It would be among the most extraordinary discoveries in scientific history: fragments of an alien spacecraft from another Solar System that landed on Earth.

This week Harvard astrophysicist Professor Avi Loeb said he may have made just such a find after retrieving metallic objects from the seabed where a meteorite crashed into the Pacific Ocean near Papua New Guinea in 2014.

His claim has been met with disbelief from other scientists who have offered alternative yet still extraordinary explanations for the metal spherules.

Remnants of a supernova, a shard of a distant exoplanet struck by a giant meteorite and nuclear weapons testing have all been posited as more likely explanations.

Prof Loeb says analysis of the spherules’ composition proves they came from beyond the Solar System.

However, the former chair of the Harvard Astronomy Department has yet to submit his findings to a journal for peer review.

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