Prospecting Neptune's orbit

Neptune has Trojans like Jupiter – which Saturn and Uranus don’t.

As distant as these 'stroids are, like 2005 TN₅₃, what we've observed have high absolute magnitude - so must be physically large. We're not dealing with pushover midgets like the Venus-coörbitals.

We can mostly just see L4, the Greeks. Since 2006 its L5 has drifted into the way with Sagittarius A*, and Neptune’s kidney-beans extend very wide as seen from down here. So the L5 population haven’t been as well observed. But we have managed to catch sight of a few Neptunian L5s.

Talk is that Neptune cannot “efficiently” capture Trojans anymore: J. Horner and N. Evans, Mon. Not. R. Astron. Soc. 367 (2006), L20; S. Kortenkamp, R. Malhotra, and T. Michtchenko, Icarus 167 (2004), 347. These big ol’ rocks are presumed to have been captured during the ice-giant migrations. They are blueish like Centaurs: Scott S. Sheppard and Chadwick A. Trujillo, "A Thick Cloud of Neptune Trojans and Their Colors", Science 313 (28 July 2006), 511-14; 513.

But we’re not here to give; we’re here to take away. Whatever we build here, we can shoot to any nearby system, by way of Oberth gravity-boosts from Uranus, Saturn, and/or Jupiter. Maybe even via Neptune if we're doing a fryby to catch these planets on the way back.