A new dynamical modeling of the WASP-47 system with CHEOPS observations

Among the hundreds of known hot Jupiters (HJs), only five have been found to have companions on short-period orbits. Within this
rare class of multiple planetary systems, the architecture of WASP-47 is unique, hosting an HJ (planet-b) with both an inner and an
outer sub-Neptunian mass companion (-e and -d, respectively) as well as an additional non-transiting, long-period giant (-c). The small
period ratio between planets -b and -d boosts the transit time variation (TTV) signal, making it possible to reliably measure the masses
of these planets in synergy with the radial velocity (RV) technique. In this paper, we present new space- and ground-based photometric
data of WASP-47b and WASP-47-d, including 11 unpublished light curves from the ESA mission CHaracterising ExOPlanet Satellite
(CHEOPS). We analyzed the light curves in a homogeneous way together with all the publicly available data to carry out a global
N-body dynamical modeling of the TTV and RV signals. We retrieved, among other parameters, a mass and density for planet -d of
Md = 15.5 ± 0.8 M⊕ and ρd = 1.69 ± 0.22 g cm−3
, which is in good agreement with the literature and consistent with a Neptune-like
composition. For the inner planet (-e), we found a mass and density of Me = 9.0 ± 0.5 M⊕ and ρe = 8.1 ± 0.5 g cm−3
, suggesting an
Earth-like composition close to other ultra-hot planets at similar irradiation levels. Though this result is in agreement with previous
RV plus TTV studies, it is not in agreement with the most recent RV analysis (at 2.8σ), which yielded a lower density compatible with
a pure silicate composition. This discrepancy highlights the still unresolved issue of suspected systematic offsets between RV and TTV
measurements. In this paper, we also significantly improve the orbital ephemerides of all transiting planets, which will be crucial for
any future follow-up.