According to a study recently published in The Astronomical Journal, if aliens were trying to detect planets in our solar system, the key planet just could be Neptune, thanks to its interactions with a distant region of dust and frozen volatiles called the Kuiper Belt.
From their release:
“The planets may be too dim to detect directly, but aliens studying the solar system could easily determine the presence of Neptune - its gravity carves a little gap in the dust,” said Marc Kuchner, lead author of the study.
Kuiper Belt objects occasionally crash into each other, and this relentless bump-and-grind produces a flurry of icy grains. But tracking how this dust travels through the solar system isn’t easy because small particles are subject to a variety of forces in addition to the gravitational pull of the Sun and planets.
The particles also run into each other, and these collisions can destroy the fragile grains.
“People felt that the collision calculation couldn’t be done because there are just too many of these tiny grains too keep track of. We found a way to do it, and that has opened up a whole new landscape,” said Kuchner.
That "new landscape" consists of using similar methods to find planets in other solar systems. Of course, aliens might be able to detect our solar system using tricks of astrophysics that we haven't yet dreamt of, but this seems like it could be a useful field of inquiry for earthly astronomers.
(h/t Phenomica | Journal article)