GeminiFocus July 2017 - Page 9

Figure 6. 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 sce- nario 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 re- moved through friction with a sea of small pebbles (the “s” in L2s). This idea was deemed to be inefficient, as it re- quires what was considered a much too mas- sive 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 pro- duce a near 100% binary fraction will inevita- bly provide reformation of our — admittedly poor — understanding of the planet accre- tion history in the outer Solar System. I can’t, in good conscience, conclude with- out a mention of the CFHT and the amaz- ing 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 sig- natures that could inform us of Neptune’s migratory history, and indeed the formation of the outer Solar System. Other publica- tions by our group are in the pipeline which follow this theme; there is much to come. July 2017 Wes Fraser is an astronomer at Queen’s Univer- sity Belfast. He can be reached at: [email protected] REFERENCES Bannister, M. T., et al., “The Outer Solar Systems Origins Survey. I. Design and First-quarter Dis- coveries,” The Astronomical Journal, 152: 70, 2016 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. Fraser, W. C., et al., “All planetesimals born near the Kuiper belt formed as binaries,” Nature As- tronomy, 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 or- bit,” Nature, 365: 819, 1993 Tsiganis, K., et al., ”Origin of the orbital architec- ture of the giant planets of the Solar System,” Na- ture, 435: 459, 2005 GeminiFocus 7