Humans have always wondered whether or not Earth has been visited by aliens at least once in its history. But, a Harvard professor said humans have already been visited by extraterrestrial objects as late as 2017.

Theoretical physicist Avi Loeb presented his theory on the peculiarly-shaped object that recently entered our solar system. He discusses his hypothesis about this unknown object in his book entitled “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth.”

The “Oumuamua” interstellar object was first seen in 2017 in Hawaii’s Haleakala Observatory by the Pan-STARRS telescope. The researchers discovered that the object came from the direction of Vega, one of the stars in the Lyra constellation. The object traveled roughly 25 light-years to reach Earth and passed across the ecliptic plane on September 6.

Oumuamua, “scout” in Hawaiian, sped up three days after the researchers first spotted it. By October 7, it finally passed Earth and quickly moved towards the constellation Pegasus and the darkness beyond.

Loeb, the team leader of the astronomy department at Harvard University, insists that the idea that Oumuamua is the first interstellar object discovered in our solar system. He denies that the object is another comet, as the idea is too bound to the “familiar.” In a New York Post interview, the head of the department was asked what he thought would happen when a caveman saw a phone. He says that since rocks surrounded the caveman, he would think that the phone was just another shiny rock.

Loeb says that two facts support the Oumuamua being an advanced extraterrestrial technology instead of a comet. One, the object measured five to ten times longer than it was wide. This cigar-like form is highly unnatural for space objects. Two, the movement of the object was unexpected. He claims that the Oumuamua was excessively pushed away from the sun.

More on the second fact, the sun’s gravitational pull should have made Oumuamua travel quicker as it got closer and slower as the sun flung it away from it. However, this did not happen to the object. Loeb noted that despite accelerating by only a little, it was still a statistically significant amount.

So, are we alone? Has an extraterrestrial civilization passed by our world in 2017? What if it even left something here for us when it did?