Volcanism, A Molten Core And Geomagnetism Options

[Bob Shaw]

One of the few things we can say with certainty about all the rocky planets of the Inner Solar System is that they have as many differences as similarities.

The presence of Earth's Moon, and it's putative 'Big Whack' origin makes our own world seem pretty much atypical, though I'm bound to say that the 'Goldilocks Zone' of liquid water seems helluva interesting. Terrestrial plate tectonics seem to be mediated (at the very least) by water in the mantle; other planets don't have the water we have; none of them have active plate tectonics. Venus turns inside-out every now and again, Mercury seems to do not a lot except shrink, and Mars builds up giant shield volcanoes but not much else. But Earth is saturated with water, and it simply squirms...

...perhaps we should treat Earth as a small 'Ice Giant' rather than a member of the rocky worlds!

Bob Shaw

[Guest_BruceMoomaw_*]

Heat-flow measurements from orbit MAY be practical with a microwave radiometer -- it's always been one of the instruments highly ranked for a US lunar polar orbiter, had we ever flown a full-scale one, and it may yet fly at some point. But the atmosphere of Mars -- let alone the thick one of Venus -- hopelessly fouls up such measurements for those worlds. (I imagine you could do it for Mercury. I'm getting contradictory news on whether it's possible for airless ice-covered worlds, because of the different thermal properties of ice.)

One interesting footnote: an abstract from this year's LPSC ( http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1454.pdf ) suggests that you COULD use a thin plate just lying on the surface to measure Venus' heat flow, rather than having to drill a hole and stick a chain of temperature sensors down it -- because the surface temperature of Venus, thanks to its thick air, changes very slowly compared to that of the Moon and Mars. But several days would still needed for the measurement.

[The Messenger]

Is there really compelling evidence that core properties dominate the Earth's magnetic field? I think a good case can be made that the oceans are a major player: They are conductive, tidal flow and barriers are both aligned in general East-West directions, and there is certainly galvanic action. If there is a net East-West galvanic moment, we could have tremendous continent to continent current flow.

It is an interesting hypothesis, because it implies dumping corrosive metals in the ocean has the pontential for disrupting the Earth's magnetic field. Is it just a coincidence that the Atlantic magnitosphere anomally overlays one of the most complex oceanic currents?

[Guest_BruceMoomaw_*]

Messenger, I think you're off in scientific La-La Land again. If the oceans were generating substantial magnetic fields, it would be instantly apparent by comparing measured magnetic field strength in the middle of a continent as compared to that by a shoreline or in the middle of the ocean.

[Guest_Richard Trigaux_*]

Heat-flow measurements from orbit MAY be practical with a microwave radiometer -- it's always been one of the instruments highly ranked for a US lunar polar orbiter, had we ever flown a full-scale one, and it may yet fly at some point.  But the atmosphere of Mars -- let alone the thick one of Venus -- hopelessly fouls up such measurements for those worlds.  (I imagine you could do it for Mercury.  I'm getting contradictory news on whether it's possible for airless ice-covered worlds, because of the different thermal properties of ice.) 

One interesting footnote: an abstract from this year's LPSC ( http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1454.pdf ) suggests that you COULD use a thin plate just lying on the surface to measure Venus' heat flow, rather than having to drill a hole and stick a chain of temperature sensors down it -- because the surface temperature of Venus, thanks to its thick air, changes very slowly compared to that of the Moon and Mars.  But several days would still needed for the measurement.

Further reflexion lead me to think in a similar way. On the Monn and on Mercury there are places which don't see any Sun heat for days or month, and even never. In such places the radiated heat must be equal to the geothermal flow.
But on Mars and Venus, can a radiometre measure the geothermal flow from space? The probe I was speaking about (I still don't remember the name) was measuring the heat received and emitted by the Earth with enough sensitivity to detect the difference, Earth absorbing heat because of the temperature increase by greenhouse effect. So we could also measure an excess due to geothermal activity. I just don't know the order of magnitude of the two effects. On Venus we can expect that there is no going on increase of greenhouse effect (no climate change) but on Mars this is less sure, we observed changes in ice cap from year to year.
And also for a global measure in geothermal heat, we must account with volvanoes. A giant eruption every 50 million years can evacuate more heat than the constant heat leak.

[Rob Pinnegar]

It is an interesting hypothesis, because it implies dumping corrosive metals in the ocean has the pontential for disrupting the Earth's magnetic field.

Yeah. The odd ton or two of battery acid will definitely be able to overcome the effect of all that salt. I'd stick to discussing the environmental impact.

This is reminiscent of people worrying that gravity boosting of spacecraft could throw Jupiter out of its orbit.

[Rob Pinnegar]

But on Mars and Venus, can a radiometre measure the geothermal flow from space?

In principle, maybe, but the problem is that the amount of power delivered by the Sun to the Earth is something like ten thousand times larger than the amount of geothermal energy that the Earth produces. This would be similar for Venus, and not too much different for Mars.

You'd need to know the albedoes of Venus and Mars to four or five significant digits to pick up the geothermal flow, and it would also be necessary to chart the solar constant to a high degree of accuracy.

It's a nice idea, Richard, but I don't see it being implementable in the near future.

[Guest_Richard Trigaux_*]

It is an interesting hypothesis, because it implies dumping corrosive metals in the ocean has the pontential for disrupting the Earth's magnetic field.

Yeah. The odd ton or two of battery acid will definitely be able to overcome the effect of all that salt. I'd stick to discussing the environmental impact.

This is reminiscent of people worrying that gravity boosting of spacecraft could throw Jupiter out of its orbit.

As a people informed in environment issues, I can say that dumping toxics in the ocean can expectably arise problems of... toxicity, but certainly not of disturbing the magnetic field, ask this to Greenpeace and others, they will confirm (and certainly laugh). This is NOT AN ENVIRONMENT ISSUE. There are already enough real environment issues without adding imaginary ones.

Earth magnetic field is precisely tracked by satellites today, and is known down to the core (we cannot "see" into the core because it is conductive) and if there was magnetic effects in ocean currents, they would be noticed for long ago. The only mysteries are into the core, which dynamic is not really understood, and with some "magnetic anomalies" into the continent, which are very probably metallic deposits.

[Guest_Richard Trigaux_*]

In principle, maybe, but the problem is that the amount of power delivered by the Sun to the Earth is something like ten thousand times larger than the amount of geothermal energy that the Earth produces. This would be similar for Venus, and not too much different for Mars.

You'd need to know the albedoes of Venus and Mars to four or five significant digits to pick up the geothermal flow, and it would also be necessary to chart the solar constant to a high degree of accuracy.

It's a nice idea, Richard, but I don't see it being implementable in the near future.

However this probe was able to pick a minute difference, what Earth is currently absorbing due to the increase of temperature. This implied to measure the albedos and solar constant with the highest possible accuracy available today. The question is here: is the geothermal flow also measurable with this technology? If the outward geothermal flow is much weaker than the inward greenhouse heat absorbtion, you are right. They did not mentioned the geothermal flow about the probe and its result, so likely it could not be measured.

[The Messenger]

Earth magnetic field is precisely tracked by satellites today, and is known down to the core (we cannot "see" into the core because it is conductive) and if there was magnetic effects in ocean currents, they would be noticed for long ago. The only mysteries are into the core, which dynamic is not really understood, and with some "magnetic anomalies" into the continent, which are very probably metallic deposits.

If we are talking purely about alignment and origin, I still think the oceans are worthly of a good head scratch - Magnetic moments originating in the oceans could be selectively magnitizing the underlying core materials - a small dynamo driving the otherwise chaotic ramblings of a much larger one. This is consistent with metal deposits in the continental crusts piling up in anomalies, since they don't get their daily dose of order.

[Guest_BruceMoomaw_*]

The heat-balance satellite Richard is thinking of probably ERBS, put in orbit by Challenger in October 1984. It's an indication of how difficult it is to study global-warming questions WITHOUT satellites that it took a couple of years of measurements by ERBS to answer as fundamental a question as whether Earth's current cloud cover is, on balance, heating or cooling the planet. (It turns out to be substantially cooling us -- at least as it exists now, dominated by cumulus rather than cirrus clouds). ERBS, like UARS, is about to be shut down at last; but the newer big Earth Observing System satellites (especially "Aura") have greatly improved instruments to look into the same matter.

By the way, "Triana" -- the satellite which Al Gore devised in a misguided brainstorm to hang at the L-1 Earth-Sun point just to beam back continuous pictures of Earth -- was equipped, at the insistence of the National Academy of Sciences, with similar energy-balance instruments that might actually have made it worthwhile. But while the satellite was constructed during the Clinton Administration, it's now sitting in a warehouse because the current GOP government refuses to launch it and thereby give Gore favorable publicity.

As for orbital heat-flow measurements: any atmosphere whatsoever simply complicates the transfer of geothermal heat energy into space so much that there is no conceivable workable way to measure it from space -- except, of course, for flat-out local volcanism such as Mars Odyssey and Venus Express are looking for.

[RNeuhaus]

http://www.windows.ucar.edu/tour/link=/phy..._magnetism.htmlhttp://www.windows.ucar.edu/tour/link=/physical_science/magnetism/generating_magnetism.html

Scientists think, although not certain, there are two essential ingredients for generating a magnetic field. Those two ingredients are

* magnetic material
* currents

A bar of iron can be made into a magnet by wrapping it with wires and running a current through the wires.

It is believed a planet, or a star, can generate a magnetic field if it has both of the two ingredients above. It must have enough magnetic material, and it must have currents moving inside the magnetic material. If a planet does not have enough of either of these two ingredients, it will not have a magnetic field. Planets which do not have magnetic fields include Venus (moves very slowly), and Mars (most the iron is on the surface, and not molten).


Venus lacks of magnetic field (Richard has told us) due to very slow rotation.
Mars lacks of magnetic field due to it lacks molten iron.

Rodolfo

[JRehling]

Venus lacks of magnetic field (Richard has told us) due to very slow rotation.
Mars lacks of magnetic field due to it lacks molten iron.

Rodolfo

There's certainly more to it than that, for the simple reason that Mercury has a magnetic field, even though it also rotates very slowly.

The complete story is unknown, but I suspect that some kind of rotational flux is required: variation in rotational period as a function of distance from the axis within some magnetic medium. If a world had an iron core and rotated extremely rapidly, but lacked that flux, I can't see why that would create much of a magnetic field. So I think we'll find that Earth and Mercury have portions of their cores that rotate at different rates (this is already known to be true of Earth), while Venus does not.

[gpurcell]

If we are talking purely about alignment and origin, I still think the oceans are worthly of a good head scratch - Magnetic moments originating in the oceans could be selectively magnitizing the underlying core materials - a small dynamo driving the otherwise chaotic ramblings of a much larger one. This is consistent with metal deposits in the continental crusts piling up in anomalies, since they don't get their daily dose of order.

As I recall, Triana also has to go up on Shuttle, which has posed a problem on the manifest even before Columbia....

[Guest_BruceMoomaw_*]

Triana can be easily launched on an expendable rocket -- once it gets past the GOP. At a minimum, if they're not going to fly it, its energy-balance instruments should be reinstalled on some of the solar-astronomy satellites headed for the L-1 point. But then this White House isn't wildly enthusiastic about global-warming research either, as you may have noticed (although the GOP Congress did force refunding of the Orbiting Carbon Observatory, which is a step in the right direction).