Exoplanets

• Why is it difficult to detect planets around other stars?

  Brightness difference
• Planet detection can be direct of indirect.
• There are 2 main techniques for indirect planet detection:

  1. doppler
  2. transits
• Doppler method: this relies on the velocity of the star (not the planet) measured from a spectrum. This is done via the Doppler effect.
• Gravitational tugs: The force of gravity pulls the Earth towards the Sun.
• Transits method: A method of measuring the distance between two stars by observing the transit of a planet across the star.
• • A transit is when a planet crosses in front of a star.
  • The planet blocks the star light and reduces the star's apparent brightness giving us the planet's radius.
• The fraction of light lost during the transit is proportional to the fraction of the star's circular area that is covered by the circular area of the planet.
• Habitable zone: it is the region in a solar system where the average temperature of a planet's surface allows fro the presence of liquid water. (273-373K)
• Orbits of some extrasolar planets are much more elongated (have a greater eccentricity) than those in our solar system
• Most of the detected exoplanets have greater mass than jupiter.
• Planets with smaller masses are harder to detect with a Doppler technique.
• Hot Jupiters orbit very close to their stars.
• Planetary migration:

  • A young planet's motion can create waves in the planet-forming disk.
  • These waves can tug on a planet, causing its orbit to migrate inwards
• Planetary migration or gravitational encounters may explain how Jupiter-like planets moved inward.
• Exoplanet atmospheres: if the transiting planet has an atmosphere, then the light that passes through the atmosphere may be absorbed.