Exoplanets: Definition and Discovery
Exoplanets are planets that exist outside our solar system, orbiting stars other than the Sun.
- Definition: An exoplanet (or extrasolar planet) is a celestial body that revolves around a star outside the solar system.
- Types of Exoplanets:
- Hot Jupiters: Gas giants that orbit very close to their stars.
- Super-Earths: Planets larger than Earth but smaller than Neptune, potentially with rocky surfaces.
- Ocean Worlds: Bodies with significant amounts of water, possibly supporting life.
- Discovery Methods:
- Transit Method: Measures the dimming of a star as a planet passes in front of it. Used by the Kepler space telescope, which discovered over 2,300 exoplanets.
- Radial Velocity Method: Detects wobbles in a star's movement caused by the gravitational pull of an orbiting planet, employed by the HARPS spectrograph.
- Direct Imaging: Captures images of planets directly by blocking the star's light, though this method is challenging and requires advanced technology.
- Gravitational Microlensing: Observes light from distant stars that is bent by the gravity of a planet passing in front, revealing the presence of planets.
- Significance: Studying exoplanets can yield insights into planetary formation, evolution, and the potential for life beyond Earth. The discovery of Earth-like exoplanets in the habitable zone raises questions about the existence of extraterrestrial life.
- Notable Exoplanets:
- Proxima Centauri b: Closest known exoplanet, located in the habitable zone of Proxima Centauri, our nearest stellar neighbour.
- TRAPPIST-1 System: Features seven Earth-sized exoplanets, three of which are located in the habitable zone.
- Future Exploration: Upcoming missions like the James Webb Space Telescope aim to characterise exoplanet atmospheres and identify potential biosignatures.
