for storage. Energy security: an indigenous resource, relevant for a country that imports over 85% of its crude oil. Remote Himalayan regions: in cold deserts such as Ladakh, direct-use heating could reduce dependence on diesel and other transported fuels. Asset reuse: abandoned oil and gas wells and the sector’s drilling skills can lower exploration costs. Small land footprint compared with solar parks and hydro reservoirs. The Critical View Exploration risk and upfront cost: drilling is the largest cost, and dry or low-yield wells are common. After more than a century of use worldwide, global capacity is still only about 15.67 GW. Resource quality: the 10.6 GW figure is a theoretical potential, not a proven, bankable reserve. Most Indian sources are low-to-medium enthalpy, which limits power output to modest binary plants. Difficult terrain: the Himalayan sites lie in high seismic zones, with short working seasons, poor access and fragile cold-desert ecosystems. Environmental concerns: non-condensable gases (CO₂, H₂S), mineral scaling and the risk of contaminating groundwater. Induced seismicity is a concern for EGS — South Korea’s 2017 Pohang earthquake (M 5.4) was linked by a government inquiry to an EGS project. Regulatory gaps: clarity is needed on resource rights, leasing and tariffs. Electricity is in the Concurrent List (Entry 38, List III), so Centre–State coordination is essential. Local and cultural stakes: many hot springs, such as Manikaran, are pilgrimage and tourism sites, so community consent and benefit-sharing matter. ✎ Mains Practice Question Geothermal energy can provide firm, low-carbon power, yet it has remained at the margins of India’s renewable energy strategy. Examine the potential of and constraints on geothermal energy in India, in the light of the National Policy on Geothermal Energy, 2025. 15 marks · 250 words Science & TechnologyGeneral Studies Paper III 02 24 Years of X-ray Data Point to a Super-Eddington Black Hole Behind Ultraluminous X-ray Source NGC 4490 ULX-8 ImportantGS-III · S&T — Space, AstrophysicsPrelims-orientedPIB · Ministry of Science & Technology (DST) · 2 Nov 2026 Analysing X-ray observations from 2000 to 2024, a team led by Indian astronomers concludes that ULX-8, among the brightest X-ray sources in the interacting galaxy pair NGC 4490/4485, is most likely powered by a stellar-mass black hole accreting matter at or beyond the Eddington limit. ◈ The Basics — Accretion, the Eddington Limit and ULXs X-ray binaries: a compact object — a neutron star or black hole — pulls gas from a companion star. The gas spirals inward in an accretion disc, heats to millions of degrees and emits X-rays. Eddington limit: the luminosity at which the outward pressure of radiation on infalling gas balances the inward pull of gravity. It rises with mass: about 1.3 × 10³⁸ erg/s per solar mass. Ultraluminous X-ray sources (ULXs): point sources outside a galaxy’s nucleus with X-ray luminosity above about 10³⁹ erg/s — more than a typical stellar-mass object should emit within the Eddington limit. Not to be confused with AGN: Active Galactic Nuclei are powered by supermassive black holes at galactic centres; ULXs are off-centre and far smaller. Three Competing Explanations for a ULX Intermediate-mass black hole (IMBH): a black hole of roughly 10²–10⁵ solar masses accreting below its (much higher) Eddington limit. Stellar-mass black hole, super-Eddington: a normal black hole fed so fast that it exceeds the limit through thick discs, strong winds and beaming. Neutron star, super-Eddington: confirmed for some ULXs by the discovery of pulsating ULXs. The first, M82 X-2, was found with NASA’s NuSTAR in 2014. Figure 5 — The Eddington balance and the three candidate engines of a ULX Accretion onto a compact objectCompanion starWinds / outflowsAccretion disc → X-raysEddington limitGravity pulls gas inRadiation pushes it outL(Edd) ≈ 1.3 × 10³⁸ erg/s per solar massWhat powers a ULX? Three modelsIntermediate-mass black hole~10²–10⁵ solar masses, below Eddington— no super-Eddington physics neededStellar-mass black hole ← ULX-8~5–100 solar masses, at/above Eddington— thick disc, winds and beamingNeutron star (pulsating ULXs)Strongly super-Eddington; X-ray pulsations— first found in M82 X-2 (NuSTAR, 2014)ULX: off-nuclear source, L(X) > ~10³⁹ erg/s The 24-year record favours the highlighted model for ULX-8. Legacy IAS schematic; not to scale. What the Study Found Data: archival and recent observations from Chandra (NASA), XMM-Newton (ESA) and Swift (NASA), spanning 2000–2024 — one of the longest X-ray records of this source. Persistent brightness: ULX-8 stayed exceptionally luminous throughout, though its brightness varied substantially. No state transitions: it did not show the dramatic switches between accretion states (e.g. “hard” and “soft” states) typical of ordinary black hole X-ray binaries. Its spectrum matched a persistently active ultraluminous accretion flow. Evolving conditions: long-term spectral changes indicate that accretion conditions around the compact object are changing over time. Verdict: the researchers present strong evidence for a stellar-mass black hole accreting at or beyond the Eddington limit. Figure 6 — False-colour X-ray images of NGC 4490/4485 with ULX-8 marked Left: Chandra; right: XMM-Newton (EPIC-pn and MOS1/2). ULX-8 sits away from the galaxy’s centre — the defining trait of a ULX. Image courtesy PIB / DST; reproduced with credit for educational use. ▤ Prelims Hooks Target: NGC 4490 (the “Cocoon Galaxy”), interacting with the smaller NGC 4485, in the constellation Canes Venatici. “NGC” stands for the New General Catalogue of nebulae and star clusters. Institutions: Indian Institute of Astrophysics (IIA) and Raman Research Institute (RRI), Bengaluru — both autonomous institutes of DST — with IUCAA (Pune) and IISER Mohali. Journal: Monthly Notices of the Royal Astronomical Society (MNRAS). Future missions: ESA’s NewAthena X-ray observatory (planned for the late 2030s) and India’s proposed timing and spectroscopy mission XSat. India’s current X-ray capacity: AstroSat (2015), India’s first dedicated multi-wavelength space observatory; and XPoSat (launched 1 January 2024), its first X-ray polarimetry mission. Why It Matters — and the Caveats Black hole growth: super-Eddington accretion is one proposed route by which black holes gain mass quickly — a question relevant to the early growth of supermassive black holes. Value of archives: the result rests on combining openly archived data from several missions over decades, a model for research by institutions without their own large telescopes. Indian astronomy: it adds to India’s growing output in high-energy astrophysics, building expertise for future national missions. Caveat: the conclusion is probabilistic (“most likely”). The absence of detected pulsations does not fully exclude a neutron star, and a definitive mass would require dynamical measurement of the companion star’s orbit. ✎ Mains Practice Question What are ultraluminous X-ray sources? Discuss how long-term, multi-mission observations help determine the nature of their compact objects, and the role that India’s space-based astronomy missions can play in such research. 10 marks · 150 words Environment & EcologyGeneral Studies Paper III 03 Biosphere Reserves in India: The MAB Framework, India’s Network of 18 Reserves, and the Conservation–Livelihood Balance Core TopicGS-III · Environment — Conservation, Protected AreasPrelims + MainsPIB · Ministry of Environment, Forest & Climate Change · PIB Backgrounder, 2 Nov 2026 3 November is observed as the International Day for Biosphere Reserves. India has 18 notified Biosphere Reserves (BRs), of which 13 are in UNESCO’s World Network of Biosphere Reserves (WNBR) — the most in South Asia, according to the MoEFCC. ◈ Background — Biodiversity and the MAB Programme Levels of biodiversity recognised by the Convention on Biological Diversity (CBD) — opened for signature at the 1992 Rio Earth Summit and in force since 1993: genetic (variation within a species, e.g. rice varieties), species and ecosystem diversity. India’s standing: one of the 17 megadiverse countries, holding about 7–8% of recorded species on 2.4% of the world’s land. It contains parts of 4 of the 36 global biodiversity hotspots: the Himalaya, Indo-Burma, the Western Ghats & Sri Lanka, and Sundaland (Nicobar Islands). Man and the Biosphere (MAB) Programme: launched by UNESCO in 1971 as an intergovernmental scientific programme to improve the relationship between people and their environment. Biosphere reserves are its “living laboratories” for sustainable development. Rulebook: the Seville Strategy and the Statutory Framework of the WNBR (1995). Sites undergo a periodic review every 10 years and remain under the sovereign jurisdiction of the country concerned. The Day: proclaimed by the UNESCO General Conference in 2021; first observed on 3 November 2022. Three Functions, Three Zones Every biosphere reserve pursues three linked functions: conservation of ecosystems, species, genetic resources and associated cultural diversity; sustainable economic development within ecological limits; and logistic (scientific) support — research, monitoring, education and training. Core area: a legally protected zone for long-term conservation, with only non-destructive research and monitoring. In India it usually coincides with a National Park or Wildlife Sanctuary. Buffer zone: surrounds or adjoins the core; permits activities compatible with conservation — research, environmental education, regulated ecotourism. Transition area: the outermost zone, with settlements, agriculture and sustainable resource use. It has no fixed outer boundary and is where communities, scientists and managers work together. Global average share: 18% core : 30% buffer : 52% transition — most of a reserve is meant for people, not exclusion. Figure 7 — The three zones of a biosphere reserve Protection is strictest at the centre and loosens outward, while human use increases outward. Image courtesy PIB (source: UNESCO); reproduced with credit for educational use. ◈ Biosphere Reserve vs National Park vs Wildlife Sanctuary National Park: declared under Section 35 of the Wild Life (Protection) Act, 1972; no rights or human activity other than those permitted; the highest protection status. Wildlife Sanctuary: declared under Section 18 of the same Act; certain rights (e.g. grazing) may be allowed. Biosphere Reserve: not created under any specific statute. It is designated by the Union Government under the national Biosphere Reserve programme (1986) and covers a whole landscape, including people. Legal protection comes from the PAs and forest laws within it. India’s Network Beginning: the first BR, the Nilgiri Biosphere Reserve (1986), spans Tamil Nadu, Kerala and Karnataka; it was also the first Indian site in the WNBR (2000). 13 in the WNBR: Nilgiri (2000), Gulf of Mannar (2001), Sundarbans (2001), Nanda Devi (2004), Nokrek (2009), Pachmarhi (2009), Similipal (2009), Achanakmar–Amarkantak (2012), Great Nicobar (2013), Agasthyamalai (2016), Khangchendzonga (2018), Panna (2020) and Cold Desert, Himachal Pradesh (2025). 5 national-only BRs: Manas, Dibru-Saikhowa, Dehang-Dibang, Great Rann of Kutch and Seshachalam. Extremes: Great Rann of Kutch is the largest by area; Dibru-Saikhowa (Assam) is the smallest. World Heritage overlaps: Nanda Devi, Sundarbans and Khangchendzonga (India’s first “mixed” World Heritage Site, 2016) also carry World Heritage status. Figure 8 — Biosphere Reserves of India Starred sites are in UNESCO’s World Network. The map stars 12; per the MoEFCC count of 13, the latest addition, Cold Desert, is not yet starred. Image courtesy PIB (source: MoEFCC); reproduced with credit for educational use. 18Notified BRs 13In UNESCO’s WNBR 1971MAB launched 1986India’s first BR (Nilgiri) ▤ Scheme at a Glance — Biosphere Reserve Support Scheme: ‘Biodiversity Conservation’, a Centrally Sponsored sub-scheme under the umbrella scheme ‘Conservation of Natural Resources and Ecosystems’. Nodal Ministry: MoEFCC (Biosphere Reserve Division). Implementing agencies: State Forest Departments, following each reserve’s approved Management Plan. Funding pattern: grants-in-aid shared 60:40 (Centre : State); 90:10 for North-Eastern and Himalayan States. Integrated Management Plans (5-year), piloted since 2022–23: Nanda Devi (Uttarakhand), Pachmarhi (Madhya Pradesh), Dehang-Dibang (Arunachal Pradesh) and Agasthyamalai (Kerala & Tamil Nadu). Priorities: habitat restoration, biodiversity monitoring, scientific research and sustainable livelihoods, with reserve authorities, research institutions and communities working jointly. Case Study — The Lantana Elephants of the Nilgiris Lantana camara, a shrub native to tropical America and introduced to India as an ornamental during the colonial period, is now one of the country’s most damaging invasive alien species. It smothers native undergrowth, reduces fodder for herbivores and alters fire behaviour in forests. Indigenous communities in the Nilgiri BR turn uprooted Lantana into life-size elephant sculptures, furniture and crafts. In 2021, 125 such elephants were displayed in London; others have appeared at Bengaluru Airport and Rashtrapati Bhavan. Takeaway: invasive-species removal becomes a livelihood and an awareness tool — a useful Mains example of the BR idea, and of Target 6 of the Kunming–Montreal Global Biodiversity Framework (cutting the introduction and establishment of invasive species by at least 50% by 2030). Why It Matters Landscape-scale conservation: BRs connect protected cores with the surrounding land used by people, supporting corridors and ecosystem services such as water, soil and climate resilience. Global commitments: contributes to the Kunming–Montreal GBF (2022) — especially Target 3 (“30×30”), conserving 30% of land and sea by 2030 — and to India’s updated National Biodiversity Strategy and Action Plan. Science and tradition: BRs are sites to combine traditional knowledge with modern monitoring. The Critical View Weak legal status: without a specific statute, the buffer and transition zones lack enforceable rules. In practice, protection often extends no further than the PAs inside. Overlapping designations: many BRs coincide with tiger reserves and national parks (e.g. Panna, Similipal, Achanakmar), so the BR label can become a relabelling of existing areas rather than a distinct management model. Thin people-centred component: the transition zone — the heart of the MAB idea — tends to get less attention than core protection. Links with the Forest Rights Act, 2006, Biodiversity Management Committees and People’s Biodiversity Registers under the Biological Diversity Act, 2002 are uneven. Limited funding: modest grants, dependence on the State share and release delays constrain management plans. Development and climate pressures: examples include debate over large development proposals in Great Nicobar, rising seas in the Sundarbans, and coral stress in the Gulf of Mannar. Way Forward Give BR zones clearer legal recognition, or bind them through State-level notifications and management rules. Scale up the Integrated Management Plans beyond the four pilots, with measurable biodiversity and livelihood indicators. Make community institutions — Gram Sabhas, BMCs, forest-rights holders — co-managers of buffer and transition zones. Build climate adaptation into management plans for coastal and Himalayan reserves, and keep reserves compliant with UNESCO’s periodic reviews. ✎ Mains Practice Question Biosphere reserves seek to reconcile biodiversity conservation with the livelihoods of local communities. Evaluate how far India’s biosphere reserve network has achieved this objective, and suggest measures to strengthen it. 15 marks · 250 words