Emissary

It's not as if an emissary from outer space will have slipped into school uniform and be loitering around seeking a partner.

An emissary from a distant solar system has contacted us.

What I think is really exciting about this is that, after two centuries of observing this fuzzy little blob of light among the stars, Earth now has a robotic emissary in orbit at Vesta.

The president sent an emissary to renegotiate the terms.

It's not as if an emissary from outer space will have slipped into uniform and be loitering around seeking a partner.

The small group around Ch’en Tu-hsiu that had remained at headquarters hastily sent an emissary—Chang Kuo-t’ao—to Nanch’ang. Though Chang set out immediately, he did not reach Nanch’ang until July 31, the day before the rising.

Near-synonym: missionary