Comet NEOWISE surprises some stargazers with two tails

Astronauts Bob Behnken, Doug Hurley, and ISS commander Chris Cassidy speak with Bill Hemmer.

As stargazers try to catch a glimpse of NEOWISE as it soars across the nighttime sky, careful viewers may notice the comet has two tails trailing behind it.

An unprocessed image from the WISPR instrument on board NASA’s Parker Solar Probe shows comet NEOWISE on July 5, 2020, shortly after its closest approach to the Sun. The Sun is out of frame to the left. The faint grid pattern near the center of the image is an artifact of the way the image is created. The small black structure near the lower left of the image is caused by a grain of dust resting on the imager’s lens. Credits: NASA/Johns Hopkins APL/Naval Research Lab/Parker Solar Probe/Brendan Gallagher

The comet’s main tail or dust tail, which is always whitish in color because its particles easily reflect sunlight at every wavelength, is made of fragments from the comet that have been ejected from its nucleus and curves outside the path of the comet’s trajectory, according to Forbes.

This outstanding composition shows the blue ion tail and the grey/white dust tail of comet NEOWISE as it nears its closest approach to Earth. The dust tail is curved and diffuse while the ion tail is straight and highly collimated. Both are caused by extremely different physical processes.
 
DAMIAN PEACH / IAN SHARP

The dust that makeup up the main tail are pulled by three forces: the sun, the comet itself and the force from the sun’s radiation.

Differently sized particles are all subjected to the same amount of gravitational acceleration but smaller dust grains are affected more than larger ones by solar radiation and move at different speeds, making the tail appear wider.

The second slightly narrower tail, however, actually becomes prominent before the main dust tail, according to Forbes.

At some point in the comet’s trajectory, ultraviolet light radiating from the sun becomes strong enough that it heats up and ionizes the comet’s carbon monoxide – the weakest ice-based molecule in the makeup of a comet, according to the magazine.

The carbon monoxide absorbs the sunlight and fluoresces at 4200 Angstroms, the wavelength for blue light, making it appear blue, according to an article from Case Western Reserve University.

The main dust tail is always a grayish-white, the same color as the comet itself.

The ion tail always points away from the sun in a straight line because it distorts magnetic field lines as it interacts with charged wind particles from the sun, according to the university.

The ion tail is made up of single molecules that are all equal in mass, meaning they’re affected by the forces around them equally and follow the same, narrower path, according to Forbes.

In early photos of comets, the blue ion tail is the only one visible.

NEOWISE, the brightest comet in the sky since Hale-Bopp in 1997, was discovered in March and can be seen by the naked eye for most viewers in the Northern Hemisphere this month.

While many comets have two tails, including all “great comets,” it’s also possible NEOWISE has an extra ion tail.

“Parker Solar Probe’s images appear to show a divide in the ion tail,” NASA said of NEOWISE. “This could mean that comet NEOWISE has two ion tails, in addition to its dust tail, though scientists would need more data and analysis to confirm this possibility.”