Did the Sun strip the outer layers off Interstellar Comet 3I/ATLAS as it flew through the Solar System?

This mightn't have been a bad thing!

It's now been more than a year since the Interstellar Comet 3I/ATLAS made the news as it entered the Solar System from interstellar space, swung by the Sun and then started to head back out into deep space. 

The path Comet 3I/ATLAS took as it flew through the Solar System

Even though it's a receding object now, it's still the subject of a lot of study and investigation.  

3I/ATLAS provided quite a rare opportunity for humans to investigate material comparatively close-up that was not only from elsewhere in the galaxy but also older than the Solar System itself.  One problem is that 3I/ATLAS has spent an enormous amount of time travelling through interstellar space, where dust, cosmic rays and other energetic particles can gradually change the chemistry of a comet's outer layers.

In other words, are we actually seeing what this comet was made of when it formed, or material that's been altered by its long journey through the galaxy or the celestial dust and grime plus a bit of being zapped along the way?

Luckily, the Sun might have given astronomers a lucky break.

Based on what we know about the gases escaping from 3I/ATLAS, Tessa Frincke and Darryl Seligman of Michigan State University calculated that solar heating removed the equivalent of a surface layer about 1.7–5.2 metres thick. If you include the likely amount of dust removed as well, some estimates put the total depth of the material stripped away at more than 10 metres.

In their work, Frincke and Seligman conclude that "it is possible that the surface has been eroded down to layers of unaltered material."

A few things to bear in mind. The calculations do not actually establish that this happened. We also don't have a full picture of the comet and what gases made up different parts of the comet, meaning gases might have escaped without actually exposing the pristine material of the comet itself.

One of the next thing researchers are planning to do is to compare the gases being emitted from 3I/ATLAS as it entered the Solar System to those as it heads back out. This might help determine if what we are seeing comes from the interstellar comet or gases and dust collected along the way. 

Even with these provisos, it's a tantalising way to investigate this latest visitor from deep space.

A supernova remnant that looks too amazing to be real

Hard to believe it's not AI.

We had a chat last week about White Dwarf stars not always being white.  

These are the incredibly dense leftovers of stars like our Sun, after they've expanded into red giants and thrown off their outer layers. The nuclear processes that produce heat and energy stop. The remaining hot core then spends billions, or even trillions, of years slowly cooling down, eventually becoming a black dwarf. 

BUT if a white dwarf has a nearby companion star, material can fall onto it. Under the right conditions, this can lead to a runaway nuclear reaction and a supernova. Two white dwarfs merging can also produce a spectacular explosion.

There's another way to make a supernova. Really massive stars, generally those born with more than about eight times the mass of our Sun, live surprisingly short lives. They burn through their nuclear fuel at an enormous rate before their cores finally collapse.

Both of these types of supernova explosions are very rare. They're also BIG. A supernova can throw off several times the mass of the Sun at up to a few percent of the speed of light. A supernova can even briefly outshine all the other stars in its host galaxy.*

There are between 100 billion and 400 billion stars in the Milky Way, and a supernova happens in our home galaxy about every 50 years or so. We normally don't see them for the same reason there's such a wide range of estimates of the number of stars; much of our view of the Milky Way is obscured by interstellar dust.

From Earth, we normally see a local supernova every few hundred years. The last one in the Milky was that was seen by people was Kepler's Supernova (SN 1604) in 1604. Modern instruments have been able to pick up supernova remnants such as Cassiopeia A that happened in 1680 and more recently supernova G1.9+0.3 that went off closer to the galactic centre roughly 140 years ago and the most recent supernova in our galaxy that we've found. Both would have been spectacular and possibly spotted by supernova hunters in other galaxies millions in the future, but we sadly missed them entirely from Earth because of that pesky dust blocking the view.

Throughout human history, only 5 supernova were known to have been widely observed and recorded before the invention of the telescope.  SN 1181 was observed in August 1181 by Chinese, Arabic and Japanese astronomers for 185 days. (There's no record of European astronomers spotting it. They might have had better things to do at the time.) There were do doubt others in the centuries before that people saw and there are some reports of "guest stars", but they remain highly speculative. 

The matter thrown out during a supernova explosion form what we call a supernova remnant. These start out as fairly dense and small objects and expand to reach quite a few light years in size. 

These supernova remnants are interesting critters from an astronomer's point of view, both visually and for learning about the next generation of stars are formed. These "shockwaves" spread out at high speed and astronomers can use them to calculate just how long ago the supernova occurred. 

We'd previously found the remnants of 4 of the 5 pre-telescope supernova, but exactly where SN 1181 was in the sky eluded astronomers. There was a pulsar called 3C 58, but this wasn't confirmed as being left over from SN 1181. In 2013, an amateur astronomer Dana Patchick was searching for planetary nebulae in WISE infrared data and found an object now called Pa 30. This is widely considered to be the remnants of the 1181 event. 

A remarkable image of Pa 30 was released this week by the Gemini North telescope located on Maunakea in Hawai‘i. It's hard to believe this image is of a real object as it looks like something an AI would generate if you prompted to make an image of a "giant space fireworks explosion and make it fabulous". 

The spikes captured by Gemini North are not actually smooth streaks, but rather a series of tightly knotted clumps of matter, some spanning distances measured in light days.  You can read more about this image here.

Unlike the familiar Type Ia supernova, which can completely destroy a white dwarf, the explosion that produced Pa 30 appears to have left a surviving star behind. Astronomers think it may have been an unusual Type Iax supernova, possibly involving the merger of two white dwarfs. Pa 30 is the only known supernova 1ax remnant in the Milky Way. 

 Are there any supernova remnants that I can see or image with my telescope?

Yes! You won't be able to see Pa 30 as it's very faint and hard to spot. There are plenty of others to catch.

The most famous is probably M1 or the Crab Nebula. This is the result of the 1054 supernova which was recorded at the time. Just about any telescope will show it, with an 8" or larger scope bringing out the finer details.

You can even see some in binoculars under quite dark skies such as the Vela supernova remnant in our southern skies. It's a challenging object visually, but one worth pursuing knowing you've seen the leftovers of a supernova in Australian skies. It's massive too, stretching some 8 degrees across the sky or about 16 times the diameter of the Full Moon in the sky. It's just very faint.

This is also a favourite for astrophotographers, and you'll find lots of examples in the BINTEL Society Facebook group that you can view here.

Are we due for another Milky Way supernova?

I certainly hope so! There was one in the Large Magellanic Cloud in 1987 that was visible with just your eyes, but nothing locally we've been able to view recently. People conjecture about various individual stars that about to "go off", but there's no star we can point to with certainty. We know all stars of a certain mass or larger will eventually go supernova, but pinning it down to a certain date within any of our lifetimes is not something we can do for now. 

Japan's MMX Mission launched on time, heading for a landing in the South Australian outback in 2031

We chatted last week about the ambitious mission from the Japanese Space Agency, JAXA, and how it was planning to obtain samples from the Martian moon Phobos and return them to Earth in 2031, landing in the South Australian outback.

MMX on the way to Mars. Image via JAXA

With typical care and efficiency, the Japanese rocket launched on time during the week, with the news being widely picked up on mainstream media and online. Wonderful to see such an ambitious and inspiring mission grabbing the world's attention. 
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Cheers,

Earl White

BINTEL 

24th October 2026

* This is a very complex, yes fascinating topic so apologies if I've had to cover it in brief. Comment below if you'd like it discussed in more detail.