Comet 3I/ATLAS update

 

I saw a headline in the news last week that said, "3I/ATLAS Comet Changes Course Again - NASA Warns of Unpredictable Path."

Oh, brother!

What does the author of such an article want us to believe? "Changing course" for where, exactly? Are we to believe that it's turning around and coming for earth? And does "Unpredictable Path" mean that the comet will soon be lost, because we won't know where to look for it?

I realize that headlines like this are mere click-bait. I shouldn't pay any attention to them at all. But apparently a lot of people are paying attention to them! At least, judging from the comments on these types of incendiary articles and YouTube videos, it appears as though a large number of people believe that aliens are in control of 3I/ATLAS. I hope these commenters are just trolling us.

But okay. Let's take the headline at face value. If the comet has truly changed course and is now on an unpredictable path, that means my sky chart software will no longer permit me to find the comet. After all, it's been nearly a week since the article was published. By now the comet must be far off-course from where my software thinks it is!

I use Cartes du Ciel to control the pointing of my telescope. In order to find comets with Cartes du Ciel, I must provide it with a comet file (a list of all known comets and their orbital elements). Cartes will use that file indefinitely to show me where all known comets are in the sky. However, whenever new comets are discovered, I can't use that old comet file to find new comets, because it obviously doesn't have any information about new comets. Thus, I need to update my comet file from time to time. I get my updated comet files from the Minor Planet Center's website.

The last time I downloaded the comet file from the Minor Planet Center was back on October 20th of 2025. So, the file I'm using can't possibly be accurate if 3I/ATLAS changed course a week ago. Right? Sounds like a good test of the news article headline.

Ever since reading that headline, I had been waiting for a clear night to take another look at 3I/ATLAS. And last night I finally got my chance. At 2 AM, the comet's location (according to Cartes du Ciel) would be high enough in the sky to begin shooting. I centered the symbol for 3I/ATLAS in Cartes, right-clicked it with my mouse, and then clicked "Slew telescope to 3I/ATLAS" in the dropdown menu. The scope obeyed and aimed itself at the spot where the comet was supposed to be. 

And wouldn't you know it? When I took a picture, the comet was dead-centered in the frame! Imagine that! The comet changed course onto an unpredictable path, but my old comets file from 3 months ago had no problem helping my telescope to center it in the field of view of my camera.

Was it perfectly centered? Well, let's take a look. The center of the comet is at a pixel value of x=1360, y=1057. The image is comprised of an array of pixels that is 2742 columns, by 2199 pixels. Thus, the exact center of the image should be at x=1374, y=1099.

Hmmm. After pointing the telescope using the old comet file in Cartes du Ciel, the comet missed the exact center of my frame by 14 pixels in x, and 42 pixels in y. How far off is that in terms of arcseconds? The sky coverage represented by each pixel of my camera is 1.67 arcseconds. So, 14 pixels translates into 23 arcseconds, and 42 pixels translates into 70 arcseconds.

To put this in terms that might be easier to grasp... At opposition, the planet Jupiter has a disk diameter of between 45 and 50 arcseconds. Thus, the comet missed being dead-center on my image by about 1.4x the diameter of Jupiter!

Honestly, that's not even outside the range of error of my telescope's pointing capabilities! 

But here's what everyone needs to understand as they read sensationalized headlines about 3I/ATLAS "changing course": Every comet's orbit is altered slightly whenever it passes nearby to a large planet. The same goes for the asteroids. Astronomers have to keep updating the orbits of all of the million and a half asteroids lying out there in the Main Asteroid Belt. That's because as the years go by, the asteroids are getting tugged each time they pass near (by millions of miles) Jupiter or Mars. As comets like Halley's Comet approach the inner solar system, their orbits are altered if they happen to pass near Uranus, Saturn, Jupiter, Mars, Earth, Venus, and Mercury. 

Astronomers already predicted the change in 3I/ATLAS' path as it passed near the sun. The JPL Small Body Database Lookup website showed us the "bend" in 3I/ATLAS' path months before it reached the bend! Cartes du Ciel already accounted for that bend in the file I downloaded last October. Passing nearby Mars and Venus probably altered 3I/ATLAS's path a little more. As it approaches Jupiter, it will get altered again, slightly. 

All of these adjustments are normal for solar system objects, and astronomers know how to recalculate orbits for perturbations caused by the sun and major planets. There is no need for Avi Loeb, and others, to invoke some additional phenomenon, like aliens firing up rocket engines, to account for changes in 3I/ATLAS's path. Besides, as my uncropped picture below illustrates, the path of 3I/ATLAS doesn't appear to have changed at all. And it was, contrary to the news headline, quite predictable.

Here's the uncropped version of last night's image.

UPDATE - January 5th: 

Please understand that my images of 3I/ATLAS on this page don't necessarily prove one way or the other that the comet has not changed course. As I mentioned in the original post, there are many factors that can alter a comet's course. One thing I forgot to mention is the comet's own out-gassing from being heated up by the sun. Natural out-gassing acts just like a rocket engine.

My purpose here isn't to address any changes in course for 3I/ATLAS, but rather to throw some cold water in the face of the media for blasting us with deceptive headlines. The media headlines about 3I/ATLAS have been way over the top in favor of alien control of the comet. So, when they used the provocative phrases, "3I/ATLAS Changes Course Again" and "Astronomers Warn of Unpredictable Path," we all know the author's intentions. To spread fear and panic, so that we'd take the bait and click on their headlines. 

"Changes course," in this case, is intended to cause us to wonder if the alleged alien spacecraft might be turning around to come after earth. And "unpredictable path" is intended to make us believe that it is no longer acting like a (predictable) natural object and therefore is controlled by the whims of the aliens on board.

These misleading headlines are unfair because their authors know that the vast majority of their readers are not astronomers. Lacking the tools of the astronomers, most of their readers likely think about the solar system and spacecraft in terms of Star Trek and Star Wars. On television and at the movie theater, we watch aliens like the Borg (Star Trek), maneuver their giant-size spaceships through the galaxy at warp speed. Such a machine could turn around at Jupiter and arrive on earth within hours.

I'm merely pointing out with my images that the course change (if any) of 3I/ATLAS is not at all like a fictional spaceship moving at "impulse" speed. If that's the imagery you're thinking of, then I hope I'm throwing some cold water in your face, too!

I took the image below in the wee hours this morning (January 5), two days after the one at the top of this page. And, yes, my planetarium software (without any updates to the three-month-old comet file), is still pointing my telescope accurately toward the comet. Here is my full frame (at reduced scale) showing the comet at the center. How is that possible if the comet "changed course" and is now on an "unpredictable path"? Note that the comet is much fainter after just two days, so it's not coming toward earth following its alleged course change. It's still heading toward Jupiter, faster than a speeding bullet.


UPDATE - January 12:

It's now been a week since my previous update. And guess what? My picture from early this morning shows that my old comet file is still successfully predicting the position of 3I/ATLAS! Today's image, in fact, is even more accurate than the one I took on January 3rd (top of page). In that photo, the comet landed very nearly in the center of the frame, being only 14 pixels off in x, and 42 pixels off in y from the exact center of the field of view. That represented an error in terms of arcseconds equal to a little more than the diameter of Jupiter. Nine nights later, my scope aimed itself at 3I/ATLAS, such that the comet landed 11 pixels off in x and 34 pixels off in y. Clearly, we're talking here about telescope pointing accuracy and not a change in the comet's course! Else, why is the comet even closer to the center in last night's image than it was on January 3rd?

Below is my image taken at about 01:30 this morning (showing the full frame but reduced by 35%). The newspaper article that announced a "changed course" and "unpredictable path" for 3I/ATLAS was published on December 27th, 2025. It is now 16 days after that announcement. And I haven't updated my comet file since October 20th, 2025. If the comet changed course, how is my telescope still accurately pointing at its position?

Comet 3I/ATLAS on January 12, 2026

 




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