Beginning of Activity in Long-Period Comet C/2015 ER61 (PANSTARRS)
Karen J. Meech et al 2017 AJ 153 206
Observations show the onset of activity on comet C/2015 ER61 (PANSTARRS) at about r = 8.8 AU in early 2015 — marking the first time we’ve been able to watch a long-period comet turn on.