- Rimmer ("White Hole")
A Solar flare is a massive ejection of super-heated plasma and electromagnetic energy from a star.
The explosion caused a massive solar flare, which in turn knocked the planets out of orbit, crashing into each other. Due to Lister's "trick shot", one of the planets successfully sealed up a White Hole, restoring the damage the White Hole had done to the timeline. ("White Hole", Series IV)
Behind the scenes
Extensive model work was done for the "pool with planets" scene that never made the broadcast episode of "White Hole".
This included Starbug firing the missile at the sun in close-up, and also the massive solar flare being ejected from the sun, which in the broadcast episode was only seen hitting the planets, but not actually being ejected from the star.
These model shots were excised for time, but can be viewed on the bonus features on the Series IV DVD.
The same incident occurs in the Red Dwarf novel Better Than Life, which follows a different continuity/timeline to the television series. This time, although it works to avoid a rogue planet, it also causes Starbug to crash into another ice planet. The planet turns out to be "Garbage World", which was actually once Earth. (Better Than Life)
- Solar flare article on Wikipedia