Earth Around a Red Star

Post date: Sep 26, 2011 4:12:27 PM

The current potential habitable exoplanets, HD 85512 b and Gliese 581 d, orbit red stars. HD 85512 is a K5V and Gliese 581 is a M3V type star, both dimmer than the Sun. Here we used the Scientific Exoplanet Renderer (SER) to visualize how Earth will look like at the position of these two exoplanets, considering both the effect of color and stellar flux (Figure 1). Certainly, terrestrial evolution and composition will be different in such systems, but this visualization gives an idea of how much light is reflected from those stars at the exoplanets positions. They will look less interesting under the light of red dwarf star (Figure 2), but this is something usually not considered by artistic representations. We want to portray exoplanets for SER with their reflected stellar fluxes, which gives a visual idea of their proximity to the parent star (Figure 3). Hot exoplanets will be bright and cold ones will be dim. 

Figure 1. Comparison of the appearance of Earth at the position of two known potential habitable exoplanets. Under HD 58812 Earth is closer to the star and looks brighter with a pinkish tone. On Gliese 581 it is farther and looks much redder and barely visible. However, a planet exactly like Earth in those situations will probably become a Venus-like world on HD 58812 and a frozen Mars-like world on Gliese 581. More cloud cover or a denser 'greenhouse' atmosphere, respectively, are necessary for such exoplanets to be habitable.

Figure 2. Appearance of Earth under the light of Gliese 581, a red dwarf star. The image has been enhanced for visibility from the stellar-flux-correct comparison shown on Figure 1. It is speculated that any vegetation around a planet of a red dwarf star will also look darker due to a photosynthesis adaption to the star spectral type. Oceans will also look much darker.

Figure 3. Terrestrial planets showing their relative reflected solar flux from a distance to appear as the same size. This is similar to the view from a camera with a fixed aperture. Mercury is over exposed and Mars is underexposed. Light reaching jovian planets is to dim for them to be visible in this scale. This example shows the need for a logarithmic intensity scale to fit al possible visual ranges.