KITP: habitable worlds

Finding and characterizing habitable exoplanets.

Enric Palle on Earth as an exoplanet.
Drake Deming on using JWST to find exoplanets

Then Lisa Kaltenegger on biosignatures
Jim Kasting on habitability and 3D GCMs.

Missed Palle’s talk. It is online…
Talked about transmission spectra, reflectance, variability, polarization, red edge.
Caught the discussion, some interesting banter.

On the “red edge” – there will be something like it on any efficient biosphere because plants must absorb efficiently near the peak transmission spectrum of the star, and there must be some heat rejection at some Teff less than the peak spectrum.

It will not generally be chlorophyll, it is a porphyrin pigment – its appearance is contingent evolution, but there are certainly many other pigments with metal ion complexes which can do quantum efficient energy capture and transfer (eg phycocyanin or bacteriorhodopsin). Which is incorporate will be contingent, not deterministic. But there ought to be qualitative similarities in whatever compound life elsewhere co-opts – just not that shade of green…

Nice discussion on Peromyscus

we can use JWST to play the Spitzer game of taking differential spectra of star+planet and star only during transit to get low res planet spectra.

NB: reviews in Nature 2009 and ARAA 2010.

JWST is bigger and more sensitive than Spitzer, so go to Super-Earths.
Might see hints of habitable signs, maybe even partial biosignatures.
eg use NIRSPEC at R=1000, and MIRI photometry.

Pop synth models suggest we should look for habitable Super-Earths transiting M-dwarfs.
yay. Hope to have a few usable targets in the sky – need to find them first.

Lots o’plots on what we might do with JWST.
Looks good. And, if-and-when it flies, we ought to find ways to use it that are even better than we predict.

Check the KITP online talks for Kaltenegger and Kasting
Lots of details on atmospheric spectra and potential observables, what is robust and what is not, maybe.


  1. #1 Lab Lemming
    April 3, 2010

    How does the red edge apply to a chemosynthetic biosphere?

  2. #2 Steinn Sigurdsson
    April 3, 2010

    A priori there is no need for one, since chemosynthetic organisms don’t need to absorb light strongly.
    There might still be need for radiative cooling, but it could be locally adaptive so no edge, just general lower albedeo on the red side of the spectral peak of the star.

  3. #3 Lab Lemming
    April 4, 2010

    If we see an absorption that we can’t explain with known, simple molecules, wouldn’t that be a good clue for life all on its own without overthinking it like this?

    Oh wait, that means the kupier belt is alive…

  4. #4 kurt9
    April 14, 2010

    Of course not all plants are green or use chlorophyll. There’s the copper beach tree just outside my window that I am looking at now, with its dark red leaves. Not a single green leaf in sight.