Exoplanets are a diverse group of planetary bodies orbiting stars beyond our Solar System. Advances in detection methods have revealed a wide range of exoplanets, from gas giants to rocky worlds, and studying them provides valuable insights into the nature of planetary systems and the potential for life beyond Earth.

1. 1. Discovery Methods

• • • Radial Velocity (Doppler): Measures the star’s motion caused by the gravitational pull of an orbiting planet. Variations in the star’s spectrum can indicate the presence of a planet.
    • Transit Method: Observes the dimming of a star’s light as a planet passes in front of it, blocking a portion of the light. This method provides information about the planet’s size and orbit.
    • Direct Imaging: Captures images of the planet by blocking out the star’s light, allowing for observations of the planet’s atmosphere and surface features.
    • Gravitational Microlensing: Detects the bending of light from a background star caused by the gravitational field of a planet in front of it.

1. 2. Types of Exoplanets

• • • Hot Jupiter’s: Gas giants that orbit very close to their host stars, resulting in high surface temperatures.
    • Super-Earths: Planets with masses larger than Earth’s but smaller than Uranus or Neptune. They may be rocky or have thick atmosphere.
    • Mini-Neptune’s: Smaller than Neptune but larger than Earth, often with thick atmospheres.
    • Earth-like Planets: Planets with conditions like Earth, potentially in the habitable zone of their star where liquid water could exist.
    • Ice Giants: Planets with large icy or watery compositions, such as Uranus and Neptune.

1. 3. Habitable Zone

The habitable zone (or Goldilocks zone) is the region around a star where conditions might be right for liquid water to exist on a planet’s surface. This zone depends on the star’s luminosity and the planet’s atmosphere.

1. 4. Atmospheres and Composition

• • • Atmospheric Composition: Exoplanet atmospheres are studied to determine their composition, which can include gases like hydrogen, helium, methane, carbon dioxide, and water vapor.
    • Surface Conditions: Understanding surface conditions helps assess the potential for habitability and the presence of features such as oceans, mountains, or deserts.

1. 5. Notable Exoplanets

• • • Proxima Centauri b: Located in the habitable zone of Proxima Centauri, the closest star to the Sun.
    • Kepler-22b: An exoplanet located in the habitable zone of its star, similar in size to Earth.
    • HD 209458 b (Osiris): One of the first exoplanets discovered using the transit method and known for its “hot Jupiter” characteristics.