Once-in-a-Lifetime Cosmic Event Could Be Visible to the Naked Eye

A comet zooming through the solar system could soon be visible to the naked eye from Earth in what will be a once-in-a-lifetime event. And some astronomical predictions indicate that the object may never return to our cosmic neighborhood. C/2022 E3 (ZTF) is currently located around 100 million miles away from Earth and will make a close approach to our planet in early February 2023. Comets are "cosmic snowballs" made up of frozen gases, dust and rock that orbit the sun. As they approach our star, these objects are blasted with increasing amounts of radiation, releasing gases and debris. This process forms a glowing atmosphere around the comet (known as a coma) and two vast tails of gas and dust. Based on how the comet is currently moving, astronomers estimate that it will come within roughly 26 million miles of Earth on February 1, data from NASA's Jet Propulsion Laboratory (JPL) Solar System Dynamics group shows. This is equivalent to more than 109 times the average distance between the Earth and the moon.

As with all comets, C/2022 E3 (ZTF) moves much faster when it is closer to the sun and decelerates as it speeds away again. By the time of its closest approach to Earth in February, the comet will be traveling at a speed of around 128,000 miles per hour relative to our planet, the JPL data shows. As C/2022 E3 (ZTF) approaches the Earth, it may become visible to the naked eye as soon as the second half of January under very good conditions, Robert Massey, deputy executive director of the U.K. Royal Astronomical Society, told Newsweek. Current estimates indicate that the comet is expected to reach at least magnitude +6—roughly the limit that the human eye can see—or perhaps even slightly brighter by around the time of its close approach to Earth. "The current prediction is that the comet will reach magnitude +5 around the start of February," Massey said. "So far, the observed brightness is in line with that model." But it is "notoriously hard" to predict the brightness of comets and it is possible that it might not be visible at all or appear more prominently in the sky than expected, Tania de Sales Marques, an astronomer at the Royal Observatory Greenwich in the United Kingdom, told Newsweek. If current brightness predictions are correct, C/2022 E3 (ZTF) will be the first naked eye comet since NEOWISE put on a spectacular show in 2020, although astronomers expect it to be less impressive. Once this comet has passed by the Earth, it will travel away from the sun and inner solar system. What happens next though is something of a mystery due to uncertainties regarding its future trajectory. "We don't have an estimate for the furthest it will get from the Earth yet—estimates vary—but if it does return it won't be for at least 50,000 years," Jessica Lee, an astronomer at Royal Observatory Greenwich, told Newsweek. Some data indicates that the comet appears to be on a hyperbolic orbit—essentially an open one—meaning it might never return to the inner solar system, Massey said. The shape of the comet's orbit looks like a very open curve. "Some predictions suggest that the orbit of this comet is so eccentric it's no longer in an orbit—so it's not going to return at all and will just keep going," Lee said. While astronomers only discovered C/2022 E3 (ZTF) this year, the object would have formed with the rest of the solar solar system around 4.6 billion years ago, she said. Given that C/2022 E3 (ZTF) is a long-period comet—those with orbital periods of more than 200 years—Massey said it likely originated in the Oort Cloud, the most distant region of our solar system. This Oort Cloud is a vast, spherical shell of icy bodies believed to encircle the solar system that may contain billions or perhaps even trillions of objects. This region is thought to extend from between 300 billion kilometers (around 186 million miles) and 15 trillion kilometers (around 9 trillion miles) away from the sun, according to some estimates. These estimates indicate that the Oort Cloud lies in interstellar space. The region is only loosely bound to our solar system, with its outer edge marking the extent of the sun's gravitational influence. The cloud is thought to be a remnant of material leftover from the formation of the solar system. Scientists have yet to observe an object in the Oort Cloud itself, so for now it remains a theory. But this region—which is far enough from the sun to be cold enough for ice to remain solid—is thought to be the source of many long-period comets that pass through the inner solar system.

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Every now and then, objects in the Oort Cloud are disturbed—perhaps by the gravitational influence of passing stars—sending them hurtling toward the sun. Most hyperbolic comets will only travel through the solar system once before being slingshotted out by the sun unless something alters its orbit. As a result, most known long-period comets have only been seen once in history given their extremely long orbital periods. Countless others have never been seen by humans at all. C/2022 E3 (ZTF) was first spotted by the Zwicky Transient Facility (ZTF)—an astronomical survey conducted by the Palomar Observatory in California—on March 2, 2022. The facility surveys the entire sky every three nights, using a wide field of view camera installed on a 48-inch telescope. "By comparing images of the same part of the night sky taken on different nights, you can see changes or new objects," Lee said. "To identify an object as a comet they would have looked at its appearance, location and how it was moving." Astronomers at the facility are aided in this effort by a deep-learning algorithm that helps to identify objects with comet-like tails in image data. There is currently no accurate size estimate for C/2022 E3 (ZTF) because it is newly discovered and still distant, meaning it is not reflecting much light. The coma and tail of the comet surround it, making it difficult to accurately observe the body itself. "It is made hard by the fact that the nucleus is concealed by the outgassing material making up the comet tails," Massey said. "My guess is someone is working on [a size estimate]." The comet will likely fade below naked eye visibility—if it ever reaches this point—by the second week of February next year. C/2022 E3 (ZTF) is currently visible with good binoculars or a telescope in the early hours of the morning before dawn. But by April it will be close to the sun in the sky and significantly fainter, so will be very hard to find even with this equipment.