Thrae (designated Thraol e and RS 1135-7-8-8237694-454 e) is a temperate E-Class exoplanet orbiting a red dwarf in the galaxy Maffie II. The fourth planet of the Thraol system and the third largest overall, it is an Earth twin with just about the same radius, mass, composition, and temperature. While specific conditions on the two planets vary, Thrae is a hospitable world teeming with life. A space-faring Type I civilization known as the Thraebals have evolved on this planet and colonized many worlds of their home system.
Thrae and its inhabitants resides in a part of the Local Group not yet explored by humanity. This has led the Thraebals to develop without interference from an all-powerful alien race. Their society is structured and organized, with very little conflicts breaking out after the creation of the Thrae Planetary Union.
Thrae is one of the most similar planets to Earth within the entire Local Group. Based on its mass, radius, and temperature, it has an Earth Similarity Index of 0.981, an unbeaten record. Conditions on the planet are slightly tougher than those on Earth. The higher gravity and atmospheric pressure leads to greater surface pressures, and the long rotation period has created very strong winds around the equator. Despite this, the requirements for life - energy, water, atmosphere, etc. - are found here in an astonishing abundance. Life emerged fairly quickly and became multicellular after just 1.12 billion years.
Physical Properties and Terrain
Thrae is an Earth-sized planet, meaning that its mass and radius values are very similar to those of Earth. It has a diameter of 12,648 km, less than 1% smaller than Earth. However, Thrae has a substantially higher iron content than Earth, as evident by the higher mass of 1.077 Earth masses. The planet's density works out to be 6.0728 g/cm^3, higher than any planet discovered in the Sol system.
Thrae's core is rather large. While Earth's iron core is about 17% the planet's volume, the core of Thrae is between 20 and 30%. This can be explained by the rather large quantities of iron that reside in the inner regions of a red dwarf's protoplanetary disk. Forming closer to the frost line, Thrae was unable to acquire enough metals to become a full-fledged iron planet like Trappist-1c. However, evidence has shown that Thrae may have stolen most of the iron from the regions that would later form Thraol c (Merda) and Thraol d (Threv). Only Thraol b (Kzrokah) was able to become a pure iron world.
The surface of Thrae is quite different from that of Earth. Only about a third of the surface is covered in water. Most of it is concentrated into two large seas and two minor seas, with smaller lakes being scattered about. The larger water-holding areas were formed by the subduction of silicates with metals chemically bound to the rocks. Sizable depressions in the surface formed, and with the temperature on the young Thrae being rather hot, water chemically bound to mantle rocks was released and became clouds. For about 10,000 years, huge floods and rainstorms drenched the planet.
After the original monsoons, many of the seas spilled over and flooded lower areas of the planet. Some of these areas were eroded over billions of years to form sea basins. However, the rest of the excess water pooled into impact basins that were created about 2.77 billion years into Thrae's history. Around this time, two dwarf planets smashed into each other and pelted Thrae with huge debris. 99.6% of life was wiped out, but since it had gotten so far it was able to bounce back after just 420 million years.
A little over two dozen giant impact basins were created from the Dwarf Planet Smash-Up. All of them are between 100 and 500 km across, similar in diameter to the largest minor moons of Merume. They are all filled up completely with water and provide a great habitat for aquatic organisms.
The land of Thrae is mainly coated in blue plant life. Most of that blue life consists of huge forests stretching for dozens, if not hundreds, of kilometers. Due to the planet's long rotation period of 157 Earth days, the equator has become rather hot for life. Only more resiliant plants can survive here. This is why there is more blue life at higher latitudes, closer to the poles. In these areas the entire surface can be coated a beautiful blue color. However, at around 50-60 degrees latitude, the climate becomes too cold for plants. This is where tall glaciers of ice begin to form and replace the usual hill-dotted landscape. The north pole has the highest ice cap, which can tower several kilometers above the rest of the surface. The southern glaciers are darker in color and not as tall.
The poles aren't the only sources of ice on Thrae. Mountain ranges in the northern latitudes are often coated a shiny white due to cold temperatures and constant snowfall. Below a certain altitude, however, snow cannot exist. The surface is warm enough for ice to melt into liquid water. Some of this melted water has formed a huge river system around the northernmost major sea. These rivers snake through huge blue forests and bizarre, hilly terrain. Many large hills have formed all over the ice-free parts of the surface. Some are caused by plate tectonics, others are just really big dunes caused by the high winds. Generally, hills closer to the equator are dune-related as the winds can get strong enough to push up surface material over thousands of years.
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