As we speak, the comet 12P/Pons-Brooks (Pons-Brooks, for short) is making its way around the inner region of the Solar System for the first time in more than 70 years – and might soon become visible to the naked eye.
At approximately 30 kilometres (19 miles) across, this giant icy lump is comparable in size to Mount Everest, says astrophysicist Dr Paul Strøm, and is “one of the brightest known periodic comets”.
A Halley-type comet, Pons-Brooks completes its journey around the Sun every 71.3 years and was last spotted in our skies in 1954.
Although it wasn’t officially named until its discovery by Frenchman Jean-Louis Pons in 1812 and subsequent rediscovery by the British-American William Robert Brooks in 1883, the first recorded sightings of the comet actually date back as far as 1385.
When can I see the 12P/Pons-Brooks comet?
The 12P/Pons-Brooks comet can be seen tonight and can be seen up to 21 April 2024. It will be best visible towards the end of March.
If you’ve got a pair of binoculars or a small telescope knocking about, you should be able to see Comet Pons-Brooks already. It started the month in the western evening sky, just below the Andromeda Galaxy and is steadily moving through the tip of the constellation of Pisces.
Towards the end of the month, Comet Pons-Brooks will move along the line of brighter stars in Aries, approximately in the direction of Jupiter. It may brighten towards the end of the month, reaching naked-eye visibility if you find a dark spot on a clear enough night.
“In particular, on the 31 March 12P/Pons–Brooks will be only 0.5 degrees from the bright star called Hamal, equivalent to a full moon diameter away,” which should make it easier to spot, Strøm says.
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For those in the US, the comet might also be visible in the sky during the total solar eclipse on 8 April 2024.
Comet Pons-Brooks is expected to reach its perihelion – the point at which it is closest to the Sun – on 21 April, by which point it will have disappeared into the sunset, literally. After swinging around the Sun, the comet will be much dimmer and only observable to those in the Southern Hemisphere.
Why is it called a 'devil' comet?
It’s not the first time Pons-Brooks has been visible in recent months – the astute amongst you may remember the so-called ‘Devil Comet’ that was spotted in July 2023 is this very comet.
Pons-Brooks is what’s known as a cryovolcanic comet, meaning that every so often it randomly erupts (like a volcano), spewing out dust, gas and ice into the surrounding space. When it did this last year, it instantaneously became 100 times brighter, with the outburst forming a devil-horned shape – hence the name.
The reason this bizarre eruption occurs is that as the comet gets closer to the Sun, it warms up, meaning that the icy material can vaporise and rupture out from beneath the surface as the pressure builds.
The gas then forms part of the bright coma, which is the halo of evaporated material that surrounds the solid nucleus.
“When we look at a comet, we are looking at sunlight reflecting off this kind of fog, so comets are at their brightest when they are closest to the Sun,” Dr Darren Baskill, astronomer lecturer at the University of Sussex, tells BBC Science Focus.
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“But then the bright sunlight also restricts our view, so the best time to observe a comet is a bit of a trade-off between the two.”
As the comet streams along, it leaves a tail of glowing material behind it that reflects the sunlight too. These tails can stretch for millions of kilometres and can be shaped by charged particles from the Sun – known as ‘solar wind’ – as they interact with it.
The comet exhibited similar outbursts on 5 October, 1 November, 14 December and most recently 18 January – albeit less dramatic ones.
The closer the comet gets to the Sun, the more intense this activity can become, which is why the comet appears to brighten.
What does the 12P mean?
Pons and Brooks are easy to make sense of, right? They’re named after people who discovered it. But what’s with the alien numbers and letters often associated with comets?
“The 12P in the comet’s name is because this was the 12th comet that was observed to periodically return,” explains Baskill.
“Comets originate from the very edge of our solar system, and so some have orbital periods of tens of thousands of years or even more, and are never seen to return.”
Short-period comets like Pons-Brooks, on the other hand, take less than 200 years to return to the inner Solar System.
Perhaps the most famous of the short-period comets is Halley's Comet, which has a similar period to Pons-Brooks of around 75 years. Sadly, Halley's Comet isn’t expected to return until 2061, so you’ll have to wait a little longer to spot that marvel.
According to NASA, the current number of known comets (short and long period) is about 3,910, although astronomers estimate there could be as many as a trillion – that’s a 1 with 12 zeros after it – out there in the Solar System.
When is the next comet?
Keep your eyes peeled in June and July for the 13P/Olbers comet, which may be visible with binoculars for Northern Hemisphere observers. This comet is another Halley-type comet with an orbital period around the Sun of 69 years.
Later on in 2024, the C/2023 A3 comet will be making its way to the inner Solar System – this one could be a cracker. Reaching peak brightness in September and October, experts think C/2023 A3 has the potential to rival some of the brightest stars in the sky, which could earn it the esteemed title of “Great Comet”.
About our experts:
Dr Paul Strøm is an assistant professor in the astronomy and astrophysics group at the University of Warwick working on the PLATO space mission. He also works on various astrophysical topics mainly focused on far-UV observations aimed at understanding the formation environments of young planets. His research paper titled ‘Exocomets from a Solar System perspective’ was published in the journal Publications of the Astronomical Society of the Pacific.
Dr Darren Baskill is an outreach officer and lecturer in the Department of Physics and Astronomy at the University of Sussex. He previously lectured at the Royal Observatory Greenwich, where he also initiated the annual Astronomy Photographer of the Year competition.
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