Aether is a world in the Dasha System and is home to the Luminoth, while is twin Dark Aether is home to the Ing. It first appeared in Metroid Prime 2: Echoes, and on some occasions was mentioned in Metroid Prime 3: Corruption.
Long ago, a meteor formed of Phazon crashed onto the planet, which caused a new dimension to be created in the form of Dark Aether.
The Luminoth originally had no home planet, though after meeting with the Chozo, they were influenced to take their species on a planet as they did. They ended up on the rogue planet Aether, and thus had to generate their own light sorce via the Light of Aether, which eventually threatened the planet, causing the new species to create the Energy Controllers which would better keep it under control.
As mentioned above, a meteroite from the completely Phazon covered planet Phaaze, struck the planet, causing a new dimension to form which was later known as Dark Aether. Soon enough, species from this new dimension started to creep out of their dimension and into the light world, though all of them evaporated into thin air.
Not only did this meteroite create a new threat to the Luminoth and their new planet, though it also caused other drastic effects as well - Torvus, a once lush forest was flooded, and most of the planet was turned into a large crator.
Samus is sent to Aether on a mission to find a missing squad of Space Marines that had crashed on Aether. Samus then finds herself sucked into an interdimensional/interplanetary war once she absorbs the Energy Control Module. Samus then had to travel to each temple and it's Dark Aether counterpart to restore Aether's planetary energy.
In the end, Samus would eventually restore the planet's life and light back to how it was originally.