Infernum

Currently unofficial lore, and in progress.

Infernum

Orbital characteristics
Semi-major axis	0.025 AU (3,739,900 km)
Eccentricity	0
Orbital period (sidereal)	1.041053241 days (24.9852778 h)
Average orbital speed	264.63 km/s
Inclination	76.3°
Star	Solakku
Physical characteristics
Mean radius	1.497 RJ
Mass	3.1 MJ
Escape velocity	86.62 km/s
Axial tilt	12.1° (to orbit)
Albedo	0.5
Temperature	3,187 K (2,910 °C; 5,280 °F)
Atmosphere
Composition by volume	90% hydrogen 9.4% helium 0.5% iron 0.06% carbon monoxide 0.04% titanium monoxide

Infernum (natively Valotolave, lit. "burning land") is a hot jupiter planet orbiting close to Solakku. It orbits with a short period of about 25 hours, making it observable as transiting Solakku several times per Avalon day. Its close proximity to Solakku is responsible for tidal effects on the surface of the star, which trigger observable stellar activity.

It is the largest planet in the Solakku system and one of the brightest. Observations of it have historically contributed significantly to avali understanding of several concepts in astronomy and astrophysics. Like other planets which may be observed by the naked eye, Infernum has contributed significantly to avali folklore.

No moons orbit Infernum, as its hill sphere is too small to fit any other celestial body.

Physical Characteristics

Composition

The upper atmosphere for Infernum is observed to contain 90% Hydrogen, with almost 10% Helium, with the remainder being traces of various molecules such as titanium monoxide and carbon monoxide. However, the overall ratio of gases within the planet is estimated to be closer to 80% Hydrogen and 20% Helium. A significant amount of silicates and iron are observable in Infernum’s spectrum, dredged up by the high temperatures.

Size and mass

Infernum measures about 16 Earth radii, or 50 times the size of Avalon. However, this figure is only a rough average. In reality, Infernum is prolate as it is being stretched by the gravity of Solakku. Its radius is additionally being inflated by the high temperatures puffing it up even before being stretched.

Infernum’s mass sits at 985 Earths or 36,000 Avalons, making it the heaviest planet in the Solakku system, only eclipsed by the star Crest. This mass is still by far not enough to have it be considered a brown dwarf, despite the fact that Infernum visibly radiates light on its far side. This mass is also slowly dropping as Infernum undergoes mass loss from Solakku’s gravity slowly stripping material from Infernum’s atmosphere. The high temperatures also aid in allowing atoms to be accelerated away from the planet. However, this process is very slow and is expected to take many times longer to completely strip the planet of its atmosphere than it will take for its orbit to drop past the roche limit.

Atmosphere

Infernum’s atmosphere consist primarily of hydrogen and helium, with smaller amounts of other compounds such as iron, titanium monoxide, carbon monoxide and even water and ammonia vapors.

A thick cloud layer of silicate and iron vapors is constantly maintained everywhere on the planet. As these are highly opaque, they make direct observation of deeper layers of the planet difficult. They are also highly reflective, raising Infernum’s albedo to 0.5. It is assumed that, just like clouds on other planets, these are capable of precipitation, in this case in the form of droplets of molten iron, which re-evaporate in the hotter deeper layers of the planet.

The atmosphere of Infernum is also characterized by intense winds circulating heat between the near and far side at speeds of up to 12 km/s. The temperature of the day side is about 3,187 K (2,910 °C; 5,280 °F), which drops to 1,853 K (1,580 °C; 2,880 °F) on the night side. The day side temperature is actually high enough to ionize hydrogen. These hydrogen ions flow to the far side and recombine into neutral atoms, before cycling back towards the near side.

Internal structure

Due to difficulty of observation, Infernum’s internal structure is hard to discern, but it most likely contains a mantle of metallic hydrogen with a layer of liquid hydrogen coating it before the puffy atmosphere. At the very center should be a rocky core, from which the planet originally grew.

The temperature of Infernum’s interior is estimated to be even more extreme below the cloud layers than the visible layers of atmosphere, probably growing to 10,000s of Kelvins.

Formation

It is highly improbable that Infernum formed in its present location. Gas giants generally form past the frost line, which is where temperatures allow volatile chemicals to freeze solid, and contribute to the mass of growing terrestrial planetoids. This eventually pushes them past a mass where they are able to start accreting a thick hydrogen and helium envelope, eventually developing into a gas giant.

However, this close to Solakku, there would have been neither enough rocky nor gassy material available to form a gas giant directly. Instead, Infernum is likely to have formed as just described, and then migrated inwards to its current orbit. The mechanics by which this could have occurred are numerous, but the amount of distance Infernum would have had to cross means it was potentially extreme.

Most likely, Infernum formed together with Valaya in relatively close orbits, before an encounter with a heavy object from interstellar space pushed both planets into closer orbits, though Infernum was affected more strongly. This theory also explains why there are only two terrestrial bodies in-between the orbits of Valaya and Infernum, as the latter’s migration would have disrupted the orbits of every object within this space.

Orbit and rotation

Infernum has an incredibly close orbit to Solakku, only 0.025 AU, which is 21 times closer than even Magnus. It completes this orbit once every 25 hours, meaning it is seen transiting Solakku several times per day from Avalon. Its orbital eccentricity is negligible and can be assumed to be zero, the result of its orbit having long since circularized under the gravitational pull of Solakku. Its inclination is incredibly high, on an almost polar orbit around Solakku, further indicating that it migrated to its current orbit after a major disruption to the Solakku system.

This orbit is continuously decaying due to tidal forces removing energy from Infernum’s velocity. It is assumed that Infernum originally circularized on a much higher orbit, but has been spiraling inwards for millions of years. As the effects of tidal friction become more pronounced the deeper the planet falls into Solakku’s gravity well, this decay is accelerating and will eventually bring the planet within the roche limit, at which point its hydrogen and helium composition will be rapidly pulled apart. The rocky core at its center might survive for some time longer, but will also eventually be destroyed, with all of Infernum’s mass adding to that of Solakku. This process is estimated to begin in anywhere from 5 to 25 million years.

Infernum is tidally locked to Solakku due to its proximity. However, Infernum is not a solid body, meaning the atmosphere is free to rotate at a different speed at different latitudes. The rotation of its magnetosphere is instead used as a reference point for measuring Infernum’s rotation. Notably, Infernum possesses an axial tilt which is only misaligned from its orbital plane by 12.1 degrees, which is counterintuitive to its probable origin as a planet in roughly the same plane as the others. This implies either its axis shifted over time after gaining its inclination, or the event which pushed it towards its current orbit was an impact, rather than gravitational influence of a passing object.

Magnetosphere

Infernum possesses a magnetic field with a mean strength of 0.12 mT with a highly asymmetric shape. Though a magnetic dipole, it interacts with the solar wind from Solakku, which compresses and weakens it against the direction of Infernum’s orbit. Infernum’s high orbital velocity causes its magnetic field to leave a bow shock within Solakku’s corona, visibly disturbing the solar winds.

These interactions serve to generate strong radio signatures, including short bursts in a wide range at and above 1 MHz and even as high as 50 MHz or more. These can be picked up on Avalon with shortwave radio receivers.

Observation

Infernum’s surface is incredibly difficult to observe. Most of the time, the whole planet is obscured by the brightness of Solakku in the background. Even if the planet is visually located next to the star, its high albedo means it reflects a lot of incoming light from Solakku on the day side, making it incredibly bright and obscuring details. It is possible to observe the night side of Infernum using amateur equipment by blocking the light from the day side, revealing a deep red glow of thermal photons emitted in the upper atmosphere.

Exploration using probes is also inadvisable, due to the required proximity of the spacecraft to Solakku. The closest approach ever performed to Infernum by spacecraft still only reached a distance of 0.01 AU (1,496,000 km).

However, Infernum’s shadow cast by Solakku is easily observable via a telescope with proper filters. Infact, Infernum may sometimes be observable by the naked eye when Valaya has eclipsed Solakku and it briefly becomes visible as a bright dot before it too is eclipsed. Prehistoric records also suggest observations of Infernum all across Avalon, including its far side, using thick material like pieces of wood to block out the light of Solakku, revealing Infernum as a white spot next to the star.

These observations strongly shaped early astronomy, as Infernum is the easiest to observe evidence of another planet orbiting Solakku, due to its short orbital period making its motion visible over just a few hours of observation. Infernum’s name was most likely derived at this time and many old myths connect it to Solakku. It is most often seen as Solakku’s younger packmate, closer in existence to a moon, but burning with flame which it still has to borrow from its larger companion whom it flies with. It is said that once its nurturing period is over, it will have grown into another star similar to Solakku.

Observations of Infernum’s transit across Solakku became easy to obtain after the invention of the telescope and formed the basis of a Solakku-centric model of the Solakku system. They also helped to inform early theories of universial gravitation and orbital mechanics. Crucially, coordinated observations taken from different locations on Avalon allowed measurement of the stellar parallax to Solakku and first semi-accurate estimation of the distance between Avalon and Solakku. Repeating this experiment with Avalon in different positions in its orbit also aided in confirming the scale of the Valaya moon system.