Hidebehind

The Hidebehinds are a phenomenon encountered in deep-space travel, and are a common topic of discussion among (usually-inebriated) human sailors. The common myth of the Hidebehind depicts them as a class of unidentified object or entity manifesting via transient sensor pings, generally found in low orbit around uninhabited worlds in the outermost peripheries of the Human Sphere (particularly in Sectors 1 and 2). Hidebehind apparitions occur in remote and uninhabited star systems usually multiple light-hours away on the outermost limits of sensor ranges, when a ship first-enters a star system. These ghost pings are, naturally, a source of widespread interest for navigators and starship crews, and have spawned a fair few urban legends and ghost stories over the years. Most are just that; even well-inhabited star systems have millions of unmapped and unregistered rocks and other junk in orbit of the system's star - given that it took centuries to fully map the Sol system, it is to be expected that most star systems have millions of rogue and uncatalogued objects in orbit. The tales of Hidebehinds circulate among sailors in those circles, and often with sketchy footage or black-box recordings to back them up, though no certifiable evidence of their existence has come to pass quite yet.

What elevated the Hidebehinds to be interesting and unique, rather than simple space debris, is that they display some unusual behaviours. When a ship enters a new system, the light from its arrival hasn't yet reached the Hidebehind's location yet, and when it does the Hidebehind generally disappears. The Hidebehind usually simply completes its orbit and disappears behind the planet, at which point it simply doesn't re-emerge. Speculation has arisen as to whether the hidebehind transitions into slipspace at this point, or goes to ground, though other alternatives have been suggested. A handful of particularly dedicated efforts on some of the higher-profile cases have tried to track their orbital velocities and measure where they may have landed on their respective planets, though none of these investigations have borne fruit.

Naturally, Hidebehinds are a very common focus in conspiracy theories, especially surrounding the actions of Office of Naval Intelligence stealth warships and (more recently) the Covenant. Some particularly suspicious sailors attribute their sightings as a bad omen associated with misfortunate slipspace jumps [eg materialising into the middle of an object, simply disappearing, appearing far away from the target destination etc], and it's not uncommon for conspiracies to paint the Hidebehind phenomena as a sign of UNSC/ONI stealth ships or spy probes. The latter became an especially common suggestion during the height of the UNSC-CMA Cold War and the Insurrection, though such sentiments were (naturally) ignored by official sources.

The rise of widespread contact with ex-Covenant (and more specifically, Jiralhanae) sources has given rise to some speculation that the Hidebehinds display a similar pattern of behaviour to the Gryunjalla of the Jiralhanae early space age, though such speculation remains just that.