Interstellar object 3I/ATLAS reaches solar conjunction and perihelion, a key test for the ‘alien mothership’ hypothesis

On July 1, astronomers from the Asteroid Terrestrial-impact Last Alert System (ATLAS) spotted an object crossing our solar system on a trajectory that will take it directly back into interstellar space. We had our third confirmed visitor after 1I/’Oumuamua and 2I/Borisov.

It quickly turned out that the object was a comet, and a rather interesting one. The object has unusual chemistry and polarization, as well as a rare (but not entirely unprecedented) anti-tail, which is not the result of an optical illusion.

But the object’s trajectory took it away from the view of many terrestrial telescopes. Currently, the object is behind the Sun. On Tuesday, October 21, the object will be in solar conjunction, meaning it will be directly behind the Sun from Earth’s perspective.

We have observations of the object from Mars orbiters and we may be able to observe it from Jupiter’s orbit. Unfortunately, while the Sun blocks Earth’s view, our interstellar object will be at perihelion, or at its closest point to our host star.

As comets approach the Sun, they heat up and release volatile gases and dust from the surface. 3I/ATLAS is no exception to this, outgassing 6.4 AU from the Sun, one AU being the distance between Earth and the Sun. Being able to observe it up close would probably yield something interesting, helping us for example to gather clues about the object’s previous environment or origin.

While frustrating, a controversial astronomer has alarmed conspiracy theorists by suggesting the object may not be natural and may do something unusual when out of our view. According to Harvard Professor Avi Loeb, if the object is in fact of extraterrestrial technological origin (a very unlikely claim, given that we haven’t observed any pieces of extraterrestrial technology so far), then it may choose to perform an “Oberth maneuver” when out of sight, using the Sun’s gravity to change its trajectory and speed.

Since the discovery of the object, Loeb has repeatedly asserted that the alien spacecraft hypothesis is largely an educational exercise and that there is a (fairly high!) possibility that the object is not natural. In a recent interview, he went so far as to suggest: “If you want to take a vacation, take it before (October 29), because who knows what’s going to happen?”

“At this time, I estimate that there is a 30-40% chance that 3I/ATLAS does not have an entirely natural origin,” he wrote earlier this month. “This low-probability scenario includes the possibility of a Trojan horse-like black swan event, where a technological object masquerades as a natural comet.”

These are high odds, considering we’ve never seen extraterrestrial intelligence before and very few other scientists take this seriously. As Tom Statler, NASA’s lead scientist for small solar system bodies, told the Guardian about these claims: “It looks like a comet. It does comet things. It looks very, very strongly, in almost every way, like the comets that we know.

“It has some interesting properties that are a little different from those of comets in our solar system, but it behaves like a comet,” he added. “And so the evidence overwhelmingly indicates that this object is a natural body. It’s a comet.”

Nevertheless, the highly unlikely hypothesis of an extraterrestrial craft will soon have its key test, as it will reach perihelion on October 29 and have a chance to perform a maneuver.

“The most technically likely scenario involves a mothership releasing mini-probes that perform a reverse Oberth maneuver to slow down at perihelion and intercept the Earth, taking advantage of the Sun’s gravitational assist,” Loeb suggested in a question-and-answer session.

“The change in angular momentum per unit mass must be of the order of ~(0.36 au)*(68 km/s), where 0.36 au is the change in orbital radius required to reach the distance from the Earth to the Sun from the 3I/ATLAS closest approach distance (where 1 au=149.6 million kilometers) and 68 kilometers per second is the speed of 3I/ATLAS at perihelion. The amount of the Fuel required for this maneuver depends on the mass of the mini-probe. The mini-probe can potentially reach Earth a few months after perihelion.

If the object were to perform a maneuver, we would be able to see unexpected and unexplained changes in the object’s trajectory and mass if it ejected mini-probes. More likely, as a natural object, we should see it continuing its trajectory out of the solar system, although some changes in the object’s trajectory can be expected as it gets closer to the Sun and is bombarded with more radiation.

“For now, 3I/ATLAS appears to be a natural comet,” Loeb writes in a new blog post. “But the slim possibility of an Oberth maneuver should be seriously considered as a black swan event with low probability, because of its enormous implications for humanity.”

Scientists, including SETI (search for extraterrestrial intelligence) and NASA, have consistently rejected the hypothesis because the object can be better explained as an interstellar comet. When the object continues its path out of the solar system after perihelion, the alien mothership scenario will seem truly ridiculous.