Today’s Image of the Day from NASA Earth Observatory features Comet ZTF in a photo that was captured on January 19, 2023.

Comets have two tails – one that is composed of ionized gas and another made of dust. These tails are formed as radiation from the sun vaporizes materials within the comet.

“In the dust tail, large grains scatter the sun’s light in all directions, some of which is detected by cameras and telescopes on Earth – like the moon and planets,” says ESA.

“In the ion tail, molecules are much smaller but glow through a process called ‘fluorescence’: ionized atoms and molecules in the gas are struck by photons of light which they absorb, becoming ‘excited.’ They then spontaneously re-emit photons at another wavelength, in a different colour, depending on the molecule.”

Comet ZTF’s bright green appearance reveals that the emissions are predominantly composed of diatomic carbon.

“The two tails point in slightly different directions because the forces act on dust and ions in different ways. While the larger dust particles are pushed by pressure from sunlight, the ions are much lighter and electrically charged so are easily carried by the solar wind and its magnetic field,” explained Jorge Amaya from ESA’s Space Weather Office.

“Recently, a strange phenomenon has occurred with comet ZTF as it appears to have a third tail. This is, in fact, an optical illusion, due to our point of view of the dust trail.”

Image Credit: ESA/ Óscar Martín

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By Chrissy Sexton, Earth.com Editor

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