Not just outer space, but outer-outer space, beyond the solar system, maybe from Vega. It is the object named Oumuamua, which famously passed by the Sun and through the solar system along an orbit inclined at a very steep angle to the ecliptic. Now a pair of Harvard astronomers has suggested that it may have been flat, or pancake-shaped, and have inferred that it might be a solar sail or other part of a spacecraft from a distant star system.
Specifically, as reported in Haaretz, Harvard astronomer Avi Loeb and postdoc Shmuel Bialy drew this inference on the basis of several anomalies. First, the reflectance of the object varied greatly with time, a phenomenon that is observed if the object is rotating and irregular. The variation of the reflectance was several times more than that of any asteroid, which suggests that it might be very long and narrow, or perhaps flat and thin.
Additionally, Oumuamua appeared to undergo some acceleration beyond that provided by the force of the Sun’s gravity. Comets similarly undergo acceleration owing to the reaction forces caused by gases evaporating from their surfaces; these gases generally form the tail of the comet. The evolution of these gases also causes the rotation rate of a comet to vary, whereas Oumuamua, which did not display a tail, rotated at a constant rate, so it is probably not an icy comet. Radiation pressure from the sun could have brought about the observed acceleration only if the object was flat and thin, consistently with the variation of the reflectance.
Finally, and somewhat technically, Oumuamua is approximately stationary with respect to the average velocity of stars in the region, which strikes the astronomers as peculiar.
Professor Loeb and Dr. Bialy speculated on the basis of this evidence that the object might be artificial and indeed similar to a light sail. That is, they speculate that it could be part of an interstellar space probe or perhaps just a piece of space junk from another star system.
They published an article in The Astrophysical Journal Letters. I have read the abstract, but unfortunately not the article, for 2 reasons: First, I speculate that the cost of purchasing a single article will be outrageously high (a speculation at least as well-founded as the speculation that Oumuamua is all or part of an artificial spacecraft). Unfortunately, and additionally, the journal’s document delivery service has been temporarily suspended and is expected to resume early in 2019; consequently, I cannot right now test my hypothesis.
Amusingly, Prof. Loeb told The Harvard Gazette,
... there was nothing else I could think of which could account for our observations, because this object is weird. So, my approach was to follow the maxim of Sherlock Homes [sic] — ‘When you have excluded the impossible, whatever remains, however improbable, must be the truth.’”
I cannot think of anything else either, and I would not automatically rule this explanation out, but I confess that I looked up the quotation (which more properly should have been “eliminated the impossible”) and found that it is sometimes called the Holmesian fallacy. It is a fallacy because it assumes incorrectly that you know all the impossibilities. I will not rule out an alien spacecraft, because it does not seem impossible, but I will be unsurprised if someone develops a more naturalistic explanation.