Dataset for Polarized Signatures of the Earth Through Time: An Outlook for the Habitable Worlds Observatory

The search for life beyond the Solar System remains a primary goal of current and near-future missions, including NASA's upcoming Habitable Worlds Observatory (HWO). However, research into determining the habitability of terrestrial exoplanets has been primarily focused on comparisons to modern-day Earth. Additionally, current characterization strategies focus on the unpolarized flux from these worlds, taking into account only a fraction of the informational content of the reflected light. Better understanding the changes in the reflected light spectrum of the Earth throughout its evolution, as well as analyzing its polarization, will be crucial for mapping its habitability and providing comparison templates to potentially habitable exoplanets. Here we present spectropolarimetric models of the reflected light from the Earth at six epochs across all four geologic eons. We find that the changing surface albedos and atmospheric gas concentrations across the different epochs allow the habitable and non-habitable scenarios to be distinguished, and diagnostic features of clouds and hazes are more noticeable in the polarized signals. We show that common simplifications for exoplanet modeling, including Mie scattering for fractal particles, affect the resulting planetary signals and can lead to non-physical features. Finally, our results suggest that pushing the HWO planet-to-star flux contrast limit down to 1 $\times$ 10$^{-13}$ could allow for the characterization in both unpolarized and polarized light of an Earth-like planet at any stage in its history.

This dataset contains all modeled spectropolarimetric signatures used to conduct this work. Each .zip file contains the output folders for one of the four eons: Hadean, Archean, Proterozoic, and Phanerozoic (i.e., Modern). Each of these top-level folders then contains individual folders for each specific model run. The names for each of these individual folders describes the specific model. Finally, each individual folder then contains files for the spectropolarimetric signatures, where each file contains four columns of data representing the spectra for that specific model at that specific planetary phase angle. Please refer to the README.txt as well as the accompanying manuscript for more information.