A comet first discovered in the distance in 2017 may finally soon be visible to amateur astronomers.
Comet C / 2017 K2 (PANSTARRS), called K2 for short, was then the most distant active comet ever seen, a title it recently handed over to the mega comet Comet Bernardinelli-Bernstein, discovered last year. But even down a superlative, K2 is remarkable for activity. The comet began to spew gas and dust into the outer solar system, whereas it is more typical for comets to wake up around Jupiter’s orbit, much closer.
Five years later, the icy body finally draws within reach of Earth and its amateur astronomers. K2’s closest approach to our planet will be on July 14, and it will come closest to the sun on December 19.
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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 traveler.
“It should lighten to the order of 8 or even 7, still too faint for the naked eye,” EarthSky wrote.
Sharp-eyed viewers can usually see stars in the order of 6 under dark sky conditions without assistance. In the case of this comet, you also need to have 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 figure out how large its core is. Early observations from the Canada-France-Hawaii Telescope (CFHT) suggested that the core of K2 could be between 18 and 100 miles (30 to 160 kilometers) wide; Hubble Space Telescope observations suggested it could be a maximum of 11 miles (18 km), EarthSky said.
In 2017, Hubble images determined that the comet’s coma (or fuzzy atmosphere) is likely to include oxygen, nitrogen, carbon dioxide, and carbon monoxide, all of which turn from solid to gas as the comet heats up.
An archive search of CFHT images suggested that K2 was active at least as far back as 2013, when it was between Uranus and Neptune’s orbits, NASA said at the time.
However, all predictions for comet activity can be changed. Comets tend to fall apart or glow unpredictably when it draws close to the intense heat and gravity of our sun. However, that property makes them even more interesting for astronomers who want to understand how comets are put together.