Malmuria

The Malmuria are an alien species native to the "tenth planet" Malmur, which occupies a highly elliptical orbit in the Solar System. The Malmuria raid Earth for food once every 2,006 years, when Malmur passes by Earth.

Anatomy & Physiology
Malmuria are highly unusual creatures of recent aquatic ancestry. They have a black, ovoid body roughly the size of a human torso, with a cluster of ten tentacles emerging from each side. A third set of ten tentacles sits at the bottom of the body, which the Malmuria use to walk. Malmuria have ten eyes, each one on a retractable stalk that can be withdrawn completely into the body.

Biochemistry
Malmuria breathe methane in place of oxygen. They can consume the same kinds of molecules for food that Earthly life does, although they must modify them first in unspecified fashion.

Diet
Malmuria are omnivores. Due to their homeworld's devastated state, they feed exclusively on paste made from organic matter harvested from Earth.

Reproduction & Life Cycle
There are male and female Malmuria, who mate with specialized tentacles. The natural lifespan of Malmuria is unknown. While many Malmuria are several tens of thousands years old, this is because they spend most of their lives in cryogenic hibernation, only emerging for less than a year at a time.

Homeworld
The Malmuria inhabit Malmur, the tenth planet of the Solar System. Malmur is a small terrestrial approximately twice the size of Earth's moon. It is originally of extrasolar origin, and found its way to the Solar System after being ejected from its original system under unclear circumstances.

Orbit
Malmur has an extremely eccentric orbit lasting 2,006 years. Its orbit takes it thousands of AU into space at aphelion and closer than Venus during perihelion. The orbit makes two close passes by Earth near perihelion, during which time the Malmuria invade Earth for food.

Atmosphere & Climate
Malmur's atmosphere is thinner than Earth's and consists mostly of methane. It is usually extremely cold, and no weather events are ever observed on Malmur.

Terrain
Malmur's terrain consists mostly of dusty plains. When it approaches the sun, solar panels unfold across its entire surface, concealing the planet from Earth observation and gathering vast amounts of solar energy. Most Malmuria day-to-day life takes place beneath these solar panels.