Wes Fraser
Figure 1.
Blue Binaries Suggest a Smooth
Migration for Young Neptune
A Large and Long program using simultaneous ultraviolet
and near-infrared data from Gemini North and the Canada-
France-Hawai‘i Telescope lead to the discovery of a peculiar
population of blue-colored, tenuously bound binaries residing
among the otherwise unanimously red “cold classical” Kuiper
Belt objects. These widely separated binary objects could have
survived perturbing forces during the early phases of Neptune’s
migration, helping us to better understand the planet’s accretion
history in the outer Solar System.
A Brief History of the Kuiper Belt
Rendering of the outer
Solar System. Small
points correspond to
the >1700 known and
tracked objects. Colours
correspond to different
dynamical classes - the
cold classicals are in red,
the resonant plutino
and two-tino objects
are in purple and yellow,
the transitory centaurs
are in white, and the
non-resonant excited
objects are in light blue.
A handful of the orbits
of this class are shown
by the dotted blue lines.
The gas-giant planets are
the larger circles, and the
largest 10 dwarf planets
are identified with white
circles. Distances at 30, 50,
and 100 AU are shown by
the dashed white circles.
The Kuiper Belt is complicated, and weird. Consider its shape
(see Figure 1). First a disclaimer: the community uses the term
belt pretty loosely. Imagine instead a broad torus hundreds of
astronomical units (AU) thick and tens of AU tall, with a 30 AU
radius hole cut out of the middle. That’s the true shape of the
Kuiper Belt.
Beyond its poorly named shape, what really catches a scientist’s
eye is the Belt’s layered dynamical structure. The first Kuiper Belt
Object (KBO) discovered, 1992 QB1, belongs to the so-called
cold classical population, named for what may have been ex-
pected to reside beyond Neptune: a population of planetesi-
mals on circular, low inclination orbits, in a ring (or belt).
Unlike the asteroid belt, whose empty Kirkwood gaps can clear-
ly be attributed to the clearing effects of mean-motion reso-
July 2017
GeminiFocus
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