Moon Rock Reveals Hot Molten Core

[Ichingcarpenter]

A moon rock brought back by astronauts from the last Apollo mission in 1972 has finally proven its worth by revealing that the moon used to have a hot, convecting molten core that generated a magnetic field.

The moon’s magnetic field was probably about one-fiftieth as strong as Earth’s current field. The discovery is consistent with the theory that our moon was born when a giant asteroid barreled into Earth and broke off chunks that clustered together to become an orbiting satellite.

The rock is a special sample because it dates from about 4.2 billion years ago, but somehow managed to avoid being subjected to major shocks from asteroid impacts, which tend to erase evidence of any magnetic fields.
“It is one of the oldest and most pristine samples known,” said MIT graduate student Ian Garrick-Bethell, lead author of a study published Thursday in Science. “If that wasn't enough, it is also perhaps the most beautiful lunar rock, displaying a mixture of bright green and milky white crystals.”

Thanks to this super specimen, scientists were able to detect magnetic traces in it that suggest the moon used to have a magnetic field in ancient times. The field was likely caused by an active hot liquid core, like the one inside Earth today.

"We believe the moon's core is still molten now, but the difference is that it doesn't have this dynamo, this convecting current that supports and generates a magnetic field," Garrick-Bethell told Wired.com. "It's possible that it stopped because the moon is much cooler now."

It was astronaut Harrison “Jack” Schmitt, the only geologist ever to walk on the moon, who hand-selected the specimen that led to this discovery.

http://blog.wired.com/wiredscience/2009/01/moon-magnet.html

[Poll_Blind]

1. Does anyone know what the estimates are on the continued existence of Earth's molten core?

I mean, from what I know it's gonna be a long time before we have to worry about it solidifying. Just wondering if anyone knew of any estimates on how long we've got.

PB

[Orrex]

3. Hillary Swank and a crew of experts are working on this right now

Rest assured!

[pokercat999]

4. I don't think this is something you or for that matter the next

several hundred generations of your future relatives have to "worry" about.

[Confusious]

5. The orbit of the moon causes the core to stay molten

Because of gravitational action, so probably when the moon finally flies out of it orbit in a couple billion years.

[Poll_Blind]

6. Oh? Crap, I thought we owned the moon! I mean, that it was locked in Earth orbit...

..., well, I was gonna say 'forever', but now that I realize we're talking astronomical units of time I guess you can't really bank on anything, can you?

PB

[Xithras]

7. The moon has nothing to do with the heat in the core.

Lunar tidal pull may help with tectonic processes on the surface, but it has virtually nothing to do with the source of the mantle and cores heat. We're talking no more than a fraction of a percent. The heat actually comes from four sources.

1. Stored heat from planetary formation. Remember physics...heat doesn't just vanish into nothing. Space is a good insulator and the planets crust acts as a blanket. The core still contains a considerable amount of heat left over from the planets formation.

2. An even bigger source was gravitational heat. As the planets mantle seperated, heavier metals were pulled to the core by gravity. This generated an almost unfathomable amount of friction and heat, and still generates some today. Another large percentage of the heat present today is either new heat generated by this process, or latent heat left over from the planets early days.

3. Then you have "compressive" or "latent" heat (depending on who you ask). The core of the planet is cooling, causing the metal to slowly solidify. As it does so, it expands slightly which compresses the rocks around it. This compression generates a massive amount of heat.

4. The previous three generate a lot of heat, but the overwhelming majority of the heat (up to 90% by some estimates) comes from plain old radioactive decay. Elements like uranium are rare on the surface because they're heavy and settled to the core of the planet during its formation (making gravitational heat in the process). Uranium and other heavy radioactive elements below the crust keep the planet warm, like a giant nuclear reactor.

The core is cooling off as we speak, and scientists long ago realized that the primary energy source for our planet is slowly winding down. This is a good thing for us, since hotter cores are responsible for increased volcanism. We really don't need another Deccan Traps on the planet today.

By most estimates, the core has about two billion years left before it cools to the point of irrelevancy. As those two billion years pass, eruptions and plate tectonics will simply slow down over eons until they vanish. All bets are off if the prediction of plate locking in 350 million years comes to pass though. There has been some speculation recently that plate tectonics may come to an end when the final subduction zones around the Pacific Plate are consumed in 350 million years. If that happens, the mantle will lose its cooling ability and will superheat, possibly adding a few billion more years of heat to the planets core. Of course, that superheating may also melt the surface again.

[TechBear_Seattle]

8. It may help, but the barycenter of the earth-moon system is just below the earth's crust

A http://en.wikipedia.org/wiki/Barycenter#Barycenter_in_astronomy">barycenter is the center of mass around which a gravitational system of multiple objects revolves. Enjoy the graphics in the Wikipedia link.

The barycenter of the earth-moon system is about 1,700 km down, barely 27% of the distance from the equator to the center and almost 1,200 km from where the outermost edge of the planet's core is believed to be. Gravitational "kneading" probably helps to keep the mantle hot, which in turn would insulate the core and slow its cooling. It would not be enough to heat the core directly, however.

[Ediacara]

2. By "giant asteroid" they mean "a planetoid roughly the size of Mars"