Mysterious Exoplanets: Kepler-36

Supervisor: Dr. Paul Wiegert

Can extend to MSc?:  Yes

Project Description (Abstract):

Extrasolar planets or 'exoplanets' are planets which orbit not our own Sun, but other stars in the Galaxy. The discovery of these exoplanets has revealed that our planetary system is just one of a wide array of possibly planetary configurations. One of the most prolific planet-finding missions was NASA's Kepler Space Telescope: it discovered planets by looking for the slight dip in a star's brightness (called a 'transit') which occurs should a planet around it happen to cross our line of sight.

One of the puzzling planetary systems it found is called Kepler-36, which currently has two known planets. The mystery arises because the two planets orbit their star very close to one another, but their compositions seem to be wildly different (Carter et al, 2012). The inner planet Kepler-36b (a 'super-Earth') has a density of 6.8 g/cm^3 (similar to iron, which has 7.87) and the outer, Kepler-36c (a 'mini-Neptune'), has a density of only 0.86 g/cm^3, less than water. Modern planet formation theories suggest that two planets that form at the similar distances from their star should have similar compositions: how did the Kepler-36 planetary system form?

This project will begin with an exploration of how the Kepler-36 densities were measured, and consider alternative explanations. Is it possible that one or the other planets' densities are not what we think they are? If the project is pursued at the graduate level, we would then consider the dynamical pathways that might have created such a system: could the planets have formed elsewhere and then had their orbits changed (a process called 'migration') to bring them closer together?

The Kepler-36 system provides unique opportunities to learn about the extremes in exoplanetary systems.

Carter, J. A. et al (2012). "Kepler-36: A Pair of Planets with Neighboring Orbits and Dissimilar Densities". Science. 337 (6094): 556–559. Freely accessible. doi:10.1126/science.1223269

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