A comet first spotted in the distance in 2017 may soon finally be within sight of amateur astronomers.
Comet C/2017 K2 (PANSTARRS), or K2 for short, was then the most distant active comet ever discovered, a title it recently relinquished to megacomet comet Bernardinelli-Bernstein discovered last year . But even with a superlative, K2 is remarkable for activity. The comet began spewing out gas and dust in the far outer Solar System, while it is more typical for comets to wake up much closer to Jupiter’s orbit in the interior.
Five years later, the body of ice is finally within reach of Earth and its amateur astronomers. K2 will be closest to our planet on July 14th and closest to the Sun on December 19th.
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Assuming K2 survives the heated journey and continues to brighten, EarthSky (opens in new tab) predicts that people with small telescopes will soon be able to spot the stranger.
“It should lighten to an 8 or even 7 power, still too dark for the naked eye,” wrote EarthSky.
Keen-eyed viewers can usually make out magnitude 6 stars unaided in dark sky conditions. In the case of this comet, you also need areas away from light pollution to spot it with a telescope.
“The darker the sky, the better the contrast,” advised EarthSky.
As the comet approaches us, professional observatories may be able to figure out how big its core is. Early observations by the Canada-France-Hawaii Telescope (CFHT) suggested that the core of K2 could be between 30 and 160 kilometers wide; Hubble Space Telescope observations suggested it could be 11 miles (18 km) at most, EarthSky said.
In 2017, Hubble imagery determined that the comet’s coma (or fuzzy atmosphere) likely contains oxygen, nitrogen, carbon dioxide, and carbon monoxide, all of which turn from solid to gaseous as the comet warms.
An archival search of CFHT images suggested that K2 was active as early as 2013 when it was between the orbits of Uranus and Neptune, NASA said at the time.
However, all comet activity predictions are subject to change. Comets tend to break apart or brighten unpredictably as they approach the intense heat and gravity of our Sun. However, this property makes them all the more interesting for astronomers who want to understand how comets are composed.