At this morning's Gaia DR2 prep workshop (parallel-working meeting), we gathered a group of people to discuss ideas for using Gaia DR2 data in the service of exoplanet science. We were focusing on easy ideas that could be executed quickly after the data release. These ideas fell into some broad categories. One is to use the astrometry and photometry to get stellar radii and thereby get better estimates of planet radii for the Kepler planets. Another is to use Gaia-based stellar age estimates to compare planetary systems around stars of different ages. Or compare ages for planetary systems of different architectures (as they say). One of my favorite age estimates is the (square of the) vertical action in the Milky-Way disk! Along the same lines: Test theories for pumping or damping of eccentricities with stellar ages. Because of recent work around Flatiron, there was substantial talk of whether Gaia could detect signatures of stars that have recently accreted their planets. There might be different signatures on different time-scales.
Late in the day, I worked some more on my #hackAAS project to look at the dimensionality of stars in element-abundance space. I think (but am not sure) that the best way to think about this problem for the purposes of chemical-tagging applications is in terms of how well we can predict unmeasured abundances. Because this gets at the value or trade-offs between measuring more elements or measuring the elements you already have but better. I need to write first and data-analyze second, but the data are so fun to play with!