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The Climates of Other Worlds: Searching for the Next Habitable Planet
Many planets "able" to host life, in the earth-size regime.
Past exoplanet discovery due to Kepler mission, uses the planet transit technique. Successor is called TESS (all-sky transit survey), will cover a different population as well (brighter stars), hope to use JWST to search for biosignatures with IR spectrograph to follow up discoveries.
What she does: Combines observational data with theoretical simulations with computer climate models.
Habitable: liquid, bioessential elements, energy
Liquid water is not very stable, all life we know requires it, so we search for it.
Liquid water stable on the planets surface in the habitable zone, a function of distance and host stellar mass.
Snowball earth - 800 million years ago, it was covered in ice from pole to pole, while it still lay in the habitable zone.
Influence on liquid water:
- stellar effect
- planetary system
- planetary properties
She focuses on :
- SED of host start
- atmosphere and surface of planet
- and the presence of additional companions in planets system and the changes in orbital configurations due to that.
Models:
1D radiative transfer, atmospheric gas absorption
radiative convective climate models
energy balance models
3d general circulation models (GCMs) (most sophisticated):
- long been used to predict climate on earth, now being used to predict anthropogenic CO2 induced climate change
- predicted we were instead in a mudball state (not snowball)
- used to propose photosynthetic life surviving snowball earth (narrow swath of open water near the equator)
- what happened to liquid water on mars? (its frozen now)
M-dwarf stars are long-lived, cool and small.
- most numerous stars in the galaxy
- easier to detect planets around m-dwarfs (transit techniques work better as ratio is smaller)
- smaller planets prevalent around smaller stars
Closer planets ⇒ tidal locking (day=year)
Starlight interacting with atmosphere and surface:
- albedo = reflectivity
- snow/snow albedo depends on wavelength
- Ice-albedo feedback
- ice absorbs red light, blue light is reflected
red dwarfs ⇒ more light is absorbed by the ice compared to our sun
their study: 3 planets at equivalent stellar flux distances (earth-like instellation)
dialed down intellation and observed where the planets went into snowball state
M-dwarf didn't freeze over until 27% instellation reduction (shallow slope ⇒ less susceptible to snowball state)
shortwave heating (direct from star) in the Mdwarf due to CO2 and water absorbing (earth-like atmosphere) in IR, M-dawrf are more stable against convection
M-dwarf absorbs more radiation, similar overall temp with a lower instellation.
M-dwarfs have warmer poles
M-dwarfs are easier to thaw from a snowball state
They have a more stable climate: harder to freeze, easier to thaw
Hadley circulation: responsible for the net circulation of heat
Weaker hadley cell on the M-dwarf on deglaciating planet, due to increased shortwave heating
Historesis plots: lag in physical response when you reverse a change implemented
Redder star = smaller historesis
Looking at a new surface type: NaCl2H20 hydrohalite . Hydrohalite is highly reflective in IR.
Obliquity affects habitability.
Insolation = amount of radiation incoming.
Combining both observations and theory = how to most accurately assess planetary habitability
Drafting slides:
- easy slide:
- what is the habitable zone? why search for water?
- harder slide:
- how does type of star affect presence of ice on a planet?