Suloom is a hot, Mars-like D-class planet orbiting a red dwarf, known as Saihera, in the Flower Galaxy. It hosts multicellular life on its terrestrial surface, taking on many forms across the landscape, and is famous throughout the galaxy because of this.
Suloom is smaller and less massive than Earth, which means it is classified as a 'sub-earth'. Its high density implies that there is a substantial iron core inside the planet, generating its weak (but still existing) magnetic field. The small magnetosphere is not very effective at blocking the stellar wind from Saihera (its parent star) and that constantly whittles down its ever-thinning atmosphere, possibly threatening the existence of the life below.
Tidal locking and anomaly
Owing to Suloom's proximity to its parent star, it is tidally locked, which means one side of the planet constantly faces the star. From space though, the planet seems uniform and there seems not to be any differentiation between the terminator line and the point below its red dwarf star, which is evidence of some kind of temperature distribution around the planet. What is even more striking is that the night side, while not as explored as the dayside (for obvious reasons), seems so far to have the exact same terrain and environment as the dayside! (Aside from a temperature difference of 2-3°C) Astronomers, geologists, chemists and astrobiologists working at this planet are still scratching their heads over this, but an explanation could be finally coming.
One of the most plausible theories relates to the recent discovery (~150 years ago) of large sinkholes all over Suloom. The origin of these sinkholes is still unknown, but it is likely to do with previous asteroid or comet impacts. The sinkholes then compose a vast web of tunnels under Suloom's surface and are responsible for the temperate environment on Suloom's night side. In the tunnels, ecosystems comparable to the ones found in other places of Suloom can be found.
Another interesting and noteworthy quirk about Suloom is its strange atmosphere. Somehow, it is 44% diatomic oxygen, and a similarly large sector is made of water vapour. Now, this is still very little oxygen, because the atmosphere pressure is still only 0.00324 atmospheres, a mere 27% the atmospheric pressure of pre-terraformed Mars, so you really could not breathe here if you wanted to.
The oxygen is likely caused and replenished by some kind of photosynthesis that is being carried out by plants on Suloom's surface. The explanation for the water vapour is less understood - the most likely cause is from geological activity. Other plausible explanations include infalling comets, or the life underground that uses chemical energy and makes waste products such as water.
There is an unreasonably low amount of lifeforms on Suloom - only 26 have been documented despite extensive researching, 23 of these fitting into only 4 known ecosystems on the entire planet. Two of the ecosystems are very widespread - one covering the entire dayside and the other the entire nightside, and the two others occur exclusively underground. Nevertheless, some interesting lifeforms do exist here.
Inside the caves, there are giant mats of fungi-like microscopic organisms, feeding on the minerals to produce energy. Here, they build up a thin layer of carbonic acid and slowly release carbon dioxide, which leakes into the surface through the various sinkholes. There, they sometimes build a thin layer of CO2 close to the surface of Suloom.
This gas is sometimes used by purple plants on the surface as a way to photosynthesize, as they take in water and carbon dioxide to make glucose, to make food.