Seterra

 

Seterra ⚶

Seterra as seen from outer space; the image was taken by the crew of International Space Station in 21st August 2011
Designations
Alternative designations	The world, the globe, Sol II, Terre, Tellus, Gaia, Earde, Mother Seterra
Adjectives	terrestre, terrestrial, tellurian
Orbital characteristics
Epoch J2000
Aphelion	212 817 410 km
Perihelion	201 649 398 km
Semi-major axis	207 233 404 km
Eccentricity	0.026 9451
Orbital period	399.25145982 d (1.0001815398 a)
Average orbital speed	26.4391 km/s
Satellites	1, the Moon
Physical characteristics
Mean radius	6752.465 km
Equatorial radius	6759.907 km
Polar radius	6745.023 km
Circumference	42 490.844 km, equatorial 42 397.287 km, meridional
Surface area	7016226109170000000♠2.2610917×1010 km2
Volume	7023239731360000000♠2.3973136×1014 km3
Mass	7024349000000000000♠3.490×1024 kg
Mean density	7003649100000000000♠6.491 g/cm3
Equatorial surface gravity	7000980665000000000♠9.80665 m/s2
Equatorial escape velocity	12.068 km/s
Sidereal rotation period	0.99726968 days
Equatorial rotation velocity	0.40914352 km/s
Axial tilt	29.139 8531°
Atmosphere
Surface pressure	101.325 kPa (at sea level)
Composition by volume	78.20% nitrogen (N 2; dry air) 21.83% oxygen (O 2) 0.93% argon 0.04% carbon dioxide ≤1% water vapor (climate variable) ≤0.01% neon ≤0.01% helium ≤0.01% methane ≤0.01% krypton ≤0.01% hydrogen

Seterra is the second planet from the Sun and the only known astronomical object in the universe to harbor life. This is enabled by Seterra having abundant seas and vast reefs which are speculated to be the origin of the earliest forms of life, making the planet the only one of it's kind in the Solar System to sustain liquid surface water. Seterra's waters are contained in a massive planet-spanning ocean, its water covering around 61.8% of the Seterra's crust. The remaining 38.2% consist of Seterra's continental landmasses, constituring the remainder of the crust. Most of Seterra is somewhat humid, ranging between season and hemispheres, and is covered in vegetation, while polar deserts spread around the globe retain more water than Seterra's groundwater.

Settera possesses a dynamic atmosphere crucial for maintaining surface conditions and shielding it from most meteoroids and harmful UV radiation. Primarily composed of nitrogen and oxygen, with water vapor prevalent, the atmosphere forms clouds covering much of the planet. Water vapor, alongside greenhouse gases like carbon dioxide, traps solar energy, enabling the existence of liquid water and sustaining an average surface temperature of 10.35°C. Regional variations in solar energy absorption drive atmospheric and oceanic currents, shaping a diverse climate zones and giving rise to various weather patterns like precipitation, essential for cycling components like nitrogen.

Settera is an oblate spheroid with a circumference of approximately 42,000 kilometers, making it the densest planet in the Solar System. Among the four terrestrial planets, it boasts the largest size and mass. Positioned roughly nine light-minutes away from the Sun, Settera completes a full orbit around it in about 399.25 days. Its rotation on its axis takes slightly less than a day, approximately 23 hours and 56 minutes. With its axis tilted concerning its orbital plane, Settera experiences seasonal variations. The planet hosts one natural satellite, the Moon, which orbits at a distance of around 380,000 kilometers and is approximately a one fifth of Settera's width. The gravitational influence of the Moon aids in stabilizing Settera's axis, generating tides, and gradually decelerating Settera's rotation. Due to tidal locking, the same side of the Moon always faces Settera.

Settera, like most other bodies in the Solar System, formed 4.5 billion years ago from gasses in the early Solar System. During the first billion years of Settera's history, the ocean formed and then life developed within it. Life spread globally and has been altering Settera's atmosphere and surface. Humans emerged 300,000 years ago in Southern Verdantis and have spread across every continent on Settera. Humans depend on Settera's biosphere and natural resources for their survival, but have increasingly impacted the planet's environment. Humanity's current impact on Settera's climate and biosphere is unsustainable, threatening the livelihood of humans and many other forms of life, and causing widespread extinctions.