Before the geth revolt 300 years ago, the quarians colonized Haestrom to study the mysterious instability of its sun, which threatened premature eruption into a red giant. As a scientific outpost of minimal military value, Haestrom was ill-equipped to repel geth forces during the insurrection and fell quickly under their control.
Captured geth planetary survey data indicates that despite sustaining damage, Haestrom's architecture remains as it was before the war, preserving a quarian architectural style that no longer exists anywhere else in the galaxy.
Because Haestrom's sun has overwhelmed the planet's protective magnetosphere, humans foolhardy enough to venture into geth-controlled Haestrom must exercise extreme caution. Minutes of radiation exposure will overload shields and hours of exposure will kill. Furthermore, solar output renders surface-to-orbit communication nearly impossible.