Gielinor is the planet that you live on, and that the aliens attempted to asplode.
The aliens wanted to destroy this planet because they saw it as a threat. When Guthix created existence, he started with the aliens. Each time he created a new race, he made it capable of advancing technologically faster than the previous one. Because of this, the aliens were afraid that other planets would eventually become stronger than them and destroy them. Then, they urgently tried blow up each one with their fleet. However, you saved your planet.
-Gielinor is the fastest-developing planet, and because of this it's also the youngest.