Planet Profile: Salsola

The following planet profile was submitted to SciFi Ideas by Christmas Snow.

Salsola is a super-Earth planet with about twice Earth’s mass. The planet orbits a K-class star – an orange dwarf – that is less luminous than our sun. The closer orbit by itself is not sufficient to hold temperatures to the average temperatures on Earth. This is supplemented by the higher content of carbon dioxide which acts as a greenhouse gas. The planet has formed within the inner portion of the accretion disk of the primordial solar system. It is rich in rocks and metal, and very poor in volatiles such as water, hydrogen and carbon dioxide.

At a given time shortly after its formation, Salsola has been impacted by a planet larger than Mars. The planet is named “Ira”, the Latin word for “Wrath”. Ira originated from the outer solar system and is presumed to have been tugged-in by a gas giant. It is rich in volatiles and accounts for much of the added volatiles. Ira’s impact course is not aligned with Salsola’s orbit, leading to Ira’s collision at one of the poles, flipping the entire axis of rotation on its side. The end result was a high axial tilt of roughly 90 degrees, similar to that of Uranus. This tilted axis has given the planet its name “Salsola”: The botanical name of the tumbleweed, as the planet tumbles on its axis rather than spinning like a top.

The unique axial tilt, super-earth size and dense atmosphere have affected evolution of life on the planet to produce the strangest organisms and unique ecological niches. We shall discuss the key differences that made Salsola so different from Earth, and yet so hospitable to life.

THE KEY DIFFERENCES

There are several key differences that distinguish Salsola from Earth: Higher atmospheric density and pressure, higher gravity, higher geological activity, and a higher axial tilt. The combined effect has made life so different, yet so Earth-like at the same time.

Moon system: The impacting object had sufficient energy to fling much of the impacting material back into space, yet most has merged with the planet. The remaining debris has orbited the planet to form planetary rings. Volatile materials have evaporated into space long before debris has coalesced to form the moon. Debris that formed at the impact site was flung in the same direction as that of Ira, making the planet’s equator and its new moon’s orbit tilt at 90 degrees relative to its orbital plane. The higher gravity means the debris cannot fly high into space, therefore making room for just one moon to form. The moon is smaller than Earth’s moon for the same reason. The nature of the impact is identical to that which took place on Earth to form our moon. This has made the debris orbit the planet more slowly than planetary rotation. Tidal effects slow down the planet’s rotation and accelerate the lunar orbit, making the moon slowly break loose of the planet’s gravity within few billions of years.

Geological activity and gravity: A more massive planet has higher gravity and a more vigorous geological activity under a thin crust. The tectonic plates are therefore more numerous, yet smaller. Continents are more numerous and scattered almost uniformly among bodies of water. Combine the two and you get shallower seas, lower mountains, lots of earthquakes and volcanic eruptions releasing carbon-dioxide out of the rocks. Continental drift is more significant and has put evolution on the fast lane by faster climatic changes. Volcanoes release more carbon dioxide, creating a greenhouse effect that compensates for the cooler and dimmer parent star. All living forms absorb carbon dioxide readily. Remaining carbon dioxide is absorbed by the water and converted to carbonic acid. The acid reacts with the rocks to form carbonate rocks. The higher volcanic activity of a super-earth releases the carbon back into the atmosphere at a greater rate, making the cycle run faster.

Atmospheric density: The impacting planet has contributed most of its volatiles in the form of Ammonia and water ice. Some Carbon dioxide added, while most has been generated in greater part thanks to volcanic activity. Ammonia was oxidized by living plants which release oxygen, giving water and nitrogen gas. The more abundant atmosphere combined with higher gravity gives a much higher atmospheric pressure at the surface. Combined with flatter topography, weather is governed by global winds to a greater extent and local climates are of a lesser significance.

High axial tilt: The 90 degrees high axial tilt creates extreme seasonal changes that generate strong winds. Compounded with the denser atmosphere, the results are super-hurricane winds and turbulent seashores which have cast away many plants and animals to the shores. Over time, many have adapted to live close to the shore and eventually venture into the land. I will shortly explain how this affects the climate, the climate zones and the type of living forms which have evolved.

DAY-AND-NIGHT CYCLES

An observer at the pole never sees the sun in winter. We shall start the “year” when the sun is at its lowest point – the nadir – The point just underneath the observer. As the year progresses, the sun spirals on its way up. At equinox, it crosses the horizon and spirals up around to the pole. At summer solstice, the sun is at the zenith. It keeps spiraling on the way down, crosses the horizon and ends a one-year cycle at the nadir. The equator is different: There is a constant day and night cycle. The sun is high at each of the two equinoxes, and is low at each of the two solstices (draws closer to the horizon, light is dim and temperatures drop). As it happens twice each year, the equator has two seasonal cycles for each year, and not just one. The equator lies between two hemispheres with opposing seasons, and heat convection of such a dense atmosphere evens-out seasonal temperature changes. Having two seasonal cycles rather than one, means faster seasonal changes don’t give time for temperature to fluctuate much. The two factors contribute to a more stable temperature at the equator.

This cycle is not the same throughout the planet. The equator has a year-round standard day-and-night cycle. As we get closer to one of the poles, we get more days of “all-time-light” in summer and “all-time-night” in winter around each corresponding solstice. The temperate zones between equator and poles (referred to as “Midway”), have “transit seasons”: daytime grows shorter in the fall, daytime grows longer in spring. The more we move to the poles, the shorter those “transit seasons” are and we get more “all-time-light” and “all-time-night”. At latitude 45, halfway between pole and equator (both North and South), we get equal times for all-time-light, shortening days, all-time-night and lengthening days. At the poles, we get an all-time-light summer, and an all-time-night winter.

SEASONS

The sun’s position in the sky dictates the seasons. The polar seasons are dominated by cold nights with no daylight in winter, and scorching heat with no nights in summer. The equator experiences a normal day-and-night cycle. The only difference from that cycle on Earth is the wide seasonal fluctuation of the sun’s latitude. The sun is above the equator during each of the two equinoxes. Winds are calmer and temperatures are higher at the equator. These are the two equatorial summers. The two equatorial winters occur when the sun’s latitude is close to the horizon at each of the two solstices. This makes two seasonal cycles per year, compared to one cycle for each of the hemispheres.

WEATHER PATTERNS

As each pole faces the sun for an entire season when the other faces away from the sun, there is sufficient time for the sunny side to heat-up and the dark side to cool down over large areas. The great difference between the two poles creates a unique wind pattern: The hot pole creates polar updrafts. The cold pole creates polar downdrafts. As each hemisphere faces the sun, it is warmer than the other, causing intra-polar winds: Dark side receives air from the sunny side through the higher atmosphere. The air converges at the pole, where it gets sufficiently colder and sinks. It flows back to the sunny pole closer to the ground, where it picks-up humidity from bodies of water it crosses. When it reaches the sunny pole it heats-up and floats to the upper atmosphere. It flows back to the dark side. On its way it cools down and loses humidity as precipitation, mostly around the equator. The remaining humidity precipitates as snow at the South Pole. As the poles switch seasons, the ice caps will melt very quickly. Therefore, the planet has no permanent polar ice caps. The denser atmosphere and stronger winds make heat convection more apparent, evening-out temperatures across the planet more efficiently than on Earth. Polar temperatures rarely go below -50 centigrade in winter, and rarely above +50 centigrade in summer.

During each equinox, both hemispheres receive same amount of heat from the sun. The intra-polar winds subside and we have the more familiar wind pattern we experience on Earth.

CLIMATIC ZONES

The planet is divided into three types of climatic zones:

Equatorial zone: The tropical zone around the equator has a moderate climate and higher rainfall. As the air crosses the equator from hot to cold pole, it loses much of its humidity at this zone. Winds are much calmer around equinox seasons (the two summers) and solar illumination is at its peak. During solstices (The two winters), the sun draws nearer to one of the poles. Winds on the surface blow from cold to warm pole.

Polar zones: all-time day in summer melts the ice cap which took shape during the winter. Floods are very common at this time. All life-forms take advantage of this daytime and abundance of water before the summer desiccates everything. Temperatures cool down in the fall, but pole is too dry and life has to wait till next spring.

Temperate zones: Halfway between the temperate (equatorial) zone and the Polar Regions, there is an in-between climate on both sides of the equator. The area is often referred to as “Midway”: Midway is close enough to get some summer rain before the intra-polar winds cross the equator to the wintering pole. The sun crosses the Zenith twice (towards summer solstice then towards fall equinox again) creating a longer summer that is moderate compared to the polar summer. Midway experiences an important transit period between full-time days and full-time nights as seasons change and this has an impact on how plants and animals follow the seasons.

BIOMES AND ECOSYSTEMS

The wild seasonal fluctuations between the North and the South Pole combined with the dense atmosphere and higher gravity has lead evolution into paths which we never encounter here on Earth. The most distinguished feature is the size and the type of flying organisms. The high density and oxygen content allow elephant-sized animals to take flight. Some have developed lighter-than-air flight, and this is not confined to animals. There are such plants as well. The reason is obvious: Strong winds allow animals to migrate with ease. Extreme seasons force them to do so. Animal migration and long-distance seed dispersal are unlike anything we experience on Earth. It takes place on a greater scale of magnitude and diversity. Winds blow faster at the poles than at the equator, because the equator is wider than the polar latitudes, just as a river flows more slowly as it widens. The winds are still strong enough and trees have to adapt to the stronger winds as well as the higher gravity.

The equatorial zone receives rainfall year-round, yet temperature is much colder in winter, making the term “tropical” into a misnomer. The wind is calmer than at the poles, allowing some wind-tolerant trees to develop. The landscape is dominated by cold rain forests.

The temperate zone – Midway – is dryer yet receives enough rain, in particular during the dark winter. Humidity and occasional rains throughout the year support a diverse ecosystem. Vegetation is sparser than at the equator. The dominant biomes are sub-tropical bush lands close to the tropics, gradually changing into Savannas and occasional deserts as we stray towards the pole. In the near-polar regions, vegetation is sparse and comprises savannah and arid regions. Annual vegetation is common closer to the poles. It dies towards the summer and becomes dry enough to start fires.

The polar zone – It is the most extreme biome, comprising deserts almost exclusively. Plants close to the poles are adapted to the high-velocity winds. Sand formed by erosion is constantly blown away, making the polar deserts almost completely nothing more than hard soil made-out of rocks and pebbles. Soil is so compact that water absorption is poor. Ice caps which formed during the winter make floods and most water streams end-up at sea. Still, some plants make a living out of that water. Other plants became carnivorous. The dominant biome is therefore called the “flood-desert”.

The aerial zone – It is not a geographical zone. It is a completely airborne ecosystem, making advantage of the strong and fast winds for mass migration. The ecosystem has developed to benefit of the huge biomass of aero-plankton, of which the mini and micro plants make-up 80% of the mass, while the mature bubble-weeds make-up a mere 20%. Nevertheless, there is abundance of bubble-weeds over which avian lizards and bird-like creatures claim their nesting sites. The aero-plankton makes use of dark color to heat-up the air in bubble organs. Some harbor anaerobic bacteria just like the bubble-weeds. These bacteria produce lifting gas like Methane, Ammonia and Hydrogen. The plants have evolved to adjust their buoyancy and ride the winds which blow in the right direction, where climate is comfortable. Sky-whales and smaller flying grazers follow the winds to graze in the air. Even the sky-whales have found themselves becoming host for avian nesting on their backs. The nesters mostly comprise predators which aggressively defend their flying platform, be it a bubble-weed or a sky-whale. This has ushered the era of symbiant relationship between plants and animals.

EVOLUTION OF LIFE ON THE PLANET

Evolution of life on Salsola as well as on Earth has begun at sea. The sea-weeds were confined to the high seas where the crushing waves could not tear them off the sea-floor or turn water into a murky soup and dim the light. That necessitated free-floating weeds at the high seas. Over time, weeds developed floatation bubbles to remain close to the surface and capture more light. They remain under the surface, yet currents often carried them towards land, then high waves tossed them ashore. Over time, anaerobic bacteria generating methane and hydrogen have found refuge inside the floatation bladders. The plants with larger bubbles have become airborne and the first bubble-weeds evolved. Those were large enough for avians to nest upon, creating symbiant relations with the quetzal lizards, a flying reptilian. Other plants remained small and became part of the aero-plankton. Fish-like animals tossed ashore by waves and tidal forces were able to adapt. Snake-like swimmers were more adept to move on land under the high gravity. That’s why snake-like animals are very common, comprising many unrelated species. Other sea-weeds tossed ashore have adopted life on land. They were first confined to bodies of fresh water, especially pools of rainwater, and then began their adaptation to living on land. The motive was the wide seasonal fluctuations which made rivers and lakes dry-out. Fast continental drifts contributed to climatic changes which forced that type of adaptation. It is believed that life took hold on land at around the equator, where rains are common during solstices.

PLANTS

Early plants reproduced by spores, but eventually the equivalent of flowers became the dominant mode of reproduction. This allowed plants to populate all continents. Animals began their race to populate the land and air, and wherever plants take a hold, animals will follow. Bubble-weeds and aero-plankton are common in the dense atmosphere and high winds, because they cope better with the forces of the winds. With time, floating plants have adapted to the changes in temperature by consuming or storing more of the floatation gas. This helped them to sink when temperatures were too low, and ride the winds which take them to the warm side. Conversely, they floated higher when they drew closer to the deserts and sought refuge in cooler latitudes. All animals riding on the surface of large plants have taken advantage of that. On ground, trees have developed thick cone-shaped trunks with perpendicular branches, like a well-groomed Christmas tree. They populated the equatorial zones, to form the cold rainforests. The rainforests have sparser foliage compared to those of Earth and conditions on the forest floor were more favorable for light-loving plants. Winds were still a concern even at the forest floor, and many plants developed crawling stems which rooted wherever they touch the ground.

The equator features another plant that scientists name the “Banner tree”. It is an unusual tree that thrives year-round wherever temperatures are not too cold. The tree grows on light just like any other plant. During the solstices, the equator receives almost no light yet wind is abundant. The leaves of the banner tree grow in pairs, and they have fused with a flexible tissue along the rims. They are elongated and they wave in the wind like banners, rubbing against each other as they bend. The leaves have different chemical make-ups at the rubbing area, generating opposite electric charges (just like rubbing amber) of static electricity on each leaf. The two leaves act like the two sheets of a capacitor storing electrons, allowing them to flow through the leaf axils and generate an electric current. This allows the banner tree to harness electric power from wind to synthesize when light is not present.

The “Chernolithops” is a specialized plant adapted to polar deserts. “Cherniyii” is the Russian word for “Black”, and “Lithops” means stone-like. It is a dome-shape plant which looks like a round pebble. In spring, the plant looks black because of the Melanin it has produced in the fall. The black color will help it to warm-up faster with the upcoming of spring, and break dormancy. Snow begins to melt, and the warmer temperature speeds-up its metabolism, allows it to flower, attract pollinators and make the first seeds. As the polar summer draws closer, the melanin breaks-down and the plants becomes pale-green. The lighter color prevents it from overheating. By peak summer the seeds are mature and ready for dispersal. Intra-polar winds are strong enough to carry the seeds. The seeds are black and look like half-inflated nylon bags. These will warm-up under the sun and the air expands, turning the seeds into hot-air balloons. The seed rises high enough to ride the wind heading to the other pole, where winter is, to land on the ice caps. The seed will sprout when spring arrives and the polar ice caps begin to melt, just at the time when winter begins at the other pole, where the seed came from. The plant’s growing season is therefore twice a year, in spring. That is, spring at one pole, then at the other: Two springs in one year.

ANIMALS

Animals at sea have evolved in a similar manner like on Earth, with some secondary differences. Mollusk-like animals look like snails or slugs on Earth and possess no bones. Many have developed shells as well. However, they are five-fold symmetric, contrary to Earth’s mollusks. Early in the planet’s history, a second group of animals has diverged to form the earliest vertebrates which are five-fold symmetric as well. They form the fish-like creatures out of which some will colonize the land.

Echinoderm-like are primitive creatures with an outer shell of loose “tiles” under their skin. Those may be spiny, rough or smooth. They are bilaterally-symmetric, contrary to the Earth’s five-fold symmetric ones (Sea-urchins, starfishes and sea cucumbers). The arthropod-like group called the “Tessellates” has diverged from the echinoderm-like very early in history. They evolved into shrimp-like and crab-like. Those on land have evolved into insect-like organisms mimicking Earth’s insects in detail. Many are nevertheless bigger thanks to the oxygen-rich atmosphere. Their gills evolved into lungs that breathe more efficiently than tracheas of Earth’s arthropods. Their other advantage is the lack of need to molt. Their outer skin comprises of plates which can grow, a legacy from their echinoderm ancestors. They grow just like the “scales” of a tortoise shell and spare the animals the dangerous moments of molting. The flying tessellates divide into two groups: Those which have limbs modified into wings, and those which have back scales modified into wings.

Vertebrate animals comprise many snake-like creatures, many of which never needed to evolve legs as they left the sea. Others have evolved their fins into legs. Those legged ones gave rise to all flying animals apart from tessellates.

Many animals coped with seasonal droughts by hibernating. Some became amphibian, leaving the water ponds for new ones, and then hibernating when no more ponds are in sight. However, the term amphibian is not a valid classification all by itself: Many species belonging to tessellates, mollusk-like, vertebrates and even mixotrophs have adopted an amphibian way of life. This is in contrast with Earth’s amphibians (frogs, salamanders, tritons, etc…), which stands as a group on its own with one common ancestor.

MIXOTROPHS

Amazingly, a third group of mixotrophs has evolved. It combines features of plants and animals. They move often vigorously, actively searching for food. When there isn’t enough food, they can absorb minerals and photosynthesize. Mixotrophs date back to the days when organisms were all unicellular. The earliest multicellular ones were colonial aggregates which have later evolved into sponges. Instead of a larger organism, the aggregates divide and multiply while remaining attached, each becoming a “polyp”. Each aggregate develops its own cilia, digestive system, food filtering and respiration system. Their anatomy and behavior were very simple and identical to those of sponges on Earth, yet they could photosynthesize without the need for symbiant algae. An offshoot group evolves into coral-like and are called Coralloids: They develop into polyps, but each polyp has a more complex anatomy. Both sponge-like and coral-like mixotrophs disperse eggs which give birth to a swimming larva. The larva turns into an adult phase (a group of polyps) just like Earth’s corals. Sponges are simple creatures that settle on the seafloor, not too close to the shore. While water is clearer, light is dimmer at the deep. Sponges grow more slowly as a consequence. Coralloids have overcome this problem. The first coralloid diverged from its “sponge” ancestors by giving birth to a larva which remains motile throughout its adult phase. It may even engage in feeding and reproduction. Just like sponges, the coralloids develop into polyps. The polyps remain attached to each other. A single polyp becomes dominant, and swims with the other polyps on its back. Those inferior polyps engage in respiration, photosynthesis, food collection, photosynthesis and mimicking leaves of weeds for camouflage. A coralloid that is cut into two, may reassign a polyp which takes-over the tail part and each part becomes a new coralloid. This has given rise to the “snake weeds”, a group of coralloids which camouflaged themselves among the floating weeds, often resembling them completely. Their adherence to seaweeds habitats and their slow swim caused them to get stranded on the beach. Over time, some have learned to move on ground, populate bodies of fresh water and marshes, become amphibian and some even live their entire lifecycle on trees. They look like hairy caterpillars and have diverged much from their ancestral snake weeds: The dominant polyp developed a mouth to feed and simple eyes, and engaged in reproduction. The polyps resume respiration, photosynthesis and protection by venom.

Not all castaway coralloids have evolved this way. Some remained at sea. The continental drift has created landlocked seas several times over the planet’s history. As the landlocked seas often happened to be closer to the pole, water evaporation was at a point that sea level changed wildly. The seas may receive much water from melting ice caps in spring and lose much water by evaporation under the harsh sun and become briny. They may dry-out almost completely in some areas. The coralloids stranded in such seas find no use in migrating and had to become sessile: They were hibernating in one way or the other: Those in the shallows have developed a calcareous skeleton in which they hibernate throughout the dry summer. Those in the deep have formed a glassy skeleton, which is more translucent and allowed better photosynthesis for longer. As the seas become too shallow by evaporation, the coralloids enclose themselves inside the skeleton and hibernate.

We therefore find that coralloids on Salsola have both types of anatomy found among Earth’s corals: The motile ones – on land or at sea – are just like Earth’s soft corals. Those that protect themselves from predators and bad weather with an outer shell are like Earth’s hard corals. Air breathing coralloids living on land, however, have never evolved on Earth.

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Article by Christmas Snow