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5 things we know – and 5 we don’t – about ‘Oumuamua

Mysterious ‘Oumuamua is the 1st confirmed interstellar object to pass through our solar system.

By Phil Davis/NASA Science

1. We know it’s not from around here.

The object known as 1I/2017 U1 (and nicknamed ‘Oumuamua) was traveling too fast (196,000 miles per hour, that’s 54 miles per second or 87.3 kilometers per second) to have originated in our solar system. Comets and asteroids from within our solar system move at a slower speed, typically an average of 12 miles per second (19 km per second) . In non-technical terms, ‘Oumuamua is an interstellar vagabond.

Artist’s concept of the interstellar object ‘Oumuamua. Image via ESA/Hubble, NASA, ESO, M. Kornmesser.

2. We’re not sure where it came from.

‘Oumuamua entered our solar system from the rough direction of the constellation Lyra, but it’s impossible to tell where it originally came from. Thousands of years ago, when ‘Oumuamua started to wander from its parent planetary system, the stars were in a different position so it’s impossible to pinpoint its point of origin. It could have been wandering the galaxy for billions of years.

3. We know it’s out of here.

‘Oumuamua is headed back out of our solar system and won’t be coming back. It’s rapidly headed in the direction of the constellation Pegasus and will cross the orbit of Neptune in about four years and cover one light year’s distance in about 11,000 years.

4. We don’t really know what it looks like.

We’ve only seen it as a speck of light through a telescope (it is far away and less than half a mile in length), but its unique rotation leads us to believe that it’s elongated like a cigar, about 10 times longer than it is wide. We can’t see it anymore. Artist’s concepts are the best guesses at what it might look like.

5. We know it got a little speed boost.

A rapid response observing campaign allowed us to watch as ‘Oumuamua got an unexpected boost in speed. The acceleration slightly changed its course from earlier predictions. Davide Farnocchia, of the Center for Near Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory, said:

This additional subtle force on ‘Oumuamua likely is caused by jets of gaseous material expelled from its surface. This same kind of outgassing affects the motion of many comets in our solar system.

6. We know it’s tumbling.

Unusual variations in the comet’s brightness suggest it is rotating on more than one axis.

This illustration shows ‘Oumuamua racing toward the outskirts of our solar system. As the complex rotation of the object makes it difficult to determine the exact shape, there are many models of what it could look like. Image via NASA/ESA/STScI.

7. We don’t know what it’s made of.

Comets in our solar system kick off lots of dust and gas when they get close to the sun, but ‘Oumuamua did not, which led observers to consider defining it as an asteroid.

Karen Meech, an astronomer at the University of Hawaii’s Institute of Astronomy, said small dust grains, present on the surface of most comets, may have eroded away during ‘Oumuamua’s long journey through interstellar space. She said:

The more we study ‘Oumuamua, the more exciting it gets.

It could be giving off gases that are harder to see than dust, but it’s impossible to know at this point.

8. We knew to expect it.

Just not when. The discovery of an interstellar object has been anticipated for decades. The space between the stars probably has billions and billions of asteroids and comets roaming around independently. Scientists understood that, inevitably, some of these small bodies would enter our own solar system. This interstellar visit by ‘Oumuamua reinforces our models of how planetary systems form.

9. We don’t know what it’s doing now.

After January 2018, ‘Oumuamua was no longer visible to telescopes, even in space. But scientists continue to analyze the data gathered during the international observing campaign and crack open more mysteries about this unique interstellar visitor.

10. We know there’s a good chance we’ll see another one … eventually.

Because ‘Oumuamua is the first interstellar object ever observed in our solar system, researchers caution that it’s difficult to draw general conclusions about this newly-discovered class of celestial bodies. Observations point to the possibility that other star systems regularly eject small comet-like objects and there should be more of them drifting among the stars. Future ground- and space-based surveys could detect more of these interstellar vagabonds, providing a larger sample for scientists to analyze. Meech said:

I can hardly wait for the next interstellar object!

Bottom line: What science knows and doesn’t know about ‘Oumuamua, the first confirmed interstellar object to pass through our solar system.

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