1) Quick fact-check (most important points)

NASA classifies 3I/ATLAS as an interstellar comet, not an identified spacecraft. Their tracking and imagery show cometary outgassing and a trajectory typical of a hyperbolic interstellar object.
NASA Science

Reputable news agencies agree it poses no threat to Earth. Reuters reports 3I/ATLAS is passing through and will remain far from Earth; it will approach the Sun near the orbit of Mars.
Reuters

High-quality images and telescope data show comet-like behavior (coma, growing tail) — not artificial lights or propulsion. LiveScience and others summarize the observations.
Live Science

Viral videos and posts claiming Musk confirmed aliens appear to originate from unverified/tabloid sources or edited clips. Numerous viral uploads exist on YouTube and social platforms, but I could not find the claim on Elon Musk’s verified accounts or in credible press releases. Treat such clips skeptically.
YouTube
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NASA has publicly responded to sensational claims, reiterating the object is being observed as a comet and urging reliance on scientific analysis.
IFLScience

2) How you can quickly verify claims like this (checklist)

Check the person’s verified account (Elon Musk on X/Twitter, SpaceX official account) — is the quote there? If not, be skeptical.

Check NASA / ESA / major observatory pages for press releases or data (they post on discoveries and hazards).
NASA Science

Look for reporting from established outlets (Reuters, AP, Nature, Science, LiveScience). Viral videos often precede reputable coverage.
Reuters
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Search for fact-checks from dedicated sites or trusted science communicators; social-platform “context” labels sometimes flag manipulated media.

Examine original data if available (Minor Planet Center, NASA image releases, telescope observatory pages).