Relevance: GS-III Science & Technology · Space Applications

Source: GRAPES-3 study, June 2026

1 · What happened

Scientists from India and Japan, using the GRAPES-3 telescope in Ooty, have found a clever new way to watch the Earth’s upper atmosphere and the Sun’s magnetic field — not with a camera, but by counting tiny particles called muons. They studied about two decades of non-stop data (2001–2022), covering several solar cycles. The result: a ground-based detector can track changes in the upper atmosphere and in space weather in real time, with great accuracy — without depending only on costly satellites.

2 · What is GRAPES-3?

GRAPES-3 (Gamma Ray Astronomy PeV EnergieS – phase-3) is a ground-based cosmic-ray observatory at Ooty, Tamil Nadu, at a height of 2,200 metres. Unlike a normal telescope that uses lenses and mirrors to catch light, GRAPES-3 is a giant muon detector — it senses invisible particles raining down from the sky.

Where do these particles come from? Cosmic rays are super-fast particles from deep space. When they hit our upper air, they break apart and create showers of new particles — including muons, which then fall to the ground. GRAPES-3 catches and counts these muons. Here is the journey from sky to “hit”:

1	Cosmic rays arrive. Highly energetic particles from deep space strike the Earth’s upper atmosphere.

2	A particle shower forms. They smash into oxygen and nitrogen molecules, creating a cascade of secondary particles, including muons.

3	Muons reach the ground. They survive just long enough to rain down on the detector.

4	A muon passes through a tube. Inside each proportional counter — a gas-filled steel tube with a thin central wire — the muon knocks electrons loose from the gas.

5	A “hit” is recorded. The loose electrons rush to the wire and make a small electric pulse. Counting these pulses over time reveals the hidden story in the sky.

• Massive grid: the muon telescope has 16 modules, and each module holds 232 of these tubes (about 3,712 in all) — making it one of the most sensitive muon detectors on Earth.
• Orthogonal (right-angle) layering: the tubes are stacked in layers, each turned at a right angle to the one below. This crossing pattern lets scientists work out the exact direction from which a muon came.
• Concrete shielding: thick concrete between the layers acts like a filter — only strong, high-energy muons get through, so weak background noise is screened out.

3 · Why it matters for India

• Space-weather early warning: sudden changes in muon counts hint at solar storms and Coronal Mass Ejections (CMEs) — huge bursts of charged matter from the Sun. Early alerts help protect satellites, GPS navigation and power grids from damage.
• A low-cost climate tool: upper-atmosphere temperature changes the rate at which muons decay. So muon data acts as a cheap, continuous thermometer for the upper atmosphere — without launching new satellites.
• Made in India: the detector was built largely in-house, showing the strength of indigenous (home-grown) scientific infrastructure.

The road ahead: linking ground-based muon data with ISRO’s solar observatory Aditya-L1 could give India a single, self-reliant system to predict extreme space weather.

UPSC Value Box

GRAPES-3 Gamma Ray Astronomy PeV EnergieS – phase-3; cosmic-ray (muon) observatory at Ooty, Tamil Nadu (2,200 m). Operator Tata Institute of Fundamental Research (TIFR), with Japanese institutions. Cosmic rays Very high-energy particles from deep space that strike the atmosphere. Muons Secondary particles created when cosmic rays hit the upper air; reach the ground and are counted. CME Coronal Mass Ejection; a large burst of charged matter from the Sun that can disrupt satellites and grids. MACE Major Atmospheric Cherenkov Experiment; a gamma-ray telescope at Hanle, Ladakh — among the world’s highest. LIGO-India Upcoming gravitational-wave observatory at Hingoli, Maharashtra. Aditya-L1 ISRO’s solar observatory studying the Sun from the L1 point in space.

MCQ Practice Question

Q. With reference to the GRAPES-3 experiment, consider the following statements: It is a ground-based cosmic-ray observatory that detects muons, located at Ooty in Tamil Nadu. It is operated by the Indian Space Research Organisation (ISRO) and works as an optical telescope using lenses and mirrors. Data from GRAPES-3 can help in forecasting space-weather events such as solar storms. Which of the statements given above is/are correct? (a) 1 and 2 only    (b) 2 and 3 only    (c) 1 and 3 only    (d) 1, 2 and 3

Answer: (c) 1 and 3 only Statement 1 — Correct: GRAPES-3 is a ground-based cosmic-ray (muon) observatory at Ooty, Tamil Nadu. Statement 2 — Incorrect (the trap): It is run by TIFR, not ISRO, and it is a muon detector, not an optical telescope — it uses no lenses or mirrors. Statement 3 — Correct: Sudden changes in muon counts help warn of solar storms and CMEs, protecting satellites and power grids.