We could be the last humans to ever see the green comet hurtling past Earth from the outer reaches of the solar system in late January and early February.

C/2022 E3 (ZTF), or Comet ZTF for short — the name astronomers gave this space snowball after the Zwicky Transient Facility discovered it in March — hasn’t been in our cosmic neighborhood since the last Ice Age.

Researchers calculated that the icy ball of gas, dust, and rock orbits the sun roughly ever 50,000 years, which means that Neanderthals were still walking the Earth and humans had just migrated out of Africa for the first time when the comet last whizzed by.

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With no telescopes or binoculars, those ancient peoples may not have spotted the comet at all. And there may never be an opportunity to see it again.

Read more: Business Insider