A year later, the debate about 'Oumuamua intensified when one of the world's foremost astronomers, Avi Loeb, submitted a paper to the Astrophysical Journal Letters. In it, Loeb and his colleague, Shmuel Bailey, argued that 'Oumuamua's strange properties indicated that it was "a new class of thin interstellar material, either produced naturally, through a yet unknown process […] or of an artificial origin". Since then, Loeb has maintained that the most rational, conservative explanation is that 'Oumuamua was produced by an alien civilisation.