The Hilda population is trapped in the interior 3:2 mean motion resonance with Jupiter. The populations orbits are such that the objects form a triangle with the corners 60 degrees ahead of Jupiter, 60 degrees ahead of Jupiter, and on the opposite side of the Sun from Jupiter. The objects therefore do not have close encounters with Jupiter and stay long time stable.
NEOWISE observed more than 1700 Hilda asteroids during the cryogenic portion of the mission. The figure shows the results of the thermal modeling of these objects, revealing their diameter and albedo distribution. The results showed that the population is dark and dominated by C-, P- and D-type asteroids at all sizes, with only a handful of possible interlopers with different taxonomic types. The results were published in Grav et al. (2012) and the electronic table of diameters and albedos for all the Hilda objects observed are available at the publishers website.