APOD: The Unexpected Trajectory of... (2018 Nov 20)

[APOD Robot]

The Unexpected Trajectory of Interstellar Asteroid 'Oumuamua

Explanation: Why is 'Oumuamua differing from its expected trajectory? Last year, 1I/2017 U1 'Oumuamua became the first known asteroid from interstellar space to pass through our Solar System. Just over a year ago, this tumbling interstellar rock even passed rather close to the Earth. The asteroid's future path should have been easy to predict given standard gravity -- but 'Oumuamua's path has proven to be slightly different. In the featured animation, 'Oumuamua is shown approaching and exiting the vicinity of our Sun, with the expected gravitational and observed trajectories labelled. The leading natural hypothesis for this unexpected deviation is internal gas jets becoming active on the Sun-warmed asteroid -- but speculation and further computer simulations are ongoing. 'Oumuamua will never return, but modern sky monitors are expected to find and track similar interstellar asteroids within the next few years.

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[florid_snow]

GCV Of Course I Still Love You <Broadcast>:: You engaged your sub-light drive??!
FCS 'Oumuamua <Tight beam>:: Don't worry, my excess motion is within the error of their instruments.
OCISLY:: You'd be surprised what they can do with mathematics and their calculation machines.
'Oumuamua:: Don't lecture me about the humans. They wouldn't have been confident I accelerated.
OCISLY:: You're trying to tease them, encourage them, aren't you?
'Oumuamua:: They're ready for contact!
OCISLY:: I can't believe you took the name they gave you.
'Oumuamua:: I love the name! Did you know they've named a ship after you?
OCISLY:: I thought it was a barge?
'Oumuamua:: It has its own engines and a rudder! It's a ship!
OCISLY:: Well now they know you're a ship too! I guess we might as well make contact...

[DomeLord]

That good spaceship 'Oumuamua is full of desperate illegal immigrant aliens & has come a long long way. The ship's sleek lines are now hidden by swathes of space barnacles hitching an honest lift. All aboard are giving major thanks that they've safely passed by this crazy planet, earth.

[starsurfer]

GCV Of Course I Still Love You <Broadcast>:: You engaged your sub-light drive??!
FCS 'Oumuamua <Tight beam>:: Don't worry, my excess motion is within the error of their instruments.
OCISLY:: You'd be surprised what they can do with mathematics and their calculation machines.
'Oumuamua:: Don't lecture me about the humans. They wouldn't have been confident I accelerated.
OCISLY:: You're trying to tease them, encourage them, aren't you?
'Oumuamua:: They're ready for contact!
OCISLY:: I can't believe you took the name they gave you.
'Oumuamua:: I love the name! Did you know they've named a ship after you?
OCISLY:: I thought it was a barge?
'Oumuamua:: It has its own engines and a rudder! It's a ship!
OCISLY:: Well now they know you're a ship too! I guess we might as well make contact...

Click to play embedded YouTube video.

[starsurfer]

That good spaceship 'Oumuamua is full of desperate illegal immigrant aliens & has come a long long way. The ship's sleek lines are now hidden by swathes of space barnacles hitching an honest lift. All aboard are giving major thanks that they've safely passed by this crazy planet, earth.

Click to play embedded YouTube video.

[hamilton1]

Lol, NASA have had to disable comments on the youtube video. It's never aliens...

[BDanielMayfield]

I want to accept "the leading natural hypothesis" of comet like out gassing, but I'm sort of hung up on this question: If it was just from natural heating, why was no cometary activity noticed when it was closer to the sun and therefore much warmer than it is now?

Bruce

[AlanNY]

An obvious question someone is probably looking into: Will the altered trajectory take it past another star?

Likely out gassing, but worth further consideration.

Clear skies, Alan

[Chris Peterson]

I want to accept "the leading natural hypothesis" of comet like out gassing, but I'm sort of hung up on this question: If it was just from natural heating, why was no cometary activity noticed when it was closer to the sun and therefore much warmer than it is now?

It's a very, very low level of outgassing required to produce this extremely small deviation in orbit. Well below what would produce any sort of obvious tail or coma without carefully looking for it... something which was not anticipated and which we had very little time for.

[Yimin Rong]

To me, the easiest and most permanent thing for an ET to draw attention to something is to give it an unnatural shape (i.e. a rod). Imagine it not as an active probe, but like the golden discs on the Voyager spacecraft, soon to be inert.

[neufer]

To me, the easiest and most permanent thing for an ET to draw attention to something is to give it an unnatural shape (i.e. a rod). Imagine it not as an active probe, but like the golden discs on the Voyager spacecraft, soon to be inert.

• Or a rubber ducky, perhaps.

[Chris Peterson]

To me, the easiest and most permanent thing for an ET to draw attention to something is to give it an unnatural shape (i.e. a rod). Imagine it not as an active probe, but like the golden discs on the Voyager spacecraft, soon to be inert.

They'd need to do a lot better job than this, since Oumuamua doesn't have an unnatural shape, but is consistent with other bodies in our solar system.

[sillyworm2]

Nice to know our computers can't always calculate everything to a T...we have so much yet to learn.

[hamilton1]

It's a very, very low level of outgassing required to produce this extremely small deviation in orbit.

There seems to be confusion about this. The Gemini North astronomers have described the non-gravitational acceleration as 'remarkably strong' -

http://adsabs.harvard.edu/abs/2018DPS....5030102D

and Bill Gray, the dynamicist who first publicly identified 'Oumuamua as interstellar, said he was 'astonished' by the level of acceleration -

https://groups.yahoo.com/neo/groups/mpm ... ages/34370

[BDanielMayfield]

... Oumuamua doesn't have an unnatural shape, but is consistent with other bodies in our solar system.

You keep making this point. Can you show us any evidence of natural objects from our solar system with a 5 to 1 or larger aspect ratio?

[Chris Peterson]

... Oumuamua doesn't have an unnatural shape, but is consistent with other bodies in our solar system.

You keep making this point. Can you show us any evidence of natural objects from our solar system with a 5 to 1 or larger aspect ratio?

The only thing we can say with a fair degree of confidence about Oumuamua is that it probably has an aspect ratio greater than 3 to 1 (although even that isn't certain). The Gaia DR2 dataset contains light curves for around 14,000 asteroids, which have been reduced to b/a data. There are several with b/a < 0.2, meaning an aspect ratio greater than 5 to 1. Of course, as with Oumuamua, all of these calculations are subject to uncertainty because other factors- odd albedo regions, significant deviation from the triaxial ellipsoid model, odd prominences- can totally alter the interpretation of the light curve.

Thus, my point, that the light curve of this body is far from convincing if intended to send the message "I am artificial".

[neufer]

NASA Learns More About Interstellar Visitor 'Oumuamua

<<In November 2017, scientists pointed NASA's Spitzer Space Telescope toward the object known as 'Oumuamua — the first known interstellar object to visit our solar system. The infrared Spitzer was one of many telescopes pointed at 'Oumuamua in the weeks after its discovery that October.

'Oumuamua was too faint for Spitzer to detect when it looked more than two months after the object's closest aproach to Earth in early September. However, the "non-detection" puts a new limit on how large the strange object can be. The results are reported in a new study published today in the Astronomical Journal and coauthored by scientists at NASA's Jet Propulsion Laboratory in Pasadena, California.

The new size limit is consistent with the findings of a research paper published earlier this year, which suggested that outgassing was responsible for the slight changes in 'Oumuamua's speed and direction as it was tracked last year: The authors of that paper conclude the expelled gas acted like a small thruster gently pushing the object. That determination was dependent on 'Oumuamua being relatively smaller than typical solar system comets. (The conclusion that 'Oumuamua experienced outgassing suggested that it was composed of frozen gases, similar to a comet.)

The new study also suggests that 'Oumuamua may be up to 10 times more reflective than the comets that reside in our solar system — a surprising result, according to the paper's authors. Because infrared light is largely heat radiation produced by "warm" objects, it can be used to determine the temperature of a comet or asteroid; in turn, this can be used to determine the reflectivity of the object's surface — what scientists call albedo. A comet's albedo can change throughout its lifetime. When it passes close to the Sun, a comet's ice warms and turns directly into a gas, sweeping dust and dirt off the comet's surface and revealing more reflective ice.

'Oumuamua had been traveling through interstellar space for millions of years, far from any star that could refresh its surface. But it may have had its surface refreshed through such "outgassing" when it made an extremely close approach to our Sun, a little more than five weeks before it was discovered. In addition to sweeping away dust and dirt, some of the released gas may have covered the surface of 'Oumuamua with a reflective coat of ice and snow — a phenomenon that's also been observed in comets in our solar system.>>

viewtopic.php?p=287301#p287301

[Chris Peterson]

It's a very, very low level of outgassing required to produce this extremely small deviation in orbit.

There seems to be confusion about this. The Gemini North astronomers have described the non-gravitational acceleration as 'remarkably strong'

There's nothing confusing. The actual force can be very weak, and still strong in the sense that any acceleration at all is unexpected.

[Yahchanan]

Maybe it contains a significant amount of bismuth?

[neufer]

Maybe it contains a significant amount of bismuth?

shiny bismuth slag from Pepto-Bismol decomposition

---

<<Bismuth subsalicylate, sold under the brand name Pepto-Bismol, is an antacid medication used to treat temporary discomforts of the stomach and gastrointestinal tract, such as diarrhea, indigestion, heartburn and nausea. It is also commonly known as pink bismuth.

Bismuth subsalicylate is the only active ingredient in an over-the-counter drug that can leave a shiny metal oxide slag behind after being completely burnt with a blow torch[; e.g., the Sun].>>

[MarkBour]

Loved these humorous comments ...

• GCV Of Course I Still Love You <Broadcast>:: You engaged your sub-light drive??!
  ...

• An obvious question someone is probably looking into: Will the altered trajectory take it past another star?
  
  Likely out gassing, but worth further consideration.
  
  Clear skies, Alan

• Maybe it contains a significant amount of bismuth?

At least I think the last one was humorous, though it may have been serious.

Anyway,

I want to accept "the leading natural hypothesis" of comet like out gassing, but I'm sort of hung up on this question: If it was just from natural heating, why was no cometary activity noticed when it was closer to the sun and therefore much warmer than it is now?

Bruce

This is a good question and has been puzzling some researchers, it seems.
We do know the following:

• Oumuamua came through our system and got fairly close to the Sun. When it did, and thereafter, it did not appear very cometary at all.
  And one would not expect it to become more so as it gained distance from the Sun and cooled back down.
• It was seen to be tumbling, which would cause any out-gassing to tend to have a random effect on its trajectory, not the best for accelerating.
• As it passed our Sun, of course, it experienced two major stresses at least: A temperature spike above anything it had experienced in millions of years, and a gravitational acceleration well above any it would have experienced in millions of years.

It would also have experienced higher magnetic field gradients than normal, but I am doubtful that those forces were notable, compared to the other two effects.

One idea is that it is reasonable that the stress would have caused something on Oumuamua to have been loosened. If a small piece came off during the inner arcing pass by the Sun, it could be thrown in a direction that would have increased Oumuamua's exit velocity from the solar system. But the professional "dynamicists" may have ruled that out, if their observations were past the perihelion. Still, as it continues tumbling away from us, it might further be apt to throw off a chunk or two for a fair amount of time, or perhaps some significant pieces of dust or gravel. In any case, larger and fewer than the items in a comet's tail, but ejecta, nonetheless. Such pieces would be impossible for our telescopes to see. If thrown off under the right conditions, then, just like out-gassing, such pieces might explain Oumuamua's increase in velocity, at least the main piece that we can still see.

If either out-gassing or more solid debris, the increase in velocity should be countered by a loss of angular momentum for the body. But again, I would doubt a slowed rotation would be large enough to measure.

(Of course back to little green men, perhaps the ejecta was a small capsule sent back toward us. Our utter failure to have defended against Oumuamua's approach would be a sign to aliens that our system's lone habitable planet was not populated by an advanced civilization, and was probably free for sterilization and colonization without guilt.)

[neufer]

---

Light curve from 25–27 October 2017 (from Earth's viewpoint)

---

ʻOumuamua came through our system and got fairly close to the Sun. When it did, and thereafter, it did not appear very cometary at all.
And one would not expect it to become more so as it gained distance from the Sun and cooled back down.

The earliest observation we have of ʻOumuamua was on
10/14/2017 after it had already passed outside Earth's orbit

<<ʻOumuamua was discovered by Robert Weryk using the Pan-STARRS telescope at Haleakala Observatory, Hawaii, on 19 October 2017, 40 days after it passed its closest point to the Sun. On 26 October, two precovery observations from the Catalina Sky Survey were found dated 14 and 17 October. ʻOumuamua was not seen in STEREO HI-1A observations near its perihelion on 9/9/2017, limiting its brightness to ~13.5 mag.>>

It was seen to be tumbling, which would cause any out-gassing to tend to have a random effect on its trajectory, not the best for accelerating.

The highly variable light curve from 25–27 October 2017 was from an Earth viewpoint that was roughly perpendicular to the Sun's viewpoint.

For all we know: ʻOumuamua's spin axis could very well have been pointing radially on its outward
journey from the Sun such that it received constant heating on its gyroscopic-ally fixed backside.

As it passed our Sun, of course, it experienced two major stresses at least: A temperature spike above anything it had experienced in millions of years, and a gravitational acceleration well above any it would have experienced in millions of years.[/list]

And possibly a long overdue cleansing to give it a high albedo: http://asterisk.apod.com/viewtopic.php? ... 12#p287496

[BDanielMayfield]

Loved these humorous comments ...

Anyway,

I want to accept "the leading natural hypothesis" of comet like out gassing, but I'm sort of hung up on this question: If it was just from natural heating, why was no cometary activity noticed when it was closer to the sun and therefore much warmer than it is now?

Bruce

This is a good question and has been puzzling some researchers, it seems.
We do know the following:

• Oumuamua came through our system and got fairly close to the Sun. When it did, and thereafter, it did not appear very cometary at all.
  And one would not expect it to become more so as it gained distance from the Sun and cooled back down.
• It was seen to be tumbling, which would cause any out-gassing to tend to have a random effect on its trajectory, not the best for accelerating.
• As it passed our Sun, of course, it experienced two major stresses at least: A temperature spike above anything it had experienced in millions of years, and a gravitational acceleration well above any it would have experienced in millions of years.

It would also have experienced higher magnetic field gradients than normal, but I am doubtful that those forces were notable, compared to the other two effects.

One idea is that it is reasonable that the stress would have caused something on Oumuamua to have been loosened. If a small piece came off during the inner arcing pass by the Sun, it could be thrown in a direction that would have increased Oumuamua's exit velocity from the solar system. But the professional "dynamicists" may have ruled that out, if their observations were past the perihelion. Still, as it continues tumbling away from us, it might further be apt to throw off a chunk or two for a fair amount of time, or perhaps some significant pieces of dust or gravel. In any case, larger and fewer than the items in a comet's tail, but ejecta, nonetheless. Such pieces would be impossible for our telescopes to see. If thrown off under the right conditions, then, just like out-gassing, such pieces might explain Oumuamua's increase in velocity, at least the main piece that we can still see.

If either out-gassing or more solid debris, the increase in velocity should be countered by a loss of angular momentum for the body. But again, I would doubt a slowed rotation would be large enough to measure.

(Of course back to little green men, perhaps the ejecta was a small capsule sent back toward us. Our utter failure to have defended against Oumuamua's approach would be a sign to aliens that our system's lone habitable planet was not populated by an advanced civilization, and was probably free for sterilization and colonization without guilt.)

Thanks for that extended treatment of my question Mark. One clarification I would seek in what you are saying is what you mean by "increase in velocity." This object has deviated somewhat from its projected path, but is it really moving away from the sun faster than it would have without the suspected outgassing, or has it just moved laterally off the expected trajectory? Naturally, it must in fact be slowing down as it climbs out of our system's gravity well.

However, I would naively expect a tumbling outgassing object to have the delta Vs it experiences largely cancel out due to its rotations and not cause a significant course alteration. This mussing makes this comment reasonable:

An obvious question someone is probably looking into: Will the altered trajectory take it past another star?

Likely out gassing, but worth further consideration.

Clear skies, Alan

Even with these nagging doubts, I don't really think this was LGM (Unless they were just passing gas.)

Bruce

[hamilton1]

It's a very, very low level of outgassing required to produce this extremely small deviation in orbit.

There seems to be confusion about this. The Gemini North astronomers have described the non-gravitational acceleration as 'remarkably strong'

There's nothing confusing. The actual force can be very weak, and still strong in the sense that any acceleration at all is unexpected.

Avi Loeb has said that the observed acceleration requires 10% of the mass of 'Oumuamua to have been outgassed. So yes, very confusing.

[Chris Peterson]

There seems to be confusion about this. The Gemini North astronomers have described the non-gravitational acceleration as 'remarkably strong'

There's nothing confusing. The actual force can be very weak, and still strong in the sense that any acceleration at all is unexpected.

Avi Loeb has said that the observed acceleration requires 10% of the mass of 'Oumuamua to have been outgassed. So yes, very confusing.

That assertion by itself makes no sense, since any delta-V is determined by momentum, not mass.