Exoplanet

1. Definition

An exoplanet (short for extrasolar planet) is a planet that orbits a star outside our Solar System. Unlike Earth or Jupiter, which orbit the Sun, exoplanets orbit other stars in the Milky Way and beyond.

2. Discovery History

The first confirmed detection of an exoplanet orbiting a Sun-like star occurred in 1995 (planet 51 Pegasi b).
As of now, thousands of exoplanets have been discovered using various space and ground-based telescopes.

3. Detection Methods

Scientists use several techniques to find exoplanets:

Transit Method: Observing a dip in a star’s brightness when a planet passes in front of it. Used by telescopes like Kepler and TESS.
Radial Velocity (Doppler Effect): Detecting wobbles in a star's motion caused by the gravitational pull of a planet.
Direct Imaging: Taking pictures of exoplanets, usually in infrared. Difficult due to the brightness of the star.
Gravitational Microlensing: Measuring light bending from a background star when a planet passes in front of it.
Astrometry: Tracking tiny changes in a star’s position in the sky.

4. Types of Exoplanets

Exoplanets are diverse and come in many forms:

Hot Jupiters: Large gas giants orbiting very close to their stars.
Super-Earths: Planets larger than Earth but smaller than Neptune; may be rocky or gaseous.
Earth-like planets: Rocky planets in the “habitable zone,” where liquid water could exist.
Mini-Neptunes: Planets with thick atmospheres, smaller than Neptune.
Rogue planets: Planets that drift through space without orbiting any star.

5. Habitable Zone (Goldilocks Zone)

This is the distance from a star where conditions might allow liquid water to exist — a key factor for life. Planets in this zone are primary candidates in the search for alien life.

6. Important Missions & Telescopes

Kepler Space Telescope: Revolutionized exoplanet discovery (2009–2018).
TESS (Transiting Exoplanet Survey Satellite): Currently identifying thousands of exoplanet candidates.
James Webb Space Telescope (JWST): Studying atmospheres of exoplanets in detail.
Upcoming: PLATO, ARIEL (ESA missions), and others.

7. Why Study Exoplanets?

To understand the origins of planetary systems.
To find potentially habitable worlds.
To search for signs of life beyond Earth (biosignatures in atmospheres).
To explore the diversity of planetary environments.

8. Fun Facts

The closest known exoplanet, Proxima b, orbits Proxima Centauri, just 4.24 light-years away.
Some exoplanets have extreme conditions: raining molten glass, or orbiting their star in just a few hours!
There may be more planets than stars in our galaxy — possibly hundreds of billions!