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]
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Barycentric orbital
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