Universe Today
This is Part 2 of a series on interstellar comets. Read Part 1.
Once you start listing the properties of 3I/ATLAS, it becomes clear pretty quickly that this thing is distinctly different from any other comet we've ever seen. Here's just a small taste.
Its gas plume contains way more nickel than we've ever detected in other comets. Metals like nickel tend to sink toward the center of a solar system during formation — they're heavy, they like to be close to the action — so finding a comet drenched in the stuff is, well, odd. It also doesn't have a lot of water, which is a problem if you're a comet. Comets are supposed to be dirty snowballs. Water is kind of their whole deal.
As it got closer to the Sun, it got brighter — which makes sense, because it was warming up and reflecting more sunlight. But it brightened much more quickly than other comets do. The light curve was steeper than expected, like it had a hair trigger for solar heating.
For a long time, it didn't have a coma or a tail, but it eventually got them both. It just took a while longer than anyone predicted. And then, on its way out, it started accelerating. Instead of being drawn toward the Sun by gravity like a well-behaved object, it looked like it was being pushed away from the Sun. (More on that later.)
I'm going to be honest. That's a lot.
But here's the thing about comets. They're a lot like cats: they have tails, and they do what they want. And just like cats, not all of them even have tails.
Take any comet you want — even something famous like Halley's Comet — and once you start writing down enough of its properties, you'll spot all the ways it's completely unlike any other comet in the entire solar system. Halley's has a retrograde orbit, meaning it goes around the Sun backwards compared to the planets. Its nucleus is darker than coal. It loses about six meters of material from its surface every time it swings by the Sun. Start cataloging any comet's quirks and you'll fill a page before lunch, because comets are messy, complicated, wildly individual objects. No two are alike. That's just the nature of the beast.
Heck, we can play the same game with planets. Earth is the only planet with liquid water on its surface. Saturn is the only one with giant rings. Venus rotates backwards. Uranus is tipped on its side. Every planet is a weirdo if you look closely enough.
Heck, even people. You are completely and totally unlike any other human that has ever lived. But you're still human (I assume).
So at some level, we expect 3I/ATLAS to be unique — because all comets are unique. And of course an interstellar comet is going to get a lot more attention and observation and scrutiny because it's a special comet. The more we observe it, the more we're able to highlight its differences relative to other known comets. And those differences are going to get a lot more media attention because, once again, special.
Once that stranger leaves town, it's going to be the subject of town gossip for weeks. You're automatically going to highlight the differences between the stranger and your community, and you just might conclude that all strangers are weird.
And guess what? You're not entirely wrong.
Interstellar comets are weird. Yes, they're still comets. And because comets are like cats, each one is going to be a little bit different. But we expect interstellar comets to be even more different than average.
Why? Because they're different.
A stranger that comes to town is going to be different. They might look different, or speak a different language, or prefer different kinds of cheese. At one level they're going to be different because every person is a unique individual snowflake, and at another level they're going to be different because…they just are.
There's regular different, and then there's different-different. You dig?
To be continued...
