One of the early discoveries by the survey was that all of the ‘blue’ or ‘neutral’ TNOs with cold classical orbits were binaries. This result was published in Nature Astronomy [Fraser et al. 2017]. These objects have colors consistent with the neutral surfaces of dynamically excited TNOs. Our team explored dynamical simulations, which showed that these objects could have been emplaced by push-out as Neptune smoothly migrated outward- they are interlopers in the cold classical region.

The addition of z band to the Col-OSSOS project has proved incredibly valuable. We have discovered that red cold classical TNOs have unique surfaces in g-r vs r-z [Pike et al. 2017]. Unique surface properties for cold classical TNOs were expected based on their different binary fraction and albedos from the dynamically excited objects, however previous work had found them to be a similar red color to the red dynamically excited TNOs. These surfaces are distinct in the combined bands g, r, and z. This result has enabled new projects searching for cold classical surfaces in other regions of the Kuiper belt.

We were able to observe the interstellar object 1I/‘Oumuamua in the same wavelengths as the Col-OSSOS survey [Bannister et al. 2017]. Our g, r, and J band photometry of TNOs provided a powerful context for interpreting the surface reflectance of this unique object. 1I/‘Oumuamua has unusual colors compared to solar system objects, but it is not outside the range of surface reflectivity seen in the solar system. This photometry is summarized in the figure below, from Bannister et al. 2017.

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