ʻOumuamua, the Visitor from Another Star
The first object known to arrive from another star system was long, tumbling, and sped up as it left.
What was reported
On 19 October 2017, the Pan-STARRS telescope on Haleakalā spotted a faint object already heading away from the Sun. Its path showed it wasn't bound to the Sun at all: it had come from interstellar space and was passing straight through. It was named ʻOumuamua, a Hawaiian word for a scout or messenger.
It was small and reddish, probably very long and thin or flat, and it tumbled as it went. It also accelerated slightly as it moved away, more than gravity alone could explain, yet showed no visible tail of gas or dust.
Explanations offered
Most astronomers think it's a natural fragment, perhaps an icy body giving off gas too faint to see, such as hydrogen, which would explain the push. The Harvard astronomer Avi Loeb has argued it could be an artificial object, such as a light sail. It's now too far away to observe, so the question can't be settled.
- When
- 19 October 2017
- Where
- Haleakalā, Maui, Hawaiʻi, USA
- Witnesses
- Astronomers at the Pan-STARRS telescope
- Status
- Disputed
Famous cases are real, widely reported events. Each file sets out what witnesses said and the explanations that have been offered, without taking a side.