Haestrom

Mass Effect 2 & Mass Effect 3 Solar System Entry
Formerly a quarian colony, Haestrom was established to observe the phenomena on Dholen, the system's parent star. Dholen appeared to be unstable with a high possibility of erupting prematurely into a red giant.

Haestrom was lost to the geth in 1896 CE. Soon after, all communication from the planet and its attendant space stations ceased. The geth have shown no signs of treating Dholen as a threat over the past three centuries other than establishing several space stations near it. Dholen's magnetic eruptions and solar output overwhelm most communications near it, and it is unclear how the geth have compensated.

Today, spy probe scans indicate extensive orbital construction around Haestrom, housing thousands of geth platforms and an unknown number of geth software "minds." It is not known how many geth are on the planet's surface: spy probes face interference from Dholen, making remote scanning difficult. Resource estimations based on geth mining, refining, and fabricating practices suggest that the planet has at least 20 more years of use before it is exhausted. Intelligence experts speculate that the geth have not exploited all of their resources because they wish to keep some in reserve for repairs.

TRAVEL ADVISORY: Haestrom is a geth stronghold. Military spy drones using cutting-edge stealth technology are the only vehicles that have returned unharmed from geth space. All civilian traffic is prohibited.

Mass Effect 2 & Mass Effect 3 Codex Entry
Before the geth revolt 300 years ago, the quarians colonized Haestrom to study the mysterious instability of its sun. 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 hoolhardy 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.