Sightings claims of alien spacecraft are often ignored by the news media.  But when the top astronomer at Harvard University says that we may have found one, it makes headlines.

Harvard Astronomy Department Chairman, Dr. Avi Loeb, has made the astonishing claim that a mysterious object observed flying through our solar system last year, known as “Oumuamua” could have been built by alien intelligence from another solar system and sent to examine the goldilocks zone of our solar system. Goldilocks zones refer to planetary regions in space that can support life around stars.

Professor Loeb’s postulation involves a lot of complex math, orbital mechanics and astrogeology. To simplify it, we’ll unpack his findings in steps that led to Loeb’s deduction that the object could be an alien craft. 

Loeb said he went by the maxim of Sherlok Holmes, “Whenever you rule out the impossible, whatever remains, however improbable must be the truth.”

What is Oumuamua?

The story began in October 2017, when an interstellar object was first spotted by Hawaii’s Haleakala Observatory, using a space observing system called Pan-STARRS. The odd shaped object was named Oumuamua, the Hawaiian word for “Scout” and "first distant messenger”.

The Pan-STARRS space observation system is designed to find asteroids and was not expected to find anything interstellar because of its observational limits and the massive odds against an object like it coming close enough in our solar system to see it. Space is a big, wide empty place. Before the Pan-STARRS went online, Loeb calculated that the odds of seeing anything interstellar were as great as 1 in 100 million. 

It was a welcomed surprise when the observatory spotted an odd shaped celestial object moving faster than the escape velocity of our solar system, proving that it was from interstellar space. And we saw it because it traveled close enough to the sun to reflect its light and close enough to Earth for us to see the sunlight bouncing off of it.

We caught sight of Oumuamua after it had passed by its closest point to Earth and was headed away from us.

It’s just a comet, right?

From the first look it was clear that Oumuamua is not just a comet. Most comets come from the Oort cloud, a band of rocks in a distant orbit around our sun way past Pluto and at the outer edge of the sun’s gravitational sphere. That’s about a million times farther from the sun than Earth. The sun’s gravity is so weak there that objects in the Oort Cloud can easily change trajectories, turning them into comets that circle the sun in different orbits.

Clue #1 Oumuamua is no ordinary shaped comet.

When astronomers realized that Oumuamua was traveling too fast to be from our solar system and therefore the very first interstellar object seen, the science community took notice. Several telescopes were pointed toward it, including the Hubble space telescope, all trying to get as much data as possible about Oumuamua before it returned to deep space.

Oumuamua is a peculiar object for several reasons. It rotates every 8 hours and its reflected brightness continuously changes by a factor of 10, indicating that its shape is at least 5 to 10 times longer than it is wide, which is unprecedented. Meaning that when the wide side rotates into view it reflects 10 times more sunlight than its narrow side. There is no asteroid or comet in the solar system with such extreme dimensions.

Clue #2  Oumuamua is traveling at an unusual speed.

Stars travel through the universe at different speeds, which helps scientists discover where interstellar objects like Oumuamua are from by matching their speed with potential home stars. Oumuamua is traveling so relatively slow that it does not match the speed of any known star nor is it traveling in the same direction of any stars moving at that speed near our galaxy’s neighborhood.

Clue #3 Oumuamua speeding up as it leaves our solar system.

As comets fly away, the sun melts the comet’s ice causing “out gassing” as the ice evaporates off of it. Out gassing is what gives a comet a visible tail and propulsion. Water vapor and particles ejected from out gassing gently pushes the comet faster. But Oumuamua showed no visible evidence of out gassing, so what caused it to speed up? That raised a red flag for Harvard’s Avi Loeb, who began to closely study Oumuamua. Loeb calculated that the amount of out gassing needed to propel Oumuamua to its higher speed would require more than a tenth of its mass, creating a tail which should be seen by astronomers. 

Clue #4  What is propelling Oumuamua?

Other astronomers suggested that the out gassing is mostly made up of particles too small to see. But there is another oddity that disputes that explanation. If outgassing is propelling Oumuamua, it should increase the object’s spin rate as it accelerates. But Oumuamua’s spin rate remains constant, eliminating out gassing as the source of Oumuamua’s propulsion. Even if Oumuamua got a speed bump by breaking up, it would have only caused a one-time shove. Oumuamua is steadily accelerating.

Clue #5 Oumuamua is not a naturally shaped object.

Loeb deduced that the sun’s energy is pushing Oumuamua to go faster. But solar radiation is a much smaller force than out gassing so Loeb figured that Oumuamua must be smaller and less than a millimeter thick, or sheet thin to be pushed like it is by solar radiation. Such “sheet matter” requires special conditions to be made and does not occur naturally.

Clue #6  If it’s too thin for nature, how was Oumuamua made?

Loeb suggests that if Oumuamua is too thin to have been naturally created, it could be a type of solar sail manufactured by alien technology. It’s not a wild leap when you put together all the object’s anomalies. Loeb has long been interested space archeology, the idea that due to the great distances between stars, it is more likely that we will find evidence of long dead civilizations before contemporaneous life. To illustrate, when you consider the age of our planet, the technological advance of humans on it has occured in a relative blink of time. And humans have already developed extinction level technology with nuclear weapons and climate changing carbon emissions. Loeb suggests that Oumuamua may be evidence of long passed intelligent life that is only now showing up in our solar system.

Clue #7. Odds are that Oumuamua was sent to watch us.

Loeb explains that when one considers the vastness of space and calculates the chance of Oumuamua coming close enough to Earth to see it, the odds are in the billions against it randomly happening. In order for an object like Oumuamua to be seen by Pan-STARRS during its eight year operational life span, Loeb calculated that an advanced alien civilization would have had to launch a similar solar sail every few minutes to reach the abundance required to have one randomly reach us. This led Loeb to follow the maxim of Sherlok Holmes to rule out the impossible and deduce his logic to a reasonable possibility that Oumuamua was sent to our solar system with a purpose. That it may have been aimed at the habitable center of our solar system where life was most likely to be found relative to the sun’s energy.


Loeb submitted his rigorously researched paper to The Astrophysical Journal Letters, the most prestigious journal for rapid communications in astrophysics. They published it in three days, which is remarkable considering that the usual review time is several weeks.

Avi Loeb believes that science should be open to all who seek it and welcomes critical review. He hopes that mistakes can be found or confirmation added to back up his math. The highly credentialed Loeb has authored 700 scientific papers and did not expect his Oumuamua paper to become so popular. Loeb brushed off negative reactions to his daring ET hypothesis with an obvious question; after decades of searching for life using telescopes and satellites, isn’t that what we’ve been asking for?

Loeb’s theory may be confirmed when the much more capable large synoptic survey telescope system comes online in three years and which is expected to find more Oumuamuas.

To hear Dr. Loeb explain his work in his own words, check out this excellent podcast interview.