Sun Eggs
Description: an ovoid shape that does look a lot like a Terran bird’s egg. The Sun Eggs given to humanity are about the size of a human male, weigh half a ton, and are utterly impervious to any attempt to analyze them more thoroughly than ‘Well, it’s light green in color, smooth, and neither warm nor cold to the touch.’ Oh, and they don’t topple over. Or break. You can pick one up with the right tools, but Sun Eggs don’t suffer damage from anything.
Why ‘Sun Eggs?’ Well, that’s what the envoy from the half-mythical Elder Planets called them when they gave Earth three of the things. The envoy went on to solemnly inform the bemused Terran diplomatic delegation that in billions of years these Eggs would hatch into new suns, and that in the meantime humanity was to protect and cherish them. As it has been done before, with countless other races, for billions and billions of years.
…It’s a joke. It has to be a joke, or an psychological test, or some sort of religious/philosophical koan, or something. I mean, Earth’s scientists asked their counterparts in the rest of the Galactic Federation if this was, you know, actually true and to a sophont they all replied ‘No.’ None of the other races in the Galaxy have any idea what the Elder Planets are talking about, here — and they’ve all gotten Sun Eggs, too.
They all have their pet theories, of course. The ones mentioned above are fairly common among the other races, but the more paranoid species are generally suspicious of the Sun Eggs in general. Some think that the Eggs are bombs; the more sophisticated paranoids are convinced that the Eggs are being used to monitor their every move, and retain a lively suspicion that the items radiate mind control rays of some kind (how this can be done without anybody noticing is — actually, sorry, don’t go down that particular debate rabbit hole). And at least one species is apparently neurologically incapable of worrying about the problem at all. That species is one of the most envied in the Galactic Federation.
A Terran Sun Egg has been stolen at least once since they were gifted to humanity; the criminals didn’t get far. In fact, the criminals returned it once they realized that nobody would buy it from them. Even the most obsessive human collector didn’t want to contemplate what would happen if the Elder Planets decided to take offense at the theft, and none of the alien species want any more Sun Eggs. And, of course, the criminals couldn’t destroy it. So it was either abandon it, or give it back with a sincere apology. Which the Terran authorities accepted, because maybe the Elder Planets are watching Earth through the damned things. How would they know?
Knowing all of this, the question becomes: so why has the party been hired to ‘borrow’ one of the Eggs for a few weeks? And the money’s good, too. Easily good enough to buy leaving that question quite unanswered, in fact. Which is suspicious, right there.