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Exoplanets

The following fictional exoplanets each describe a potential idea I have had, inspired by scientific literature. For each of them I have done a variable amount of research into their viability though the basic idea is present. My intent is to write something about each one over the period of the blog though I would be interested to hear if anyone has any thoughts on any of them even before I write more.

Chiaro

Credit: Daniel Olah on Unsplash

Most speculative worlds I have seen presented involve sun-like stars or those with cooler redder suns. However, stars hotter than the sun seem more rarely considered.  As larger hotter stars have shorter lifetimes than our sun in order to give life time to develop a star could only be slighter different to our sun. Therefore, an F-type main sequence star seems the only plausible option and the real BW Aquarii binary star system seems a suitable source of inspiration.

An F-type star produces illumination which is slightly bluer than our sun and also produces more ultraviolet. A key challenge for life would be to manage the UV exposure though initially this can be achieved by remaining underwater. An additional difference is that due to the difference in colour, a greater amount of light can reach the planet without causing additional heating. This produces an ideal environment for plant life so Chiaro is expected to be lush and verdant.

Once life expands onto land perhaps there will be a diverge between diurnal life than can manage the higher UV exposure during the day and nocturnal life which prefers to avoid it. Perhaps an exoskeleton clad insect-like clade dominates the day and a soft skinned amphibian like clade dominates the night?

However, with a planet in orbit around a binary star the pattern of illumination during a day is slightly different than on Earth. There will be a "dawn" and "dusk" period when only one star is visible in the sky. During this period the insects and amphibians will be in direct competition.  

Elatha

Credit: Daniel Olah on Unsplash

When planets form around stars they typically have a significant amount of hydrogen in their atmosphere. Since hydrogen is so light this is most often lost in the first billion years after formation. A planet with a mass larger than Earth may however have sufficient gravity to retain a thick hydrogen atmosphere.  Life on the resulting planet would take a different path to that on Earth.

In particular, photosynthesis in the hydrogen dominated atmosphere would likely be very different. An aerial biosystem in the relatively clement conditions of the upper atmosphere would be supported by photosynthesis. Meanwhile, life on the surface would consist of extremophiles using chemosynthesis or the organic detritus falling from above. 

Jorumgand

Credit: Daniel Olah on Unsplash

Around a star called Loki orbits a large gas giant called Angrboda with several moons. Of these, three are significantly larger than the others: Fenrir, Jorumgand and Hel. Jorumgand is so named as it is mostly covered in ice though with an equatorial open ocean that moves north and south with the seasons. This climate is a stable state know as the Jorumgand state for its similarity to the World Serpent of Norse myth.

Life on Jorumgand exists mostly in the cold oceans either in the open or under thin ice. However, there is some life on the rare exposed land and on volcanic "islands" surrounded by glaciers. Since the moon is tidally locked then reflected light from Angrboda slightly increases the temperature on one side of the moon leading to a slightly larger oceanic belt.

Khthonia

Credit: Daniel Olah on Unsplash

Khthonia is the focus of my initial world building efforts and it is based on the idea that red dwarf stars comprise more than 70% of the Galactic stellar population and more than 50% of the stellar population are in binaries. Therefore, binary red dwarf systems are actually quite common but what would life look like if it evolved on a planet orbiting two red dwarfs?

Planets in circumbinary orbits around two stars have several properties that suggest they may be suitable for life, however, red dwarfs are also known to produce strong flares. The resulting increase in ultraviolet emissions and stellar wind can cause problems for habitability, including evaporating the atmosphere. Khthonia therefore began as a mini-Neptune with a rocky core slightly larger than Earth and a thick atmosphere in a close orbit around the stars. Over the first billion years the high levels of flaring evaporated most of the atmosphere to produce a habitable evaporated core that resembles a typical terrestrial planet.

As elsewhere, life on Khthonia began in the seas though with several difference to Earth. Despite being tidally locked to the barycentre of the binary stars, due to the close orbit oceanic tides are significantly larger than on Earth. This is problematic as red dwarf stars produce a greater proportion of their illumination in red and infrared which does not penetrate water as well as blue light does. Therefore photosynthetic organisms need to remain near the surface if possible. Unfortunately, this increases the risk from the frequent ultraviolet flares which can otherwise be avoided by remaining in deeper water.

For this reason algae on Khthonia developed a more complicated life style than on Earth to take advantage of the continual illumination but mitigate the risk from flares. Adaptive pressure from this situation caused algae, over time, to became the progenitors of all complex life on Khthonia. 

Xeros

Credit: Daniel Olah on Unsplash

White dwarfs are stars that have reached the end of their lifetimes, progressed through the red giant stage and their shed their outer layers to become a dense stellar core remnant. This core has a mass comparable to the sun yet is only about as large as the Earth. As it is no longer performing fusion the white dwarf is a cooling ember though such is its heat that it will take billions of years to cool completely. While it begins with a temperature of many thousands of degrees after some time has passed it reaches a temperature similar to Earth's sun and a planet that is sufficiently close could support life.

Such a close planet would not survive the red giant phase, however, there are possible mechanisms that a second generation planet could be produced around the white dwarf after it is born. This requires a binary system and therefore Xeros is a planet in orbit around both a red and white dwarf star. This is similar to the exoplanets detected around the binary star NN Serpentis.

Life on such a planet would be harsh as it likely be completely desiccated due to the high temperature of the white dwarf before it reached a temperature suitable for life to begin. Also, unlike our sun the colour of the light would have changed significantly during life's evolution. Early photosynthesis would have been adapted to a hot blue star whereas late photosynthesis would be optimised for red light.

Yomi

Credit: Daniel Olah on Unsplash

Yomi is a dark planet orbiting a pulsar, just like the planets Draugr, Poltergeist and Phobetor around the star PSR B1257+12, better known as Lich. There is perhaps a small chance that such a pulsar planet could be habitable though life would be completely different to that on Earth. The extremely thick atmosphere combined with low optical, moderate x-ray, high gamma-ray and high relativistic particle flux is clearly an unusual environment.

Due to Yomi's formation as a second generation planet from the debris produced by the pulsar's birth in a super nova it would have a different composition to Earth. In particular, it would experience significantly greater heating from radioactive elements in its core. Along with tidal heating from its proximity to the star this is sufficient to keep the planet warm enough for liquid water to exist on the surface.

Comments

  1. Wow, those exoplanets are WAY more diverse than I expected them to be. Even if they are not as numerous as, for example, those of planetocopia, all of them sound absolutely fascinating and I would love to see what lifeforms you design for them in the future. Good job!

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    1. Thanks. I have a few others as well and I will add them once I find time. Planetocopia was certainly an inspiration for planets that are different but still potentially habitable.

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