The velocity of interstellar asteroid 'Oumuamua with respect to the Local Standard of Rest of our Galaxy is low, which implies it is young, at least if it was ejected during its host star's protoplanetary phase. With this young age as our hypothesis, we assess possible origin systems for the interstellar asteroid in two ways.First, by modelling 'Oumuamua's past trajectory under the influence of the galactic tide and the disk heating (ie. scattering) to assess how far back one can reliably expect to trace its orbit. The stochastic nature of disk heating means that a back integration of 'Oumuamua can only expect to be accurate to within 15 pc and 2 km/s at -10 Myr, 100 pc and 5 km/s at -50 Myr, and 400 pc and 10 km/s at -100 Myr, sharply limiting our ability to determine a precise origin. However, we can show that if 'Oumuamua was ejected at low (∼ 1 km/s) speed, as is likely for most ejection processes, 'Oumuamua's origin system is currently within 1 kpc of Earth. This would place the origin system nearby within the local Orion Arm, and thus relatively easily accessible to telescopic study. This provides strong motivation for continued efforts to determine 'Oumuamua's place of origin, because that system could be studied in detail and shed light on the nature of this unusual asteroid.Second, with this initial assessment in hand, we perform a backwards integration of 'Oumuamua's trajectory accounting for uncertainty in its and the candidate source regions' speed and position where possible, to assess potential candidate regions. The Gaia DR2 catalog and the SIMBAD catalog were considered, with particular emphasis on young systems as detailed in the Catalog of Suspected Nearby Young Stars ) and moving groups as compiled in Gagné et al. (2018). Though disk heating prevents making any but a statistical link to local star-forming regions and moving groups, our best candidates are the Carina and Columba moving groups, the Lupus SFR, the T-Tau stars V391 Ori and BD+11 414, and the M dwarf GJ 1167 A. 'Oumuamua passed through at least a considerable subset of the Carina and Columba moving groups at a time comparable to their ages, making it perhaps the most plausible source region, if the asteroid was ejected by the planet-forming process.During the writing of this paper, a second interstellar comet 2I/Borisov was discovered. Though unlikely to be young due to its high velocity with respect to the LSR, we performed a similar analysis and found three stars in the Ursa Major group (GJ 4384, EV Lac, and GJ 102), one brown dwarf of the AB Dor group (2MASS J03552337+113343), and 8 Gaia DR2 stars (including EV Lac) to have plausible encounters at speeds <30 kms −1 and within 2 pc. We do not find any plausible encounters at speeds lower than 13 kms −1 .

The sub-Saturn (∼4–8 R ⊕) occurrence rate rises with orbital period out to at least ∼300 days. In this work we adopt and test the hypothesis that the decrease in their occurrence toward the star is a result of atmospheric mass loss, which can transform sub-Saturns into sub-Neptunes (≲4 R ⊕) more efficiently at shorter periods. We show that under the mass-loss hypothesis, the sub-Saturn occurrence rate can be leveraged to infer their underlying core mass function, and, by extension, that of gas giants. We determine that lognormal core mass functions peaked near ∼10–20 M ⊕ are compatible with the sub-Saturn period distribution, the distribution of observationally inferred sub-Saturn cores, and gas-accretion theories. Our theory predicts that close-in sub-Saturns should be ∼50% less common and ∼30% more massive around rapidly rotating stars; this should be directly testable for stars younger than ≲500 Myr. We also predict that the sub-Jovian desert becomes less pronounced and opens up at smaller orbital periods around M stars compared to solar-type stars (∼0.7 days versus ∼3 days). We demonstrate that exceptionally low-density sub-Saturns, “super-puffs,” can survive intense hydrodynamic escape to the present day if they are born with even larger atmospheres than they currently harbor; in this picture, Kepler 223 d began with an envelope ∼1.5× the mass of its core and is currently losing its envelope at a rate of ∼2 × 10−3 M ⊕ Myr−1. If the predictions from our theory are confirmed by observations, the core mass function we predict can also serve to constrain core formation theories of gas-rich planets.