HD 152843 c has the longest orbital period of any known low-density exoplanet

Star system: HD 152843 | Distance from the Sun: 353 light years

The two planets in the HD 152843 system have nearly equal masses but differing radii, and the outer planet HD 152843 c has the longest orbital period of any known low-density exoplanet. HD 152843 c is also located in the Saturn valley, the observed lack of planets larger than Neptune but smaller than Saturn. The orbital periods of the planets suggest they are near a 5:3 mean motion resonance, and the brightness of the host star and the low density of HD 152843 c make it a key target for atmospheric characterization.

Scientific study

HD152843 b & c: the masses and orbital periods of a sub-Neptune and a super-puff Neptune (external link)