# SAC Seminar - Kevin Schlaufman: The Typical Terrestrial-mass Planet Discovered by Transit Surveys and Its Implications for Planet Formation and Evolution

### Time

Monday 12 August 2019,  at 13:15 - 14:00

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.

Best regards,

The SAC Seminar Team