Brother Chapter to the Thousand Sons they have dedicated their existence to eradicating and cleansing their name of the traitors that taint their name.
Founded on the planet Il-Karum the chapter had its first real test of survival on after they're only Battleship carrying an unknown and forgotten chapter crashed landed on an icy waste land. They got there after chasing down a Tyranid Hive Ship through several star systems before successfully defeating their foes. The battle however left their vessel crippled and it tumbled through through the atmosphere, breaking apart in the air and scattering the ship over large parts of the northern continent.
The planet itself was at the time a no-go zone in the Veiled Region. It was in orbit around what was known as "The Soul of Malal", a Black Hole that was devouring its partner star.
The location created a unique need for the surviving Marines. Going outside was a death sentence, it was too cold and the radiation would kill even the most hardened warrior in minutes.
The crash revealed a subterranean series of caves and caverns that had in it non-sentient life. Below the surface was practically a paradise compared to barren icy wastes above with geothermal pools keeping things nice and warm.
Initially the survivors were perplexed as to why there was life on this planet but they couldn't survive outside. The answer came from observations made of lifeforms that would investigate the crash site and would die within a few moments of being exposed to the faux-sunlight from the dying star above.
What was protecting them was a layer of mineral that the imperium had never discovered before that lay beneath the ice but above the caves.
Over the months and years ahead the Marines disassembled and re-purposed what they could from the wreckage, used the geothermal vents as sources of power and heat.
After they identified the mineral that protected the lifeforms in the caves they were able to reforge they armour and structures to integrate it. This provided them with much needed protection for the Survivors.
With the ability to explore the planet they were able salvage more of the wreck.
Over the next 100 years scans of the planet revealed that the mineral is everywhere.
Its theorized that the unique nature of the star system created the mineral.
137 Standard years after the crash a Chaos Cruiser detected the crash site under the new mountain of snow and began to investigate.
The resulting battle after the Chaos forces realized that the wreck was still inhabited meant the Marines now had a means to get off the planet.
The Marines were able to force their way on to the Cruiser still in orbit and over the next few days of intense battle were able to take it over and leave The Soul of Malal.
Setting course to the nearest Imperium world they made their way home.
While on course they discovered what this sect of Chaos had done and more importantly that they were related as they were traitors from their own Regiment. Enraged they re-christened themselves The Suns Solar.
Upon the reintegration with the Imperium they vowed to wipe out the Thousand Suns.
