Uranus and Neptune's Magnetic Fields

[renormalised]

Recent models for the formation of these two planets have come up with some hypotheses as to how the strange field geometries of these two planets came about....

The phase diagram of water and the magnetic fields of Uranus and Neptune (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-50V5NMY-2&_user=3928936&_coverDate=08%2F22%2F2010&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_acct=C000061806&_version=1&_urlVersion=0&_userid=3928936&md5=f7a7470e709a2fa75c78db9b8af9e9c 9&searchtype=a)

Numerical dynamo models of Uranus' and Neptune's magnetic fields (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4K8SC5Y-2&_user=3928936&_coverDate=10%2F31%2F2006&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_acct=C000061806&_version=1&_urlVersion=0&_userid=3928936&md5=76ab1fab3a69634cf8398b29d3ecb91 d&searchtype=a)

Dynamic Ionisation of Water Under Extreme Conditions (http://prl.aps.org/abstract/PRL/v94/i12/e125508)

Weird Water Lurking Inside Giant Planets (http://www.newscientist.com/article/mg20727764.500-weird-water-lurking-inside-giant-planets.html)

Superionic Water (http://www.nature.com/news/2005/050321/full/news050321-4.html)

What they have hypothesised is that the magnetic fields of these planets are not being generated in the cores of the planets but in the flow of hydrogen ions at very high temperatures in the mantles of these two worlds. The hydrogen ions occur in a substance known as "superionic water", which is essentially a type of "ice" that occurs at high temperatures and pressures underneath the atmospheres of the two planets. The oxygen ions in the ices form a lattice like structure through which the hydrogen ions (stripped away from their original water molecules by the high pressures) are free to travel.

It's essentially a partially degenerate phase of matter somewhere between a solid and a liquid in nature...acting much like a metal.

This flow, because it is occurring at a distance from the core, means that the currents being generated that create the magnetic field of the two planets are substantially offset from the axis of rotation of the two planets. The geometry of the planet's magnetic fields are therefore shaped by the offset position and the rotational dynamics of each of the planets.

[CraigS]

Very interesting .. modelling different states of water under extreme conditions.

This article set me into motion as I was unaware that any probe has ever detected 'big' water on Neptune (this does not mean there isn't any .. it just means I don't know whether there is or there isn't. (I'm not not sure about Uranus).

Forgive me if I'm a little sceptical but mostly, (& I'm not saying this is one), whenever I've gone looking to find where the hard data showing 'big' water presence, I usually end up with wobbly statements rather than "this much H2O was detected by such and such a probe", etc. It just happened again checking thru Wiki on Neptune.

It seems that many scientists like to imagine H2O on these planets, in abundance but I can never quite put my finger on the hard evidence. Is it just me or has anyone else ever noticed this ? I'm happy to have my perception corrected.

Cheers

[renormalised]

The problem with detecting water on any giant planet is its density. It's a lot denser than the normal atmospheric constituents, even when they're in their liquid forms or solid forms. So, it gradually sinks down into their atmospheres to the bodies of these worlds. You will have some in the lower atmospheres though. But it's usually too deep to detect spectroscopically. That's why, when Galileo sent its atmospheric probe into Jupiter, they found a relatively dry atmosphere (at least in that area where it went in). In any case, the probe never got low enough down in the atmosphere to get to the water layers. It was crushed beforehand by the pressure.

But they can tell it's present through lightning. Water is a polar molecule, so it can carry a charge. You need water molecules/ice to create the charge separation in clouds to generate lightning. When convection brings it up through the atmosphere, it forms ice and the charge separation occurs in the clouds.....zap!!!!.....one massive bolt comes flying out:):)

Lightning on Jupiter is rather spectacular....the megabolts that arc between thunderheads on Jupiter are several thousand times as powerful as any on Earth.

[CraigS]

So other molecules could also create the charge separation ?

Mars is another one. I've tried to find hard evidence of 'big' H2O on the Northern pole, everywhere. Mostly they say 'is believed to exist'. However, recent orbiting surveys have detected 'trace' amounts of H2O in the atmosphere above the pole. However from the same measurements, they also say that it is 'mostly' frozen CO2.

More evidence they commonly cite for Mars is geological features that resemble features on Earth where we know H2O has flown. However, can they differentiate what happens when massive amounts of CO2 sublimates and flows through soil like that on Mars, from H2O doing the same ?

If so, how do they do these tests, here on Earth ?

(I'm probably on my own on this one I guess I'll continue my search, quietly).

Cheers

[renormalised]

Most of the polar water ice on Mars is on the south pole. The Northern pole is mostly CO2....it just about disappears during the northern summer. The water in both polar caps is protected from direct sublimation by a covering of dirt and sand. There's enough water in the south pole to cover Mars in a layer of water about 7-11 metres deep.

[multiweb]

Shame it's got a very weak magnetosphere or we could send arnie for a terraforming mission there. :)

[CraigS]

Ok. So I've just read thru the Wiki entry on Mars. It has 70 matches for the word 'water'. Wherever claims about water are made, I've read thru the reference material. There is a lot of indirect evidence for the existence of 'big' water, mostly geological and mineralogical. The landers have sampled small amounts of water on the surface, also.

Most 'big' deposits are inferred to be at the poles. I say 'inferred' because the only measurement taken from orbit of the southern region were taken by the Mars Express MARSIS instrument which used primarily, ground penetrating radar as its detection mechanism. The radar could penetrate to considerable depths, but at the end of the day, the chemical composition of the material being penetrated is still inferred. Having said this, the lander samples are clearly not inferred.

Whilst there is a lot of supporting evidence, models still play the key role in statements made about the abundance of 'big' H2O water on Mars.

I would never take a stand against a martian geologist who lives on the south pole of Mars, however !
:):P:)
Cheers