2025AJ....169..200Z

We present the discovery of a Jupiter-like planet, HD 73344 d (${m}_{d}=2.5{5}_{-0.46}^{+0.56}\,{M}_{J}$, ${a}_{d}=6.7{0}_{-0.26}^{+0.25}$ au, ${e}_{d}=0.1{8}_{-0.12}^{+0.14}$) based on 27 yr radial velocity (RV) observations from ELODIE, Lick/Hamilton, SOPHIE, APF, and HIRES. HD 73344 also hosts a compact inner planetary system, including a transiting sub-Neptune, HD 73344 b (P_b = 15.61 days, ${r}_{b}=2.8{8}_{-0.07}^{+0.08}\,{R}_{\oplus }$), and a nontransiting Saturn-mass planet (P_c = 65.936 days, ${m}_{c}\,\sin \,{i}_{c}=0.36{7}_{-0.021}^{+0.022}\,{M}_{{\rm{J}}}$). By analyzing TESS light curves, we identified a stellar rotation period of 9.03 ± 1.3 days. Combining this with $v\,\sin \,{i}_{* }$ measurements from stellar spectra, we derived a stellar inclination of $63.{{6}^{\circ }}_{-16.5}^{+17.4}$. Furthermore, by combining RVs and Hipparcos-Gaia astrometric acceleration, we characterized the three-dimensional orbit of the outer giant planet and constrained its mutual inclination relative to the innermost transiting planet to be 46° < ΔI_bd < 134° (1σ) and 20° < ΔI_bd < 160° (2σ), strongly disfavoring coplanar architectures. Our analytical calculations and N-body simulations reveal that the two inner planets are strongly coupled with each other and undergo nodal precession together around the orbital axis of the giant planet. During nodal precession, the orbital inclinations of inner planets oscillate with time and therefore become misaligned relative to the stellar spin axis. The formation of such systems suggests a history of planet-planet scattering or misalignment between the inner and outer components of protoplanetary disks. The upcoming release of Gaia Data Release 4 will uncover more systems similar to HD 73344, and enable the study of the flatness of exoplanet systems with a mixture of inner and outer planetary systems on a statistical level.