Ahu

Ahu is the 4th planet from the Sun. Ahu neighbors its sister planet, Huayalo.

Formation
Ahu was thought to have originated from a much larger celestial body, the same body in which Huayalo may have originated from.

After Kayuey's formation, Ahu experienced a much more stable axial tilt and rotational orbit. Similarly, Ahu acts as a "moon" to Huayalo, mutually stabilizing its axial tilt and orbit as well.

Atmosphere
Compared to Huayalo, Ahu has a much greater percentage of pure atmospheric oxygen.

Surface
More than barely half of Ahu's surface is comprised of glaciers that extend to miles-high heights; the northern glacier can barely extend up to 40 miles in height, while its giant southern counterpart easily reaches heights of 500 miles in height.

Ahu also contains one large ocean sandwiched between the two glacial poles as well as multiple large islands and archipelagos scattered throughout the ocean. Most of these islands and archipelagos are completely barren with silicates, with a large methane lake lodged in a landmass.

If the planet didn't have self-regulatory cooling atmospheric conditions, it would be a water planet due to its extreme volume of water.

Planetary Layers
Ahu's core layers and crust are thinner than those of Huayalo in terms of size..

Origin
It is unclear as to how life on Ahu evolved, but similar theoretical proponents to the birth of Huayaloan life had also been theorized for Ahuan life as well.

Unlike Huayalo, life in Ahu, both past and present, has not had any opportunities of evolving past micro and multi-cellular lifeforms due to two factors; the cyclical nature of extinction events and the surface limitations for which the life can rapidly evolve. Thus, life on the planet is in a constant state of a revised copy where previously-existing life dies off in extinction and similar lifeforms become the replacement.

Another theory suggests that ancient life may be stored within Ahu's looming glaciers, although there still doesn't exist any method to prove or disprove this.

Methane-dependent organisms
A large methane lake lies on Ahu's largest body of land. The methane lake is responsible for hosting the necessary conditions for its multi-cellular life. Methane is the main driver of life in Ahu, allowing for the development of a "lifeform biome", where 50% of Ahu's largest landmass is entirely covered with the life. However, once life becomes quite the common norm, then there is a greater risk for a breakup of a glacier shelf due to a methane greenhouse effect.

"Extinction Events"
Every 20 to 30 million years, a major extinction event occurs on the planet, usually caused by a glacial breakup or collapse of some sort. Once the methane-based life becomes the status quo for the planet, a global warming effect ensues which increases risk of glacial collapse. For example, a 5-mile tall glacial ice pack can create a wave of three miles in height and over 2000 miles in distance. when it collides with the oceans.

In extreme cases, an entire 500-mile high column of the southern glaciers might collapse and can produce enough tidal force to wash over the planet six times. Barring this extreme circumstance, it is estimated that the next major mass extinction event will occur in the year of 1178.

Trivia

 * Ahu most resembles a mixture between Earth and its once "snowball" phase.