Comet NEOWISE (C/2020 F3) is the current darling of the skies and it’s been putting on quite a show. When it sped through the inner Solar System a few weeks ago, astronomers and the public alike watched as it dramatically shed gas and dust into space.
But you can’t see this with the naked eye. Researchers led by Michal Drahus and Piotr Guzik of Poland’s Jagiellonian University used the international Gemini Observatory to observe up close the materials escaping from the comet over time.
One set of observations, obtained on 1 August 2020 from the Gemini North telescope on Hawaii’s Maunakea, displays a spiralling stream of molecular gas that reveals the rotation of the comet’s nucleus.
This time-lapse sequence, compressed to just 17 seconds, represents about one fifth of the approximately 7.5-hour rotation period of the comet.
The observations took place over several evenings, and were limited by the comet’s relatively close proximity to the Sun and the resulting short observing windows.
Some comets follow highly elongated orbits which send them close to the Sun where they warm up and cause the frozen gases to vaporise, releasing molecules and debris into space. It is thought that most comets release gasses in geyser-like jets and that is what researchers think is happening in the Gemini images.
As the vaporised material erupts from the comet, its rotation causes it to appear to spiral outward, much like the water from a spinning garden hose. The very same material impacts the comet’s rotation, causing its nucleus to spin-up or spin-down – though for most comets, the effect is too weak to detect.
NEOWISE is considered the brightest comet visible from the Northern Hemisphere since 1997’s Hale-Bopp. It’s estimated to be traveling at 64 kilometres a second, or 230,000 kilometres an hour.
Its closest approach to the Sun took place on 3 July and it’s now heading back to the outer parts of the Solar System, not to pass through again for another 7000 years or so.
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