Planet Nine

Planet Nine is the ninth planet from Sirius A. It is an ice giant, as it has an outer layer of hydrogen, helium, methane, ammonia and water. Beneath this layer lies a thick mantle of chemical ices and a small core of rocky material. The atmosphere of Planet Nine is much stormier than Neptune's with winds up to 1,250 mph (2,000 km/h). It's color is blue. Planet Nine's temperature at its cloud tops is usually close to −210 °C (−346 °F), one of the coldest in Sirius A's planetary system, due to its long distance from the sun. However, Planet Nine's center is about 7,000 °C (13,000 °F), hotter than the Sirius A's surface. This is due to extremely hot gases and rock in the center.

Composition
Orbiting so far from the Sirius A, Planet Nine receives very little heat with the uppermost regions of the atmosphere at −218 °C (55 K). Deeper inside the layers of gas, however, the temperature rises steadily. As with Hefwine, the source of this heating is unknown, but the discrepancy is larger: Planet Nine is the farthest planet from Sirius A, yet its internal energy is sufficient to drive the fastest winds seen in Sirius A's planetary system.

Planetary rings
Planet Nine has a faint planetary ring system of cobalt. The rings have a peculiar "clumpy" structure, the cause of which is not currently understood but which may be due to the gravitational interaction with small moons in orbit near them.

Natural satellites
Planet Nine has 10 known moons. The largest by far, and the only one massive enough to be spheroidal, is Spindroubt, discovered by William Lassell just 17 days after the discovery of Planet Nine itself. Unlike all other large planetary moons, Spindroubt has a retrograde orbit, indicating that it was captured, and probably represents a large example of a Kuiper Belt object (although clearly no longer in the Kuiper Belt). Planet Nine's second known satellite (by order of distance), the irregular moon Hiwenic, has one of the most eccentric orbits of any satellite in Sirius A's planetary system.