View Full Version : Why is Uranus on its side?

2005-Jan-27, 01:46 PM
Has anybody got an answer as to why Uranus is 'lying on its side'?

2005-Jan-27, 02:03 PM
Originally posted by Jakenorrish@Jan 27 2005, 01:46 PM
Has anybody got an answer as to why Uranus is 'lying on its side'?
The answer is that we don't know. Either it formed that way, or it got that way through some later event or catastrophe, or both.

2005-Jan-27, 04:03 PM
Yes, that's right. The space probe, Voyager 2 found that one of the most facinating, unexplanitory influences of Uranus' sideway position is its effect on the tail of the magnetic field. The magnetic field itself is in fact tilted 60 degrees from the planet's axis of rotation. The magnetotail was shown to be twisted by the planet's rotation into a rather long "corkscrew" shape behind the planet. Its just a plain unusual position. It's in fact thought to be the result of a collision with a planet-sized body very early on in our solar system's history....

But, of course anton is right - we don't have a definate explanation.

2005-Jan-27, 06:28 PM
There was a program called "if we had no moon" it discusses the consiquenses of if there was no moon orbiting the earth, it also talks about Uranus and why it is on it's side.

They say it is possible that when uranus was forming, a moon - now one of it's moons, can't recall the name - hit it throwing it off slightly.

2005-Jan-27, 07:37 PM
A new theory (well, ok, not a theory, a very obscure proposition that came to me while reading another story Sun could have traded with another star (http://www.universetoday.com/am/publish/sun_material_collector.html)) is that it could have been struck by a Kuiper belt object that was thrown towards the inner solar system by a passing star.

Still, this doesn't really explain how the moons came to be orbitting in the same plane. I don't understand orbital mechanics well enough to say whether or not the moons could have migrated to their current orbits after the event which knocked Uranus on its side.

John L
2005-Jan-27, 08:13 PM
Originally posted by Duane@Jan 27 2005, 02:37 PM
Still, this doesn't really explain how the moons came to be orbitting in the same plane.
That's my problem with the catastrophy model for knocking Uranus over on its side. Why would the moons follow, too? Why would the rings as well? I think Uranus formed that way. Something passed through the initial debris disk while the planets were still forming creating a disruption that formed into Uranus, its moons, and rings, all orbiting around Uranus perpendicular to the ecliptic.

2005-Jan-27, 08:17 PM
For the moons, ok, but the ring is a transient thing. It could easily have formed well after the event.

2005-Jan-28, 02:46 AM
There was a program that aired on PBS - I think it was a "Nova" program - back in the mid-to late 80's called "The Planet That Was Knocked On Its Side", which made a lot about probable impact. I don't remember what it said about the moons/rings, but it seemed to make sense at the time. Rings are so small and faint that I think it wouldn't take much of an impact to create those, but the moons following along are a different story.

2005-Jan-28, 03:07 AM
Errata: The program was "The planet that got knocked on its side".

The following is from http://www.solarviews.com/eng/vgrur.htm

Incomplete rings and the varying opacity in several of the main rings leads scientists to believe that the ring system may be relatively young and did not form at the same time as Uranus. The particles that make up the rings may be remnants of a moon that was broken by a high-velocity impact or torn up by gravitational effects.

2005-Jan-28, 07:44 PM
"if we had no moon"

if you can you should really chk it out!

2005-Jan-28, 08:50 PM
How does a gas giant get knocked on its side by a solid object?

2005-Jan-28, 08:53 PM
I think Uranus formed that way. Something passed through the initial debris disk while the planets were still forming creating a disruption that formed into Uranus, its moons, and rings, all orbiting around Uranus perpendicular to the ecliptic.

I must agree, altho this doesn't answer the question of what/how? The problem with all of the impactor theories, especially those requiring recent impacts, is they don't account for the heat generated by the impact. Uranus is about as cool as one would expect, if it formed without incident where it presently is. The case could be made that it formed farther out, where it was initially cooler, and got bumped inward-- but that stretches credulity. While there are a lot of ways to trade off momentum and planets and comets with a passing solar system, after this much time it is hard to argue for any specific scenario, especially as Neptune appears undisturbed.

From Uranus' point of view, the sun is a pointlike gravitational source, so there is little tendency to regularize axial tilt due to tidal influence. It may be that most objects further out have random tilts, and we are just prejudiced by our local neighborhood. In summary, idunno. S

2005-Jan-29, 12:30 AM
I raised the point about Uranus's moons myself, in another thread on this topic. I thought it pretty much proved that Uranus must have formed with it's present inclination. Since then I've been thinking about it a bit more, and I've come to the conclusion that I was mistaken.

The equatorial bulge of the planet, spinning at the rate that it does, would exert a gravitational influence on any close-in moon that was not in an equatorial orbit. Eventually, it would drag that moon into an orbit in the same plane as the equator. Before it got to that plane, the most noticable effect would be a precession of the orbital plane about the axis of the planet, but eventually, it would migrate to the equatorial plane.

So why isn't our moon in the plane of our equator? Because it's not close enough to us, and we're too close to the sun. The gravitational influence of the earth's equatorial bulge is small enough to be overwhelmed by the gravitational influence of the sun, and the moon winds up orbiting closer to the ecliptic than it does to the equator.

In Uranus's case, it's a longway from the sun, and the moons we're talking about are close to the planet.

2005-Feb-01, 01:49 PM
Hi theThorn,

really good point that.....

2005-Feb-02, 02:50 AM
We can make informed coment about what may have laid Uranus on its side. The probebilaty that something either hit or came very close to it early in the history of this solar system is the most likly option. There would have been quiet a bit of lose stuff whizzing about. I saw a question back there re gas giants and how they behave if in colision. Remember that the hart of a gas giant is so dence that it is a solid. ( very dence mater ) Its even posible that some ort cloud objects were ripped away from Uranus, thinking Pluto and Charion. After a few million years it would be hard to see the link.. Can we run that program back to see where they came from? no but we can guess, speculate. To puch the boundries, to question the facts is good. It enforces the science.

2005-Feb-02, 10:38 AM
If something were to put it on its side just by going close to it, it'd have to be pretty huge yeah?

2005-Feb-02, 05:15 PM
it'd have to be pretty huge yeah?

Yeah. The complicated part of that is explaining Uranus' present cool temperature, and why Neptune was unaffected. You end up trying to figure a serial probability-- 1) It had to have happened a long time ago 2) It had to be a massive object 3) It had to be moving very fast 4) The Uranus collision had to occur when Neptune was on the other side of the solar system.

You end up with it being very unlikely. But stuff that happens doesn't have to be likely, for single-case occurrences-- it only has to be possible. :unsure: Steve

2005-Feb-02, 09:47 PM
No it would not need to be huge. It would only need to have the energy. That is iether the speed or the gravity. Think small black hole rushing past.... which of the planets could have been involved. We dont know.
As said by Stev., It only has to be possible. The actuall avents that shaped this solar system may not always have been so well ordered.

2005-Feb-03, 09:53 AM
Other possibility:
We don't know much about the formation of our solar system.
Standard view is that huge cloud of gas/plasma colapsed forming Sun in the centre and planets around it.
Although computer simulations show that it maight have happened the model runs into the problems :
Uranu's and Venu's rotation.
Formation of the moons.
How much time does it take for a particle to meet another particle on the oposite side of Sun?
If so, what force causes different velocities of these particles ?

Sun carries 1% of angular momentum, while planets cary 99%.
Sun has 99% of the mass, while planets have 1%.
If the mass of the cloud spined and then colapsed into the star, shouldn't the star carry big angular momentum?
How did Sun lose it's angular momenut to the planets?

My idea is: Ejections of the planets. Huge flares from young Sun were cast away, forming the planets roughly in order Neptun, Uranus, Saturn, Jupiter etc.
The main stream of the plasma in the flare forms the planet, small bobles form the moons. Geometry during the formation is snail-like.
At that point the heavier elements will form the core, not later during some tectonic migrations.
That's why Uranu's moons followed Uranu's equatorial plain and why Neptun was not affected. It might very well be on the other side of Sun.
Such a flare and not another body could hit young Earth forming the Earth-Moon system.
Could the same flare change the Venu's rotation?

Implications: All planets and the moons will show roughly the same composition Oxygen, Nitrogen,Carbon,Helium,Neon etc, but mainly Hydrogen in the atmospheres. Ni, Fe and heavier in the cores. Si, Mg and others on the surface and crust.

Predictions: Hydrogen will eventually chemically react with oxygen (forming the water), carbon (forming carbon dioxide) or both (forming life context).
Majority of the planets and the moons will possess the water and carbon dioxide in some form.
If the celestial body can't maintain the gasous H2O,CO2 due the week gravity , it still should be possible to find ice on the poles (even Mercuty has it).
Majority of the atmospheres in the Solar system will be made of Hydrogen, if not suffice Oxygen/Carbon to react with.
Otherwise the atmosphere will be made mainly of Nitrogen and/or CO2/H2O.

Sun was more violent in the past (as observations of our Solar system suggest).
Observations of other Sun-like stars show that they are more violent (their flares rich several hundreds of millions km into the space, (no conditions for life there, that was what they looked for)).

If Sun for every reason become violently active (as it is the case right now), we should witnessed an ejection of a planet.
Hopely that planet should be a small and shouldn't destroy Earth and should be named after me so I will left my name here. B)

Is this utter nonsense? (I mean the hole THEORY, not the last sentence :-))

2005-Feb-03, 12:39 PM
:blink: wow; Tihomin., Fortunatly I believe our Sun has matured into a nice friendly predictable provider for our energy needs for many millina yet to come.
Your ideas regarding the formation of the Solar System may not fit the most popular explanations, but good on you for this.

2005-Feb-03, 01:36 PM
Actually, I'v got more on the most popular explanations.
Sun and it's planets formed at the same time from the same gas cloud:
Imagining gas cloud in collaps, what is the diameter of collapsing cloud?
Why would gas collaps only inside the Mercury's orbit?
Why would the collaps draw the "straight" line during the collaps and leave enough
material for the (ac)creation of inner planets?
Then comes theory of Sun travelling through the gas cloud, supernovae remnants, which explains the aboundance of heavy elements.
Our Sun is considered to be 5 bio. years old, while Earth/Moon are 4,5 bio. y. old.
Then all planets must be approximatly 4,5 bio. y old.
How would you make gas particles following Sun in a tail on the mean distance 1,5 bio. km (Saturn's orbit, which means particles on the oposite sides of Sun are 9 bio. km away from each other) form Saturn with a such a nice eliptical orbit in just 0,5 bio. y?? What about the moons.

2005-Feb-03, 03:54 PM
Thanks for the information all of you, keep it coming. It is a fascinating subject and I suppose the slow rotation of Venus is a good talking point to touch on as well.


2005-Feb-03, 03:56 PM
Originally posted by Guest@Feb 3 2005, 03:54 PM
Thanks for the information all of you, keep it coming. It is a fascinating subject and I suppose the slow rotation of Venus is a good talking point to touch on as well.

Sorry, that last message was me. Forgot to log in!

2005-Feb-03, 07:36 PM
How did Sun lose it's angular momenut to the planets?

There is no consensus as to the exact mechanism of momentum transfer between the protosun and the accretion disc. One may suppose that there is some analogy between the spin-down of a feeding pulsar and the spin-down of the protostar. In this model, the infalling material is ionized by its fall/collision with the protostar. Ions are deflected by the magnetic field of the protostar. Net result: some of the material is jetted from the poles and lost to the system; some is driven outward by local heating, to rejoin the accretion disc (eventually). Both actions, though, are at the expense of the rotation of the protostar.

Ask 10 planetary scientists, get 8 different answers. The version above is my jaundiced slant (I am no professional)-- it actually does not require that the protostar have an intrinsic magnetic field. The ions, by participating in the protostar's rotation, produce their own.

If you keep looking at all standard theories as critically and creatively, you could do well. Good work. Steve