Mars May Have Liquid Iron Core

mikef2501 writes "Science Daily News reports that results from three years of radio tracking by the Mars Global Surveyor spacecraft indicate that the core of Mars may not be geologically dead after all -- it may still contain at least partially molten iron (original news release found here)."

Comments

Mars?

[RaboKrabekian]

I thought a Mars had a core of chewy nougat surrounded by peanuts and caramel?

Thank you, I'll be here all week.

What makes a core hot?

[stefanlasiewski]

Ok, here's a question for you geology geeks. What makes a planet core hot?

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?

[sc7007]

Radioactive decay is correct. (MS in Geology/Geophysics). Frictional heating, while certainly present, is insignificant.

Re:What makes a core hot?

[palndrumm]

It's both.

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?

[CheshireCatCO]

People have already answered the question pretty well, but I'm going to try to offer a slightly broader picture. (Why, yes I do teach. Why do you ask?)

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.

Hmmm...

[Strange Ranger]

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.

Re:Odd

[barakn]

The Earth's outer core is liquid, but the inner core is solid. A solid inner core will naturally be crystalline. The real question is whether it is one giant crystal or many interlocked crystalline domains of random orientation.

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?

[General Wesc]

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?

[barakn]

Hmmmm... magnetic fields generated by liquid core dymanos are generally dipoles (except when they are flipping over). Mars' magnetic field is extremely weak in the northern hemisphere (blasted off by an enormous collision). In the south it is patchy: in some areas it comes in stripes of opposing polarity. This suggests it is remanent magnetism frozen in place when the rocks first formed. There must have been a reversing dipole field at one time, and each stripe of rock formed between field reversals.

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?

They didn't measure displacement. of the surface

[barakn]

The satellite's orbit is what is used to measure tidal bulges. Here's how it works, in layman's terms: A satellite orbiting Mars will describe a roughly ellipsoidal shape. One can draw a straight line through the point where the satellite is closest to Mars and the point where it is farthest (a.k.a. major axis). In the absence of tidal bulges, orbit after orbit, this line will remain pointed in the same direction in space. This works even if Mars's mass is not arranged in a perfectly spherical manner (caverns, dense mineral deposits, huge volcanoes, etc.).

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.

Not original but still a classic

[madsenj37]

Geology Rocks!