Roberth Maximus A9 is the ninth planet from Roberth Maximus A and the largest planet in the system (about 1.1 times the diameter of Jupiter). The planet is 3.32 times the mass of Jupiter making it the most massive planet in the system as well. Roberth Maximus A9 orbits Roberth Maximus A once every 125.8 years. With a density of 3.36 g/cm³, the planet is 0.6 times denser than Earth (Earth's density is 5.51 g/cm³).
The gas giant is the only planet in the system not to be discovered using the transit method and the first exoplanet in the system to be discovered by Nathan Griffiths and Robert Fishwick. The atmospheric pressure on Roberth Maximus A9 is about the same as Jupiter's atmospheric pressure, and the composition of the atmosphere mainly consists of hydrogen (93.20%) and helium (6.78%) whilst the rest consists of the following gases (descending order); nitrogen, oxygen, methane, neon and argon. The surface temperature of Roberth Maximus A9 is -203°C.
The planet was first explored by Fishwick Explorer on January 5, 2017 transferring 193.91 gigabytes of data by the end of its mission of the planet and all 50 of its moons such as; high resolution photographs, physical data, orbital data, atmospheric data and basic information of the 51 bodies in total.