ʻOumuamua
Interstellar object · First visitor from another star
ʻOumuamua was the first object ever seen that came from outside our Solar System. It was oddly long and thin, tumbled as it flew, and sped up slightly as it left – without showing a visible tail.
- 2017Discovered
- A few hundred metres longSize
- ~26 km/sArrived at
Take a closer look
A race against time
ʻOumuamua was only spotted after it had already passed the Sun and was speeding away. Astronomers around the world rushed to point their biggest telescopes at it, but they had only a few weeks before it grew too faint to see. Everything we know comes from that short chase.
A shape from flickers
No telescope could see ʻOumuamua as more than a dot of light. But that dot grew much brighter and dimmer every few hours as the object tumbled. That told scientists it was very stretched – either long like a cigar or flat like a pancake, and slightly reddish in colour.
Coming from Vega’s way
ʻOumuamua arrived from the direction of Vega, a bright star in the constellation Lyra. But it didn’t come from Vega itself: when ʻOumuamua was passing that part of the sky long ago, Vega wasn’t there yet. Its true home star is still a mystery.
How we found out
- 2017
On 19 October, Robert Weryk spots it with the Pan-STARRS telescope in Hawaiʻi – after it had already swung past the Sun.
- 2017
It is named ʻOumuamua, Hawaiian for “a messenger from afar arriving first”.
- 2018
Measurements show it was gently pushed as it left, like a comet – but no gas or dust could be seen.
- 2023
One study suggests hydrogen gas escaping from its ice could explain the push.
Was ʻOumuamua an alien spaceship?
Some people wondered! But almost all scientists think it was a natural fragment of ice or rock. In science, extraordinary claims need extraordinary evidence.
See it yourself
Gone for good – it is now far too faint for any telescope, and leaving the Solar System forever.
From the encyclopedia
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