'Oumuamua, the first interstellar visitor
The first object ever seen passing through the Solar System from another star, a puzzling, elongated body with no visible tail.
Key facts
- Designation
- 1I/ʻOumuamua
- Type
- Interstellar object
- Orbital period
- none: it is on a one-way, hyperbolic path
- Closest to the Sun
- 0.26 AU (about 38 million km), on 9 September 2017
- Farthest from the Sun
- none; it is leaving for good
- Tilt of orbit
- about 123°
- Nucleus
- roughly 100 to 400 m long, probably elongated or flat
- Discovered
- by Robert Weryk with the Pan-STARRS1 telescope in Hawaii on 19 October 2017
- Returns
- never: it is heading out of the Solar System
Orbit
'Oumuamua was moving too fast to be held by the Sun's gravity. Far from the Sun it travels at about 26 km/s relative to the Sun, and its path is a hyperbola, open at both ends. It passed the Sun in September 2017, swept past Earth at about 24 million km in October, and is now leaving towards the constellation Pegasus.
Size and nature
It was found only after it had passed both the Sun and Earth, and it was never more than a point of light. Its brightness changed greatly every few hours as it tumbled, showing that it is very elongated or flattened, perhaps several times longer than it is wide. It showed no coma or tail, yet careful tracking found a small extra push away from the Sun, like a comet's gas jets. Explanations include gas that telescopes could not see, such as hydrogen or nitrogen. It is reddish, like many icy bodies in the outer Solar System.
History
Robert Weryk found it in images from the Pan-STARRS1 telescope on Haleakalā, built to look for near-Earth asteroids. At first it was listed as a comet, then as an asteroid, and finally as the first of a new class: interstellar objects, given the letter I. Its Hawaiian name means roughly 'a messenger from afar arriving first'.
Why it matters
It proved that pieces of other planetary systems pass through ours. Some interstellar dust may reach Earth too, but no meteorite has been shown to come from another star.
Space missions
- Comet Interceptor A mission that will wait in space for a pristine comet, then split into three to meet it.
Key dates
| Date | What happened |
|---|---|
| 9 September 2017 | 'Oumuamua, the first known interstellar object, passed closest to the Sun. |
| 19 October 2017 | Robert Weryk discovered 'Oumuamua in Pan-STARRS images. |
Did you know?
'Oumuamua had probably been travelling between the stars for hundreds of millions of years.
It was spotted only 40 days after it passed the Sun, too late for any spacecraft to chase.
Comet Interceptor is designed to wait in space so it can reach a future visitor like it.