A megacomet has just passed safely close to Earth, but there’s still a chance it will get brighter throughout the summer as it reaches its closest approach to the sun in December.
Comet C/2017 K2 (PANSTARRS), known as K2 for short, made its closest approach to our planet on Thursday July 14. It passed 168 million miles (270 million kilometers) from Earth (beyond the orbit of Mars).
This aloof approach meant K2 was a bit dark, despite its size. The megacomet was first spotted in 2017 by the Panoramic Survey Telescope and Rapid Response System (PanSTARRS) in the outer reaches of the solar system.
But there’s more to come, as K2 is now continuing its journey towards the sun and will make its closest approach to the star it orbits, the so-called perihelion, in December. The comet, which is visible these days through large amateur telescopes, may brighten in the warmer environment closer to the sun and move into the middle binocular range if we are lucky.
Related: The huge and strange comet K2 circles the solar system, surprising scientists as it goes
Early observations of the comet revealed a potentially large nucleus (or core) and a huge envelope of gas and dust. At that time, the comet was between the orbits of Saturn and Uranus, about 1.49 billion miles (2.4 billion km) from the sun, about 16 times farther than Earth is. of the sun. The fact that K2 was already sporting the gas coma surprised scientists, because at this depth in the solar system, temperatures are so cold that comets, made mostly of water ice, are believed to be as still and dead as rocks.
Scientists are still debating the size of the comet. The Canada-France-Hawaii Telescope (CFHT) has suggested that K2’s core may be between 18 and 100 miles (30 to 160 km) wide, but data from the Hubble Space Telescope has shown it may be only 11 miles (18 km) wide.
Comet activity is always difficult to predict, as we cannot say exactly how the sun’s heat will affect K2 or if it will survive the passage. Now at about magnitude 7 or 8, the comet should remain visible in telescopes for at least the rest of the summer. Naked-eye visibility is magnitude 6, by comparison.
Perihelion will occur on December 19 and so far the comet has become brighter as it heads towards the inner solar system. So we can only hope that in the coming weeks the comet will get a bit brighter so that more people can see it beyond images from larger observatories.
The perihelion will also be distant, as K2 will be about 1.8 astronomical units from the sun (nearly twice the distance between Earth and the sun), when it comes closest.