What would an observer within 100 LY be able to piece together about our solar system? Could they see Earth? I'd imagine it's a bit too close, but Jupiter would definitely be visible. Not sure about Mars, but if our system garnered so much interest to an alien species just from observing Mars and Jupiter that they bothered sending a probe, what about them tipped them off that there could be life here? Assuming 3I/ATLAS really is an interstellar probe, it will send its data next year and depending on how close the alien system is situated will take tens or hundreds of years to return to them. Realistically though, we should've already recieved radio signals from any nearby alien species capable of interstellar travel, so it's safe to say this interstellar object is not actually probe. It's still quite remarkable how close it gets to Mars and Jupiter though all things considered.