NASA Astronomy Picture of the Day 9 January 2023: Comet E3 ZTF, seen by Neanderthals, shot

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Comets are cosmic snowballs of frozen gases, rock and dust roughly the size of a small town. A comet also orbits the Sun, but unlike an asteroid, it's mostly composed of ice and dust. When a comet gets close to the Sun, its ice and dust content start to vaporize. So, when seen in a telescope, a comet appears fuzzy and has a tail. So, if you're an avid comet watcher, there is exciting news for you. A comet which was last seen by Neanderthals is all set to pass Earth this year.

NASA's Astronomy Picture of the Day is a stunning image of the comet C/2022 E3 (ZTF) which is a long-period comet that originated in the Oort cloud, captured by Jose Francisco Hernández, an astrophotographer. The comet has a period of around 50,000 years, meaning the last time it flew past Earth closely, it was seen by Neanderthals during the Upper Paleolithic period on Earth. According to NASA, it is presently located around 100 million miles away from Earth, but is rushing towards our planet fast.

Comet ZTF may become visible to the unaided eye. Discovered early last year, this massive snowball has been brightening as it approaches the Sun and the Earth. C/2022 E3 (ZTF) will be closest to the Sun later this week, at which time it may become visible even without binoculars to northern observers with a clear and dark sky. As they near the Sun, comet brightnesses are notoriously hard to predict, though.

In the featured image taken last week in front of a picturesque star field, three blue ion tails extend to the upper right, likely the result of a variable solar wind on ions ejected by the icy comet nucleus. The comet's white dust tail is visible to the upper left and much shorter. The green glow is the comet's coma, caused by glowing carbon gas. Comet