| |
 |
| Paper: |
Detecting Surface Liquid Water on Exoplanets |
| Monograph: |
10, HWO25 Proceedings Part I: Community Science Case Development Documents |
| Page: |
439 |
| Authors: |
Jacob Lustig-Yaeger; Nicolas B. Cowan; Renyu Hu; L. C. Mayorga; Tyler D. Robinson |
| DOI: |
10.26624/MBAN7590 |
| Abstract: |
Planets with large bodies of water on their surface will have more temperate and stable climates, and such
planets are the ideal places for life-as-we-know-it to arise and evolve. A key science case for the Habitable
Worlds Observatory (HWO) is to determine which planets host surface liquid water. Aside from its implications for planetary climate and astrobiology, detecting surface water on terrestrial exoplanets would place
important constraints on our theories of planet formation and volatile delivery. Rotational variability in the
reflectance of an exoplanet may reveal surface features rotating in and out of view, including oceans. Orbital
changes in reflectance and polarization, meanwhile, are sensitive to the scattering phase function of the planetary surface, including specular reflection from large bodies of water. Although these techniques are applicable
to all temperate terrestrial exoplanets, we focus in this document on the directly-imaged planets that are more
likely to drive the HWO coronagraph design. Identification of water oceans relies on detecting a liquid, and
using other lines of evidence to narrow that liquid down to being water. Liquids have smoother surfaces than
most solids, and hence exhibit specular reflection instead of diffuse reflection. In practice, this makes lakes
and oceans look dark from most illumination angles, but mirror-like at glancing angles. HWO is uniquely
capable of identifying surface liquid oceans via their optical properties. Given that discovering an ocean on
an exoplanet would confirm its status as a habitable world, this science case is literally the raison d’ètre of the
Habitable Worlds Observatory.
This article is an adaptation of a science case document developed for HWO’s
Solar Systems in Context, Characterizing Exoplanets Steering Committee. |
|
|
|
|
|
