While mining the outer asteroid belt a miner uncovers a large metal object, could be a probe or a torp, or garbage left in space. He reports the find his company which in turns sends the characters on a retrieval mission.
Curious characters examining the object discover it is a probe. Although the hardware systems look like any type of frontier technology the language is unlike they have seen before.
As they dig deeper into the guts of the probe they'll realize it requires power (the power cell was knocked out when it hit an asteroid).
As soon as the probe receives power a holo display is initiated, the party sees images of the star system (planets, moons, etc.), as the camera pans towards the home star it appears as if a light-filter is blocking some of the light, but then you realize it's a ship. A big ship.
How old is the probe?