We know the terrestrial mountain ranges, the canyons and the Martian valleys, the frozen peaks of Pluto … what do the surfaces of the exoplanets discovered so far look like? In a future with increasingly sensitive astronomical observation tools, we could discover it by studying the brightness oscillations of their mother stars: the ones we use today to deduce their existence and hypothesize their mass and composition.
No rocky planet of the Solar System is perfectly "polished": mountains, depressions, craters and other elements make their surfaces irregular (and interesting). We can expect it to be the same for extrasolar planets, but how to find out, from here?
Lights and shadows. Moiya McTier, astronomer at Columbia University, presented to the American Astronomical Society on January 11 some preliminary analyzes that show how one works in exotopography, a still young branch of astrophysics dedicated to the topographic aspect of exoplanets. Mc Tier used the maps of the 4 rocky planets of the Solar System and the Moon elaborated by the US Geological Survey to determine what their light curve would look like in the passage around the Sun (the Earth was considered in two versions: with or without oceans ).The Solar System on Google Maps
He has thus noticed that the sharp rises in elevation linked to important reliefs or depressions correspond to as many "jolts" in the data: the characteristics of the landscape therefore leave their mark even in the luminous imprint of a planet when it passes in front of its star.
Ambitious enterprise. But from here to being able to read it even for worlds so far away, the jump is important. The next generation of telescopes, such as the 30 Meter Telescope or ESO's European Extremely Large Telescope, will perhaps be able to distinguish some of these oscillations from simple "noise", but after at least twenty hours of planetary transit data.
The next generation of telescopes, with mirrors of 100 meters in diameter, should be up to the task, but under certain conditions.
False alarms. To better distinguish the significant signals, star and planet should be of similar size (the ideal pair would be a white dwarf with a planet similar to Mars). Some events could then create confusion: flares or star spots, the presence of exosatellites, earthquakes or oceanic events, as well as atmospheric distortion could create signals similar to those caused by variations in the planetary surface.
If, however, we were able to exclude all this buzz, obtaining topographic maps of extrasolar planets would be extremely interesting, to study the rotation speed and the length of the day, the arrangement of possible oceans and above all the habitability.