The sale of an extremely rare Mars rock has been slammed by a renowned paleontologist.

A massive 24-kilogram meteorite, the largest known fragment from Mars on Earth, was purchased for $US5.3 million ($8.1 million) by an anonymous buyer in New York last month.

Known as NWA 16788, the meteorite is massive compared with most Martian meteorites, which tend to be small fragments.

The government of Niger also expressed concern about how the artefact got into the hands of Sotheby’s, the famous auction house where it was sold.

In a statement on X, it “expressed doubts about the legality of its export, raising concerns about possible illicit international trafficking”.

“For everything we sell, we ensure that all necessary documentation is properly arranged at every stage of the process, following best practices and matching the involved countries’ requirements,” Sotheby’s stated.

Nonetheless, they admitted to having noted concerns expressed by the Nigerien government and other parties, stating, “We are re-evaluating the information we have in light of the raised concerns.”

Concerns have also been raised that the meteorite will not be able to be used for educational purposes if it ends up in private hands.

“It would be unfortunate if it ended up locked away by a wealthy individual. It belongs in a museum, where it can be studied and appreciated by children, families, and the general public,” stated Steve Brusatte, a paleontology and evolution professor at the University of Edinburgh in Scotland, speaking to CNN prior to the sale.