100th Millennium Wiki


The Castro-Lux system is a star system on the edge of the Treana Molecular Cloud Complex and is home to the capital of the Areial Union, Eiar. It contains 9 bodies with liquids on their surface, a stupendously large amount for such a system.

Two of them are oceanic planets, three of them hydrocarbonia planets and the remaining are all hydrocarbonia moons. As a result, this system has attracted much attention among civilizations originally descended from hydrocarbonia worlds, who actually sort of want to conquer it.


Castro: A small M7.5V red dwarf with 8 planets.

  • Myach: A small desertic dwarf planet, and the most suitable for a colony not on the water-bearing planets of the system.
  • Oblachno: A large ringed gas giant with easily differentiable bands.
  • Testament: A tidally locked, puffy waterworld. It has many culturally diverse cities on its surface and is nearly subject to permanent study, in one way or another.

    First clear image of Testament

  • Ingentis: One of the largest planets in the entire system, Ingentis is a gas giant. It has one moon, and even more magnificent rings than Oblachno.
  • Obliqua: A strange world, Obliqua is a hydrocarbonia world but it is tilted on its side. It has thin rings and an atmosphere rich in methane.
  • Glacipsum: A distant, very cold ice giant.
  • Parvastra: Most likely the least significant of Castro's worlds, Parvastra is a tiny iceball.
  • Eiar-Ver: A binary planet.
    • Eiar: A cool hydrocarbonia world with many interesting features and capital of the Areial Union. It is warmer than normal due to tidal heating.
    • Ver: A desert world slightly warmer than Eiar.

Lux: A small L6.6 brown dwarf. (9 planets)

  • Eostre: A tidally locked waterworld. Basically Testament, but orbiting Lux. (Lux b)
  • Soranus: An angry-looking desert world that is surprisingly not tidally locked to Lux. (Lux c)
  • 5 unnamed ice worlds.
  • Imset: A shiny reflective snowball orbiting Lux at 0.69 AU. No jokes please. (Lux i)
  • Khione: A completely frigid dwarf planet. It takes 4.39 years to orbit Lux, and is the coldest independently orbiting body of the entire system. (Lux j)

Elorus: A large gas giant with 26 moons. It orbits both Castro and Lux.

  • Mote: A small hydrocarbonia moon orbiting Elorus. It has seas of neon. (Elorus 4)

Ogian: A hydrocarbonia planet orbiting both Castro and Lux.

Brigid: The largest gas giant and the furthest out, Brigid is only heated by tidal heating from its moons.

  • Eurus, Nerthus and Mokosh (Brigid 5, 6, 7): 3 hydrocarbonia moons orbiting Brigid.

Discovery by Outside Civilizations

Discovered in 82621 by the UNFG-funded Treana Young Fusor Survey Telescope (TY-FuST for short), this star system initially doesn't look special. From the stars' perspective, this is just a somewhat young binary consisting of a red dwarf and a brown dwarf. It wasn't until a multitude of planets had been discovered around Castro, the primary star, that this system gained a bit of interest.

Testament (Castro d) could be habitable and had an absurdly low density, which sparked confusion among scientists. As a result, the UNFG sent a few solar sail probes to investigate Castro's planetary system. What they found out shocked the entire scientific community - Testament was in fact an oceanic planet. This was a huge surprise, considering the young age of the system. What surprised scientists even more was that both Obliqua and Eiar, two planets in the Castro system, were hydrocarbon worlds.

Further exploration

The probes were next directed to Lux, the brown dwarf of this system. In fact, the system around Lux seemed like a normal brown dwarf system. But again, this system is young, so it's a slight surprise that Eostre managed to cool down so quickly to become an oceanic world.

But the most surprise came from the outer 3 planets. Somehow, there were 5 hydrocarbonia worlds here.

Eiar's Civilization

The probes, when they passed over Eiar, did not notice much at first. Later heat signature scans indicated a concentration of life-forms deep underground, but when they sent drilling probes they were astonished to find a massive, well-lit city on the scale of twenty kilometers across in the deep cave. The inhabitants were also surprised and ran like hell, so time was spent in orbit studying the planet's language so that proper contact could be made. This contact was made in 77,049 CE.