Rare mirage of comet's second tail as it approaches Earth

The "once-in-a-lifetime" comet Tsuchinshan-ATLAS looks like it has grown a second tail after reaching its closest point to Earth in more than 80,000 years, new images reveal. But in fact, the extra tail is an optical illusion caused by our planet's position relative to the object seen with the naked eye.

C/2023 A3, commonly known as Tsuchinshan-ATLAS, is an unusually bright comet that likely originated in the Oort Cloud , a reservoir of icy objects at the outer edge of the solar system. It was first spotted in early 2023 traveling between Saturn and Jupiter as it headed toward the inner planets. Subsequent observations have shown that the comet likely orbits the Sun once every 80,660 years, suggesting that it may have disintegrated.

Comet Tsuchinshan-ATLAS was spotted with a thin streak of light, called a retrograde tail , pointing in the exact opposite direction to its bright tail. (Image: Michael Jäger).

Tsuchinshan-ATLAS became visible to the naked eye after orbiting the sun in late September. However, it reached its peak brightness over the past few days after reaching its closest point to Earth on October 12, when it was about 70.6 million kilometers (44 million miles) away, about 180 times farther than the moon. The comet is likely to be visible to millions of people across large swaths of the globe.

On October 13, astrophotographer Michael Jäger captured images of Tsuchinshan-ATLAS streaking across the night sky near Martinsberg, Austria. In addition to showing the usual bright tail, enhanced versions of the images show that the comet has a fainter streak of light, called an 'antitail ,' emanating from its body in the opposite direction, according to Spaceweather.com.

On October 14, Jäger took another, even clearer picture of the comet and its appendage. The comet's tail is made up of two parallel trails of dust and gas that have been blown away from the comet by solar radiation, meaning its tail always points away from the sun.

Antitails thus seem to defy physics because they can point toward the sun. However, these additional tails are not made up of debris blown off the comet. Instead, they are made up of dust that the comet has recently left behind in the plane of its orbit around the sun. When Earth passes through this plane, as it did over the weekend, this leftover debris is illuminated by the sun and reflected back to Earth, creating the impression of a second tail.