Explosive 'devil comet' grows seemingly impossible 2nd tail after close flyby of Earth — but it's not what it seems

The explosive, green "devil comet" that recently swept close to Earth appeared to grow an impossible second tail as it passed us, new photos reveal. But this extra limb, known as an anti-tail, is actually an extremely rare optical illusion caused by the comet's proximity to our planet. 

12P/Pons-Brooks (12P) is a 10.5-mile-wide (17 kilometers) comet with a green hue, which is given off by pairs of carbon atoms, known as dicarbon, in its tail and coma — the cloud of gas that surrounds its icy crust, or nucleus. 12P is cryovolcanic, meaning it occasionally erupts when solar radiation superheats the comet's icy innards, or cryomagma, causing pressure to build up in the nucleus until the core splits and shoots its guts into space. When this happens, the comet's coma expands and reflects additional light, making the comet shine brighter than normal.

12P spends the majority of its highly elliptical, 71.3-year orbit around the sun out of sight in the Oort Cloud — a reservoir of comets toward the edge of the solar system. But in the last year, the comet sped through the inner solar system as it made its closest approach to the sun. And as it got closer to our home star, it frequently erupted. 

During the comet's initial eruptions last year, its expanded coma grew, giving the impression that it had grown a pair of demonic horns, which earned it its sinister nickname. But these horns did not appear in subsequent eruptions.

12P made its closest approach to the sun since 1953 on April 21 this year when it slingshotted around our home star and began heading back out toward the outer solar system. On June 2, the comet made its closest approach to Earth, when it reached a distance of around 1.5 astronomical units from our planet, which is approximately 1.5 times further away from Earth than the sun.

On June 3, astrophotographers Michael Jäger, Gerald Rhemann and Lukas Demetz captured a striking photo of 12P from Namibia. In addition to its normal blurry tail, the comet sported a much longer and sharper tail known as an anti-tail, in this photo, which appeared to point in the opposite direction to the other tail. 

Related: Explosive, green 'devil comet' has hidden spiral swirling around its icy heart, photo trickery reveals