Panthal

Panthal - formerly known as Panthalassa - is the second planet in Crossroads system. Second largest planet in its system Panthal is also the only known and documented example of an "ocean-planet", a planet with no solid grounds covered only by a vast, single ocean. It has a population of 83 million people divided in two main cultural groups: Citizens and Seawanderers.


History

Panthal is about the same age as its parent star, 4.1 billion years. However the planet did not start its life as it stands nowadays. Indeed Panthal formed farther from its star that it stands now. It was larger, composed of a rocky and metallic core that accreted gas and water ice in the outer protoplanetary disk of the young star. This ice-rich planet, comparable to the Solar system outer gas giants Uranus or Neptune, was slowly pushed closer to its star by gravitational influence form other planets and a braking effect inside the disk.

As a result to this migration the planet started to heat. Volatile compounds in its atmosphere were blown off through hydrodynamic escape and frozen light elements sublimated. Eventually most of lighter elements - hydrogen and ammonia especially - were ejected from the planet and only heavier atmospheric elements remained around the rocky core and its thick cover of water ice. When Panthal's orbit stabilized about half an astronomical unit from its parent star, the planet was receiving enough sunlight to allow upper ice layers ' melting in a thick nitrogen and carbon dioxide atmosphere. This melting lead to the huge, planet-size ocean we know.

Composition & Structure

Internal structure & Chemical composition

Panthal is differentiated, and possesses, from the centre to the outside, a metallic core, a rocky envelope, an ice/liquid layer and a gaseous atmosphere as shown on the scheme below.

Structure.png

The metallic core is mainly composed of iron and nickel and the rocky envelope of silicates, closely resembling Earth's internal structure. The outer frozen layer is made of high-pressure water ice with trace elements such as ammonia.

Hydrosphere

Panthal's hydrosphere is its main feature. The hydrosphere encompasses both the planet-wide ocean and water vapour present in the atmosphere, actually the whole water cycle. Panthal's ocean is about 110 km deep, resting on a high-pressure hot ice bed. At ocean's bottom water pressure ranges in the Gigapascals - 10'000 times surface pressure - and temperature can be as high as 45°C. Ice can only maintain in these conditions thanks to the high pressure.

Water Cycle is similar as on Earth with the main difference there are no continents and rains pour directly into the ocean. Evaporation is intense, especially in equatorial regions, creating dense cloud coverage. Cyclones are particularly strong on Panthal. Indeed energy available in equatorial regions is larger than on Earth and there are no landmasses to cut cyclone's path. Thus the huge depressions are able to circle several times around the planet before reaching northern latitudes where available energy is not sufficient to sustain them.

Atmosphere

The atmospheric pressure on the surface of Panthal averages 380.1 kPa. It is 52% nitrogen and 48% oxygen, a low percentage of carbon dioxide with trace amounts of water vapour and other gaseous molecules. Panthal's atmosphere is almost 4 times thicker than Earth's atmosphere and 2 times richer in oxygen. This has several effects. It makes flight easier but increasing fire risks. It also presents health issues - all detailed below.

A strong greenhouse effect is active in the atmosphere, instrumental to keep the planet warm. It is not maintained by carbon dioxide - 190 ppm compared to around 400 ppm on Earth - but more by the large, dense atmosphere that reproduce large carbon dioxide amounts. Average surface temperature is 31°C (304 K) when without the heat-retention effect it would be - 3°C (270 K).

Magnetic field

Panthal possess a magnetic field generated within the molten outer core region where heat creates convection motions of conducting materials, generating electric currents. These in turn produce Panthal's magnetic field. Its field is only 10% stronger than Earth's magnetic fields as Panthal's rocky core is Earth-sized. The field forms the magnetosphere, which deflects particles in the solar wind. The collision between the magnetic field and the solar wind forms Van Allen radiation belts as on Earth. When the plasma forms these belts enters the atmosphere at the magnetic poles, it forms auroras, again as on Earth but usually on a larger scale.

Orbit & Rotation

Panthal orbits its star at an average distance of 0.497 Astronomical Units (74.5 million km) on a quasi circular trajectory (eccentricity of 0.008) almost coinciding with Crossroads stellar equator (inclination of 0.2647°). It completes its orbit in 128 Earth's days, about a third of a calendar year.

It takes Panthal on average 38.41 hours to rotate around its axis, 1.6 Earth's day. This longer rotation period significantly affected human life on the planet. Panthal's axis is tilted 21.17° against its orbital plane. Only two degrees smaller than Earth's axial tilt this allows similar season cycles on Panthal as on Earth.

Moons

Panthal has three moons, from the larger to the smaller: Amphitrite, Clymene and Beroe. They were named from mythological figures associated with sea in the ancient Greek pantheon. They have a deep strategic importance as Panthal's main minerals sources. They are all placed under Spacers State's jurisdiction - not to be confused with the Spacers Guild - and house a population of about one million, most of Spacers' population.

Amphitrite is a rocky moon 1'248 km large, orbiting about 394'000 km from Panthal in 12 Earth's days on a rather inclined orbit (22°).

Clymene is a ferrous moon 408 km large - large enough to be a sphere, possibly a captured asteroid - orbiting on a very inclined orbit (88°) 750'000 km from Panthal in 30 Earth's days.

Beroe is a rough moon 87 km large - possibly the derelict of a former, larger moon - orbiting on a close, circular orbit 80'000 km above Panthal's surface in 1 Earth's day.

Habitability

Panthal provides liquid water, an environment where complex organic molecules can assemble, and sufficient energy to sustain life on its surface and lead to the development of a native biology. Native life evolved several billions year ago in the planet-wide ocean despite its lack of mineral elements, basing its chemistry on minerals present in dissolved form in the ocean and bring to the planet by micrometeors. Panthal's native photosynthesis cracks water, carbon and nitrogen compounds to create its needed biological molecules. Hydrogen and oxygen are the main waste products. Nitrogen and carbon assimilated through photosynthesis are freed trough organic decomposition and oxygen is used by larger organisms in their own internal chemistry. Nitrogen and oxygen amounts are thus stable in Panthal's hydrosphere and atmosphere trough biological activity.

Panthal's environment can support human life but has specific issues:

  • High atmospheric pressure and oxygen percentage

Surface pressure is 3.8 times Earth's and oxygen amounts for 48% of that atmosphere. Compared to Earth an human still breathe much more nitrogen and oxygen combined than on Earth. Someone not used to that atmosphere would suffer from nitrogenous euphoria for several days while being invigorated by the oxygen. After some time on the planet however the body adapts and resumes normal functions.

Another effect of a higher atmospheric pressure is on flight. Pressure, hence density, limit the mass of creature that are able to fly on their own muscular force. On Panthal few organisms made it to the air as 99.9% of life forms are aquatic but it is interesting for humans. Indeed flight is so easy under these pressure conditions that a human in good health bearing artificial wings is able to lift up, flying on its own.

  • High surface gravity

Panthal's surface gravity is 1.5 times Earth's. Human visitors experience contradictory effects. In the first days they feel better, invigorated by the extra load on their muscles - and helped by oxygen - but they will soon feel tired, their body not used to such a constant load. After some time, depending on each individual's physical conditions, they will adapt. It has been shown higher gravity have positive effect on health on the long term.

For Panthal natives these problems do not exist as they are fully adapted to their environment. They experience problems when they leave it, most notably pulmonary problems as their blood is not adapted to handle "low" amount of oxygen. In a lower gravity environment they will have a stronger physical strength and greater speed than average humans but these are not perpetual either.

  • Time issues: longer day & shorter local year

Panthal's day is on average 38.41 hours long, or 1.6 Earth's day. It means that on average daylight is 19 hours long and it is closing 25 hours at solstices. Such an extended day had severe consequences on the human’s natural cycle that is set up on a 24 hours cycle. Travels to different time zones and the associated jet-lags have however proven that humans are able to naturally adapt their cycle to their new local time. Moving from a 24 hours cycle to a 38 hours one was not impossible but proved more difficult than moving to another time zone while keeping an unchanged cycle. This is an issue with offworlders travelling to Panthal.

Over generations Panthalians have fully adapted to this new cycle. Measured in standard time one Panthal's day is exactly 38 hours, 24 minutes and 36 seconds long. The native use a 38 hours clock that is running with a slight difference from standard time. Indeed to remove the remaining 24 minutes and 36 seconds each of the 38 hours have been extended by 37.9 seconds. This clock system, and the local calendar based on it, has been severed of any link to standard time measure to avoid any unwarranted confusion yet they are sometime used together – see below.

Panthalians use local clock in their daily activities. However they have to use two different calendars for dates. The local clock is setting up the base for the local calendar which measures Panthal’s revolution around its sun. It is accomplished in 128 Earth's days, or 80 Panthal's days. In one standard year Panthal experiences almost three local years, which lead the natives to speak of several summers or winters. A standard year is then composed of a first, second and third season of each type. The drift between the two calendars is not compensated as they had been severed from each other but it might become a problem in the future when Panthal’s seasons do not correspond any more with the calendar period they are supposed to occur in.

An example of date would be: May 2nd, RM 13 or 42nd day, year 1465 or 42nd day, year 2 RM 13 or 2nd day of the second summer, RM 13.

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