Our Solar System Has a New Interstellar Visitor -- Here's Hoping it's a Comet

We get hit with stuff from space constantly. More than you might think. Somewhere around 20,000 meteors larger than a softball hit Earth every year. A few hundred are big enough to recover and catalog. Why aren't they more of a big deal? So far, every single one has been from our own solar system, mostly from an asteroid belt between Mars and Jupiter, some from the Moon or Mars after they're hit by other meteors. So, there's not much new to be learned by these objects. We're just glad they aren't the size of buses, and they mostly disappear into our oceans.

It's extremely rare anything enters our solar system from outside its boundaries. Astronomers call these objects 'interstellar'. They know immediately when an object has arrived from interstellar space: its trajectory and velocity can't be explained by gravitational interactions within our solar system. Meaning, it's not orbiting the sun or any other object. It's literally passing through. And it's moving much faster than your average meteoroid.

When they do show up, it's a rare opportunity to learn just what is out there. These objects form in star systems not our own, so they carry valuable data. But it's no exaggeration to call it rare. Before this year, interstellar objects have entered our solar system twice.

An interstellar object called Oumuamua passed through in 2017. It moved at a staggering 58,000 miles an hour, far faster than any objected knocked from the asteroid belt at the edge of our solar system. Then in 2019, an object called Borisov arrived, with a bright coma and tail, consistent with your typical comet. But again, its speed set it apart. It was moving at over 71,000 miles an hour, faster than any comet in our solar system.

On July 1st of this year, the southern ATLAS telescope at Cerro Tololo in Chili discovered a third.

The telescope is part of three positioned around the globe to detect near-Earth objects that pose a collision risk. This new object was in no danger of hitting Earth. But it did cause concern. First, it is the fastest interstellar object ever observed, moving at 134,000 miles an hour. And -- unlike its two predecessors -- its path is exceptionally straight.

The good news is, the speed and trajectory confirm it is just passing through our solar system. But something traveling so fast and so straight begs another question: what the heck is it?

Well, it's large, maybe the largest interstellar object observed to date. Estimates suggest a size as large as 12 miles long. Imagine the island of Manhattan flying at 134,000 miles through space, that's what is out there right now. 

And it's ancient. It's the oldest object ever seen by humanity. 

We know this because its path indicates it originated from the Milky Way's thick disk of stars, a region high above and below the part of the galaxy we're in, where stars are 8-12 billion years older than our sun. 

This interstellar object -- officially called 3I/ATLAS -- is older than our own solar system, by billions of years. It comes from somewhere formed in the early Galaxy -- places we weren't even sure existed. If it was designed by ancient aliens, it was made to survive across light-years.

And there's something unusual flying off of it, being released in staggering quantities: water.

It's another first for interstellar objects. The Swift Space Telescope used ultraviolet images of 3I/ATLAS to spot it. It's releasing water at a rate of about 88 pounds per second. It's hard to comprehend that much water -- it's all the rain on Earth in a single day, but released every second.

Is it an ancient alien probe, sent eons ago to scout us? 

Well, it's the first thing astronomers attempt to rule out. Because most likely, 3I/ATLAS is a natural comet. 

First, they examine the trajectory. If it is moving too fast, on an odd incoming angle (not lining up with the galactic plane where most stars orbit), it indicates it might have been sent intentionally rather than wandering naturally. And, disturbingly, 3I/ATLAS checks this box. It is, indeed, coming in at an odd angle and at tremendous speed. But this alone isn't enough to call it intentional. In fact, the angle would be consistent with an object originating in the Milky Way's 'thick disk'.

The other key indicator an object might be alien is a change in speed, independent of the objects around it -- astronomers call this non-gravitational acceleration. It suggests some kind of ship, with hidden engines, able to navigate independently.

The thing is, a detailed analysis estimates that 3I/ATLAS is experiencing non-gravitational acceleration. But it's extremely slight, and could be attributed to dust particles ejected, exerting recoil forces. Slight or not, it's another box checked in favor of 3I/ATLAS being, well, unnatural.

Of course, a comet has one major trait that's easy to identify. It's called a coma, a gas and dust cloud that surrounds it as it gets warmed by the sun. And 3I/ATLAS does exhibit an active coma -- but with unusual characteristics, different than your typical comet. 

When comets warm and develop a visible coma, they show cyanide gas first. But 3I/ATLAS showed water first, with the cyanide gas appearing later. This indicates the object has sources of ice on board, outside its nucleus.

In fact, before the cyanide gas appeared, a spectroscopy detected atomic nickel emissions in the coma. Again, this is highly unusual, and not found in the majority of comets.

Add to this, the carbon dioxide levels of 3I/ATLAS are unusually high. Astronomers figure this means the object formed in a very cold region of the Milky Way, far from its parent star. Wherever it was made, it was in deep space more extreme than typical comets.

Lastly, the coma has an unusual red hue, indicating its composition differs from typical comets.

But despite the unusual water trail, high CO₂ levels, odd nickel emissions, and the mysterious red-tinted coma that make 3I/ATLAS chemically and physically different from most comets, NASA is confident the object is, in fact, a comet. NASA's official website calls it "Comet 3I/ATLAS".

Let's hope they're right. If it is an ancient alien probe that just confirmed to its creators Earth is here, we may not want to know what happens next.