SIMP J013656.5+093347 is Likely a Planetary-Mass Object in the Carina-Near Moving Group

We report the discovery that the nearby ($\sim$ 6 pc) photometrically variable T2.5 dwarf SIMP~J013656.5+093347 is a likely member of the $\sim$ 200 Myr-old Carina-Near moving group with a probability of $>$ 99.9% based on its full kinematics. Our $v\sin i$ measurement of $50.9 \pm 0.8$ km s$^{-1}$ combined with the known rotation period inferred from variability measurements provide a lower limit of $1.01 \pm 0.02$ $R_{\mathrm{Jup}}$ on the radius of SIMP0136+0933, an independent verification that it must be younger than $\sim$ 950 Myr according to evolution models. We estimate a field interloper probability of 0.2% based on the density of field T0-T5 dwarfs. At the age of Carina-Near, SIMP0136+0933 has an estimated mass of $12.7 \pm 1.0$ $M_{\mathrm{Jup}}$ and is predicted to have burned roughly half of its original deuterium. SIMP0136+0933 is the closest known young moving group member to the Sun, and is one of only a few known young T dwarfs, making it an important benchmark for understanding the atmospheres of young planetary-mass objects.