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Mars May Have Liquid Iron Core
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This restaurant was advertising breakfast any time. So I ordered french toast in the renaissance. - Steven Wright, comedian
Mars? (Score:4, Funny)
Thank you, I'll be here all week.
Re:Mars? (Score:1)
That's a Snickers, you insensitive clod
The Core (Score:2)
Re:The Core (Score:1)
If you saw the first trailer, it was about how every so often the core slows, stops, and then reverses after a long pause. Fine. We need to restart it and this is really hard. Decent premise.
Now, it seems as though the whole movie has changed reasons. In the new trailer, the reason the core stops is because the US, evil country that every one seems to know it is, has created a seismic weapon to kill other countries and they have incidentally stopped the core.
Then the isssue is one of, why couldn't they use the simiar device to restart it? They go through a whole lot of effort in the trailer to explain how nearly nothing could do it, but they just stopped it fairly easily.
Also, in the trailer, other oddities have seemed to happen. If you watch it, you'll notcie that stopping the core not only produces giant lightning storms, but also makes lightning become much more attracted to marble historic landmarks than it ever was before. It also seems to make marble landmarks fairly explosive.
So, just like ID4 and Armageddon, this movie is going to require herculean efforts to suspend disbelief long enough to enjoy the completely fine acting I'm sure it will have.
What makes a core hot? (Score:3, Interesting)
I've heard some people say it's heat caused by friction resulting from gravitational pressure (I think this is what they taught me in school), but I've had several Geology Doctorates say that the heat actually results from radioactive decay (Similar to radioactive decay in some granite).
So, which is it? Help my geoneophyteness!
Re:What makes a core hot? (Score:1)
I believe that for the most part it's simply when the gravity causes the dust cloud to contract forming a planet the momentum turns to heat. smaller planets have solid cores because they've lost all the heat they gained from this.
There is one moon (Europa?) which actually has volcanic activity from the stretching caused by Jupiter's gravity as it revolves around the planet, but no planet can get much energy from tidal foces.
Re:What makes a core hot? (Score:3, Informative)
Re:What makes a core hot? (Score:3, Informative)
When a dust cloud first condenses into a planet, there's a lot of heat generated from friction between dust particles, collisions with other planetoids, impacts from meteorites, and so on. So the newly-formed planet is very hot, and mostly molten. As the planetary system ages, there's less and less other material impacting on the planet, so less heat being produced that way, and the planet starts to cool. However, decaying radioactive isotopes produce a significant amount of heat as well, which dramatically slows the cooling rate of the planet. If there were no heat-producing isotopes in Earth's core, it would've cooled enough to be completely solid long ago.
So the core of a planet gets hot through friction from collisions with other objects during formation, and stays hot due to the heat produced by decaying radioactive isotopes.
Re:What makes a core hot? (Score:5, Informative)
There are basically 4 ways to heat a planet:
1. Heat of accretion. As stuff comes from a long ways a way and smashes into the planet, the graviational potential energy is turned into heat. Important early on for all planets. This heat is leaked out over time.
2. Differentiaion. If the planet is liquid (or gaseous), the heavier elements/compounds will tend to sink to the middle and the light components will rise to the top. This reduces the overall graviational potential energy, releasing more heat. Most planets have differentiated about as far as they are likely to, so this doesn't really help much anymore, either. Saturn and Neptune might be having a form of this happening today, with a helium rain in their atmospheres.
3. Contraction. If a planet shrinks in radius, gravitational potential energy is released. (Yet again.) This is possibly what is keeping Jupiter warmer than solar heating alone would make it.
4. Radioactive decay. This depends on composition, of course (gas giants, being mostly hydrogen, aren't terribly prone to this one). Rocky/metallic planets experience a fair bit of this after 4.5 billion years, mainly from potassium and uranium isotopes. (He says, trying desperately to remember his planetary geology class 4 years ago.)
Note that friction and pressure are not in the above list. Higher pressure does not always mean more heat! (The ideal gas law doesn't always work!) Friction requires moving bits inside the planet. In fact, that is where the frictional heat comes from. So you still need a source of energy to get things moving, meaning friction can't be the ultimate source of energy.
That might be more information that you wanted, but I wanted to give a bit of context for the answer.
Re:What makes a core hot? (Score:2)
The core heated up through the release of gravitational potential. In layman's terms, all the meteors and gas that fell into the gravity well that formed the earth picked up a lot of energy falling that far. When they impacted, that energy was converted to heat, with the mechanism for that conversion being friction. This imparted most of the energy to the earth. At this point, the earth was largely molten, so the lighter materials floated to the surface, concentrating very light materials in the crust, denser rocks in the mantle, and the very dense iron and nickel sank to the center, forming the core. This also released energy.
method 3, contraction, would be minimal in a terrestrial planet such as Mars. This is much more of an issue for a gas giant.
method 4, radioactive decay, is thought to be fairly important in preserving the original heat of the earth. It is believed that most of the radiogenic isotopes in the earth were concentrated in the crust during differentiation. Although the atoms of radiogenic elements are themselves massive, most of their compounds are of similar density to other crustal material. This keeps the thermal gradient in the crust much higher than it would be due to conduction of heat from the mantle alone. However, since most of this heat is released within 25 to 50 miles of the earth's surface, this is not heating the core significantly, but it does slow down the release of energy.
There is one other source of heat in the core. The core was originally 100% liquid. Over time, however, the molten metal at the center has begun to freeze, becoming a solid mixture of iron and nickel. This solid core is denser than the surrounding liquid, meaning that more gravitational energy is released. Perhaps more importantly, for those of us who remember our high-school chemistry, there is a certain amount of heat released when a liquid freezes to form a solid, the 'latent heat of fusion'.
For the Earth/Moon system and the moons of the large gas giants, there is also heating from tidal stress. This is the engine driving the massive vulcanism on Jupiter's innermost large moon, Io. Since Mars' two natural satelites, Phobos and Deimos, are just moderately large asteroids, they are not nearly massive enough to create any significant tidal force on Mars.
Tidal Forces? -- (was Re:What makes a core hot?) (Score:2)
I don't see anyone mentioning friction caused by tidal forces here. But I have read of it being a cause of internal heating.
As I understand it, even a body like our moon, that has one hemisphere constantly facing its primary, will experience heating from friction. The moon's orbit around the Earth is not perfectly circular. So Earth's position in the sky moves a little bit. And the moon's orbit is not directly above the equator, so the Earth's equatorial bulge will result in tidal friction. Plus, the Sun appears to move around the moon's sky, resulting in Tidal Friction.
Phobos and Diemos are much smaller, and less massive, than our moon. But Mars's orbit is more eccentric than the Earth's.
As I recall, one simplifying assumption Newton made was to do his gravitational calculations as if the heavenly bodies were point-sources. Spherical bodies could be treated like point sources, as the greater force from the near hemisphere was cancelled out by the far hemisphere. But spinning bodies, with equatorial bulges, obviously aren't spherical. So, Tidal Forces can alter a satellite's orbit's eccentricity and the body's period.
It is my understanding that, given enough time, tidal forces would lock all binary systems so they presented the same faces to one another.
Re:Tidal Forces? -- (was Re:What makes a core hot? (Score:2)
Interesting to note that most Moons in the solar system are locked to always show the same face.
We always see the same side of the moon, regardless of the time or date.
Hmmm... (Score:3, Funny)
So that goofy Mission to Mars movie could turn out to be right? Underground liquid water warmed by the hot core that can support life?
Of of all the SF movies to get it right. Geesh.
One centimeter? Can someone please explain? (Score:2)
Even if you could map the surface of Mars down to millimeter resolution in 3 dimensions (which is very far from anything they are remotely claimed to have done), it would be highly problematic to even define what is meant by a sphere with a mean radius of more than 672,400,000 cm (and a highly heterogenous composition) having a 1 cm physical eccentricity due to a specific cause. An apparent 1.6 parts per trillion variation in mass distribution can't possibly be attributed to any one cause until we've completely mapped the entire volume of the planet. Large underground caverns or deposits of dense minerals can (and do) cause many times this much variation here on the much-measured Earth.
Can someone please explain how this finding could possibly make sense, given the many known, larger confounding factors, and the general paucity of data about the overall geology and underground 3-D mapping of Mars? To me, this smells like bad science. We don't know enough about Mars to make conclusive parts-per-trillion determination, much less confidently attribute them!
Re:One centimeter? Can someone please explain? (Score:1)
Re:One centimeter? Can someone please explain? (Score:1)
I imagine they calculated the tidal effects mathematically based on the material Mars is made of, the size, and the distance from the sun. Possibly they did it based on measurements of the magnetic field, but that seems unlikely.
Keep in mind that I'm not an expert. I took one atronomy ("football physics") class a year ago and have forgotten most of it.
They didn't measure displacement. of the surface (Score:4, Informative)
The important thing to note is that a tidal bulge is actually a wave that displaces any given point on Mars twice a day. As the satellite is orbiting, it gets a little extra gravitational nudge from the tidal bulges roughly twice each orbit. The overall effect is to cause the major axis of its orbit to drift a little bit, or precess. It is cumulative over time, so even if the major axis drift per orbit is small, after hundreds of orbits it will be quite noticeable. So that is how a bulge can be measured without actually measuring actual ground displacement.
so does this mean... (Score:1)
Odd (Score:1)
I've heard theories [columbia.edu] (not from the link) about the Earth's core being crystalline.
So where does Mars get off having a liquid one?
Re:Odd (Score:2, Informative)
Note that the liquid core is exterior to the solid core. It's the high pressures at the center that cause it to be solid. Mars, with a much lower mass, would have a lower central pressure, so it's not surprising that it is liquid (ignoring differences in temperature, of course).
Magnetic field? (Score:3, Interesting)
Wouldn't a molten iron core (rather than solid) mean the magnetic field is stronger? I recall that Jupiter has an extremely strong magnetic field because of the liquid hydrogen core. It seems like a half-decent measurement of Mars' magnetic field should give us a decent idea of what its core is like.
Re:Magnetic field? (Score:2, Interesting)
The set of equations used in magnetohydrodynamics is so complicated we don't even understand the Earth's magnetic field very well. Rotation, turbulence, magnetism frozen in to the solid core, the chemical evolution of the liquid iron (sulphur or no sulphur?) and a myriad other factors all play a part.
My personal guess is that Mars' core doesn't generate much of a field because it is small and so doesn't have a large moment of inertia. But ha! What do I know?
Re:Magnetic field? (Score:2)
To get a magnetic field, you need three things:
1. A liquid, metallic* interior (so it can move and carry charges about)
2. A reasonably fast rotation rate
3. Convection in the liquid metal.
* (Actually, any charge carrier works, as far as I know. Salty water might be able to do it, I suppose.)
Mars meets criterion 2. And now apparently it meets 1. It isn't clear that there is convection going on, though, so that itself might be keeping the field from being present.
Then again, dynamo theory is pretty shaky stuff. (As someone already said.) I tend to trust it in the big picture (the stuff I outlined above), but not in the details. So exactly how much a planet needs to meets the three criteria is anybody's guess. (That is, how fast does it need to rotate? How metallic does the interior have to be? How much convection?) Mercury and Venus certainly create certain... issues... with this theory, for a start.
Not original but still a classic (Score:2, Funny)
Magnetic field? (Score:2)