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Foreword

The universe encompasses more than just the visible sky; it is a remarkable realm filled with endless enigmas. Through the exploration of the universe, we gain insights into our origins, the uniqueness of Earth, and the life cycles of stars and planets. This understanding ignites our curiosity and opens doors to new discoveries. The universe represents not merely a field of science but an infinite source of wonder, contemplation, and inspiration. India’s inaugural venture into the study of such a universe is the first dedicated space observatory – Astrosat. It marked a significant milestone by successfully completing ten years on 28 September 2025. Initially intended for a five-year mission, it has surpassed expectations and continues to deliver invaluable astronomical data throughout this decade.

Read More at:

https://astroforeveryone.com/articles/f/india%E2%80%99s-pride-in-space-astronomy-the-astrosat-achievements

Introduction

The truth we have grasped since childhood is that eight planets revolve around the Sun. Nevertheless, a fundamental question has persistently occupied the human mind: "Is our solar system unique? Or do planets also exist around other stars?"

Until a few centuries ago, the answer to this question was limited to speculation. Astronomers studied stars and thought, "These might also have planets," but there was no evidence.

However, technological progress over the past thirty years has provided a clear answer to this question. Researchers have employed modern telescopes, spectrometers, and accurate measurement techniques to identify thousands of exoplanets. This confirms that planets orbit stars, much like the Sun.

This discovery fundamentally changed humanity's perspective:

• The universe is not solely filled with stars; it also hosts thousands of planetary systems.

• Some of these planets may bear similarities to Earth.

• This further strengthened the investigation into whether we are alone or if life exists elsewhere in the universe.

Therefore, the search for exoplanets emphasises two essential aspects:

1. The universe is incredibly vast.

2. The probability of life emerging is greater than previously thought.

Original discovery

For centuries, humankind has been intrigued by the possibility of planets orbiting stars beyond our own. For a long time, this idea was simply a theory. However, in 1992, a significant breakthrough took place. Polish astronomers Aleksander Wolszczan and Dale Frail employed a radio telescope to study a pulsar star identified as PSR B1257+12.

A pulsar is a specific kind of neutron star that forms after a supernova explosion. It is characterised by its swift rotation and the release of radio waves. By examining slight fluctuations in the radio signals, Wolszczyń and Friel identified that three planets orbit the pulsar.

This marks a crucial milestone in the history of astronomy because:

1. This represents the initial occurrence in which definitive evidence has been found that confirms the existence of extrasolar planets.

2. This discovery further strengthened the notion that "our solar system is not unique."

3. Scientific evidence has emerged indicating that there may be many more planets orbiting different stars across the universe.

However, the planets that were initially discovered are not suitable for supporting life as we understand it on Earth. Since they orbit a dead star (a pulsar), the chances of life existing on them are virtually non-existent. Nevertheless, this discovery marked a significant breakthrough in the field of exoplanet research.

Scientists have contemplated the possibility of planets existing around truly habitable stars. The response to this question surfaced in 1995. Swiss astronomers Michel Mayor and Didier Queloz discovered a planet orbiting a typical sun-like star referred to as 51 Pegasi. They named the planet 51 Pegasi b.

Reasons this holds significance:

1. For the first time, an exoplanet has been found orbiting a typical star.

2. This discovery provides strong scientific evidence supporting the notion that "there may be many systems akin to our solar system scattered across the universe."

3. The method utilised — the Radial Velocity Method (Doppler Spectroscopy) — later became the foundation for the search for thousands of exoplanets.

Some fascinating information about 51 Pegasi b:

• It is a gas giant, akin to Jupiter.

• The distance from Earth is roughly 50 light-years.

• It orbits close to its star, completing one orbit in just 4.2 days.

• Large planets that orbit near such stars are known as "Hot Jupiters."

This discovery represented a transformative change in the realm of astronomy. Planets that were previously considered mere science fiction or products of imagination were now confirmed to exist. Since then, the study of exoplanets has expanded considerably. In 2019, Mayor and Queloz were awarded the Nobel Prize in Physics for this pioneering discovery.

Exoplanets discovered to date (as of September 2025)

According to the latest statistics:

• To date, more than 6,000 extrasolar planets have been confirmed.

• Furthermore, more than 10,000 candidate planets are still being monitored.

• They have been found in more than 4,200 star systems.

Types of exoplanets

Exoplanets are distinct from the planets located in our solar system.

1. Hot Jupiters: These exoplanets exceed the size of Jupiter and possess orbits that bring them in proximity to their star.

2. Super-Earths: ranging from 2 to 10 times the size of Earth, with some possibly having conditions favourable for life.

3. Mini-Neptunes: Gaseous planets that are similar to Neptune but smaller in size.

4. Earth-like Planets: These planets resemble Earth in size and orbit within a "habitable zone" (a region favourable for life).

Methods for exploration

Scientists utilise a range of methods to detect exoplanets:

• Transit Method: Observing the reduction in brightness as a planet passes in front of its star. (NASA's Kepler Mission has discovered thousands of planets using this method.)

• Radial Velocity: Observing how a star fluctuates due to the gravitational influence of a planet.

• Direct Imaging: Although it is pretty challenging, a few have been captured directly through imaging.

• Gravitational Microlensing: Detecting planets through the observation of temporal fluctuations in the light emitted by distant stars.

The search for existence

• Scientists are specifically exploring Earth-like planets located within the "Habitable Zone."

• To date, more than 361 candidate planets have been discovered within the habitable zone.

• Notable: Kepler-452b, planets in the TRAPPIST-1 system, and Proxima Centauri b.

Future research

• The James Webb Space Telescope (JWST) is examining the atmospheres of exoplanets.

• Ariel Mission (ESA, set to launch in 2029) – will investigate the atmospheres of various exoplanets.

• Nancy Grace Roman Space Telescope (NASA, 2030) – Will reveal discoveries about a significant number of planets.

Conclusion

The search for extrasolar planets stands as a significant testament to human curiosity. The discovery of thousands of worlds beyond our solar system not only fascinates us but also increases the possibility of life existing elsewhere. This endeavour seeks to answer the question of whether Earth is a unique planet or if many Earth-like planets inhabit the universe. Ongoing research on these planets will unveil a new path for human civilisation.

అజ్ఞాత లోకాల అన్వేషణ: బాహ్యసౌర గ్రహాల (Exoplanets) కథ: https://janavignanam.com/2025/09/1833/

భారతీయ అంతరిక్ష స్వప్నాలకు తొలి మెట్టు ఆర్యభట! : https://janavignanam.com/2025/08/1736/