A comet first spotted in the distance in 2017 may finally be in sight of amateur astronomers soon.
Comet C/2017 K2 (PANSTARRS), known as K2 for short, was then the most distant active comet ever spotted, a title it recently ceded to the megacomet Comet Bernardinelli-Bernstein, detected last year. But even below a superlative, K2 is notable for its activity. The comet began spewing gas and dust into the distant solar system, while it’s more typical for comets to wake up around Jupiter’s orbit much closer.
Five years later, the icy body is finally taking shape within reach of the Earth and its amateur astronomers. K2’s closest approach to our planet will be on July 14, and it will make its closest approach to the sun on December 19.
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Assuming K2 survives the heated trip and continues to brighten, EarthSky (opens in a new tab) predicts that people with small telescopes will soon be able to spot the Traveler.
“It should brighten to magnitude 8 or even 7, still too faint for the naked eye,” EarthSky wrote.
Sharp-eyed viewers can usually spot magnitude 6 stars in dark sky conditions without any help. In the case of this comet, you will also need areas away from light pollution to spot it with a telescope.
“The darker the sky, the better the contrast,” EarthSky advised.
As the comet approaches us, professional observatories may be able to determine the size of its nucleus. Early observations from the Canada-France-Hawaii Telescope (CFHT) suggested that K2’s core could be between 18 and 100 miles (30 to 160 kilometers) wide; Observations from the Hubble Space Telescope suggested it might be only 18 km away at most, EarthSky said.
In 2017, Hubble images determined that the comet’s coma (or fuzzy atmosphere) likely includes oxygen, nitrogen, carbon dioxide, and carbon monoxide, all changing from solid to gas when the comet was warming up.
A search of CFHT image archives suggested K2 was active at least as far back as 2013, when it was between the orbits of Uranus and Neptune, NASA said at the time.
All comet activity forecasts are subject to change, however. Comets tend to collapse or brighten unpredictably as they approach the intense heat and gravity of our sun. This characteristic, however, makes them all the more interesting for astronomers who want to understand how comets are assembled.