Lecture 16: Super-Earths: a New Type of Planet

• Planets vs. Stars• Internal structure• Geochemical cycles• Habitability

Direct Detection of Planets

• Three planetsorbiting HR8799

(Marois et al. 2008)

Mass-RadiusDiagram:

Hot Jupiters

Super-Earths

Super-Earths

Mass range:~ 1 - 10 MEarth

(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

Siz

e

Mass

planets

starsNuclearfusion of 1H

Electrondegeneracy

Material properties of planets & small stars

Siz

e

Mass

planets

stars

Hot Jupiters

Super-Earths

New typesof planets:

Material properties of planets & small stars

planets

Hot Jupiters

Super-Earths

New typesof planets:

Siz

e

Mass

stars

The super-Earths M-R diagram

Fix one ratio:

Earth-like Fe/Si

max ra

dius

min

radius

H2O

Valencia, Sasselov, O’Connell (2007)

(from C. Lovis)

HD 40307

CoRoT-7b: 1.7 REarth planet

Rouan et al.(2009)

Queloz et al.(2009)

Porb = 0.85 days

GJ1214b: 2.7 REarth planet

Charbonneau et al.(2009)

Porb = 1.6 days

Water vs. Dry super-Earths

Zeng & Sasselov (2010)

CoRoT-7b

GJ1214b

UN

H+He

pure H 2O

Earth Si/Fe

Fe-rich

1

2

3

1 2 5 10

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

atmosphereMatm << Mp

mantle

a well-mixedreservoir

fluxesLoss

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

QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.

Super-Earths geochemistry,e.g. the Carbonate-silicate cycle, or Sulfur cycle, etc.

Planets of differentinitial conditionscan be “driven” toa set of geochemicalequilibriaby global geo-cyclesover geologicaltimescales.

Do super-Earths have a high habitability potential ? (as compared to 1 MEarth 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.