Did an alien spacecraft visit our Solar system in 2017?

Avi Loeb, a Harvard Astronomer, certainly thinks so. He even published a paper with his findings. You can read it here. It’s only 17 pages long and lists the half dozen anomalies Avi believes could be attributed to artificial origin.

First though, let’s familiarise ourselves with the details.

The first interstellar object ever detected in our Solar system

On the 19th of October 2017, Oumuamua (Hawaiian word for Scout) is first observed. At the time it’s around 21 million miles away from Earth and heading away away from the Sun. Considered a small object, rough estimates measure it somewhere it between 300 – 3000 feet (100 – 1000 metres) long with a width ranging between 115 – 548 feet (35 – 167 metres). Oumuamua, studied through analysis of its light curve, is thought to have a red hue and be featureless. However, because of large variations in the curve, the actual shape of Oumuamua has been suggested to be anything from a cigar shape to an extremely flat pancake.

What about actual pictures? Unfortunately, because of the relatively small size of Oumuamua, it only shows as a single pixel in actual pictures. It’s just too small and too far away to get a good photo of.

Oumuamua was the first interstellar object ever detected passing through our Solar system. Unfortunately, by the time we detected it in October of 2017, it was already heading away from us. Based on its current speed and trajectory, it will eventually leave the Solar system and head back out to interstellar space.

At its closest, Oumuamua was just 23,700,000 million miles (38 million km) from the Sun. For perspective, Mercury at its closest approach to the Sun is around 29 million miles (47 million km) away.

So far, a cool discovery but pretty uneventful. Here’s where it get interesting. Let’s talk about the anomalies that set Oumuamua apart and led Avi Loeb to publish his paper positing that an alien spacecraft visited our Solar system.

Initial Anomalies

At first it was assumed that Oumuamua was a comet. Comets reside in the Oort Cloud at the very edge of our Solar system and are flung away by the perturbations of a passing star. Further study showed that Oumuamua had no cometary tail and had not inherited the motion of its parent star. In fact, the motion of Oumuamua was found to be highly unusual for a natural object originating from a nearby star.

These observations led Avi to the conclusion that Oumuamua could be artificial. He also posited that its motion might also be artificial, tailored to obscure the star system it originated from.

Stay with me. It gets even stranger.

Remember before when we spoke about the light curve? Oumuamua tumbles every eight hours with the brightness of sunlight reflected from it changing by a factor of ten. This implies Oumuamua has an extreme shape, with it being at least ten times longer than it is wide. The very best fit (90% surety) for this light curve is one of a flattened pancake, or disk-like shape rather than the cigar shaped oblong as portrayed in the media (and above in the artists impression).

The lack of heat from Oumuamua, detectable in infrared, placed an upper size limit of 200m according to Avi Loeb’s paper. However, when it had passed the Sun, Oumuamua exhibited a “push” away from the Sun which, if Oumuamua was a comet, would have caused it to lose around 10 percent of its mass and produce a tail. Neither of which happened. Additionally, the push was smooth, producing no spins or kicks in the objects trajectory and showing no stopping beyond the point where we expect evaporation of water-ice by the heating of sunlight to stop. Basically, it did everything we would not expect from a natural comet.

In September 2020, another object was discovered by the same array that found Oumuamua. This object also displayed all the same properties of no outgassing and excess push away from the Sun. It turned out to be a thin shell from a rocket booster used in a 1966 Nasa mission. Adding further weight to the idea that Oumuamua was not of natural origin or at least not made of material we are familiar with.

Alien Solar Sails?

The idea of using solar sails to push spacecraft along has been around for several decades. In fact, in 2010 the idea became science fact with the launch of IKAROS. The best analogy for solar sails is ships here on Earth. Rather than using wind to push the craft along, they use radiation pressure from stars to push themselves along.

Sufficiently advanced sails would allow a spacecraft to travel huge distances without the need for traditional propellants. Meaning the craft would be cheap to run and have less chance of breaking, due to the relatively small number of moving parts.

With all this in mind, the idea of Oumuamua being an alien craft visiting our solar system from elsewhere is a compelling one. Even if more study is needed.

If it’s not an alien spacecraft, what else could it be? A couple of compelling theories have been proposed.

Nitrogen ice theory: States that Oumuamua could be part of a dwarf planet from beyond our solar system. If composed of nitrogen ice, it would reflect two thirds of the Suns light, giving it the required push needed. Avi Loeb himself has criticised this theory.

Hydrogen Ice Theory: It has also been suggested that Oumuamua could contain a large amount of hydrogen ice. The object would have to have originated from an interstellar molecular cloud for this to be correct. The heat from the Sun would cause the hydrogen to sublimate (change from a solid to a gas, skipping the liquid state) and propel the object. This would be a difficult process to detect from Earth based telescopes, which would explain the lack of outgassing.

To try to find out once and for all what Oumuamua and other possibly similar interstellar objects found since (such as 2l/Borisov) are, there are currently two different approaches being taken.

Avi Loeb and colleagues at Harvard have created the Galileo Project, the goal of which is:

“to bring the search for extraterrestrial technological signatures of Extraterrestrial Technological Civilizations (ETCs) from accidental or anecdotal observations and legends to the mainstream of transparent, validated and systematic scientific research. This project is complementary to traditional SETI, in that it searches for physical objects, and not electromagnetic signals, associated with extraterrestrial technological equipment.”

The above text is taken direct from the Project details page. Additionally, there is also Project Lyra.

Project Lyra is a feasibility study to see if we could launch spacecraft to catch up to Oumuamua and 2l/Borisov within a reasonable time period. One of the options to catch them is, yep you guessed it, a solar sail. The craft would have to use Jupiter for a gravitational assist if we are to have any hope of getting to it within 5 to 10 years.

It is certainly exciting times in the age of space discovery. Let’s hope we set out after Oumuamua soon. After all, if we want to answer the question of whether an alien spacecraft visited our solar system or not, now seems like the best chance we have ever had. Even if it turns out to be a natural object, we could learn so much from it.