We present a study of two newly discovered heliocentric hyperbolic objects -- 2017 U7 and 2018 C2. Both are possibly thermally evolved comets. Observations of the latter in 2018 March from Xingming Observatory revealed that it has a color similar to those of the long-period comets, Trojans, and D-type asteroids: mB−mV=0.75±0.03, mV−mR=0.41±0.02, and mR−mI=0.37±0.03. A possible extremely faint coma of ∼9" across was observed. The radial profile of 2018 C2 in comparison with those of the field stars helps confirm its cometary nature. Based on our convolution model, its mass-loss rate is estimated to be 0.7±0.2 kg s−1. Assuming geometric albedo pR=0.04, its effective radius is 4.4±0.5 km, which means that the fraction of active area is merely ∼10−5-10−4. Our N-body dynamical simulations show that both objects are most likely dynamically old members from the Oort cloud. 2017 U7 has a ∼60% chance to escape the solar system in the 1.5 Myr following its current perihelion passage due to a moderate close encounter with Jupiter in 2020 May. On the condition that no disintegration occurs, 2018 C2 will revisit the inner solar system 0.13-0.14 Myr later, with perihelion distance ∼2 AU.
@article{arxiv.1806.06904,
title = {Two Hyperbolic Baldheads in the Solar System: 2017 U7 and 2018 C2},
author = {Man-To Hui},
journal= {arXiv preprint arXiv:1806.06904},
year = {2018}
}