As part of our ongoing Deep Ecliptic Survey ( DES ) of the Kuiper belt , we report on the occupation of the 1:1 ( Trojan ) , 4:3 , 3:2 , 7:4 , 2:1 , and 5:2 Neptunian mean-motion resonances ( MMRs ) .
The previously unrecognized occupation of the 1:1 and 5:2 MMRs is not easily understood within the standard model of resonance sweeping by a migratory Neptune over an initially dynamically cold belt .
Among all resonant Kuiper belt objects ( KBOs ) , the three observed members of the 5:2 MMR discovered by DES possess the largest semi-major axes ( a \approx 55.4 { AU } ) , the highest eccentricities ( e \approx 0.4 ) , and substantial orbital inclinations ( i \approx 10 \arcdeg ) .
Objects ( 38084 ) 1999HB _ { 12 } and possibly 2001KC _ { 77 } can librate with modest amplitudes of \sim 90 \arcdeg within the 5:2 MMR for at least 1 Gyr .
Their trajectories can not be explained by close encounters with Neptune alone , given the latter ’ s current orbit .
The dynamically hot orbits of such 5:2 resonant KBOs , unlike hot orbits of previously known resonant KBOs , may imply that these objects were pre-heated to large inclination and large eccentricity prior to resonance capture by a migratory Neptune .
Our first discovered Neptunian Trojan , 2001QR _ { 322 } , may not owe its existence to Neptune ’ s migration at all .
The trajectory of 2001QR _ { 322 } is remarkably stable ; the object can undergo tadpole-type libration about Neptune ’ s leading Lagrange ( L4 ) point for at least 1 Gyr with a libration amplitude of 24 \arcdeg .
Trojan capture probably occurred while Neptune accreted the bulk of its mass .
For an assumed albedo of 12–4 % , our Trojan is \sim 130–230 km in diameter .
Model-dependent estimates place the total number of Neptune Trojans resembling 2001QR _ { 322 } at \sim 20–60 .
Their existence might rule out violent orbital histories for Neptune .