We present an ultra-deep survey for Neptune Trojans using the Subaru 8.2-m and Magellan 6.5-m telescopes .
The survey reached a 50 \% detection efficiency in the R-band at m _ { R } = 25.7 magnitudes and covered 49 square degrees of sky . m _ { R } = 25.7 mags corresponds to Neptune Trojans that are about 16 km in radius ( assuming an albedo of 0.05 ) .
A paucity of smaller Neptune Trojans ( radii < 45 km ) compared to larger ones was found .
The brightest Neptune Trojans appear to follow a steep power-law slope ( q = 5 \pm 1 ) similar to the brightest objects in the other known stable reservoirs such as the Kuiper Belt , Jupiter Trojans and main belt asteroids .
We find a roll-over for the Neptune Trojans that occurs around a radii of r = 45 \pm 10 km ( m _ { R } = 23.5 \pm 0.3 ) , which is also very similar to the other stable reservoirs .
All the observed stable regions in the the solar system show evidence for Missing Intermediate Sized Planetesimals ( MISPs ) .
This indicates a primordial and not collisional origin , which suggests planetesimal formation proceeded directly from small to large objects .
The scarcity of intermediate and smaller sized Neptune Trojans may limit them as being a strong source for the short period comets .