Posted by
michael
on from the mars-doesn't-want-to-go-on-the-cart dept.
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)."
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).
-- "I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
They didn't measure displacement. of the surface
by
barakn
·
· Score: 4, Informative
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.
-- "I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
Re:What makes a core hot?
by
sc7007
·
· Score: 3, Informative
Radioactive decay is correct. (MS in Geology/Geophysics). Frictional heating, while certainly present, is insignificant.
Re:What makes a core hot?
by
palndrumm
·
· Score: 3, Informative
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?
by
CheshireCatCO
·
· Score: 4, Informative
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.
Slashdot Mirror
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).
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
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.
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
Radioactive decay is correct. (MS in Geology/Geophysics). Frictional heating, while certainly present, is insignificant.
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.
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.