Exoplanet detection has revolutionized our understanding of planetary systems. Scientists use various methods like transit, radial velocity, and direct imaging to find planets beyond our solar system. These techniques reveal crucial info about exoplanet sizes, masses, and orbits.

Characterizing exoplanets is the next frontier. By analyzing their atmospheres and properties, we can learn about their composition and potential habitability. This exciting field connects to broader themes in astrophysics, expanding our cosmic perspective.

Exoplanet Detection Methods

Transit and Radial Velocity Methods

• Transit method observes periodic dimming of star's light as exoplanet passes in front of it
  • Detects planets aligned with our line of sight
  • Measures planet size and orbital period
  • Kepler Space Telescope used this method to discover thousands of exoplanets
• Radial velocity method measures star's "wobble" due to gravitational pull of orbiting planet
  • Detects Doppler shift in star's spectrum as it moves towards and away from Earth
  • Determines planet's mass and orbital period
  • First method to discover exoplanets around main sequence stars (51 Pegasi b)

Direct Imaging and Microlensing

• Direct imaging captures actual light from exoplanet
  • Requires very large telescopes and advanced techniques to block starlight
  • Works best for young, hot planets far from their stars
  • Provides information about planet's atmosphere and composition
• Microlensing uses gravitational lensing effect to detect planets
  • Temporary brightening of background star as foreground star with planet passes in front
  • Can detect low-mass planets at large orbital distances
  • WFIRST telescope will use this method to survey Milky Way for exoplanets

Astrometry and Future Methods

• Astrometry measures tiny changes in star's position due to orbiting planet
  • Requires extremely precise measurements of star's position over time
  • Can detect planets in any orbital orientation
  • European Space Agency's Gaia mission uses this method
• Future methods may include:
  • Detecting radio emissions from giant planets with strong magnetic fields
  • Observing polarization of starlight reflected off planetary atmospheres

Exoplanet Characterization Techniques

Spectroscopic Analysis of Exoplanet Atmospheres

• Transit spectroscopy analyzes starlight filtered through planet's atmosphere during transit
  • Reveals atmospheric composition and structure
  • Identifies molecules like water, methane, and carbon dioxide
  • James Webb Space Telescope will use this technique to study potentially habitable worlds
• Doppler spectroscopy measures radial velocity variations to study planetary winds
  • Detects shifts in atmospheric absorption lines
  • Provides information about atmospheric circulation and weather patterns

Advanced Characterization Methods

• Phase curve analysis studies variations in planet's brightness as it orbits its star
  • Reveals information about planet's day-night temperature differences
  • Helps determine presence of clouds or heat redistribution in atmosphere
• High-resolution spectroscopy can detect specific molecular species in exoplanet atmospheres
  • Uses cross-correlation techniques to amplify weak planetary signals
  • Can potentially detect biosignatures in terrestrial planet atmospheres
• Polarimetry measures polarization of light reflected from exoplanet
  • Provides information about planetary surface properties and cloud composition

Types of Exoplanets

Gas Giants and Hot Jupiters

• Hot Jupiters consist of large gas planets orbiting very close to their stars
  • Have orbital periods of a few days
  • Experience extreme temperatures and intense stellar radiation
  • Often exhibit atmospheric escape and extended exospheres
• Cold gas giants resemble Jupiter and Saturn in our solar system
  • Primarily composed of hydrogen and helium
  • Can have complex systems of moons and rings
  • May host potentially habitable moons with subsurface oceans (Europa, Enceladus)

Terrestrial and Super-Earth Exoplanets

• Super-Earths have masses between Earth and Neptune
  • Can be rocky or have thick atmospheres depending on composition and formation history
  • May be more geologically active than Earth due to higher internal heat
  • Potentially habitable if located in star's habitable zone
• Earth-like planets have similar size and composition to our planet
  • Prime targets in search for extraterrestrial life
  • Challenging to detect and characterize due to small size
  • Future missions like PLATO aim to find and study these worlds
• Mini-Neptunes fall between super-Earths and ice giants in size
  • Have significant gaseous envelopes but smaller than Uranus or Neptune
  • May represent a distinct class of planets not found in our solar system