Free Astronomy Magazine May-June 2020

MAY-JUNE 2020 promising scenarios. We do not know, for example, whether biofluorescence can de- velop in biospheres other than our own on Earth, and we can only speculate on the ex- istence of extraterrestrial coral structures. Even assuming their existence, the fluores- cence efficiency of proteins and pigments of terrestrial corals depends on the environ- ments in which they live, environments that, for planets around the red dwarfs considered in the modeling, are totally unknown to us. Fur- thermore, in order for bioflu- orescence to be perceived by other systems, very high surface coverage by extraterrestrial corals is required − close to 100%. To meet this condition, the distri- bution of shallow ocean floors must be equally high, a scenario to be identified and then verified. By comparison, fluo- rescent corals on Earth cover only 0.2% of the ocean floor, reaching down to about 60 meters deep. For a moment, let us try to be opti- mistic and accept that, around one of the closest red dwarfs, there is a planet with a global distribution of fluorescent corals immersed in a crys- talline ocean, above which there is a trans- parent atmosphere. For geometric reasons re- lated to planetary orbit, we will never have the opportunity to see much more than half a hemi- sphere. Since we observe these planets as they transit their star, we will not be able to see the surplus of light due to the bios- phere either during the transit or half an orbit later, when the planet is either com- pletely hidden or too close to the star to be observed separately. We can, in fact, hope to capture the light of the corals only near the maximum elongations of the planet – when only half of the lit hemisphere is fac- ing us. According to the calculations of Kaltenegger and O’Malley-James, once bio- A n example of coral flu- orescence, by which proteins absorb near-UV and blue light and re-emit light at longer wave- lengths. [Mon- terey Bay Aquar- ium, California]