There might be giants: unseen Jupiter-mass planets as sculptors of tightly packed planetary systems

The limited completeness of the Kepler sample for planets with orbital periods ≳1 yr leaves open the possibility that exoplanetary systems may host undetected giant planets. Should such planets exist, their dynamical interactions with the inner planets may prove vital in sculpting the final orbital configurations of these systems. Using an N-body code with additional forces to emulate the effects of a protoplanetary disc, we perform simulations of the assembly of compact systems of super-Earth-mass planets with unseen giant companions. The simulated systems are analogous to Kepler-11 or Kepler-32 in that they contain four or five inner super-Earths, but our systems also contain longer-period giant companions which are unlikely to have been detected by Kepler. We find that giant companions tend to break widely spaced first-order mean-motion resonances, allowing the inner planets to migrate into tighter resonances. This leads to more compact architectures and increases the occurrence rate of Laplace resonant chains

THE EVOLUTION OF INNER DISK GAS IN TRANSITION DISKS

Investigating the molecular gas in the inner regions of protoplanetary disks (PPDs) provides insight into how the molecular disk environment changes during the transition from primordial to debris disk systems. We conduct a small survey of molecular hydrogen (H[Subscript: 2]) fluorescent emission, using 14 well-studied Classical T Tauri stars at two distinct dust disk evolutionary stages, to explore how the structure of the inner molecular disk changes as the optically thick warm dust dissipates. We simulate the observed Hi-Lyman α-pumped H[Subscript: 2] disk fluorescence by creating a 2D radiative transfer model that describes the radial distributions of H[Subscript: 2] emission in the disk atmosphere and compare these to observations from the Hubble Space Telescope. We find the radial distributions that best describe the observed H[Subscript: 2] FUV emission arising in primordial disk targets (full dust disk) are demonstrably different than those of transition disks (little-to-no warm dust observed). For each best-fit model, we estimate inner and outer disk emission boundaries (r[Subscript: in] and r[Subscript: out]), describing where the bulk of the observed H[Subscript: 2] emission arises in each disk, and we examine correlations between these and several observational disk evolution indicators, such as n[Subscript: 13–31], r[Subscript: in, CO], and the mass accretion rate. We find strong, positive correlations between the H[Subscript: 2] radial distributions and the slope of the dust spectral energy distribution, implying the behavior of the molecular disk atmosphere changes as the inner dust clears in evolving PPDs. Overall, we find that H[Subscript: 2] inner radii are ~4 times larger in transition systems, while the bulk of the H[Subscript: 2] emission originates inside the dust gap radius for all transitional sources

NGTS-1b: A hot Jupiter transiting an M-dwarf

We present the discovery of NGTS-1b, a hot-Jupiter transiting an early M-dwarf host (Teff,∗=3916 +71 −63 K) in a P = 2.647 d orbit discovered as part of the Next Generation Transit Survey (NGTS). The planet has a mass of 0.812 +0.066 −0.075 MJ making it the most massive planet ever discovered transiting an M-dwarf. The radius of the planet is 1.33 +0.61 −0.33 RJ . Since the transit is grazing, we determine this radius by modelling the data and placing a prior on the density from the population of known gas giant planets. NGTS-1b is the third transiting giant planet found around an M-dwarf, reinforcing the notion that close-in gas giants can form and migrate similar to the known population of hot Jupiters around solar type stars. The host star shows no signs of activity, and the kinematics hint at the star being from the thick disk population. With a deep (2.5%) transit around a K = 11.9 host, NGTS-1b will be a strong candidate to probe giant planet composition around M-dwarfs via JWST transmission spectroscop