Lecture 16: Super-Earths: a New Type of Planet Planets vs. Stars Internal structure Geochemical cycles Habitability

Direct Detection of Planets Three planets orbiting HR8799 (Marois et al. 2008)

Mass-Radius Diagram: Hot Jupiters Super-Earths

Mass range: ~ M Earth (Sasselov 2008)

Material properties of planets & small stars Models: Baraffe et al. four different ages: 0.5, 1, 3, & 5 Gyr Red: Pont et al. (2005) OGLE-TR-122 Size Mass planets stars Nuclear fusion of 1 H Electron degeneracy

Material properties of planets & small stars Size Mass planets stars Hot Jupiters Super-Earths New types of planets:

Material properties of planets & small stars planets Hot Jupiters Super-Earths New types of planets: Size Mass stars

The super-Earths M-R diagram Fix one ratio: Earth-like Fe/Si max radius min radius H2OH2O Valencia, Sasselov, O’Connell (2007)

(from C. Lovis) HD 40307

CoRoT-7b: 1.7 R Earth planet Rouan et al.(2009) Queloz et al.(2009) P orb = 0.85 days

GJ1214b: 2.7 R Earth planet Charbonneau et al.(2009) P orb = 1.6 days

Water vs. Dry super-Earths Zeng & Sasselov (2010) CoRoT-7b GJ1214b U N H+He pure H 2 O Earth Si/Fe Fe-rich

Super-Earths: two major families Rocky vs. Ocean (Sasselov 2008)

Super-Earths: (Sasselov 2008) Image: S.Cundiff

Earth & super-Earths vs. gas & ice giants UV / photo-chemistry surface / phase transition / boundary layer atmosphere M atm << M p mantle a well-mixed reservoir fluxes Loss

Plate tectonics is not the issue - the distinction that matters is between stagnant lid & everything else.

Super-Earths geochemistry, e.g. the Carbonate-silicate cycle, or Sulfur cycle, etc. Planets of different initial conditions can be “driven” to a set of geochemical equilibria by global geo-cycles over geological timescales.

Do super-Earths have a high habitability potential ? (as compared to 1 M Earth planets) Yes: many (though, not all) are expected to have same geophysics & geochemistry as Earth; have stable surface conditions - keep atmospheres easily; have plate tectonics, hence stable geo-cycles; stable dynamics (orbits & rotation).

Main points to take home: 1) Planets vs. Stars: planets break the hierarchical structure in the universe - consist of heavy elements. 2) Internal structure of super-Earths: two basic families (water & dry), and mini-Neptunes. 3) Global geochemical cycles: the carbon dioxide cycle keeps the climate stable on Earth 4) Habitability in general: liquid water, solid surface, stability & protection.