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K2 will not be as bright as Comet Neowise in the summer of 2020. Despite its size, it will not be visible to the naked eye. (Virtual image) © IMAGO/blickwinkel

Comet C/2017 K2 broke records when it was discovered in 2017. It is now approaching Earth and can already be seen with small telescopes.

Frankfurt – Discovered in 2017, but now comet C/2017 K2 (PanStarrs) is only really interesting to observers on Earth. The reason: On July 14, 2022, the comet, nicknamed K2, reached its closest point in its orbit to Earth, and then it was especially easy to observe from Earth – this is still possible until autumn.

Comet K2 packs a big punch: When it was first spotted by the PanStarrs telescope system in Hawaii in 2017, it was thought to be the most distant comet discovered en route to the inner solar system. At the time it was between the orbits of Saturn and Uranus – about 2.4 billion kilometers from the Sun. It is now in the inner solar system and is already approaching its closest point, about 270 million kilometers from Earth. Since then it has continued to fly towards the sun. The comet will reach its closest point to the sun, the so-called perihelion, on December 19, 2022.

Comet C/2017 K2 (PanStarrs): When and how to best observe the comet

That’s good news for observers in Earth’s northern hemisphere: With a small telescope, the comet should be visible all summer long. However, the best time to observe wasn’t the day it was closest to Earth – the day before, the largest full moon of the year (a supermoon) was in the sky, making observations difficult due to its brightness. A few days later the moon rose after midnight, so the sky was darker and the comet was better closed.

But how do you find the comet? It can be found in the south after dark. It remains in the constellation Ophiuchus until about the end of July, after which it moves on to be near the star Akrab in the constellation Scorpius. Around mid-September, in the dark, it no longer rises high enough above the horizon to observe it well. Free astronomy programs and apps such as ‘Stellarium’, ‘SkySafari’ or ‘Star Walk’ can be used to determine the exact position of the comet.

Comet C/2017 K2 (PanStarrs): What telescope observers can see

Those observing the comet with a small telescope should be able to see a diffuse or fuzzy patch of light (the cometary coma) around the nucleus of comet C/2017 K2 in suitably dark skies. Experienced observers may be able to see that the coma (fog and dust that collects around the comet’s nucleus) is larger than that of many other comets. Part of the comet’s tail may also be visible in the telescope. Long exposures of the comet should show both the comet and its tail in all their glory.

Watch the comet live stream

If you don’t have a telescope but want to observe the comet, you’ll find what you’re looking for online: The Virtual Telescope Project is showing the comet live starting July 15 at 12:15 am.

Comet C/2017 K2 (PanStarrs) broke records with its discovery

Comets are mostly rock and dust held together by ice. As a comet approaches the Sun from the icy outer regions of the Solar System, the ice heats up and sublimates, the comet becomes active and gas begins to escape. The comet’s coma and characteristic tail appear. Comet C/2017 K2 was already active when it was discovered in 2017 – although it was still 2.4 billion kilometers from the Sun.

However, the comet’s early activity appears to have little to do with the sun. “K2 is so far from the Sun and so cold that we know for sure that the activity is not due to the evaporation of water ice like other comets,” said lead researcher David Jewitt of the University of California, Berkeley after observing the comets with the Hubble Space Telescope in 2017. “We believe the activity is due to the sublimation of hypervolatiles as K2 first entered the planetary belt of the Solar System. That’s why he’s so special. This comet is so far away and so incredibly cold that the water ice there is frozen like rock.”

An even more distant comet has been discovered

A comet, Bernardinelli-Bernstein, has since been discovered even further out in the solar system (4.4 billion kilometers from the Sun). It is also already active and flying around the interior of the solar system. However, it does not come closer to the Sun than Saturn’s orbit.

Early telescopic observations of comet C/2017 K2 indicated that the comet could have a nucleus 30 to 160 kilometers in diameter. However, later observations with NASA’s Hubble Space Telescope showed that the core may be smaller, about 18 kilometers or less. Another sign that the comet may be large (or at least very active) is the size of its coma: it is 130,000 kilometers in diameter – 10 times the diameter of planet Earth. Observations also suggest that its tail is about 800,000 kilometers long.

Comet C/2017 K2 (PanStarrs) imaged by Nasa and ESA's Hubble Space Telescope in June 2017. Visible is the cometary nucleus surrounded by the diffuse and fuzzy coma.  (file image)
Comet C/2017 K2 (PanStarrs) imaged by Nasa and ESA’s Hubble Space Telescope in June 2017. Visible is the cometary nucleus surrounded by the diffuse and fuzzy coma. (File image) © NASA, ESA and D. Jewitt (UCLA)

Comet nuclei are typically up to three kilometers in size – K2 is larger

Most comets have a nucleus about one to three kilometers in diameter. Some can also be as large as 16 kilometers. The well-known comet Hale-Bopp has a diameter of 60 km, Bernardinelli-Bernstein has a diameter of about 150 km. Like Bernardinelli-Bernstein, comet C/2017 K2 is believed to have originated in the Oort Cloud at the edge of the Solar System. From there it travels into the interior of the solar system for about three million years. (ear)

Observing space tips and newsletters

In addition to the comet and super moon, many shooting stars can also be seen in the sky in July. You can get more such tips and references to current articles by subscribing to the Frankfurter Rundschau free space newsletter.

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