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2009 MS9 is a trans-Neptunian object (TNO) whose perihelion brings it closeto the distance where some long period comets are seen to become active.Knowing this, and the fact that this object appears to brighten in excess ofit's predicted nucleus brightness suggests that 2009 MS9 has a delayed onset ofactivity brought on by the sublimation of a species more volatile than water.In this paper we characterize 2009 MS9's physical properties and investigatepotential outgassing through composite images, sublimation models, andmeasurements of spectral reflectivity. We find that deep composite images ofthe object at various epochs along its orbit show no evidence of dust yet placesensitive limits to the dust production. We estimate the nucleus radius to be11.5 km $\pm 3.5$ km using thermal IR modeling from NEOWISE data and use thisand data pre-perihelion to estimate a geometric albedo of 0.25. We compare aCO-sublimation activity model to its post perihelion heliocentric light curveand find this data supports an active fractional area of $5 \times 10^{-6}$assuming 2 $\mu$m sized grains and other typical comet parameters. The spectralreflectivity of the surface materials obtained with the Gemini Observatory andCFHT at different epochs shows a reddening spectral slope. We compare thephysical properties of 2009 MS9 to both TNO and comet populations, andspeculate that 2009 MS9's reddening may be due to the buildup of a dust mantleon the surface and could be an explanation of why TNOs exhibit a colorbimodality.

TNO or Comet? The Search for Activity and Characterization of Distant Object 418993 (2009 MS9)