This essay was one of my assignments in Imaging Other earths course on Coursera.org and is based on the science learned thoughout this course.
Our imaginary planet is called Hypatia  and is orbiting a K- type star .
K-stars or orange dwarfs are smaller and dimmer than the Sun and more abundant in our galaxy. They may be more favourable for life [3,4] as they produce less UV radiation than sun-like stars and have far less magnetic dynamo than the red dwarfs – which may result in violent stellar flares, harmful to life on near-by planets. Above all, orange dwarfs are longer lived than our sun, giving life the possibility to evolve even further.
This particular star’s mass is 0.81 Msun and its radius is 0.85 Rsun. It has a Luminosity = 0.316 Lsun and a temperature of 4700 K. Its life time is 18 Gy compared to 10 Gy of our Sun.
What are the prerequisites of habitability ?
Hypatia is located in the habitable zone of its host star at 0.6 AU, far enough as to not get tidally locked  and its rotational period is 190 days.
Even if a planet is found within the HZ of its primary does not mean it has all the prerequisites for life to arise and survive.
Apart from surface liquid water and an atmosphere, life needs to arise on a chemically dynamic planet, so some tectonic activity is needed to help control the amount of C02 as well as for mixing chemicals . Too much C02 in the atmosphere would increase the greenhouse effect resulting in a very hot environment.
A magnetic field provides protection against the solar wind coming in and knocking particles off and so it is necessary for a planet to be able to hold on its atmosphere.
There is a self generating magnetic field inside of a moving, conducting liquid iron core. For this to keep moving, plate tectonics are also necessary to cool its upper part and generate convection – as well as rotation of the planet around its axis.
Seasonal changes and tides (as a result of the gravitational pull from the sun or moons) seem also to play an important role.
Hypatia is a rocky planet with 1.5 Earth’s mass, a similar density and a radius of 1.2 Earth’s radius.
Its gravity is 1.149 g(earth) so it holds on to a more massive atmosphere which keeps the planet warmer and protects it from the harmful radiation.
The surface consists of many small continents surrounded by oceans; the land has mountains (but not as high as the earth’s, given its greater gravitation) vast valleys and many lakes surrounded by extensive woodland. It has volcanic activity and plate tectonics and so a powerful magnetic field.
The average equilibrium temperature at 0.6 AU is 247 K, but since Hypatia has a similar green house effect as the earth’s, holds on to a more massive atmosphere and it has a small albedo (most of its surface is covered by water and forests), the actual average surface temperature is around 280 K.
A small tilt of its axis results in seasonal changes throughout the year.
The climate is warm and humid enough and the conditions for life to start have been met long ago, so flora and fauna flourish all over the planet.
Plants are not very tall, consisting of complex massive structures with thick and juicy leaves which provide plenty of food and shelter for the other creatures. There are hundreds of species living on the land, in the water and the air. Many animals have developed flying abilities because in the denser atmosphere it is easier to float. Bird-like creatures are also bigger with larger wingspans; these Birds are the only life form feeding on other animals, mostly the marine ones. Insect-like forms of life, provided with powerful exoskeletons and sharp teeth, are of many sizes and shapes living in all kinds of environments and feeding upon each other.
Long evolution on Hypatia (it is 6 billion years old) has developed an intelligent life form that functions as a “bank” for all available genetic codes.
This intelligent creature has evolved from an original simple cell which at some point found a way to share genetic information with all other kind of cells. Gathering, processing and combining all information available over millions of years, it became a very complex organism, acquired knowledge of the laws of nature and was able to transform itself into a powerful being with special computer-like functions.
New mutations are intelligibly collected, selected and re-distributed to the species for better adaptation to environmental changes. Since it is the “medium” through which all creatures reproduce, It also regulates the species’ population in order for the whole ecosystem to remain in equilibrium. This is why, despite the lack of many carnivorous animals, the populations of the others are balanced.
It has the form of a glowing sphere 1-2 meters wide, feeding upon a very nutritive elixir, made by a special creature. It is surrounded by a sophisticated ergonomic multi-function membrane which acts as a bio sensor for all incoming vibrations or radiations (it can detect the whole spectrum of EMR as well as a very wide range of sounds); the detected signal is then processed and translated into comprehensible “images”. It also permits communication with the other beings (who are provided with a special bio-probe for this purpose). This magnificent membrane can also emit sounds through adjusted self-vibrations. It is capable of absorbing every form of energy available in the environment, store it in its body and re-use it when needed.
These creatures live more than 1000 years and they reproduce -when needed- by making an exact copy to which all the information is transferred. They do not need artificial technology – everything is made through bio-technology inside their bodies or in the bodies of other creatures. They know everything about their planet as they may travel by floating and navigating in the air. They live separatedly – each one taking care of its local environment- but they are in contact with each other over the entire planet through a bio-network. Once every 10 years they gather together in a big “symposium” to share and rearrange the information and decide on new biological innovations. Whatever they invent is an improvement on the biological level, as for example ways to avoid damage from UV radiation, better use of the available energy, self-repairs or auto fluorescence! Their bodies are a biochemical laboratory where they experiment on new possibilities of evolution.
I suspect that at present they are planning to construct a bio-ship suited for space travel so they can visit other planets, extend their knowledge and perhaps share beneficent information with alien life.