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Exoplanet - A large body orbiting a star other than the Sun. Extra-Solar Planets Review of planet formation The Habitable Zone Basic properties of discovered exoplanets Hot Jupiters Super-Earths Exoplanet - A large body orbiting a star other than the Sun.

Large, cool cloud of gas and dust How to make a planet Large, cool cloud of gas and dust Gas makes the star, dust is necessary for planet formation Dust is usually made of metals (Fe, Ni, Al), rocks (silicates) and ices (solid H2O, CH4, NH3) Mostly H and He (these two elements make up about 98% of our Solar System) Cloud begins to collapse under its own self-gravity

Result is a rapidly rotating disk of gas and dust How to make a planet Collapse causes Increase in temperature (conservation of energy) Increase in rate of rotation (conservation of angular momentum) Result is a rapidly rotating disk of gas and dust Again, dust means rocks, metals and ices at sufficient distance from the parent star, hydrogen compounds (H2O, CH4 NH3) are important in formation of giants (Jovian planets are far from the Sun)

Accretion How to make a planet Dust grains collide to form larger particles --> Collide small particles to form still larger particles --> Collide large “boulders” to form planetesimals (asteroids, comets, Kuiper Belt Objects)--> collide planetesimals to form planets

Contraction into rotating disk w/ hot center How to make a planet Nebular Hypothesis Solar Nebula Contraction into rotating disk w/ hot center Dust grains accrete to form larger and larger particles Large particles sweep out more material to form planetesimals Planetesimals eventually collide to form planets

Typically these conditions for the existence of life include: The Habitable Zone Typically these conditions for the existence of life include: 1. Suitable temperature for liquid water 2. Existence of water itself 3. Appropriate cosmo-chemical composition Are there other conditions or different ones? Are these necessary and sufficient conditions for life?

Distance to parent star Type of parent star ATMOSPHERE The Habitable Zone Depends on: Distance to parent star Type of parent star ATMOSPHERE Albedo: measure of the reflectivity of the earth's surface Greenhouse effect

Overview of Exoplanets Planet (IAU definitions of Planet, Dwarf Planet and Small Solar System Bodies) A "planet” is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit. A "dwarf planet" is a celestial body that: (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite. All other objects except satellites orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

Planet Detection Methods Radial Velocity – doppler shift in spectral lines of parent star As the star approaches (recedes) the light from the star is blue-(red-)shifted. The frequency and velocity can determine the mass of the orbiting body, in this case a cool, dim planet.

Hot Jupiters -Large planets, orbiting close to parent star (too close to be in the Habitable Zone) - Large masses and short orbital periods -Most have nearly circular orbits -Many have unusually low densities -Likely to have extreme and exotic atmospheres due to their short periods, relatively long days, and tidal locking

Super Earths Terrestrial (“rocky”) planet More massive than Earth, less massive than Jupiter Not necessarily “habitable”, as the name might suggest Host stars are metal-poor Some super-Earths have been found in the habitable zone around main sequence stars