push-out , the majority of planetesimals near ~ 35 AU were binary . We know this from the simple fact that no blue singles have been found in the cold classical region . Only binaries with only blue or only red components would not have formed in the current environment . This result is genuinely surprising , as it is difficult — but not impossible — to envision a planet growth scenario that , at one point , all objects were bound up in binary or higher multiplicity systems .
Various binary mechanisms have been proposed , like the so-called L2s mechanism by Peter Goldreich in which two large planetesimals ( the “ L2 ”) are temporarily captured , and sufficient angular momentum to bind the pair is subsequently removed through friction with a sea of small pebbles ( the “ s ” in L2s ). This idea was deemed to be inefficient , as it requires what was considered a much too massive sea of pebbles to produce a high binary fraction . With our new findings , however , Goldreich ’ s idea , and other binary formation mechanisms deserve another glance ; clearly , whatever mechanisms could plausibly produce a near 100 % binary fraction will inevitably provide reformation of our — admittedly poor — understanding of the planet accretion history in the outer Solar System .
I can ’ t , in good conscience , conclude without a mention of the CFHT and the amazing u-band data it is providing for us . In all respects , the blue binaries result made use of only the ( g ’ -r ’) color observed at Gemini . Much of the rest of the data , including the CFHT u-band , remain untapped , and still needs to be thoroughly analyzed . Col-OS- SOS was designed to look for KBO color signatures that could inform us of Neptune ’ s migratory history , and indeed the formation of the outer Solar System . Other publications by our group are in the pipeline which follow this theme ; there is much to come .
Wes Fraser is an astronomer at Queen ’ s University Belfast . He can be reached at : wes . fraser @ qub . ac . uk
REFERENCES
Bannister , M . T ., et al ., “ The Outer Solar Systems Origins Survey . I . Design and First-quarter Discoveries ,” The Astronomical Journal , 152 : 70 , 2016
Fraser , W . C ., et al ., “ All planetesimals born near the Kuiper belt formed as binaries ,” Nature Astronomy , 1 : article No . 0088 , 2017
Nesvorný , D ., “ Jumping Neptune can explain the Kuiper belt kernel ,” The Astronomical Journal , 150 : 68 , 2015
Paker , A . H ., and Kevalaars , J . J ., “ Destruction of binary minor planets during Neptune scattering ,” The Astrophysical Journal , 722 : L204 , 2010
Levison , Harold F ., “ Origin of the structure of the Kuiper belt during a dynamical instability in the orbits of Uranus and Neptune ,” Icarus , 196 : 258 , 2008
Malhotra , Renu , “ The origin of Pluto ’ s peculiar orbit ,” Nature , 365 : 819 , 1993
Tsiganis , K ., et al ., ” Origin of the orbital architecture of the giant planets of the Solar System ,” Nature , 435 : 459 , 2005
Figure 6 . Barycentric orbital elements of the surviving particles immediately after Neptune ’ s jump , at 27.8 AU . Dotted lines demark the cold classical region . Pairs of overlapping large and small round points mark bound binary pairs , and triangles mark single objects — all of which are the result of binary unbinding . Red-blue pairs and purple triangles are those binary and single objects which were emplanted in the cold classical region . As in Levison et al ., some objects transported outward into the cold classical region fell out of the 2:1 MMR before the jump due to Neptune ’ s non-smooth migration , while others dropped out of the resonance when the planet jumped .
January 2018 / 2017 Year in Review GeminiFocus
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