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Why does Uranus lie on its side?


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Astronomers have long wondered why Uranus “lies on its side” with an obliquity of 98 degrees. One theory that a giant impactor tipped Uranus over has been challenged. A paper accepted by the Planetary Science Journal proposes the intervention “driven by the outward migration of an as-yet undetected outer Solar System body commonly known as Planet Nine”.

Read more here.

Food for thought as we anticipate a well placed apparition of this ice giant coming up, with opposition in November in Aries.

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As far as I know, there are 2 ideas. 
an impact early in solar system history with Uranus, probably a proto-planet.

or,

an encounter with a planet (but not an impact), so that the gravitational  interaction, “turned” Uranus on its side.

Note that the rings of Uranus are also on their side, and off-centre, and current ideas suggest that the current positions of gas and ice giants have changed since solar system formation. They have migrated from closer in, to their current positions.

time will tell, hopefully.

p.s. The rings of Neptune are also peculiar, they are incomplete. This has the planetary science mathematicians scratching their heads.
p.p.s. Another anomaly, the magnetic fields of Uranus and Neptune are not centred on the planets centres (like the Earth), and are nearly perpendicular to the axis of rotation. Weird. 

Edited by DrMike
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maybe a "free" plant that just got caught up in Sol's gravitational field at some point

Can someone not design a handle and lever mechanism to make it fit the rest of sol's plant?

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Isn't the solar system a bit anomalous in having gas giants far away from the Goldilocks Zone? I thought that the majority of known gas giant exoplanets were much nearer their respective stars. In which case the explanation for the placement of the solar system giants would be indicative of some distant calamitous event. This event created the gradual migration of the planets to their present orbits. The event may be responsible for why Uranus lies on its side. Or not. 

 

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The majority of discovered exoplanets are nearer their stars simply because from this it follows that they have shorter periods ( usually of days) and high radial velocities which together make their discovery more probable than those which are further away. Our Jupiter will be very hard to spot ( visually or from its gravitational influence on the Sun) from say 100 light years away.

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12 minutes ago, Nik271 said:

The majority of discovered exoplanets are nearer their stars simply because from this it follows that they have shorter periods ( usually of days) and high radial velocities which together make their discovery more probable than those which are further away. Our Jupiter will be very hard to spot ( visually or from its gravitational influence on the Sun) from say 100 light years away.

Oh right, thanks. So there could be many systems similar to ours whose gas giants are less easily detected? I thought the 'early solar system calamity' scenario was looking more plausible these days. 

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35 minutes ago, Nik271 said:

The majority of discovered exoplanets are nearer their stars simply because from this 

what is missing from your statement above?

the words between simply and because may be relevant - certainly from dumbos like me

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11 hours ago, iapa said:

what is missing from your statement above?

the words between simply and because may be relevant - certainly from dumbos like me

What I meant is that we discover many exoplanets close to their stars because these are much easier to find than those which are further from their stars.

It does not necessarily mean that most gas giants in planetary systems exist close to their stars. Until their discovery the models based on our own solar system indicated that gas giants will not form close to their stars because there will not be sufficient lighter elements left after the star has formed. I think the current models still expect that most planets which are formed in close orbits will be rocky ones. Perhaps the gas giants we observe have migrated close to their stars after formation. There is a lot that we don't know and still to be discovered. This is where the James Webb will be useful, it can study the atmosphere of exoplanets in much greater detail. 

Edited by Nik271
typos
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On 26/07/2022 at 16:22, badhex said:

So what is it?

I've never seen one before, no-one has, but I'm guessing it's a white hole.

I was really hoping that there might be some Red dwarf fans out there that might get this reference 😅

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1 hour ago, Mandy D said:

There really must be! DA would not miss an opportunity like that!

“I don’t know what I’m looking for.”
“What not?”
“Because … because … I think it might be because if I knew I wouldn’t be able to look for them.”

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Study of exoplanet systems has (contrary to past expectation) shown that the
layout our solar system (rockies nearest, gas giants furthest) is rather atypical.
The other "reminder" I get is that the Uranian satellites are in the plane of
Uranian equator - Thus were formed after, in the debris of, any "big collision". 😎

Edited by Macavity
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4 minutes ago, Macavity said:

Study of exoplanet systems has (contrary to past expectation) shown that the
layout our solar system (rockies nearest, gas giants furthest) is rather atypical.
The other reminder I had was that the Uranian satellites are in the plane of
Uranian equator - Thus were formed after, in the debris of the "big collision". 😎

Yes, I was led to believe our solar system was a bit of an oddball compared to discovered exo-systems. Not sure about Uranus. It does make me wonder about the relevance of the Drake Equation if our system is a bit of an anomaly though. 

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6 minutes ago, Macavity said:

Study of exoplanet systems has (contrary to past expectation) shown that the
layout our solar system (rockies nearest, gas giants furthest) is rather atypical.
The other "reminder" I get is that the Uranian satellites are in the plane of
Uranian equator - Thus were formed after, in the debris of, any "big collision". 😎

Is it atypical or is it, as Nik271 says earlier in this discussion, that gas giants near their star are easier to spot? A huge planet orbiting a modest star in a few days will produce large, easily trackable perturbations of short period, whereas a gas giant orbiting at the distance of Jupiter will cause relatively small perturbations over a very long time.

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I'd be a bit wary of applying any extrapolation from the layout of planets in exoplanet systems. Big planets are easier to spot and I recall we don't have many systems yet with multiple planets to draw meaningful conclusions as to a normal order. However, you do make a good point. No one expected Hot Jupiters.

12 minutes ago, Macavity said:

Study of exoplanet systems has (contrary to past expectation) shown that the
layout our solar system (rockies nearest, gas giants furthest) is rather atypical.
The other "reminder" I get is that the Uranian satellites are in the plane of
Uranian equator - Thus were formed after, in the debris of, any "big collision". 😎

 

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OK, I concede that one. Something I read, recently? Here's another discussion on the subject:
https://aasnova.org/2015/09/25/how-normal-is-our-solar-system/

Just a minor chuckle: The authors find that for the most part, we’re a pretty typical solar system.
Our most unusual features are the lack of a super-Earth, the lack of any close-in planets, and the
low eccentricities of planets.
Monty Python "Spanish Inquisition" - Our three main differences... 🥳

Edited by Macavity
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12 minutes ago, UKDiver said:

I'd be a bit wary of applying any extrapolation from the layout of planets in exoplanet systems. Big planets are easier to spot and I recall we don't have many systems yet with multiple planets to draw meaningful conclusions as to a normal order. However, you do make a good point. No one expected Hot Jupiters.

Wikipedia's List of Multiplanetary Systems  has over 800 such systems, with an average of about 3.4 (confirmed) planets per system. What is notable about the systems we know about is that we have very little scope for detecting long period planets, as we have in our solar system.

Our principal method of detection being via transits, with the relatively limited timescales that we've been able to make observations, means that planets such as Saturn, Uranus and Neptune would be way outside our criteria for detection.   

 

Edited by Gfamily
To add 2nd paragraph
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