UNPREDICTABLE GREEN COMET: On July 1st, Comet PANSTARRS (C/2017 S3) exploded. Its green atmosphere ballooned in size, large enough to swallow Jupiter twice, and its brightness increased 16-fold. Barely a week later, the comet fizzled, dimming almost as much as it had brightened. Then it exploded again! On July 15th Comet PanSTARRS regained all it had lost and more. Michael Jaeger of Jauerling, Austria, captured the comet’s newly-formed tail on July 20th:
“The comet is already fading again, and it seems to have lost much of its tail on July 21st,” Jaeger says.
Why is Comet PanSTARRS so unpredictable? Probably because it has never felt the heat of the sun before. The comet is arriving from the Oort cloud, a vast reservoir of fresh comets in the outermost solar system. This is its first time among the inner planets. Unfamiliar warmth is making veins of fresh ice pop and fizz as the comet approaches–an entirely unpredictable process.