Mysterious interstellar object is spinning out of control

There is so much we don’t know about how the universe works.

Sometimes examples come along that remind us just how much. Such as ‘Oumuamua.

Given the Hawaiian name for ‘pathfinder’ or ‘scout’, it was first detected in September.

The PanSTARRS1 telescope found a new pinprick of light crossing our skies. It was coming from a strange direction. It was moving unusually fast.

All of which was tracked back to an interstellar origin — beyond our own Solar System.

At first it was dubbed Comet C/2017 U1. But it proved not to be a comet. So it was named ‘Oumuamua.

Now astronomers have figured out something about its origins, its incredibly long journey and its makeup.

The latest revelation is that it is spinning chaotically out of control.

And it is destined to do so for at least another billion years.


“At some point or another it’s been in a collision,” Queen’s University astronomer Dr Wes Fraser told the BBC’s Sky At Night show after his research was published in Nature Astronomy.

In the vastness of space between the planets — yet alone the interstellar distances between stars — the odds for this are incredible. But it may be what propelled it our way in the first place.

The British based researchers have been breaking down the light patterns being bounced off the unusually dull object.

It’s previously been established as being some 200m long. At eight times longer than it is wide, it is roughly the shape of a crumpled cigar.

It was initially thought to be spinning once every seven or eight hours. But the math didn’t add up.

The variations in the dull reddish light reflected off this distant object’s surface can reveal how it’s moving. Turns out, it isn’t moving in a regular pattern.

It’s not spinning serenely along its axis like most known asteroids.

It’s tumbling chaotically.

And it has probably been doing so for hundreds of millions of years.

“The tumbling actually causes stresses and strains internal to the object, and that slowly but surely squeezes and pulls on the object just like tides on the Earth to remove energy from the spin,” Dr Fraser says.

This torque has reshaped the object over the millennia. It will eventually soak up all of the energy of the spin, causing it to glide gently through space.

But that will take another billion or so years.

This in itself indicates ‘Oumuamua is quite solid. A lump of rock or metal. Otherwise it would have fragmented, or soaked up its spin long before now.

So what caused the spin?

“It’s hard to know if it was during planet formation or after the planet formation process,” he says. “Certainly, more collisions happen while planets are growing than afterwards, so that’s a very good guess. But unfortunately we can’t get a high-resolution image of this thing to see what kind of crater is on it that might be attributed to the collision that caused it to start tumbling.”

Interstellar winds. Heat radiation. Close encounters with planets. All could have contributed to its wildly gyrating, near-eternal dance.


It has sparked something of a revolution for astronomy.

It’s the fist known object to enter our Solar System from deep space.

Though the truth is there are more than likely thousands of similar interstellar asteroids captured by the gravitational pull of our Sun. It’s just that we didn’t see them arrive.

It’s estimated at least one turns up every year.

Potentially, they offer a unique sample of the mechanics of star and planetary formation across our galaxy.

But Astronomers are as yet uncertain as to what ‘Oumuamua actually is.

It looks like a rocky asteroid. It certainly didn’t flare up like a comet does when it passed very close by the Sun (37 million kilometres) last year.

But it also appears to be thickly coated by organic-carbon substances — probably generated by its long term exposure to raw interstellar radiation in the void between the stars. This could be insulating an icy core.

It’s also being seen as potential evidence for the theory of lithopanspermia — the transfer of microbial life between planets and stars through comets and asteroids. Such an object — crashing into our surface as a meteor — could have seeded the building blocks for life on Earth.

We haven’t sampled such an interstellar visitor, yet.

So it remains just an enticing idea.

‘Oumuamua itself isn’t going to hang around long. At its current speed, it will pass Jupiter in May and Saturn early next year.

It won’t be long until it has left our Solar System behind.

Meanwhile, astronomers are racing to find the next interstellar visitor. Or identify ones that have been snared by the Sun’s gravitational pull.

This involves backtracking orbits. Watching the skies in generally ignored directions. Analyzing the spectroscopy of known objects for variations in oxygen isotope ratios that indicate they are not made of the same stuff as the rest of our Solar System.


The Search for Extra Terrestrial Life’s (SETI’s) Matija Cuk does not know. Though he does have a favorite idea.
“My own favorite hypothesis is that ‘Oumuamua is a piece of a planet destroyed by tides as it was passing close to a red dwarf star in a binary system,” he writes.

“The idea is that the planet formed around the red dwarf’s companion, but its orbit was destabilized and the planet swung past the red dwarf, about to be hurled into interstellar space.”

“Red dwarf stars can be surprisingly dense, some of them are the size of Jupiter, but with a hundred times larger mass. This makes their tides very strong, and tides can disrupt bodies that come too close (like Jupiter disrupted comet Shoemaker-Levy 9 in 1994).

“If a planet can be shredded into trillions of fragments which are then ejected into interstellar space, such catastrophic events could produce more interstellar objects than regular ejections of comets and asteroids by planets.”

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