You might have seen some stories in the news media and online about Comet C/2022 E3 (ZTF). Yes, it’s probably the first time this particular comet has been visible from Earth since our cousins, the Neanderthals, were rocking the bearskin onesies.

Unfortunately, it’s not going to be a wonderous sight like some of the great comets of the past despite what’s being written about it in the news. However, each comet is fascinating in its own, unique way and it’s certainly worth the effort of locating and viewing C/2022 E3 (ZTF). You, and many, many generations of your descendants will be long gone before it comes this close to Earth again.

Image : Dan Bartlett via NASA

This comet might possibly brighten to being just visible to your eyes alone in Australia from early February. Even if you are able to spot it with your eyes, the comet will appear as a faint, small fuzzy object. A much better idea would be to try viewing it with a telescope or even in binoculars.

It passes closest to the Sun on the 12th of January and then closest to earth on the 1st of February as it heads back out from the inner Solar System. During January Comet C/2022 E3 (ZTF) will be in the far northern sky and not visible to us here in Australia and New Zealand. From the start of February, the comet will start to move further into the southern part of the skies and also brighten. You can get an idea of where C/2022 E3 (ZTF) will be appear in the sky from somewhere like Sydney from the image below:

On the evening of the 11th of February around 10pm Comet C/2022 E3 (ZTF) will be within one and half degrees of Mars and the pair would make great viewing in binoculars.

Before Comet C/2022 E3 (ZTF) is at its best in the sky, let’s go over what comets actually are and where they come from.

Comets are at their most spectacular when they arrive from the outer regions of the Solar System or interstellar space, loop around the Sun and head back out as they continue their orbits.

The changes in the night sky as the year progressed and the motion of the planets were regular and apparently eternally unchanging from the point of view of ancient peoples. Comets were unpredictable and seemed a challenge to this heavenly order that went on above our heads. It’s no wonder that the arrival of a comets wasn’t great news for our ancestors!

Comet are often called “dirty snowballs” and this description is probably not a bad description of what comets are made off. They contain a contain water ice and frozen gases (referred to “volatiles”) along with dust and rocky silicates from the early formation of the Solar System. They’re effectively invisible during most of their orbit around the Sun. Comets absorb heat as they get closer to the Sun. This causes the some of the comet’s volatiles to heat up and melt or “sublimate”.  Some materials are thrown into space by the pressure of Solar radiation, forming the comet’s tails. (Yes, a comet can have more than one tail!).  Part of the sublimated materials will cling to the comet due to its gravity and not be thrown into space. This forms a cloud called the coma and it gives the centre or “nucleus” of the comet a fuzzy appearance. (This is a super a super brief description of a comet and there’s a lot more to learn.) Comets are often discovered once they start to form a coma and “fuzz”. This distinguishes them from other solid rocky bodies. In fact, Comet C/2022 E3 (ZTF) was originally thought to be a rocky asteroid until a faint coma was spotted in images first taken at the iTelescope facility in New Mexico.

Why do some comets take so long to orbit the Sun and appear rarely?

There’s two main areas of the Solar Systems where originate. The first is the Kuiper Belt, a donut shaped region beyond the orbit of Neptune containingcomets  a vast number of both rocky and icy bodies left over from the formation of the Solar System. These are called Kuiper Belt objects (KBOs) or trans-Neptunian objects (TNOs). The gravitational effects of the outer planets will occasionally knock one of these bodies toward the inner Solar System where it will be visible from Earth. Comets from the Kuiper Belt will orbit on a plane in line with the rest of the planets and have an orbital period of less than 200 years.

The Oort Cloud is a vast region about a quarter of the way to the next star and marks the edge of the Solar System. It’s thought to contain about a trillion comets slowing and consistently orbiting the Sun. We’ve never directly observed the Oort Cloud, but its existence is strongly supported by the behaviour of some comets that appear from time to time. Like the Kuiper Belt, the icy, rocky bodies in the Oort Cloud are primeval remnants left over from the formation of the Solar System.

Image from NASA showing the vast scale of the theorised Oort Cloud compared to the Solar System

Some comets discovered have an orbit that is at a step angle to the plane that all the major planets including the Earth orbit around the Sun. (Bear in mind the Oort Cloud is a “cloud” or a ball shaped region around the Solar System and not a flat region like the Kuiper Belt, so they can head towards the Earth and the Sun from all angles.) Comets are nudged out of their obits in the Oort Cloud by passing stars, clouds of interstellar gas or even interactions with parts of our Milky Way galaxy. They then begin the long trek in towards the Sun.

There’s also a class called Halley-Type Comets, named after the famous Halley’s Comet which are thought to have originated in the Oort Cloud and had their highly inclined orbits altered by the gravity of the outer planets, as well as Jupiter class comets which have arrived from the Kuiper Belt and were influenced by the gravity of the largest body in the Solar System apart from the Sun – Jupiter. Like rest of the thousands of minor bodies in the Solar System, comets are found in a range of populations and their movements are complex.

What are “Great Comets”?

The frequency of the arrival of comets is patchy. All short period comets with the exception of Comet Halley are too faint to be see with just your eyes and they generally go unnoticed except by astronomers.

Great Comets are usually those arriving from the Oort Cloud on their first pass around the Sun. Either because of their size or their close approach to Earth they put on a spectacular display and sometimes even visible during the day.  Recent comets that you could say fall into the “Great” category include Comet Hale–Bopp in 1997 and Comet McNaught in 2007.

Comet McNaught in 2007

We don’t know when the next Great Comet is due. Fingers crossed it’s soon!

Are there comets that never return to inner Solar System?

Yes. Apart from comets that break up during their loop around the Sun, some comets from the Oort cloud and interstellar space arrive in a hyperbolic and not a parabolic orbit. This means they won’t reach a point where they can head out from the Sun and then return back towards it. They’ll simply keep travelling unless disturbed by another body. Calculations based on observations of Comet C/2022 E3 (ZTF) mean that it will return in approx. 50,000 years although this figure might change as we learn more about it.

You can’t seriously mean “interstellar” comets ????

Yes! At least one comet has been observed travelling through the Solar System that originated from another star.  Comet 2I/Borisov or sometimes simply called “Comet Borisov” arrived at the Solar System and it was calculated to be originated from another star.

The path interstellar Comet Barisov took through the Solar System

Comet Borisov’s composition proved to be not totally unlike that of other Oort Cloud comets. Have other interstellar comets visited the Solar System? No doubt there’s been many in the past. We simply haven’t spotted them. Large scale survey programs like the Vera. C. Rubin Observatory might find several visitors from outside the Solar System per year with the possibility of us being able to chase down some of them with spacecraft for closer observation.

This is a complex area and if you have any questions or things you’d like to add, please feel free to leave them in the comments below.


Earl White


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