This archive tracks four layers. A record present in 1 of them (M41) is silent in the rest, and says so.
The Horus HeresyM30–M31
[RECORD LOST]
No record for this location in The Horus Heresy.
Age of the ImperiumM32–M40
[RECORD LOST]
No record for this location in Age of the Imperium.
The 41st Millenniumpre-Rift
imperium
Minor Imperial hive world
A minor hive world of little strategic significance and the only inhabited world of the Dierna System, in the same subsector as Sandava. The Grey Knights Purifiers under Castellan Merrat Gavallan come to the system on a portent of their Prognosticars and destroy the corrupted missionary ship Envoy of Discipline before it can threaten its people.
Era Indomituspost-Rift
[RECORD LOST]
No record for this location in Era Indomitus.
Position
Map frame: 99.9, 308.3 in the archive's 0–1000 disk space (core at 500, 500).
Distance from the core: 444 units ≈ 47.2k light years, north-west of the galactic core.
Height above the disk plane: -4.6 units — invented thin-disk jitter, deterministic per record. No published source gives any location a z coordinate.
System: Dierna System
Books set here
1 title in the reading tracker touches this record. Titles link out to the tracker.
Every fact in this record, and where it came from. Editorial derivations say so.
identityhigh
wh40k.lexicanum.com/wiki/Dierna_Primus (read directly in a browser on 2026-10-03): 'a Hive World of the Imperium. A minor Hive world of little strategic significance, it is the only inhabited world of the Dierna System' (Warden of the Blade ch. 2); the Purifiers under Merrat Gavallan, on 'a grim portent foreseen by the Prognosticars', arrive aboard the Sacrum Finem and destroy the corrupted missionary ship Envoy of Discipline 'before it could threaten the inhabitants of the system' (chs. 3, 5). https://wh40k.lexicanum.com/wiki/Dierna_System: 'located in the same subsector as the Sandava System' (ch. 1); the star is Dierna (https://wh40k.lexicanum.com/wiki/Dierna, ch. 3). NAME-COLLISION CHECK: no index record uses the id or label.
book-joinmedium
MENTIONED for Warden of the Blade (grey-knights::gk-crowe::1): the novel's opening action is in the Dierna System, against the Envoy of Discipline (chs. 3, 5), but no permitted source puts a scene on the planet itself.
segmentumhigh
null: Lexicanum's infobox gives Segmentum, Sector and Subsector 'Unknown'.
classmedium
'hive': 'a Hive World ... a minor Hive world' (Lexicanum Dierna_Primus, ch. 2). Nothing else describes the surface.
gposlow
inferred: the only geography canon gives is that Dierna shares a subsector with Sandava (Lexicanum Dierna_System and Sandava_System, ch. 1), and Sandava itself sits on the unsurveyed rim (rim_xy('sandava-ii') = [110.4, 287.6]). So Dierna is placed beside it, along the same rim band (r 443.7, 3 degrees round from Sandava) at [99.9, 308.3], 23 units away; the offset is editorial and asserts only 'near Sandava'. The position carries no other information. Z -4.6 is the zPolicy value (compute-z.mjs dierna-primus 99.9 308.3).
erasmedium
m41 only, the novel's era. Allegiance 'imperium'.
no-system-surveymedium
No systems/dierna.json: the star (Dierna) and one inhabited world are named, which a survey could draw, but the world is MENTIONED, not a primary setting, so the synthesised one-world system stands. Revisit if a book is set there.