523676 (2013 UL10): The first active red centaur

Aims. We present observations of 523676 (2013 UL10), a centaur orbiting between Jupiter and Uranus that is dynamically similar to the few tens of active centaurs that are currently known. Methods. We analysed visible BVR images of the centaur obtained at the Telescopio Nazionale Galileo (La Palma, Canary Islands, Spain) to investigate the weak comet-like activity and to derive information on the nucleus surface colours and size. Results. Centaur 523676 (2013 UL10) is the only centaur known so far that has both comet-like activity and red surface colours: its nucleus has a colour index [BR] = 1.88 0.11. The nucleus R magnitude (R = 20.93 0.09) allowed us to derive an upper limit for its nucleus size of D 10 km. We estimated its dust production rate to be Qd 10 kg s1 at 6.2 au (just after its perihelion passage), resulting in a timescale for the surface blanketing process of approximately tens of years, which is very short with respect to typical dynamical lifetime inside the group. Future monitoring of 523676 (2013 UL10) is needed to further constrain the blanketing model for active centaurs and its timescale.