Discoveries regarding extrasolar planets were first published in 1989 raising the prospect of whether extraterrestrial life could be supported. Unfortunately the smallest non-pulsar planet yet found OGLE-2005-BLG-390Lb (as of January 2006), has a mass of 5.5 times Earth's and orbits the red dwarf star OGLE-2005-BLG-390L. And everything smaller orbits pulsar PSR 1257+12.
The sensitivity of current detection methods makes it difficult for scientists to search for terrestrial planets smaller than this with ease. To allow smaller bodies to be detected, NASA is studying a project called the Terrestrial Planet Finder (TPF), a two-telescope concept slated to launch around 2014.
In anticipation of this event, astrophysicists have begun speculating about the most likely locations for extrasolar terrestrial planets that might be capable of supporting life. It is believed that more than a quarter of all stars are at least binary systems, with as many as 10% of these systems containing more than two stars (ternary etc.). Therefore it may be prudent to consider how life might evolve in such environments...
The scientists on the project theorized that aiming the TPF at a red dwarf star might yield the best opportunities for seeing smaller planets. Due to the slow rate at which they burn hydrogen, red dwarfs have an enormous estimated lifespan; allowing plenty of time for life to evolve on surrounding planets. However, the dwarf's smaller nature and feeble heat/light output would mean that such a planet would need to be particularly close to the star's surface. The cost of such an orbit would be that an Earth-sized body would become tidally locked (ie. have one sideral day exactly equal to one year).
Traditional scientific theories proposed that such a tidally locked planet might be incapable of holding on to an atmosphere. Having such a slow rotation would weaken the magnetic effect that protects the atmosphere from being blown away by solar wind (see Rare Earth hypothesis). Nonetheless, the scientists employed by the programme decided to test the traditional assumptions for such a planet and start a model out for it from a proplyd through to its eventual death. Their estimations suggested such a planet could indeed hold on to its atmosphere, although with freakishly unusual results by Earth standards. Half of Aurelia would be in perpetual darkness and would be in a permanent ice age. The other half would contain a giant, unending hurricane with permanent torrential rain at the point directly opposite the local star. In between these two zones would be a place suitable for life.
The theorisations continued (with ever increasing levels of assumption) that were land to be in this habitable zone, it would be likely to form large networks of river deltas and swampland, due to rain runoff from the nearby storm.
At the far end of assumptions about Aurelia were attempts to construct lifeforms based on Earthly evolutionary models and how ecosystems might develop. The scientists assumptions included the idea that the long life of a red dwarf allows for evolution to fine tune any ecosystem on the planet (though frequent extinction level events on Earth indicate this may be wildly simplistic). The scientists involved in the project hypothesised that the vast majority, if not all, extra-solar biology will be carbon based.
This assumption is often referred to by critics as carbon chauvinism, as it may be possible for life to form that is not based on carbon. However, carbon is more flexible than other elements, allowing life it is is made of to evolve at a much faster rate. Since all environments are likely to undergo massive change, this is vital.
From this carbon-based hypothesis the scientific team assumed some form of staple photosynthesizing animal/plant hybrid would be the principle autotroph. They decided (with neglegible explanation as to why it was favoured relative to other types of carbon-based plants) upon a plant-like creature called a Stinger Fan.1. It has a heart and limited mobility. Its fan-like leaves trap the red dwarf star's energy to produce sugars. Its heart pumps them arond its body.
Feeding upon the Stinger Fans are six-legged semi-amphibious creatures called Mudpods, somewhat like a cross between a beaver and a large newt with the eyes of a snail. Upon that animal, a large emu-like carnivore, a Gulphog, is the main predator. Finally, with no apparent explanation from within the Alien Worlds programme, there is a second semi-amphibious creature called the Hysteria which was a cross between a plague of tadpoles and Piranha. These tiny creatures can form one huge superorganism and move together up banks to paralyse and consume other animals.
The planet's ecosystem suffers from a number of particular peculiarities, most notably evolutionary quirks to allow all living organisms to detect and avoid solar flares. Red dwarf stars are unstable and eject frequent solar flares. Such intense ultraviolet radiation is deadly to all carbon-based life forms as it breaks down the atomic bonds formed by organic compounds.
Blue Moon is covered in life-giving water and an atmosphere so dense that enormous creatures can take flight. The Blue Moon orbits a Water Cloud Jovian planet (a Jupiter-like planet that is cool enough to have visible rain clouds in its atmosphere) orbitting a close binary star system. The Blue Moon itself is roughly an earth mass but has an air pressure around three times that of Earth's at sea level. This allows massive creatures to become airborne their whole lives; most interesting are Skywhales, gargantuan whale-like animals which evolved away from the ocean into the air.
The Skywhales are prey to the insectoid Caped Stalkers, colony-living predators that have several different tasks. Scouts find Skywhales and mark them with a special scent, then return to the nest to spread the word. Workers then swarm out in huge numbers, detecting the whale and the working together to bring it down from the sky and kill it. Finally, there is a Queen, who stays in the nest and constantly lays eggs that become new Stalkers.
The Stalkers are also prey, for the Pagoda branches are draped with the lethal webs of the plant-like Deathtraps. Once a Stalker is helplessly caught in a Deathtrap web, the carnivore uses its tentacles to lift its catch up into its mouth, to be digested in a primitive stomach of acid.
As well as Skywhales, giant Kites also fly above the forest canopy. These parasole-like grazers can grow up to five metres in diameter and still stay airborne. Their 'tethers' help control their floating, while their jellyfish-like tentacles snatch Helibug larvae from the water-filled skyponds. Helibugs have a trilaterally symmetrical body plan, with three eyes, three wings, three legs, three mouthparts and three tongues.
The entire Blue Moon land mass is coated in two main plant types, the Pagoda Trees and the Balloon Plants. Pagoda Trees interconnect with each other to allow them to grow to more than a kilometre high. Their hollow leaves collect rainwater, since the trees are too tall to draw it from the ground. Balloon Plants release their seeds by filling them with hydrogen to float in the dense atmosphere, in a similar way to kelp on Earth.
A distinguishing feature of Blue Moon is it has no polar ice caps, the thick atmosphere keeps temperatures constant throughout the planet's surface. There is also a greenish haze over the moon from floating moss and algae, the Skywhale's main food supply.
Humans could not live on the Blue Moon: the high levels of oxygen push the atmosphere to the brink of spontaneous combustion during lightning storms. Carbon dioxide levels are thirty times higher than on Earth making the air clammy and warm. Like our moon, Blue Moon is "tidally locked," meaning it keeps the same side of the moon faced towards its planet. With an orbital time of roughly sixteen days, that means eight days of continuous night and eight days of continuous daytime, not tolerable for humans. The long days and nights also create strong cross-hemisphere winds that help keep the skywhales afloat, in addition to the density of the atmosphere.
The high pressure allows more massive creatures to remain airborne than on Earth. Along with the increased muscle power from excess oxygen, creatures can have wingspans of fifteen metres and remain airborne their entire lives.
(c) - National Geographic