In the next two decades, missions to study extrasolar planets will be able to detect and sample the light of individual Earth-like extrasolar planets. In particular, light curves can be used to identify daily and seasonal changes in their surface. Computer simulations and observations of Earth and other planets suggest that even large surface features like land, oceans, and ice areas might be identified. However, many factors like orbital parameters, phase angle, seasons, and weather (i.e. clouds) will make difficult the photometric interpretation of these surface features. Here we propose to use a dynamic computer simulation using Earth paleogeography as our approach to study this phenomenon. Our main goal is to establish a methodology to help interpret photometric observations of Earth-like extrasolar planets.
A computer simulation using photorealistic ray-tracing is being use to simulate various planetary orbital, rotational and surface configurations including the presence of clouds and seasonal features (i.e. ice cover). The imagery generated as part of the Visible Paleo-Earth will be used to study the different ocean-land-ice variations of Earth in the last 750 million years as base models for Earth as an exoplanet. Simulations will be validated by context images of the different configurations and from previous studies results. This is a challenging project in astrobiology, remote sensing, and image visualization and analysis that might provide new insights and approaches for the future characterization of terrestrial extrasolar planets from light curves.
Figure 1 to 5 show computer models of the relative reflectivity RGB light curves for a full rotation of the terrestrial planets at two different phase angles. These models and visualizations were done using the Interactive Data Language (IDL). There is information and references of previous studies on this problem in the resources section at the end. The next step in these simulations will implement synthetic infrared images added to the RGB information.
Figure 1. Full and crescent phase diurnal computer simulation of the current Earth (summer). The contrast of land and ocean areas is more notable between the red and blue filter. The landmasses structure is more notable at small phase angles.
Figure 2. Full and crescent phase diurnal computer simulation of the Earth 500 Mya. The contrast of land and ocean areas is more notable between the red and blue filter. Even that there was no vegetation and the land masses were distributed differently, the light curve looks very similar to Earth today (but shifted by 120°). Comparing this view with current Earth, it appears that vegetation can not be differentiated by simple photometry in the visible range.
Figure 3. Full and crescent phase diurnal computer simulation of Mars. There are some variations due to surface features.
Figure 4. Full and crescent phase diurnal computer simulation of Mercury. There are smalls variations due to surface features.
Figure 5. Full and crescent phase diurnal computer simulation of Venus. Planets with dense atmospheres show almost no variation in the light curves at any color.