SAC Seminar - Kevin Schlaufman: The Typical Terrestrial-mass Planet Discovered by Transit Surveys and Its Implications for Planet Formation and Evolution
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Kevin Schlaufman will be visiting SAC on August 12, and will give a seminar
Date: Monday, August 12, 1:15pm
Title: The Typical Terrestrial-mass Planet Discovered by Transit Surveys and Its Implications for Planet Formation and Evolution
Abstract: All mass--radius relations for low-mass planets published to date have been affected by observational biases. Since planet occurrence and primordial atmospheric retention probability increase with period, the ``typical'' planet discovered by transit surveys may bear little resemblance to the short-period planets sculpted by atmospheric escape ordinarily used to calibrate mass--radius relations. I'll present an occurrence-weighted mass--radius relation for the typical low-mass planets in the Galaxy observed so far by transit surveys. Even at M = 1 M_Earth, to explain its observed radius the typical planet must have 1% of its mass in a H/He atmosphere. Unlike the terrestrial planets in our own solar system that finished forming long after the protosolar nebula was dissipated, these terrestrial-mass planets discovered in transit surveys must have formed early in their systems' histories. The existence of significant H/He atmospheres around 1 M_Earth planets confirms an important prediction of the core--accretion model of planet formation. It also implies that such planets can retain their primordial atmospheres and requires an order-of-magnitude reduction in the fraction of incident XUV flux converted into work usually assumed in photo-evaporation models. Because the short-period planets likely to be discovered by NASA's Transiting Exoplanet Survey Satellite (TESS) are not representative of the Galaxy's planet population, it will be important to use occurrence-weighting when considering the implications for models of planet formation of the masses and radii of TESS discoveries.
The SAC Seminar Team