Favillum

Favillum

Favillum in natural colour. Surface features are obscured by organic compounds in its thick atmosphere.
Orbital characteristics
Semi-major axis	3580000 km (2220000 mi)
Eccentricity	0.009
Orbital period	13.7 d (0.45 months)
Satellite of	Aurorum
Physical characteristics
Mean radius	2991 km (1859 mi)
Surface area	1.124 × 108 km2 0.22 Esquarium
Volume	1.121 × 1011 km3 0.103 Esquarium
Mass	5.85 × 1023 kg 0.098 Esquarium
Mean density	5.25 g/cm3
Surface gravity	4.371 m/s2 0.446 g
Escape velocity	5.11 km/s
Albedo	0.16 (Bond)
Atmosphere
Surface pressure	1.21 atm (123 kPa)

Favillum is the second-closest major satellite orbiting Aurorum, and is the closest astronomical body to Esquarium, the third and outermost major satellite of Aurorum. It is one of the few terrestrial worlds known to have permanent detectable atmosphere and bodies of surface liquid. Like Aurorum and Candeum, Favillum is visible to naked eyes due to its close distance, making it one of the seven astronomical bodies know to humanity since antiquity. However, its hydrocarbon atmosphere and carbon surface results in a low albedo, making it the fifth brightest object in the sky of Esquarium (fourth if Celum is differentiated from Icarum).

Commonly classified as a carbon world, chemical composition of Favillum contains significantly more carbon than oxygen compared with other terrestrial worlds in the Solar System, believed to be a result of it forming in volatile-poor region closer to the Sun before being captured by Aurorum during its inward migration. The carbon-rich environment resulted in Favillum possessing a differentiated metallic carbide mantle and graphite-diamond crust.

Like other known terrestrial worlds with atmosphere, seasonal weather patterns have been observed on Favillum. Ultraviolet light from the Sun results in formation of hydrocarbon clouds known as tholin, condensation and precipitation of which forming liquid bodies of tar similar to petroleum on Esquarium despite difference in origin. A combination of unstable geology and tidal forces from Aurorum and its satellites results in active volcanism on Favillum, where volcanic activity regularly releases carbon dioxide and carbon monoxide into the atmosphere, alongside diamond and carbide lava on the surface. The resulting greenhouse effect allows Favillum to possess a relatively uniform temperature slightly higher than that of Esquarium.

Physical characteristics

Composition

Near-infrared colour mosaic image of Favillum, showing the hydrocarbon lakes beneath the smog in its atmosphere.

The average density of Favillum is 5.25 g/cm³, slightly lower than Esquarium (5.5 g/cm³). However, this is primarily caused by gravitational compression inside the latter, which otherwise comprises less dense material than Favillum.

Favillum is believed to possess an iron- or steel-rich core like other terrestrial worlds, possibly divided into solid inner core and liquid outer core. The majority of volume of Favillum, however, consist of a mantle made of carbide, including silicon carbide and titanium carbide due to its oxygen-poor environment, contrast to the silicate mantle of Esquarium. The crust of the satellite is primarily made of allotropes of carbon, with a graphite surface and a possible substratum of diamond.

Permanent bodies of liquid exist on the surface of Favillum in the form of tar. Comprising liquid hydrocarbon synthesised by ultraviolet light from the Sun, they serve as a crucial component of weather on the satellite. Similar to water on Esquarium, tar on Favillum forms various surface features, including lakes, rivers and deltas. It is believed that many temporary surface features observed during cold period might be formed by solidified organic compounds with high melting temperature. However, permanent features in general are rare on the surface of Favillum due to its active volcanism.