Harvard astronomer Avi Loeb has had a busy start to 2019. After publishing a paper last year that suggested an alien ship recently flew around our Sun, Loeb has had a whole lot of explaining to do, but as The Washington Post reports, he’s taking criticism from the scientific community in stride.

Loeb isn’t the only person that thinks what he thinks, but he’s easily the most high-profile scientific mind to come out in favor of an alien visitation theory in quite some time, and he thinks he might have the data to prove his point.

In late 2017 something sped through our Solar System that wasn’t supposed to be here. The strange cigar-shaped body called Oumuamua is thought to be the first interstellar object ever observed by mankind, but beyond a handful of educated guesses about what it might be, we know little else.

In November 2018 a research paper by Loeb and fellow astronomer Shmuel Bialy provided a number of possible explanations for what the object was. One of the possibilities, the scientists said, was that it was an alien spacecraft, or maybe just part of a larger alien ship that broke free somewhere far away.

This theory is completely at odds with what others in the field believe, which is that Oumuamua is really just an oblong chunk of rock or ice. They have not been particularly kind to Loeb’s paper, calling it sensationalist and false, but that hasn’t really damped his spirits.

“Many people expected once there would be this publicity, I would back down,” Loeb told The Post. “If someone shows me evidence to the contrary, I will immediately back down.”

That lack of evidence is part of the problem with much of the research efforts focused on Oumuamua. Scientists went back and forth for months in an effort to decide whether the object was an asteroid, a comet, or something entirely new, and there’s been little consensus. Its strange shape and the fact that it’s rapidly spinning as it now makes its way out of our Solar System have led to more questions than answers, and it’s not a stretch to say we might never know exactly what it was.