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VERSION:2.0
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PRODID:UW-Madison-Physics-Events
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SEQUENCE:0
UID:UW-Physics-Event-8632
DTSTART:20240229T213000Z
DTEND:20240229T223000Z
DTSTAMP:20260408T114741Z
LAST-MODIFIED:20240216T141843Z
LOCATION:4421 Sterling Hall
SUMMARY:Exploring the diversity of H2-H2O subNeptunes\, Astronomy Coll
 oquium\, Raymond T. Pierrehumbert\, University of Oxford
DESCRIPTION:Astronomical observations directly probe the properties of
  only the outer portions of a planet's atmosphere.  When both mass and
  radius observations are available\, the resulting mean density provid
 es further\, though highly degenerate\, constraints on the composition
  of the interior.  In this talk\, I will discuss the kinds of inferenc
 es that can be drawn when the two kinds of information are put togethe
 r.  The emphasis will be on planets whose fluid layer is composed of H
 2 and H2O with various proportions\, potentially interacting with a si
 licate core.   An important physical consideration constraining plausi
 ble interior structures is that for liquid water interiors\, the solub
 ility of H2 is constrained by Henry's Law solubility\, whereas for sup
 ercritical water interiors H2 (and other gases) are completely miscibl
 e with the interior.  We will discuss the range of possible H2:H2O rat
 ios in the outer atmosphere that can be compatible with a supercritica
 l water atmosphere.   Although an H2 layer is miscible with a supercri
 tical water interior\, there is a stable density jump at the interface
 \, which inhibits mixing between the two layers\;  an essential missin
 g piece of the puzzle is the quantification of the rate of such mixing
 .  Once mixing begins\, the moistening of the H2 layer leads to additi
 onal phenomena\, including both water vapour feedback and generation o
 f steep radiative layers near the interface through compositional stab
 ilization of the lower atmosphere.  I will also discuss thermal evolut
 ion models and implications of interaction of the H2:H2O fluid layer w
 ith a basal magma ocean. K2-18b and GJ1214b will be used as the archet
 ypes of two very different types of subNeptunes\, but I will also disc
 uss results from a recent JWST survey of subNeptunes selected to have 
 densities compatible with a potentially H2O-rich composition. 
URL:https://www.physics.wisc.edu/events/?id=8632
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