Are we about to see a new Sungrazing Comet? UPDATED!

Update – 10th October 2024 – it looks like this comet might have broken up

Observations this week of Comet C/2024 S1 (ATLAS) indicate that it may by have disintegrated as it approached the Sun. As I noted below, comets of this sungrazing group come perilously close to the Sun. The amount of energy they absorb is one of the reasons why the appear so spectacular but also why only a few of what it is a large group survive.

Images via: Federico Manzini et al.

You can see in these two images taken a couple of night apart (Oct 3rd and Oct 8th 2024 how the nucleus of the comet is no longer a bright central point, but rather a fuzzy smear – an indicator it’s spreading apart into space.

This appears to have happened some distance from the Sun and there could be some surprises ahead. However it would be a wise choice to say Comet C/2024 S1 (ATLAS) won’t be appearing in our skies later this month as hoped.  You can read the full report at the Astronomer’s Telegram here.

Cheers,

Earl White

BINTEL

10th October 2024

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Fingers crossed for another bright comet in the coming weeks – and this one could be very special.

The ATLAS sky survey  discovered another comet on the 27th of September 2024.  It’s been given the label of A11bP7I or C/2024 S1 (ATLAS).  No doubt it will score a nickname by someone in the media that’s somewhat prosaic.

This is different comet to the other visitor, Comet C/2023 A3 which is in the news at the moment as well – it’s looking like we might have two bright comets in our October 2024 skies.

Comet C/2023 A3 captured by Geoff Wyatt from Warriewood beach north of Sydney in the last week of September 2024.

This new comet might be visible in southern hemisphere skies in the days leading up to its closest approach to the Sun (perihelion) on the 28th of  October. After that, our friends in the northern hemisphere could be in for a treat.  Just how bright C/2024 S1 (ATLAS) will get is uncertain at this stage, however there are estimates it could be as bright as magnitude -7, or brighter than Venus and possibly even visible during daylight hours.

An early image of C/2024 S1 (ATLAS) via Gianluca Masi, Virtual Telescope Project taken on the 30th of September 2024

Why are there so many “maybe, hopefully, possibly, could be up to” and more when talking about comets? Why don’t we just know?

Looping around the Sun is rough on comets.

Rocky planets like the Earth and Mars and even gas giant such as Jupiter and Saturn make it around their yearly orbits of the Sun with no dramas. Our orbits, while elliptical, are almost circular and the distance between any of the major Solar System planets and the Sun doesn’t vary too much over the course of their respective years.

Comets have highly elongated,  elliptical orbits. The distance between their furthest point away from the Sun and their closest approach might vary hundreds or even thousands of times.  This means as they get closer to the Sun, the “stuff” they’re made up changes dramatically, and while we can take an educated guess at what will happen to a comet, it’s almost impossible to predict with any certainty.

It’s an overused term, but describing comets as “dirty snowballs” isn’t far from the truth. They’re a loose collection of frozen gasses and water which make up the “volatiles” onboard a comet (more on that in a moment) as well as rocks and minerals which were all formed during the early stages of the Solar System. Part of the reason why space missions like ESA Rosetta are sent to comets is to study these carriers of primordial matter from the outer reaches of the Solar System.

As they approach the Sun, comets heat up. This causes the various frozen materials or volatiles to melt and become gasses. This process itself doesn’t emit any light but comets shine either by reflecting light from the Sun or from the gas in their tails becoming ionised.  (Yes, comets can have more than one tail. There’s more on comet tails at this BINTEL article here. ) It’s hard to work out exactly just much material will be ejected from a comet, how  far it will reach into space and how bright the comet will appear from Earth.   There’s also the chance that the heat absorbed by a comet as it loops around the Sun could cause it to disintegrate altogether.  This was the fate of the only known comet to appear near the Sun that originated from deep, interstellar space, Comet 2I/Borisov.

The bottom line is that while astronomers can make a general prediction about how comets will behave, they have a habit of surprising observers.

Why the fuss about C/2024 S1 (ATLAS)?

This belongs to the Kreutz group comets, which are sometimes called sungrazer comets.  These are all comets that were once part of a much larger comet that broke up many centuries ago and were proved to all related by German astronomer, Heinrich Kreutz.  Up until 1979, only nine sungrazer comets had been found and all of these were discovered by ground based observations. (There’s also other groups of sungrazer comets.)

There’s more than 4,000 known members of the Kreutz group and most of them are tiny at only a few metres across. These have been discovered on images from spacecraft and a number have even been found by amateur astronomers trawling through the data.  By “sungrazer” we mean comets that get very close to the Sun during their perihelion – some less the Sun’s diameter.   It appears that none of these smaller members of the Kreutz group survive their close approach to the Sun,  but those that do can  sometimes go on to become “Great Comets”.

Some of you might remember C/2011 W3 (Lovejoy) or Comet Lovejoy which was discovered by famous Australian astronomer Terry Lovejoy. This graced our skies in 2011.

Comet Lovejoy in December 2011 over the European Southern Observatory Image via: Y. Beletsky (LCO)/ESO

This comet was sungrazer Kreutz group comet that made it through its close encounter with the Sun.  I remember it being visible in Sydney in among all the light pollution while it was not fully dark and appearing to stretch about a third of the way towards the horizon.

Stretching back a few decades was the famous Comet Ikeya–Seki of 1965. This was another Kreutz group comet survivor that while it did fragment into several smaller bodies, became possibly the most spectacular comet of the last thousand years or so.

Comet Ikeya–Seki- in 1965 near Kitt Peak Observatory.  Image via  Roger Lynds/NOIRLab/NSF/AURA/ – taken on Kodak Ektachrome too.

This comet was so bright it was visible during the day from downtown Tokyo.

Why are sungrazer comets so bright?

Comets that pass close to the Sun and survive their encounter often have a higher percentage of their volatiles melted and thrown into space compared to comet which are further away. Their tails (bother dust and ion) contain more material as well as appearing brighter as seen from Earth because of their illumination.  Such a journey is perilous from the comet’s point – no doubt a major reason they’re rare.

Is C/2024 S1 (ATLAS) going to be a Great Comet?

We don’t know at this stage.

It’s a decent sized comet, it a sungrazer of which a tiny number have been magnificent comets in the sky – we’ll know in the week or so leading up its perihelion and in the weeks following.  It’s rare to spot a sungrazer more than a few weeks from perihelion. The last we did was Comet Lovejoy, Stay tuned!

What type of telescope or binoculars do I need to look at comets?

Comets, especially those with a bright and large tail, stretch across a large chunk of the sky. They often appear larger than several full Moons.

Ideally you need a telescope with a wide field of view.  This will let you take in much of the comet as possible.

Binoculars will give you the best possible view of comets.  If you have a pair already, head outside and try them out for comet viewing even if you’ve only ever used them the day time. You might be surprised about you’ll be able to see.  Some affordable binoculars that we suggest would be good for comet viewing include:

Any type of telescope I should avoid to look at comets?

We normally don’t point out telescopes or other gear that you shouldn’t buy, but we’re going to make an exception for comet viewing.

Refractors are ideal for planetary and Lunar viewing and will deliver excellent deep-sky observing as well. We love them and they make ideal beginner’s telescopes.

BUT – they’re not suited to  large astro objects like comets as you won’t fit into their field of view – grab a pair of binoculars instead.

A DSLR on a tripod is a handy and easy way photograph comets. There’s already quite a few comet photos in the BINTEL Society Facebook Group. Many of them have comments on how they were taken and members of that community would be delighted to answer any questions you might have.

Comet of the Century/Lifetime/Millenium ??

One of the cool things is that like buses or trains, there will always be another comet.  You’re not going to be around to see  C/2024 S1 (ATLAS) again as even if it does make it around the Sun. The time it takes to orbit the Solar System is simply too long. While you mightn’t get to see this comet, there will be others. If  C/2024 S1 (ATLAS) does turn into a Great Comet, how long it will be before another appears to match it is hard to say.

If you get an opportunity to go comet viewing, especially at a comet like C/2024 S1 (ATLAS), make sure you grab it.

Finally….

There will be more information about A11bP7I or C/2024 S1 (ATLAS) as it wanders through the inner Solar System. We’ll keep updating this article with news as we learn more.

Cheers,

Earl White

BINTEL

3rd Oct 2024