'Oumuamua

The claim

"The first interstellar object was cigar-shaped and sped up, like an alien light sail."

Where the idea comes from

Harvard's Avi Loeb and Shmuel Bialy suggested in 2018 it could be an artificial light sail.

What the evidence shows

1. It was small (a few hundred metres at most), tumbling, reddish and showed a slight acceleration away from the Sun that gravity alone didn't explain.
2. Comets accelerate this way when ices turn to gas, but no coma or tail was seen.
3. A 2023 study in Nature showed that molecular hydrogen trapped in water ice, released as sunlight warmed it, could produce exactly that push without a visible coma.
4. Its shape is uncertain: light-curve models allow a long cigar or a flat pancake.

What is still open

It is gone, so the explanation can't be confirmed directly. The Vera Rubin Observatory should find many more such visitors.

Our verdict

Explained Strange, but a natural icy body explains it.

Sources

• Oumuamua (NASA)
• Oumuamua (Wikipedia)

Checked 31 October 2026. Spotted a newer source? Tell us.