摘要：We present a study of comet C/2017 K2 (PANSTARRS) using pre-discovery archival data taken from 2013 to 2017. Our measurements show that the comet has been marginally increasing in activity since at least 2013 May (heliocentric distance of rH = 23.7 au pre-perihelion). We estimate the mass-loss rate during the period 2013–2017 as M˙ » (2.4 1.1) ´ 102 kg s−1, which requires a minimum active surface area of ∼10–102 km2 for sublimation of supervolatiles such as CO and CO2, by assuming a nominal cometary albedo pV = 0.04 0.02. The corresponding lower limit to the nucleus radius is a few kilometers. Our Monte Carlo dust simulations show that dust grains in the coma are 0.5 mm in radius, with ejection speeds from ∼1 to 3m s−1, and have been emitted in a protracted manner since 2013, confirming estimates by Jewitt et al. The current heliocentric orbit is hyperbolic. Our N-body backward dynamical integration of the orbit suggests that the comet is most likely (with a probability of ∼98%) from the Oort spike. The calculated median reciprocal of the semimajor axis 1 Myr ago was am-ed = (3.61 1.71) ´ 10- 1 5 au−1 (in a reference system centered on the solar-system barycenter).
关键词：comets: general;comets: individual (C/2017 K2);methods: data analysis
