How We Know Interstellar Object 3I/ATLAS Is Not An Alien Mothership

By studying the object’s trajectory, it was soon confirmed to be an interstellar object, meaning an object that originated from outside the Solar System. How do we know? 

“Kepler was the first to realize that the orbits of planets are elliptical, with the Sun sitting in a special position known as the focus. Every ellipse has two foci. Ellipses have another important parameter called eccentricity. Eccentricity of zero means a circle where the two foci are in a single point (the center). The closer the eccentricity is to one, the more squished the orbit is,” IFLScience resident astrophysicist Dr Alfredo Carpineti explains.

For objects that are bound to the Solar System, like the planets and Solar System comets, the eccentricity is always lower than one.

“This is not the case for an interstellar object,” Dr Carpineti continues. “Their eccentricity is greater than one: 1.2 for ‘Oumuamua, 3.5 for Comet Borisov, and between 6.1 and 6.2 for comet 3I/ATLAS, one of the many records of this latest interstellar interloper.”

In short, we are highly confident that 3I/ATLAS is interstellar. Looking at its path and working backwards, astronomers have even found that it may have traveled relatively unscathed for 10 billion years, a time capsule from a different part of the galaxy, and another age of the universe. 

Why do people think 3I/ATLAS has alien origins?

Since its discovery, the object has captured the attention of astronomers worldwide, and for obvious reasons. It is only our third confirmed interstellar visitor, after 1I/ʻOumuamua and 2I/Borisov. Studying it could tell us about the environment it came from, though a new study may have a little bad news on that front.

While most scientists are interested in what we can learn from this natural object, Harvard professor and theoretical physicist Avi Loeb has continuously thrown out the suggestion that 3I/ATLAS could in fact be an alien spacecraft in disguise (it’s not), a theme large parts of the media and general public have run with. It’s not even the first time he’s suggested an interstellar visitor may have alien origins (it wasn’t true then either).

At first, when Loeb suggested 3I/ATLAS could be a spacecraft attempting to conduct a “dark forest” attack, he wrote on his blog that he was largely doing it as a “pedagogical” or teaching exercise. But as we have gained more observations of the object, he has made a list of “anomalies” of the object, which to him appear to suggest that 3I/ATLAS could be an alien spacecraft deliberately sent to our part of the universe.

These “anomalies” have included its extreme negative polarization, its rare anti-tail, and its odd nickel-cyanide ratio. But these anomalies have not been entirely consistent.

“The simplest hypothesis is that 3I/ATLAS is a comet and we are missing the spectral features of its gaseous coma because of its large distance from Earth,” Loeb wrote back in July. “However, in case future data will indicate the absence of a cometary tail, we will be faced with the tantalizing possibility that it did not inherit a random velocity in interstellar space but instead was sent towards the inner Solar System by design, being a member of a rare population of massive interstellar objects.”

Since the tail has been seen, both in the solar and anti-solar direction, Loeb changed tack, to the annoyance of other scientists in the same field.

“Once the coma (and tail) became inarguable, he switched gears and said that a spacecraft should have those things after all,”  Jason Wright, professor of astronomy and astrophysics at Penn State, wrote in a new blog post addressing these claims. “He has now explicitly written that no matter how much it walks like a duck, quacks like a duck, and swims like a duck, he will find ways to insist it’s at least 20% likely to be an alien spacecraft.”

How would we know if 3I/ATLAS was an alien spacecraft? 

One obvious sign would be if it performed a maneuver that cannot be explained by gravitational interactions with the Sun and other Solar System objects. A clear pivot in direction would do it, perhaps swerving it towards Earth, the only planet we have confirmed to have life, let alone intelligent life. There could be other signs too, like attempts at communication from the object, whether with visible light or in radio frequencies.

However, until there is any evidence of it acting like anything other than a comet, scientists will go with the simplest explanation: we are staring at a comet, even if it is a very rare and interesting one.

“The first thing to understand about comets is that no two seem quite alike. Planetary scientists have an expression, ‘Comets are like cats: they have tails, and they do precisely what they want,’ meaning that they don’t obey any consistent rule of behavior except that they all have tails—and even having tails is now known to not be a rule!” Wright wrote. 

“So the question isn’t whether 3I/ATLAS is anomalous: it’s from another Solar System, so of course it’s anomalous! It’s whether it’s so anomalous that there’s any reason to think it’s anything other than a comet.”

How we know 3I/ATLAS is a comet

Astronomers from NASA and the Search for Extraterrestrial Intelligence (SETI) alike have come to the same conclusion, along with most of the astronomical community. 

“From telescope observations, astronomers can tell that 3I/ATLAS is active, which means it has an icy nucleus and a coma (a bright cloud of gas and dust surrounding a comet as it approaches the Sun),” NASA explains, adding “this is why astronomers categorize it as a comet and not an asteroid.”

Loeb made similar suggestions about our first interstellar visitor, 1I/’Oumuamua, positing that “‘Oumuamua’s anomalies suggest that it might have been a thin craft—with a large area per unit mass—pushed by the reflection of sunlight”. If it was an alien spacecraft (it wasn’t), it has now passed harmlessly by, and is beyond the orbit of Neptune without making any maneuvers or making any attempt at communication. Because, like with 3I/ATLAS, chunks of rocks and ice are not prone to communication with intelligent life.

3I/ATLAS has now emerged from perihelion, its closest approach to the Sun, and the world’s telescopes are pointed at it once more, amateur and professional alike. We may learn some pretty interesting things about it as we look at it post its solar encounter. But unless it suddenly stops acting like a comet, we know what we are looking at: a natural object that may have traveled for billions of years alone. Isn’t that interesting enough?