The Unpredictable (and Disappointing) Nature of Comets – Editorial

With the news that Comet C/2019 Y4 (ATLAS) has been confirmed to be breaking apart, allow me to remind all the casual observers that more times than not, potential superstar or “great” comets almost always fizzle out and go out with a whimper rather than put on a stellar show for the ages!

If this is your first time experiencing the disappointment of a comet, then join the club!

Trust me, I understand that spark and mystique that comets bring!

For many people, comets like Hale-Bopp were the spark that got me into astronomy, it inspired me to get a telescope. About 10 years later, hearing about Comet 17P/ Holmes having that bright outburst in activity was another spark that got me back into astronomy and cemented my passion towards the heavens for good. Comet 46P/ Wirtanen, the so-called 2018 “Christmas Comet,” was the object that got me finally into astrophotography – it was the only way I could truly observe it!

46P Loop
46P Looping Sequence

Therefore, comets are always going to have a special place in my heart.

It’s been tough for us northern hemisphere observers as we haven’t had a great comet since 1997 while the southern hemisphere has had two (McNaught and Lovejoy in 2007 and 2011 respectively)!

But that hasn’t stopped news of potential good shows over the years. But if you’re living through a disappointment because ATLAS of fizzling out, then welcome to the club!

For many decades, astronomers have always been weary about raising awareness for potential great comets. If the internet wasn’t around, it’s quite possible the public could still miss out on them!

Are you over 50 and do you remember Comet West, the “Great Comet of 1976?” It was one of the brightest in history and could be studied in the daytime! No? You don’t remember hearing about it? That’s because astronomers didn’t raise public awareness on it, and you can blame the backlash and disappointment from the public over Comet Kohoutek.

Fig5-CometWest_Kohoutek-e1426728195200
The one on the left is Kohoutek – the predicted “Comet of the century.” The one on the right is West, a comet that went largely unreported due to fears of public backlash.

For those too young to remember, Kohoutek was a comet that was discovered in 1973. It was supposed to be the “Comet of the Century,” because it was supposed to be an Oort Cloud object visiting the inner solar system for the first time – hence a lot of outgassing from icy material that hasn’t been heated by the Sun yet. But that didn’t happen. Instead it never brightened to the expected levels, partially disintegrated as it got closer to the Sun, and by the time it was in a visible position at night, it was barely a naked eye object.

Does That Sound familiar?

Remember in 2013, we had two potential good comets that got people excited only to disappoint.

C/2011 L4 (PANSTARRS) reached naked eye brightness in March, but was significantly dimmer than predicted, and because it was very low above the horizon a lot of people missed it. Through a small telescope, it appeared like a dim smudge, and it was barely noticeable against the twilight sky.

C/2012 S1 (ISON) was predicted to be possibly brighter than the Moon at perihelion, when it was brightening at a certain rate while in the outer solar system. But as it got closer, the rate slowed down significantly, and never became bright enough for naked eye casual viewers – ultimately it disintegrated after perihelion in late November.

And now in April 2020, Comet C/2019 Y4 (ATLAS), another comet that brightened at an alarming rate in March has been confirmed to be breaking apart and dimming rapidly. Even though I gladly imaged it, I remember telling eager people dont get your hopes up too much.” And sure enough, almost like it was on cue, the news broke out.

Looks like we will have to wait again! What’s another 23 years and counting?!

Unfortunately, those amazing comets that do impress us are the exception rather than the norm! For every Hale-Bopp or Comet McNaught, there’s dozens to perhaps hundreds of Kohoutek’s. And the number of potential greats is literally just the tip of the iceberg to the number comets there actually are in our solar system! On any given night, there are perhaps dozens of known comets in the sky, but they’re too dim for even modest sized telescopes to detect!

Even though we know what they are, and what causes them to brighten and put on their familiar displays, the science of predicting how much outgassing and brightening of any comet is still not quite there yet. No two comets behave the same way, even if they share similar orbital periods, and have similar properties. We know enough to know we don’t know everything.

67p
Comet 67P?Churyumov–Gerasimenko as seen from the Rosetta Spacecraft on March 28, 2915

As comets get closer to the Sun, their frozen gases react to the increasing heat and create the comet that we see, thus comets get brighter and their tails get longer as they approach the Sun. Hence the predictions get made based on the rate of brightening over a select period. That sounds simple enough, right?

More times than not, however, the volatile material can vaporize from the heat when it’s further out, creating unrealistic expectations – and as we all know, many comets in recent years have done this. So that should tell the reader that it’s quite common for a comet to have a “burst” in brightness when it starts outgassing further out, but when the outgassing appears to plateau (flatten out) as it gets closer to our Sun, then that brightening rate slows down significantly.

The nucleus (the actual rock that’s only a few miles wide on average) becomes more unstable, and is prone to breaking apart when it deals with million degree Fahrenheit temperatures and solar winds!

Oh sure, sometimes comets do live up to the hype, and people like me would not have gotten into astronomy without them!

But most of the time they don’t. They could exhaust all of their icy materials that create the brilliant displays before they get close, and all we’re left with is a rock that swings around the Sun and barely makes a peep in the sky!

You can also blame light pollution, as comets that are deemed “naked eye” level but are not at the levels of bright stars and planets still require you to go to a dark location to glimpse them – and they look ghostly through a telescope. Many naked eye level comets, including that of Halley’s Comet’s notoriously disappointing 1986 appearance, would have been considered impressive or even “great” if light pollution didn’t wash them out!

Even if what we think going on is notable and exciting, as a former boss always used to tell me, “perception is reality.” Bad impressions are enough to turn people away and cause people to lose interest. Therefore, in the case of astronomy, it’s tough enough generating interest in celestial events like the appearance of a comet; so the last thing we want is to create a buzz around something that turns into a non-event for casual observers.

3-27-20 comet atlas

Comet C/2019 Y4 (ATLAS)

So if you’re living with the disappointment of a comet for the first time, just remember that comets are unpredictable, and we feel you too! Trust me, people like us WANT to see a bright comet, they’re right up there with Total Solar Eclipses in terms of rarity and mystique, and we can’t wait for that next comet that gets everyone to go outside and look up, or possibly come visit a star party, an observatory and/or planetarium, and get their passion for astronomy ignited or renewed!

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