The Sarnus Refinery's Destruction was an act of attempted murder planned by the Columi siblings, Craitheus and Marvid Qreph, with the goal of coercing Lando Calrissian into relinquishing his assets in the Chiloon Rift.
Back in 45 ABY, the Columi brothers, Craitheus and Marvid Qreph, were in the midst of trying to execute a hostile takeover of the Chiloon Rift through financial means. However, their efforts to persuade Lando Calrissian to sell his holdings within the nebula proved unsuccessful. Growing increasingly frustrated, they opted to try and eliminate Calrissian along with his allies, Han Solo and Leia Organa Solo.
The Qrephs used their operative, Vestara Khai, to execute the assassination plot, and she managed to infiltrate Calrissian's refinery located on the planet Sarnus. The purpose of the refinery was to process minerals extracted from an asteroid field within the rift, and it was equipped with tractor beams capable of drawing asteroids from space for mining operations. Vestara deliberately damaged one of the tractor beams, which resulted in an asteroid colliding with the refinery, completely destroying it and causing the deaths of thirty thousand of Calrissian's employees.
Calrissian and the Solos managed to survive the destruction and successfully traveled to the planet Valnoos, which is where the Qrephs would orchestrate a second attempt to end Calrissian's life.