Green Comet May Have Come From Mysterious Cloud at Edge of the Solar System

Comet C/2022 E3 (ZTF), which is set to make a close approach to the Earth on Wednesday, may have originated in a mysterious cloud at the edge of the solar system.

The comet, which may be faintly visible to the naked eye at night from dark sky locations, if you know where to look, is currently more than 27 million miles from Earth.

C/2022 E3 (ZTF) has already passed perihelion—its closest point to the sun—and on Wednesday it will reach its minimum distance from our planet before speeding out of the solar system altogether.

Comets are astronomical objects made up of frozen gases, dust and rock that orbit the sun. Sometimes referred to as "cosmic snowballs," these objects are blasted with increasing amounts of radiation as they approach our star, releasing gases and debris.

This process forms a glowing atmosphere around the comet's nucleus, known as a coma—in the case of C/2022 E3 (ZTF), this appears green—and two vast tails of gas and dust.

Astronomical modeling indicates that the comet is in a hyperbolic orbit—essentially, an open one—meaning it might not return to the inner solar system.

"The shape looks like a very open curve, and as with all objects, it moves much faster when it's nearer the sun and much more slowly as it moves away again, Robert Massey, deputy executive director of the U.K. Royal Astronomical Society, told Newsweek.

Given that C/2022 E3 (ZTF) is a long-period comet—defined as those with orbital periods of more than 200 years—astronomers believe it likely originated in the Oort Cloud, a vast, spherical shell of icy bodies believed to encircle the solar system.

"This is a very distant region of space that surrounds the sun at very large distances," Chris Pattison, a senior research associate with the Institute of Cosmology and Gravitation at the U.K.'s University of Portsmouth, told Newsweek.

To put into context how far away this immense region is, it is helpful to think in terms of astronomical units rather than miles or kilometers. One astronomical unit (AU) is roughly equivalent to the average distance between the Earth and the sun—or almost 93 million miles.

The inner edge of the Oort Cloud is thought to begin at 2,000 to 5,000 AU from the sun, while the outer edge could extend out to 10,000 AU or even 100,000 AU from our star, according to NASA.

By comparison, the farthest point from the sun in the orbit of the dwarf planet Pluto is a distance of only 50 AU. The Oort Cloud is so far away that even the Voyager 1 spacecraft—the most distant man-made object from Earth, which was launched in 1977 and travels around a million miles a day—will take about 300 years to reach its inner boundary and possibly another 30,000 to reach the other side.

The Oort Cloud was first identified in 1950 by the Dutch astronomer Jan Hendrik Oort to explain why new comets with elongated orbits continue to be observed passing through the solar system.

Scientists have yet to observe an object in the Oort Cloud itself, so for now it remains a hypothetical concept. But this region—which is far enough from the sun that temperatures are cold enough for ice to remain solid—is thought to be the source of most long-period comets that pass through the inner solar system.

It is estimated to contain billions or perhaps even trillions of icy objects—some the sizes of mountains or even larger. The region is only loosely bound to our solar system, with its outer edge marking the extent of the sun's gravitational influence.

From time to time, objects in the Oort Cloud are disturbed—perhaps by the gravitational influence of passing stars—and sent hurtling toward the sun.

"The Oort Cloud is a huge reservoir of comets that surrounds everything else in the solar system, but sometimes it can send comets like C/2022 E3 (ZTF) in our direction," Pattison said.

Astronomers think the cloud is the remnant of material left over from the formation of the solar system around 4.6 billion years ago.

As C/2022 E3 (ZTF) reaches its minimum distance from our planet, you will be able to watch this possible visitor from the distant Oort Cloud zoom past us online from the comfort of your home.

The Virtual Telescope Project (VTP)—a service provided by the Bellatrix Astronomical Observatory in Ceccano, Italy, that operates and provides access to robotic, remotely operated telescopes—will be hosting a livestream so you can watch the object as it flies by.

The live feed is scheduled to begin at 11 p.m. ET on Wednesday or 8 p.m. Pacific Time. The VTP will capture images of the comet speeding through space and share them with viewers in real time.

The comet is expected to continue brightening until roughly the time of its close approach, although predicting the brightness of such objects is a notoriously tricky business.

The comet's observed magnitude is currently just below +6, which means it is theoretically visible to the naked eye under ideal conditions. Some observers have already reported observing the comet with the naked eye from dark, rural locations with low levels of light pollution. It is visible as a small, diffuse smudge.

But practically speaking, it may be difficult to spot unaided, and most people will need binoculars or a telescope, as well as the help of a stargazing app.

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