Interstellar Asteroid 1I/2017 U1 'Oumuamua

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bystander
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'Oumuamua Gets an Unexpected Boost

Post by bystander » Wed Jun 27, 2018 6:10 pm

Hubble/VLT See 'Oumuamua Getting a Boost
ESA Hubble | ESO VLT | Science Release | 2018 Jun 27
New results indicate interstellar nomad `Oumuamua is a comet

`Oumuamua, the first interstellar object discovered in the Solar System, is moving away from the Sun faster than expected. This anomalous behaviour was detected using the NASA/ESA Hubble Space Telescope in cooperation with ground-based telescopes. The new results suggest that `Oumuamua is most likely a comet and not an asteroid. The discovery appears in the journal Nature.

`Oumuamua — the first interstellar object discovered within our Solar System — has been the subject of intense scrutiny since its discovery in October 2017 [1]. Now, by combining data from the NASA/ESA Hubble Space Telescope, the Canada-France-Hawaii Telescope, ESO’s Very Large Telescope and the Gemini South Telescope, an international team of astronomers has found that the object is moving faster than predicted. The measured gain in speed is tiny and `Oumuamua is still slowing down because of the pull of the Sun — just not as fast as predicted by celestial mechanics.

The team, led by Marco Micheli (European Space Agency) explored several scenarios to explain the faster-than-predicted speed of this peculiar interstellar visitor. The most likely explanation is that `Oumuamua is venting material from its surface due to solar heating — a behaviour known as outgassing [2]. The thrust from this ejected material is thought to provide the small but steady push that is sending `Oumuamua hurtling out of the Solar System faster than expected — as of 1 June, it is travelling with about 114 000 kilometres per hour. ...

Our Solar System's First Known Interstellar Object Gets Unexpected Speed Boost
NASA | STScI | HubbleSite | 2018Jun 27

Interstellar Asteroid Is Really a Comet
ESA Space Science | 2018 Jun 27

Is ʻOumuamua Really a Comet?
Canada-France-Hawaii Telescope | 2018 Jun 27

Is the Interstellar Asteroid Really a Comet?
Institute for Astronomy | University of Hawaii | 2018 Jun 27

Mysterious Interstellar Visitor Is a Comet — Not an Asteroid
Nature News | 2018 Jun 27

Non-Gravitational Acceleration in the Trajectory of 1I/2017 U1 (‘Oumuamua) - Marco Micheli et al
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Re: Interstellar Asteroid 1I/2017 U1 'Oumuamua

Post by neufer » Thu Jun 28, 2018 4:59 pm

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Re: Interstellar Comet 1I/2017 U1 'Oumuamua

Post by BDanielMayfield » Fri Jun 29, 2018 12:24 pm

So then since this object is now shown to be a comet, is the elongated shape easier or harder to explain?

As comets go 'Oumuamua is extremely weak in activity level. That suggests to me that it may have made a great many close passes by the star/stars of its origin system.

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Re: Interstellar Comet 1I/2017 U1 'Oumuamua

Post by Chris Peterson » Fri Jun 29, 2018 1:16 pm

BDanielMayfield wrote:
Fri Jun 29, 2018 12:24 pm
So then since this object is now shown to be a comet, is the elongated shape easier or harder to explain?

As comets go 'Oumuamua is extremely weak in activity level. That suggests to me that it may have made a great many close passes by the star/stars of its origin system.
Well, we don't have a clear distinction between comets and asteroids. There's a gray zone of overlap- comet-like asteroids and asteroid-like comets. Presumably there are different populations of objects defined by their formation environment, not just two. When they call this object a "comet" all they're saying is that it's outgassing volatiles. But asteroids might do that, too. In fact, we might expect that of very young asteroids. So this could be an asteroid-like body that was ejected from its stellar system very early, or a comet-like body that was ejected much later, after losing most of its volatiles.
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Re: Interstellar Comet 1I/2017 U1 'Oumuamua

Post by BDanielMayfield » Fri Jun 29, 2018 1:21 pm

Chris Peterson wrote:
Fri Jun 29, 2018 1:16 pm
BDanielMayfield wrote:
Fri Jun 29, 2018 12:24 pm
So then since this object is now shown to be a comet, is the elongated shape easier or harder to explain?

As comets go 'Oumuamua is extremely weak in activity level. That suggests to me that it may have made a great many close passes by the star/stars of its origin system.
Well, we don't have a clear distinction between comets and asteroids. There's a gray zone of overlap- comet-like asteroids and asteroid-like comets. Presumably there are different populations of objects defined by their formation environment, not just two. When they call this object a "comet" all they're saying is that it's outgassing volatiles. But asteroids might do that, too. In fact, we might expect that of very young asteroids. So this could be an asteroid-like body that was ejected from its stellar system very early, or a comet-like body that was ejected much later, after losing most of its volatiles.
Thanks. Good answer.
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Re: Interstellar Asteroid 1I/2017 U1 'Oumuamua

Post by starbrush » Wed Jul 04, 2018 11:53 am

I get the idea that outgassing could change 'Oumuamua's velocity; but I understand that the object is tumbling. Therefore how would any outgassing have a useful constant direction? Could the outgassing be so rapidly responsive e.g. to the Sun's heat that it still manages to outgas preferentially on its sunward side? At the moment my mental image is of a slow motion firecracker with no constant outflow!

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Re: Interstellar Asteroid 1I/2017 U1 'Oumuamua

Post by neufer » Wed Jul 04, 2018 12:53 pm

starbrush wrote:
Wed Jul 04, 2018 11:53 am

I get the idea that outgassing could change 'Oumuamua's velocity; but I understand that the object is tumbling. Therefore how would any outgassing have a useful constant direction? Could the outgassing be so rapidly responsive e.g. to the Sun's heat that it still manages to outgas preferentially on its sunward side? At the moment my mental image is of a slow motion firecracker with no constant outflow!
ʻOumuamua's hyperbolic trajectory left it moving on an exiting trajectory that is almost perpendicular to it's entering trajectory. Assuming that it is basically rotating around its minor axis it is likely that that fixed axis was pointing in the general direction of toward or away from the Sun either on its inward trajectory or (more likely) its outward trajectory.
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Re: Interstellar Asteroid 1I/2017 U1 'Oumuamua

Post by Chris Peterson » Wed Jul 04, 2018 2:05 pm

starbrush wrote:
Wed Jul 04, 2018 11:53 am
I get the idea that outgassing could change 'Oumuamua's velocity; but I understand that the object is tumbling. Therefore how would any outgassing have a useful constant direction? Could the outgassing be so rapidly responsive e.g. to the Sun's heat that it still manages to outgas preferentially on its sunward side? At the moment my mental image is of a slow motion firecracker with no constant outflow!
Tumbling doesn't mean some kind of random rotational movement, it simply means rotating on two axes. So unless the outgassing was perfectly isotropic (which is unlikely), there's still be a net thrust vector and consequent deviation from a purely ballistic orbit.
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Re: Interstellar Asteroid 1I/2017 U1 'Oumuamua

Post by starbrush » Wed Jul 04, 2018 2:24 pm

These are helpful, thanks to both. I guess observers will always be on the lookout for variations in rotation as well.

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Re: Interstellar Asteroid 1I/2017 U1 'Oumuamua

Post by Chris Peterson » Wed Jul 04, 2018 2:27 pm

Chris Peterson wrote:
Wed Jul 04, 2018 2:05 pm
starbrush wrote:
Wed Jul 04, 2018 11:53 am
I get the idea that outgassing could change 'Oumuamua's velocity; but I understand that the object is tumbling. Therefore how would any outgassing have a useful constant direction? Could the outgassing be so rapidly responsive e.g. to the Sun's heat that it still manages to outgas preferentially on its sunward side? At the moment my mental image is of a slow motion firecracker with no constant outflow!
Tumbling doesn't mean some kind of random rotational movement, it simply means rotating on two axes. So unless the outgassing was perfectly isotropic (which is unlikely), there's still going to be a net thrust vector and consequent deviation from a purely ballistic orbit.
Chris

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