Last week, Harvard University scientists published a paper suggesting that the interstellar object might be of foreign origin.
They also discussed the possibility that the asteroid would be "a fully operational probe sent intentionally in the vicinity of the Earth by an alien civilization."
Oumuamua approached Earth in September 2017.
It was seen in October of the same year that she began to leave.
But in November, when NASA used its Spitzer Space Telescope, focused on where it expected to find the alien object, it was not found somewhere.
David Trilling, the lead author of a new study detailing these observations and an astronomy professor at Northern Arizona University, said: "Oumuamua was full of surprises from the first day, so we were eager to see what it might look like Spitzer.
"The fact that Oumuamua was too small to detect Spitzer is actually a very valuable result."
What is more confusing is that Oumuamua has accelerated much faster than our Sun than could only be explained by gravity.
But there is a more natural, less exotic theory about what is alien life.
Davide Farnocchia of the NASA Jet Propulsion Laboratory said the subtle extra force on Oumuamua is probably caused by "jets of gaseous material expelled from its surface."
He added: "The same type of expulsion affects the movement of many comets in our solar system."
The object, which is the same size as the Empire State building in New York, caused a frenzy of interest last year when it was first seen.
The alien object triggered conspiracy theories after astronomers saw it through a powerful telescope in Hawaii on October 19 last year.
Due to its trajectory and speed, they thought it came from outside the galaxy because it was not related to the gravity of the Sun.
By making blister speeds of 30 km per second, the object was at a stage of 33,000,000 km of Earth.
Oumuamua comes from Hawaiian oumuamu, which means "scout".