PROBING THE INTERIORS OF VERY HOT JUPITERS USING TRANSIT LIGHT CURVES

Abstract

Accurately understanding the interior structure of extra-solar planets is\ncritical for inferring their formation and evolution. The internal density\ndistribution of a planet has a direct effect on the star-planet orbit through\nthe gravitational quadrupole field created by the rotational and tidal bulges.\nThese quadrupoles induce apsidal precession that is proportional to the\nplanetary Love number ($k_{2p}$, twice the apsidal motion constant), a bulk\nphysical characteristic of the planet that depends on the internal density\ndistribution, including the presence or absence of a massive solid core. We\nfind that the quadrupole of the planetary tidal bulge is the dominant source of\napsidal precession for very hot Jupiters ($a \\lesssim 0.025$ AU), exceeding the\neffects of general relativity and the stellar quadrupole by more than an order\nof magnitude. For the shortest-period planets, the planetary interior induces\nprecession of a few degrees per year. By investigating the full photometric\nsignal of apsidal precession, we find that changes in transit shapes are much\nmore important than transit timing variations. With its long baseline of\nultra-precise photometry, the space-based \\emph{Kepler} mission can\nrealistically detect apsidal precession with the accuracy necessary to infer\nthe presence or absence of a massive core in very hot Jupiters with orbital\neccentricities as low as $e \\simeq 0.003$. The signal due to $k_{2p}$ creates\nunique transit light curve variations that are generally not degenerate with\nother parameters or phenomena. We discuss the plausibility of measuring\n$k_{2p}$ in an effort to directly constrain the interior properties of\nextra-solar planets.\n