Planets revolving around other stars than the Sun are called exoplanets. The first were found in the 1990s and since then thousands have been identified. The general rule is that exoplanetary systems appear different from our Solar system, of which we have yet to find an equivalent. Exoplanets show a diversity in every parameter that we can measure. Some orbit only a few stellar radii away from their star and end up re-emitting more heat than some of the smallest stars in our Galaxy. Others occupy orbits so eccentric they resemble comets. Planets have been discovered orbiting on planes inclined with respect to the equator of their stars. Some planets orbit two stars at once instead of just one. Isn’t Nature just incredible?!
Many systems contain planets that have no equivalent in the Solar system. For instance half of the Sun-like stars are accompanied by objects more massive than our Earth, at separations shorter than Mercury’s orbit. Indeed some planetary systems contain many of these odd planets within short distances of each other, so short that they would appear bigger than our Moon as seen from their sky!
We are far from having a comprehensive model for planet formation, and how planetary orbits subsequently evolve. New space missions (TESS, CHEOPS and PLATO) will help us improve our understanding of the basic parameters of planets and of the architectures of their systems. Meanwhile we have started to explore the chemical make-up of several exoplanetary atmospheres. Current observations reveal yet another diversity, one which can actually be glimpsed within our Solar system (think how different each of the eight planets look). With refined techniques, we have started discovering planets with sizes and irradiation similar to our Earth. The study of alien habitable climates is within grasp, with the identification of biologically produced gases feasible with the upcoming James Webb Space telescope.
All planetary parameters extracted from data are relative to the mass and radius of their host star. The Birmingham group is able to combine expertise in asteroseismology - which can provide robust estimates of the fundamental stellar properties - with expertise in exoplanetary studies. Birmingham researchers are involved in analysing data from WASP, Kepler, and K2, and will take part in the SPECULOOS, TESS, and PLATO surveys. The team also has access to multiple telescopes involved in planet detection (radial velocities and transits) and atmospheric characterisation, on the ground and in space.
Images © NASA.