HR 8799 harbors arguably the first and best-studied directly-imaged planets .
In this brief article , I describe how the HR 8799 planetary system is a benchmark system for studying the atmospheres , orbital properties , dynamical stability , and formation of young superjovian planets .
Multi-wavelength photometry and spectroscopy show that HR 8799 bcde appear to have thicker clouds than do field brown dwarfs of similar effective temperatures and exhibit evidence for non-equilibrium carbon chemistry , features that are likely connected to the planets ’ low surface gravities .
Over 17 years of astrometric data constrain the planets ’ orbits to not be face on but possibly in multiple orbital resonances .
At orbital separations of 15–70 au and with masses of \approx 5–7 M _ { J } , HR 8799 bcde probe the extremes of jovian planet formation by core accretion : medium-resolution spectroscopy may provide clues about these planets ’ formation conditions .
Data from the next generation of 30 m-class telescopes should better constrain the planets ’ orbits , chemistry , gravity , and formation history .