Workshop turns more to theory: planetary structure, crusts and atmospheres; cooling and heating. Well, it is an Institute of Theoretical Physics…

Adamses Burrows and Burgasser start the morning.
We’re promised things will be stirred up a bit more.

Diana Valencia on super-earth structure and composition,
then Chris Sotin on water worlds.

Burrows: interesting figure on estimated core mass of hot giant planets (detected through transits) vs host star metallicity.

Inferred core mass has apparent correlation with stellar metallicity. Higher the stellar metallicity the more massive the inferred metal core of the planet, and the smaller and higher density is the planet. Not surprising, in some sense.

Everyone should read: Thermodynamics of atmospheric circulation on hot Jupiters by Jeremy Goodman

Likely that titanium oxide drives optical opacity in the upper atmospheres of hot giant planets, but, we ask, is it glossy white or eggshell white, or does it maybe have a light pastel tinge in a soothing green or cool blue?

low albedo, and high irradiation; we joyfully embrace the prospects of a black planet, lots and lots of them

HD 209458b is too blue in the mid infrared, models don’t fit.

Cool 3D rendering of an asymmetrically heated giant planet on final slide.

Valencia: toblerone diagram, very degenerate.
Add another ingredient and you get “Pyramints” – everybody remembers Pyramints, right? At least if you were in the UK at the right time.
Hot super-earths lose their atmosphere (cf Lammer et al 2009).
Hiding all the physics in ε – classic.

Interesting discussion of CoRoT-7b vs GJ1214b
former is clearly iron/silicate, latter is either icy or has some H/He envelope
work in progress, age of GJ124 is highly uncertain
some interesting slides on results in prep

then the eternal question: do super-earths have plate tectonics – this is important, probably depends on presence of water on and in mantle.
Don Ragan gave a very nice impromptu lecture to exoplanetary folks at a picnic in Aspen one summer a few years ago, it was my distinct impression that at least that group had not appreciated the important of trace water in silicate convection

mantle convection is not easy…
darnit, it is just another fluid, looked at from a suitably distant astrophysical perspective – oh, wait, we can’t do convection properly in any of our other astrophysical fluids either.
Ah well.

O’Neill and Lenardic ’07 say no ongoing plate tectonic in super-earths, maybe episodic like Venus under stagnant lid;
Valencia ’07 says supers should have earth like plate tectonics
good summary of difference in assumptions

importance of radioactive elements in driving convection
hm, I wonder if K40 yields in SNe and/or AGBs vary with Z…
Th/U must depend just on SNII yields, but the preponderance of those does depend on winds of massive stars, which are Z dependent. Yuck.

Good questions: are plate tectonics desirable or even necessary for habitabilty – espec their role in recycling the atmospheric gases.
If hydrated silicate mantles do plate tectonics, then habitability might well extend to at least 6-8 earth masses for plausible Fe/Si/H2O ratios (my personal willdass-guestimate).
With large systematic uncertainties, natch.

Sotin: distinguish between worlds with clear phase separations – ie liquid over solid with gaseous phase on top, vs solid-liquid-solid vs “ice rich” but heterogenous vs triple point worlds with no sharp phase separations

the key insight is hexapodia the phase curve of Ice IX VI

wot, we don’t know the value of the [ (Mg/Si/(Fe/Si) ] for Earth to within a factor of 2?!?
How, exactly, are we then expected to model mantle convection correctly?
I despair.

0.08% of the mass of the Earth is not accounted for…
the number 0.08% keeps recurring today

Hm, I see an opportunity for some wonderful neologisms,
and yet another wild and crazy inconsistent astronomical labeling system!

Estimated low mantle H2O for Earth – only about one ocean – what is cite?
Cite is a french lab experiment from 2003 or 2004 – didn’t catch the name. Anyone know?
Stevenson says max H2O fraction depends on whether silicate is liquid phase or solid; latter ought to hold much more water. ‘course which it is, may depend on how much H2O is in it.

Gives Earth 0.02% water. Yeah, that is dry.
Could easily have 10-100 times more with some creative radial transport of icy bodies in early solar system and maybe a less impressive last (lunar) impact.

NB: H2O vs other liquids, cf Titan

Maybe if we said NASA was looking for “Oil Worlds” the funding for exoplanets would sharply increase… ’cause we are, y’know…

Hm, first “Super Mercury” and now “Super Ganymede” – we need to redirect this to the “Marketing for Scientists” forum on facebook.


  1. #1 Lab Lemming
    April 2, 2010

    If you want the BSE (bulk silicate Earth) composition, a thourough overview is:
    H. O’Neill & H. Palme 1998: Composition of the Silicate Earth: Implications for Accretion and Core Formation. p 3-126. In The Earth’s Mantle: Composition, Structure, and Evolution. Ed. Ian Jackson. Cambridge University Press.

    The person who doesn’t know this composition within a factor of 2 needs to read more: most modern (e.g. post 1975) estimates agree to within better than 5%.

    Total terrestrial water is a bit trickier- but 1 to 3 hydrospheres is a good range of estimates.

    Radioactive should be minor for superearths. For earth, they are 20-45% of heat. The rest is primordial. primordial heat comes from gravitational binding energy, which goes up as M^2 (or more if you consider compression). radioisotopes go up with M (or less- K,Th,U have a nasty habit of migrating to the crust during melting, so heat the lid, not the mantle). So a 5Me super earth should have 25 times initial heat, and 5 times radio heat- with radio contributing 4-9% of total heating.