A brief description of Zubos

The planet Zubos, ("Second World" in the dominant language of its human inhabitants) is the second planet of six orbiting the F9/G0 star Zeta Tucanae, in the far southern constellation Tucana the toucan. The Zubonians call their sun Zorb. The star is almost 40% brighter than the Sun, and just slightly older, with a lower metallicity (roughly 70%), which is why its original planetary system, with the sole exception of the planet which later became Zubos, consisted entirely of gas and icy planets. The second planet was originally a rock and ice world, with a dense covering of water ice, orbiting Zorb at about 1.35 AU.

As part of their Living Planet Terraforming Project, the spacefaring aliens commonly called the Ionians, commencing about 85,000 years ago, identified Earth as a planet with a living system they wanted to seed to another nearby world to ensure its survival, and identified the planet that later became Zubos as a good candidate for this process (See The Terraforming of Zubos (*cite pending) and The Ionians and their Living Planet Project (*cite pending)). Essentially, these planetary engineers devised enormous engines to accomplish the bombardment of the planet with a large number of small rocky and metallic asteroids, steered into collision courses. Since these kinds of small bodies were relatively few in the Zeta Tucanae system, they used a significant proportion of those that did exist, in a project that was largely automated but took many hundreds of years to complete. This bombardment had the effect of covering the entire surface of the planet with a regolith of rocky material forming a crust to a depth of roughly 50 km, surmounting a mantle of ice well over a thousand kilometers thick, beneath which, at great depth, there is a plastic mantle heated by internal radioactivity, and a small molten metallic core. As soon as the rocky material was deposited, it became covered over most of the planet at depth with liquid water, as the starlight at this point gave sufficient warmth to melt the ice at the surface.

As Zorb brightened over its lifetime, what had originally been a cold icy world became one where a surface of water could persist. Before the terraforming, it was an ocean world, with a layer of melted ice forming a deep ocean atop the icy mantle. Due to the lack of rocky surface, the ocean was essentially pure water, with no ready source of organic material or minerals. The Ionian planetary engineers determined that life had not evolved on the planet at all.

Overall the current planet is larger but less dense than Earth, with a diameter of about 15,000 km. but a surface gravity just under that of Earth. The rocky covering is differentiated was caused at least in part to differentiate by rotation, which was speeded up to create an equatorial bulge, then slowed by strategically engineered late process collisions with small asteroids, fixing in place an elevated equatorial region, which rises out of the planet's deep ocean, which covers the remainder of the planet. The planet has a diurnal rotation of close to 20 hours, a year of about 1.57 Earth years, or 688 Zubonian days. The planet has a large single continent which forms an equatorial belt circling the world, comprising somewhat less than 20% of its surface, and separating the two hemispheres into enormous and very deep oceans, which do not meet anywhere and therefore do not mix. There are numerous islands close to the continental margin, but far to the "north" and "south" is unbroken ocean. The axial tilt is close to zero. The polar down to about ±80° are covered with a thick layer of sea-ice. The planet has moderately pronounced seasons, each about 5½ months in length, caused by its orbital eccentricity, which is somewhat more pronounced than Earth's. Because they are not caused by axial tilt, the seasonal variation is planet-wide, with no north/south reversal of orientation. (Conventionally, due to the orientation of the entire planetary system, which is approximately aligned with Galactic coordinates, Zubonian "north is roughly Galactic north and "south" is roughly Galactic south).

The planet has a fairly thick atmosphere consisting almost entirely of nitrogen and oxygen (like Earth's), with a higer barometric pressure at sea level than Earth, yielding a partial pressure of oxygen at sea level roughly the same as Earth's, despite the fact that the actual percentage in the atmosphere is less. Due to the greater diameter and lower density of the planet, the atmosphere hugs the surface somewhat closer than Earth's. There is a robust and effective global ozone layer, which effectively blocks much of the higher flux of ultraviolet light from Zorb, which is whiter and brighter than the Sun by a significant factor. These physical characteristics, of course, are not coincidental, but were carefully and deliberately engineereed as part of the terraforming process to create a habitable environment for living organisms which originated on Earth.

Since the planet has no plate tectonics or active vulcanism, its current form is not stable long term. The equatorial belt will gradually erode, and the planet will, without further intervention, eventually revert to its former existence as an oceanic planet, with no land. The extant continent, however, has uplands which will persist for at least tens of millions of years, and the "southern" margin of about a third of the planet is flanked by a cordillera of very high mountains, the tops of which rise well out of the habitable zone of the atmosphere, making for both a mountainous belt and significant "altiplano" region adjacent to it which are too high for human habitation at present. These areas, despite their equatorial location, are covered in glaciers.

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