# ESO observations show first interstellar asteroid is like nothing seen before

##### November 20, 2017, ESO

For the first time ever astronomers have studied an asteroid that has entered the Solar System from interstellar space. Observations from ESO's Very Large Telescope in Chile and other observatories around the world show that this unique object was traveling through space for millions of years before its chance encounter with our star system. It appears to be a dark, reddish, highly-elongated rocky or high-metal-content object. The new results appear in the journal Nature on 20 November 2017.

On Oct. 19, 2017, the Pan-STARRS 1 in Hawai'i picked up a faint point of light moving across the sky. It initially looked like a typical fast-moving small asteroid, but additional observations over the next couple of days allowed its orbit to be computed fairly accurately. The orbit calculations revealed beyond any doubt that this body did not originate from inside the Solar System, like all other asteroids or comets ever observed, but instead had come from . Although originally classified as a comet, observations from ESO and elsewhere revealed no signs of cometary activity after it passed closest to the Sun in September 2017. The was reclassified as an interstellar asteroid and named 1I/2017 U1 ('Oumuamua).

"We had to act quickly," explains team member Olivier Hainaut from ESO in Garching, Germany. "'Oumuamua had already passed its closest point to the Sun and was heading back into interstellar space."

ESO's Very Large Telescope was immediately called into action to measure the object's orbit, brightness and colour more accurately than smaller telescopes could achieve. Speed was vital as 'Oumuamua was rapidly fading as it headed away from the Sun and past the Earth's orbit, on its way out of the Solar System. There were more surprises to come.

Combining the images from the FORS instrument on the VLT using four different filters with those of other large telescopes, the team of astronomers led by Karen Meech (Institute for Astronomy, Hawaii, USA) found that 'Oumuamua varies dramatically in brightness by a factor of ten as it spins on its axis every 7.3 hours.

Karen Meech explains the significance: "This unusually large variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape. We also found that it has a dark red colour, similar to objects in the outer Solar System, and confirmed that it is completely inert, without the faintest hint of dust around it."

These properties suggest that Oumuamua is dense, possibly rocky or with high metal content, lacks significant amounts of water or ice, and that its surface is now dark and reddened due to the effects of irradiation from cosmic rays over millions of years. It is estimated to be at least 400 metres long.

Preliminary orbital calculations suggested that the object had come from the approximate direction of the bright star Vega, in the northern constellation of Lyra. However, even travelling at a breakneck speed of about 95 000 kilometres/hour, it took so long for the interstellar object to make the journey to our Solar System that Vega was not near that position when the asteroid was there about 300 000 years ago. 'Oumuamua may well have been wandering through the Milky Way, unattached to any star , for hundreds of millions of years before its chance encounter with the Solar System.

Astronomers estimate that an interstellar asteroid similar to 'Oumuamua passes through the inner Solar System about once per year, but they are faint and hard to spot so have been missed until now. It is only recently that survey telescopes, such as Pan-STARRS, are powerful enough to have a chance to discover them.

"We are continuing to observe this unique object," concludes Olivier Hainaut, "and we hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy. And now that we have found the first interstellar rock, we are getting ready for the next ones!"

More information: Discovery And Characterization Of The First Known Interstellar Object, www.eso.org/public/archives/re … eso1737/eso1737a.pdf

Karen J. Meech et al. A brief visit from a red and extremely elongated interstellar asteroid, Nature (2017). DOI: 10.1038/nature25020 , www.nature.com/articles/nature25020

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##### rrwillsj
1 / 5 (6) Nov 20, 2017
To whomever writes these clickbait headlines.... You might want to read the article first.

"We also found that it has a dark red colour, similar to objects in the outer Solar System,"
##### kujarvis
1 / 5 (7) Nov 20, 2017
First, the object enters our solar system at an oblique angle at just the right distance form the sun and speed so that it exits in the plane of our solar system while also passing near Earth.
( What is the probability? P1)
Now we find out this object has an unstable length to width ratio not ever seen elsewhere in nature. (P2)
Also this high metal content object is rotating but not breaking up so could be a solid object (P3)
Chances this is a natural object P1 * P2 * P3 = damn small
##### Whys
1 / 5 (1) Nov 20, 2017
Kujarvis, you forgot the part about the high metal content and no debri trail. I wouldn't say "damn small," but this object does seem a little suspicious.
##### antialias_physorg
4.7 / 5 (11) Nov 20, 2017
First, the object enters our solar system at an oblique angle at just the right distance form the sun and speed so that it exits in the plane of our solar system

Any object that enters our solar system will be deflected into its plane. Think about where the masses are and how the force vectors look like all the while it is incoming/outgoing.

also passing near Earth.

If it wasn't passing near Earth we wouldn't have spotted it. Duh.

has an unstable length to width ratio not ever seen elsewhere in nature

"Not seen in nature"? What does that even mean in this context?

Also this high metal content object is rotating but not breaking up

If was prone to breaking up it would have broken up long ago.

Chances this is a natural object P1 * P2 * P3 = damn small

P1, P2, and P3 are completely baseless numbers. OK, if you want to multiply 3 random numbers and find something small, fine. But it really means nothing.
##### rrwillsj
1 / 5 (2) Nov 20, 2017

c
##### kujarvis
1 / 5 (4) Nov 20, 2017
I figured the sun would be by far the greatest mass causing a course change. We have spot objects all over the solar system. "Not seen in natur"e - paraphrasing the title, P1,P2.P3 just pointing out how these improbable events are all happening in one object.
##### Captain Stumpy
4 / 5 (4) Nov 20, 2017
just pointing out how these improbable events are all happening in one object
how are you determining probability?

did you not read A_P's post?
##### javjav
5 / 5 (1) Nov 20, 2017
A pity that we didn't send an impactor. It sounds like a great opportunity to take decent pictures and collect some chunks later. Maybe we should keep a little rocket in orbit, ready to use in special occasions like this one
##### Shootist
4.4 / 5 (8) Nov 20, 2017
They should have named it RAMA.
##### TheGhostofOtto1923
5 / 5 (5) Nov 20, 2017
They should have named it RAMA
My speculation from another thread. Also

"A #2 General Products hull is a cylinder 300 feet (91 m) long and 20 feet (6.1 m) wide, pointed at both ends and with a slight "wasp-waist" constriction near the tail. The Lying Bastard, the landing vessel in which Nessus, Louis Wu, Teela Brown and Speaker-to-Animals crash-land on the Ringworld, is based on a modified #2 hull, specifically designed with most of the flight equipment and thrusters on the outside, to minimise the number of breaks in the hull, allowing a Slaver stasis field to be fitted to the inside of the ship, protecting the occupants from any danger (by freezing them in stasis in the event of attack, for example)."

-gee willikers.
##### TheGhostofOtto1923
5 / 5 (1) Nov 20, 2017
To whomever writes these clickbait headlines.... You might want to read the article first
"Oumuamua is dense, comprised of rock and possibly metals, has no water or ice, and that its surface was reddened due to the effects of irradiation from cosmic rays over long periods of time."

- Most everything old in space is red rwillikers. Even derelict alien spacecraft.
"Not seen in nature"? What does that even mean in this context?
uh this context?

"ESO observations show first interstellar asteroid is like nothing seen before..."
##### koitsu
5 / 5 (1) Nov 20, 2017
##### Shabs42
5 / 5 (5) Nov 20, 2017
To whomever writes these clickbait headlines.... You might want to read the article first.

"We also found that it has a dark red colour, similar to objects in the outer Solar System,"

Not to be too big of a dick, but do you realize that objects have qualities other than color? The shape and composition are the unique aspects.

uh this context?

It's the first interstellar object we've ever seen up close. So whatever it looks like it would have been "not seen in nature" before this. Perhaps there's something about interstellar asteroids that makes this shape more likely, or something about this asteroid's home system. Unless there's something obviously artificial, there's no reason to suspect anything unnatural.

cont'd
##### Shabs42
5 / 5 (4) Nov 20, 2017
cont'd

A similar argument can be made against his P1. Whatever the first interstellar object spotted was, it would satisfy his criteria. We found one close to Earth because we track the area in the vicinity of Earth's orbit a whole lot closer than the rest of the solar system. We'll spot more of these objects as we get more eyes on the sky, then we can get a real data set and see if this is unique in any way.
##### rockart
not rated yet Nov 20, 2017
Its cylindrical shape pretty much rules it out as an object made for instellar travel made by an intelligent ... thing.
##### Whys
not rated yet Nov 20, 2017
What else can we measure? Have we looked for any signals? Have we tried beaming anything to it? Have we shot a laser at it? Poke it!
##### Iceman81
5 / 5 (11) Nov 20, 2017
We didn't "see it up close" The "pictures" are artist impressions.
There's no way we had time to send a probe. It was here and gone in a few days - traveling 38 km/sec, passing 15 million miles from earth. Our best telescopes just saw a tiny spot of light. Scientists used variations in that light along with a Spectrograph to make all of their deductions.
##### jonesdave
3.8 / 5 (10) Nov 20, 2017
We didn't "see it up close" The "pictures" are artist impressions.
There's no way we had time to send a probe. It was here and gone in a few days - traveling 38 km/sec, passing 15 million miles from earth. Our best telescopes just saw a tiny spot of light. Scientists used variations in that light along with a Spectrograph to make all of their deductions.

Yep. Well said that man.
##### AllaBreve
1 / 5 (4) Nov 20, 2017
Asteroids are generally fragments of larger bodies or clumps of smaller bodies. The geometry of this one suggests it is a fragment. But rock fragments produced in quarries would only rarely exceed an aspect ratio of 5 to 1 due to the energy of the blast. 10 to 1 would be a complete freak unless the fragment was very small. and try sticking ten rockysnow balls together. So dynamically this rock is suspicious any way you look at it.
##### TheGhostofOtto1923
3 / 5 (2) Nov 20, 2017
It's bizarre I tell ya... bizarre.
##### Ralph
1 / 5 (1) Nov 20, 2017
A good team of scientists in a sci-fi novel would quickly identify this as an alien spaceship. Too bad we don't live in a sci-fi novel!
##### Mercury3
1 / 5 (1) Nov 21, 2017
There already is a sci-fi novel with exactly this plot: THE ORION PLAN
##### Shabs42
3 / 5 (2) Nov 21, 2017
We didn't "see it up close" The "pictures" are artist impressions.
There's no way we had time to send a probe. It was here and gone in a few days - traveling 38 km/sec, passing 15 million miles from earth. Our best telescopes just saw a tiny spot of light. Scientists used variations in that light along with a Spectrograph to make all of their deductions.

Yes, I realize that's not a real picture (I wish!). Up close was being used as a relative term :)
##### rrwillsj
1 / 5 (2) Nov 21, 2017
AB, thanks for the info. And I have no argument with your knowledge of earthside quarrying processes.

However, the briefly sighted asteroid most probably has only been in zero-gravity for it's existence. And the minerals you quarry were broken up with explosives in a one-gee environment.

I think a better way to visualize what little we know of this wayfarer would be flint.

Consider how a flint nodule is worked. Knapped to produce flakes for blades and arrowheads. That would probably be a better description of what happens when metallic asteroids collide over billions of years.

Now for a wild speculation. What we think we saw may have been the remnant metal core of a larger asteroid. Perhaps after aeons of it's original surface being eroded and abraded away? That might perhaps explain it's shape and lack of gaseous emissions?
##### antialias_physorg
3 / 5 (2) Nov 22, 2017
What we think we saw may have been the remnant metal core of a larger asteroid. Perhaps after aeons of it's original surface being eroded and abraded away?

Seems plausible. Even in the relatively sparse interstellar medium an object hurtling along at a fair clip will have some collisions with dust which eventually will turn it into it's major axis and start abrading away.

The idea of using ice shields for ships to prevent micrometeorite/dust damage during interstellar travel is out there (not just in fiction)...so the issue seems to be real.
##### TheGhostofOtto1923
5 / 5 (1) Nov 22, 2017
Seems plausible. Even in the relatively sparse interstellar medium an object hurtling along at a fair clip will have some collisions with dust which eventually will turn it into it's major axis and start abrading away
What's plausible is doing a little research and finding out its tumbling

"The WIYN observations revealed that the object is elongated in shape and rotates on an axis about once every eight hours. From the perspective of Earth, the object is seen sideways and, as it spins on its axis, end-on, explaining variations in brightness as sunlight is reflected off the comet or asteroid"

-or watching the animations in the article.

Or we could just guess I guess.
##### TheGhostofOtto1923
5 / 5 (1) Nov 22, 2017
And as it turns out most asteroids tumble

"I have reexamined this question in the light of some more recently determined cases of very slow rotation rates and find that for several asteroids, the damping time scale is expected to be considerably longer than the age of the Solar System, implying that these objects may very well exhibit non-principal-axis rotation..."
##### rrwillsj
1 / 5 (2) Nov 22, 2017
Ice shields? Why not feather pillows. Pretty much the same level of protection....

Until the fabric holding it all together rips. Then it's feathers everywhere!

Aside from the sarcasm. When any amount of energy or material collides with an snowball, what is going to hold it together? Perhaps spider-webbing type material?

Perhaps use an iceberg instead? Which would be a nastier surprize? A fracture through the body of the ice? A steam explosion with unpredictable jets of geysers? Wait, doesn't that describe a comet?
##### carbon_unit
1 / 5 (1) Nov 25, 2017
First, the object enters our solar system at an oblique angle at just the right distance form the sun and speed so that it exits in the plane of our solar system

Any object that enters our solar system will be deflected into its plane. Think about where the masses are and how the force vectors look like all the while it is incoming/outgoing.

Given that the speed it's moving at, I'd be surprised if the material in the plane of the solar system deflected it much.
has an unstable length to width ratio not ever seen elsewhere in nature

"Not seen in nature"? What does that even mean in this context?

Looks kinda like a giant joint some aliens tried to pass to us...
##### garyanderson1966
3 / 5 (2) Nov 26, 2017
Could this be a girder from the Dyson sphere around Tammy's Star.
That should get the conspiracy nuts thinking ;)
##### Tuxford
1 / 5 (1) Nov 30, 2017
Asteroids are generally fragments of larger bodies or clumps of smaller bodies. The geometry of this one suggests it is a fragment. But rock fragments produced in quarries would only rarely exceed an aspect ratio of 5 to 1 due to the energy of the blast. 10 to 1 would be a complete freak unless the fragment was very small. and try sticking ten rockysnow balls together. So dynamically this rock is suspicious any way you look at it.

Given the timescales involved, it would seem likely that most interstellar asteroids would soon (relatively) find themselves captured orbiting a larger system. So it would seem highly plausible that given aliens already inhabit the moon (wake up it this is a surprise), that this implausible object is artificial, especially given the interstellar nature. Seems plausible that some unlucky aliens likely got stuck in the interstellar void after their 'warp' drive failed.

If this seems far fetched, then you simply have not been paying attention.
##### Tuxford
1 / 5 (1) Dec 11, 2017
And now SETI seems to agree: It is most likely artificial. But likely long dead, as it is tumbling.

https://www.scien...umuamua/

##### rrwillsj
1 / 5 (1) Dec 11, 2017
I dunno Tf. A "tumbling" whatever? Could be construed as "proving" the ancient Egyptians were right about giant dungbeetles traipsing across the cosmos.
##### Aroryborealis
not rated yet Dec 14, 2017
Our creativity has provided us with magnificent tools of discovery. Hence, facilitating us with an even greater imagination.
Despite all of Science Fiction's manifestations, throughout its entire history as a media genre, is it not pretty cool to be able to say........
"A real interstellar visitor this bizarre? 'DIDN'T SEE THAT COMING!"
How wondrous it is that we can still be taken by absolute surprise.