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NASA - NASA Chat: The Moon's Earth-like Core
January 20, 2011

Artist concept of the lunar core An artist's rendering of the lunar core as identified in new findings by a NASA-led research team. (NASA/MSFC/Renee Weber)

Passive Seismic Experiment deployed on the moon by Apollo 14 A close-up view of the Passive Seismic Experiment, a component of the Apollo Lunar Surface Experiments Package (ALSEP) which was deployed on the Moon by the Apollo 14 astronauts during their first extravehicular activity (EVA-1). (NASA/JSC)

Apollo 8 image of the moon Apollo 8 image of the moon. (NASA)

More Information
Worldbook@NASA: Moon
Link: NASA Moon Facts
Link: Moon FAQ
Link: Lunar Impacts
State-of-the-art seismological techniques applied to Apollo-era data suggest our moon has a core similar to Earth's. Uncovering details about the lunar core is critical for developing accurate models of the moon's formation. The data sheds light on the evolution of a lunar dynamo - a natural process by which our moon may have generated and maintained its own strong magnetic field.

The team's findings suggest the moon possesses a solid, iron-rich inner core with a radius of nearly 150 miles and a fluid, primarily liquid-iron outer core with a radius of roughly 205 miles. Where it differs from Earth is a partially molten boundary layer around the core estimated to have a radius of nearly 300 miles. The research indicates the core contains a small percentage of light elements such as sulfur, echoing new seismology research on Earth that suggests the presence of light elements - such as sulfur and oxygen - in a layer around our own core.

The researchers used extensive data gathered during the Apollo-era moon missions. The Apollo Passive Seismic Experiment consisted of four seismometers deployed between 1969 and 1972, which recorded continuous lunar seismic activity until late-1977.

On Thursday, Jan. 20, NASA planetary scientist Dr. Renee Weber answered your questions about the inner workings of our nearest neighbor.

About Chat Expert Dr. Renee Weber

Dr. Renee Weber is a planetary scientist at NASA's Marshall Space Flight Center. She serves as the project scientist for the Lunar Mapping and Modeling Project, a software project designed to provide lunar maps and surface feature information to mission planners and other lunar researchers. Renee's scientific research focuses on planetary seismology, in particular the re-processing of seismic data from the Apollo missions. She is involved in several international efforts with goals of sending modern, broad-band seismometers to both the moon and Mars.

Chat Transcript

(Moderator Jason): We're working on answering the first few questions. To ask your own, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

Dell_Conagher: Could the fluid outer core contribute to the Moon's magnetic field?

Renee_Weber: Today no because the core is too small to convect, which causes the magnetic field generation on Earth. We think the moon's core is currently stably stratified. But in th epast the core may have been larger and able to support convection.

albertoverbay: Do you have an URL for seismograms from the moon?

Renee_Weber: I don't have that handy, but Google for IRIS, which stands for Incorporated Research Institutions for Seismology. That's where I got the data.

fsmarcondes: How is the moon related to the space weather?

Renee_Weber: The moon experiences space weather because there's no atmosphere to protect it from radiation from the sun.

Dell_Conagher: Why is the fluid outer core too small to convect?

Renee_Weber: Well, as the moon cools, the core contracts, so it's not energetic enough to convect.

albertoverbay: Thank you!

Renee_Weber: My pleasure.

SWilson: When do you think we will be able to send seismometers to the moon? Mars?

Renee_Weber: That's a great question. I'm involved in several different missions. Some are active, some are proposed, to send these to both the moon and Mars within the next decade. One is Selene-II, which is a JAXA mission. Others are the International Lunar Network, Lunette, and GEMS (Geophysical Monitoring Station on Mars).

mosshillacademy: (from Andrew, 6years old): Is there water on the moon?

Renee_Weber: There has been recent evidence of water ice in the permanently shadowed craters near the lunar poles.

Dell_Conagher: Can one tell, from how the moon's magnetic field is stratified, how strong it might have been in the past?

Renee_Weber: We use lunar samples. The magnetization of these samples is an indicator of the strength of the historic magnetic field.

Dell_Conagher: When the moon's magnetic field was stronger, could there have been interactions between its field and the Earth's?

Renee_Weber: Possibly, but we don't know what those interactions might have been.

(Moderator Jason): Do you have a question you've been waiting to ask? Go for it! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

MagnusNASA: How was the moon made?

Renee_Weber: The currently accepted model of lunar formation is by giant impact with the Earth.

SImona: Why is this now discovered? Is it because there was so much data to process?

Renee_Weber: There were other types of data that have been used to infer the presence of the core, but this is the first time a direct observation has been made with the seismic data.

LJespersen: Does the molten core support the theory that the moon was formed from a dramatic collision with the earth billions of years ago?

Renee_Weber: Yes, the collision model permits the moon to have formed in an entirely molten state, so a present-day fluid core supports the early presence of melt.

mosshillacademy: Are there any possible benefits of the moon's surface or layers to be useful practically to us here? Thinking...gardening, ecosystems, etc.

Renee_Weber: The core is really deep inside the moon. It's not interacting with anything that happens on the surface. Since there's no atmosphere, the lunar surface is a very harsh environment.

mosshillacademy: (from Andrew, age 6) Is there any possibility that it could snow in outer space, or on the moon?

Renee_Weber: No, no snow in outer space!

robert_1961: What are the likely causes of the partially molten boundary layer?

Renee_Weber: It could be residual melt from formation.

Dell_Conagher: Can the magnetic field be stratified in the fluid outer core? Or does the fluid nature prevent that?

Renee_Weber: It's the moon's core that's stratified, meaning layered. Earth's core convects, which is what drives the magnetic field.

JeffE: When do we estimate that lava was last seen on the moons surface?

Renee_Weber: Billions of years ago.

albertoverbay: Do the Chinese have seismo instruments on their lunar satellite?

Renee_Weber: Seismometers need to be deployed on the surface - so satellites can't really have them.

trialmix: Dark side of the moon... what is it? what lays there...>

Renee_Weber: It doesn't really exist. The moon experiences night and day just like Earth, but because the moon is tidally locked to Earth, we only ever see the same "face."

SWilson: What makes up the surface of the moon?

Renee_Weber: The moon's surface is rocky with many features similar to Earth: mountains, boulders, ridges, etc. There's also a lot of dust.

mainecoaster: Does the moon's core have anything to do with the abundance of water ice found on the moon?

Renee_Weber: The core and water ice aren't really related.

fsmarcondes: So.. if the moon's core is similar to the Erath's one, someday it could also became too small to convect... then we will lost our magnetic field?

Renee_Weber: Yes, but that definitely won't happen in our lifetimes. :)

Dell_Conagher: What's the average ratio of how strong the moon's magnetic field is now, to how strong the models predict it was in the past?

Renee_Weber: Now it has NO magentic field.

Eeyore3061: Did the ASLEP seismoneters moniter a 'wavelength' that would show impacts of NEO's? And if so, were they spread far enough apart to triangulate a general area for current and future visual mapping to pinpoint new craitors when compaired to the new Lunar Orbiter imagery?

Renee_Weber: The Apollo seismometers DID record meteorite impacts. Earth-based telescopes can be used to observe light flashes associated with impacts, which can be used as active sources for future lunar seismic missions.

RPEREZALONSO: Does the boundary layer around the core behave anything like the upper mantle on Earth?

Renee_Weber: Can you specifiy what kind of behavior?

TitanMan: How deep down is themoon's core?

Renee_Weber: The depth is about 1400 kms below the moon's surface - the depth of the core mantle boundary.

RPEREZALONSO: How does this discovery affect the theory of formation of the moon?

Renee_Weber: It supports the large impact model.

BellaLuna: Is it possible for volcanos to erupt on the moon?

Renee_Weber: Not today - however the lunar mare or "seas" were formed by ancient lunar volcanic activity.

LJespersen: Would it be desirable or even possible to stimulate movement within the core to create a magnetic field to protect future manned missions?

Renee_Weber: I don't think that would be possible, but that's a really interesting idea!

TitanMan: Is the moon's outer core similar to Earth's?

Renee_Weber: Yes, a liquid iron core.

trialmix: Is their trembling or earthquake in the moon>> if so... how strong is it compare here on earth?

Renee_Weber: Yes, the moon has three main types of seismic events: deep moonquakes, which occur halfway to the center of the moon and are very small, comparable to an earthquake of magnitude 1 or less; shallow moonquakes, which are about magnitude 5, but occur much less frequently; and meteorite impacts, which have a large range of magnitudes, depending on the size of the impactor.

TitanMan: Is the moon's core geologicaly active due to tidal flexing from Earth?

Renee_Weber: The tidal deformation of the moon is believed to trigger the deep moonquakes.

fsmarcondes: If the moon is the result of a collision within the Earth, why does it's core cooler faster than the Earth's?

Renee_Weber: In part because the moon is smaller.

Montsecor: Are there any working seismometers in the moon nowadays? Were the only ones delivered by the Apollo astros?

Renee_Weber: Unfortunately, the only ones that ever made it to the surface were delivered by Apollo. We're working on sending new instruments in the future.

Dell_Conagher: Oops, shows I don't know enough about stratification. :) Can the fluid layer of the core be stratified?

Renee_Weber: Yes, it can.

fsmarcondes: there is volcanos on moon? where can i find a photo of one?

Renee_Weber: Try www.nasa.gov and search for "lunar surface images."

TitanMan: What raw material's are at the Moon's Core?

Renee_Weber: The moon's core is largely iron with a smaller amount of lighter alloying elements, like sulfur.

Brian_Simmons: Can you explain what type of seismomitors are in the works for the moon and mars, and the delivery vehicles/ methods for deployment.

Renee_Weber: Yes - they're broadband instruments with higher sensitivity and lower noise floor than those of Apollo and are designed to be deployed from an orbiter.

TitanMan: Are moonquakes related to the convection process's at the moon's core?

Renee_Weber: That's been proposed but not proven - probably unlikely since we don't believe the core to be convecting today. Yet we know moonquakes still occur.

(Moderator Jason): Here's a great repository of a lot of NASA's images of the moon: http://photojournal.jpl.nasa.gov/target/Moon

SImona: Why is the Moon moving away from earth at a rate of 1.5 inches per year?

Renee_Weber: It's caused by gravitational torque on the lunar orbit.

JJ: If we lost our magnetic field what will happen? Will Earth float away? Will the Moon float away? What exact would happen?

Renee_Weber: The magnetic field isn't what keep the moon in orbit around the Earth - it's the gravitational interaction between the two bodies. If Earth lost its field, it would have catastrophic circumstances!

TitanMan: Did the moon in the past have tectonic plates similar to Earth?

Renee_Weber: There's no evidence for that to date.

trialmix: Is there any trembling or earthquake in the moon ? how strong is it compare here on earth ?

Renee_Weber: Yes, the moon has three main types of seismic events: deep moonquakes, which occur halfway to the center of the moon and are very small, comparable to an earthquake of magnitude 1 or less; shallow moonquakes, which are about magnitude 5, but occur much less frequently; and meteorite impacts, which have a large range of magnitudes, depending on the size of the impactor.

(Moderator Jason): We're working to answer your great questions. Keep them coming! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

TheSuss: Given what you're seeing now, what new types of data would you like to see collected?

Renee_Weber: More seismometers! A global distribution of seismometers, including the far side.

Emspak: What is the composition of the lunar mantle, and is it possible there are volatiles there? CHON? Water?

Renee_Weber: The large impact theory predicts that volatiles like water are largely ejected by the high energy formation - but given the recent discovery of surface water, we may have to rethink those models.

mposton: Can the seismometer data be used to search for any burried deposites of light materials (such as burried water or ice)?

Renee_Weber: Not really - you'd need a much more dense network of instruments to do that type of seismic imaging, such as is done on Earth with oil exploration.

Dell_Conagher: How was it discovered that the moon's core was stratified?

Renee_Weber: It wasn't really discovered so much as that's the result we put forth to satisfy the constrint that the moon has no magnetic field today.

trialmix: is this liquid iron core is moving or in one place only?

Renee_Weber: It's not convecting, so it's essentially "sitting still."

Alex: How much can we learn if we send just one seismometer to the moon. What are the chances of actually deploying 4 like Apollo did? (How far apart would they have to be)

Renee_Weber: Deploying multiple instruments in an expensive and risky venture. Fortunately, science can be done with only one instrument, but would require known seismic source, like the meteorite impacts I suggested earlier.

mm: What do you think about hollow Moon theory? Is there any evidence that confirm this?

Renee_Weber: None of our results support that theory.

JeffE: If the moon is geologically inactive, then what causes the shallow moonquakes?

Renee_Weber: That's a question I would REALLY like to answer! Some think it might be some type of tectonic release of energy "frozen' into the surface rocks.

Dell_Conagher: Does the discovery of the new model of the core mean that models of moonquakes may also need to be changed?

Renee_Weber: Yes, because some deep moonquakes depths are very close to the molten layer, suggesting that brittle failure can't occur.

SoCal_watcher: I thought that the current theory of the moon's formation was due to it not having a similar core as Earth's, now you're saying that does, how does it alter the theory?

Renee_Weber: The structure is similar in that it has a solid inner and fluid outer core. The large impact theory predicts that the moon would largely be formed from material originating from the impactor.

JJ: If Earth ever literally vanished in the matter of seconds (highly unlikely), what would happen to the Moon?

Renee_Weber: It would just settle into orbit around the sun.

(Moderator Jason): Do you have a question you've been waiting to ask? Go for it! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

RPEREZALONSO: Does the layer around the moon's core have properties similar to the asthenosphere? Plastic like? Semi Solid? Does convection occur on the moon?

Renee_Weber: It's difficult to constrain the properties of the partial melt layer - so we're really pushing for future seismic mission to help answer that question!

mosshillacademy: (from Andrew, age 6) What is the temperature of the moon? Is it similar to the earth's core and layers' temperatures?

Renee_Weber: It's not as hot because the moon is smaller - hence its internal pressure is also smaller.

Andrea: How many meteorite impacts in a day/month/year on the moon surface?

Renee_Weber: This would be a great Web site for that kind of information: http://www.nasa.gov/centers/marshall/news/lunar/index.html

Dell_Conagher: What's the next big question you would like to work on in lunar research?

Renee_Weber: I'm interested in addressing the seismicity of the far side of the moon. All of the Apollo instruments were located on the near side.

mposton: What challenges would placing seismometers on the far side present?

Renee_Weber: If the seismometers are located on the far side, we also need to have an orbiter to relay the data from those instruments - so a far side mission is inherently more expensive and more technologically challenging.

aggelos: If Moon has a similar core to Earth's why doesn't it have a megnetic field?

Renee_Weber: The moon's core doesn't convect like Earth's. Convection drives the magnetic field.

Antdoghalo: I heard the maria formed a while after the large impact basins formed is that true?

Renee_Weber: Yes, that's true.

Antdoghalo: Could the core melt the rock around it?

Renee_Weber: There's the partial melt layer, which is a boundary between the fluid core and solid mantle.

mosshillacademy: If you believe the impact theory, how can you explain the earth and moon to be so uniquely organized and formed at the same time? Yet the two are so very different?

Renee_Weber: The large impact model predicts that they didn't form concurrently. There are so many factors in both planets' evolutions.

aggelos: Do these meteorite impacts affect the core of the Moon?

Renee_Weber: No, only the surface and the shallow sub-surface.

aggelos: What about the theory that the moon is made of cheese?

Renee_Weber: No comment. :)

JeffE: It doesn't sound likely to have a liquid and not have it convect. What makes us believe that the moon does not have a convecting interior?

Renee_Weber: Because of the realitively small size and lower temperature of the core compared to Earth.

Dell_Conagher: I know the more seismometers the better, but what would be a good starting number that you would like to see in a mission?

Renee_Weber: You need at least four to adequately locate an event with unknown origin.

TitanMan: Is it possible that the moon has hotspots similar to Earth that cause these shallow moonquakes?

Renee_Weber: I don't think so.

aggelos: Is it likely that Moon falls to Earth if it is hit by a large meteorite?

Renee_Weber: If a large body struck the moon, the resulting ejecta COULD reach Earth, but probably would be burned up in the Earth's atmosphere.

TitanMan: If the moon was formed from the results of an impact with Earth wouldn't it have a diffrenciated core?

Renee_Weber: It DOES have a differentiated core. That's what we observed with the seismic data.

RPEREZALONSO: Do we know how the temperatures in the moon compare to the temperature of the interior parts of the earth or not yet?

Renee_Weber: We can predict based on the size of the moon's core. The temperatures are probably lower than those of Earth.

TitanMan: Why couldn't the moon have formed from a sub-nebula around Earth similar to the icy moons?

Renee_Weber: That's another theory that's been suggested previously.

Emspak: When you mentioned rethinking the impact model, in what sense? Is the impact formation model fundamentally wrong, or does it just need tweaking?

Renee_Weber: It's not the model that needs tweaking, but rather the amount of volatiles that could be entrained in lunar materials.

SImona: How many years from now do you plan on putting new seismometer on the Moon?

Renee_Weber: Hopefully within the next decade.

MoonMan: Has there been any proof that the energy "frozen" is being released from surface rocks? Do we know for sure if this why the moon geologically inactive?

Renee_Weber: The moon isn't technically geologically inactive - but because there are no obvious active plates like on Earth, we can only assume sources of seismicity. For example, as the moon cools throughout its history, it contracts. This contraction could result in some type of surface seismic activity, but we really won't know until we have more data.

spacegirl(: Does the moon have tectonic plates or something that acts like tectonic plates on earth?

Renee_Weber: No, no tectonic plates. But there are features that could be tectonic in origin, like wrinkle ridges.

SoCal_watcher: Thank you for the chat, appreciate the answer... though wish there was time for follow-up. Anyway, thanks again.

Renee_Weber: You're very welcome - appreciate you being here for the chat.

TitanMan: how high in magnitude can moonquakes go up to on the Richter scale?

Renee_Weber: There hasn't been a specific magnitude scale developed for moonquakes, so we can only compare them to earthquakes - but the largest ones could be as high as magnitude 5.

Montsecor: You talk about the seismicity of the far side, could it be that only one side is seismically active? If so, why, or how?

Renee_Weber: It could be. I don't know the answer to why - but I personally think the far side is seismically active.

trialmix: Is this far side of the moon is commonly known dark side of the moon ??

Renee_Weber: Yes, they refer to the same thing, even though the "dark side" isn't really dark.

spacegirl: Did the moon at some point have a lot of volcanic activity like very early earth?

Renee_Weber: Yes, flood basalts formed the lunar "seas."

mosshillacademy: So, you agree that the earth and moon could exist without the other?

Renee_Weber: Yes.

spacegirl: Would it be possible to drill into the moons core?

Renee_Weber: No, that would be a very expensive undertaking!

MoonMan: How cold does it get on the moon?

Renee_Weber: Very cold - cold enough that astronauts and instruments must be thermally shielded through the lunar night.

TitanMan: Do you believe the mon has a solid Iron core like Earth?

Renee_Weber: Yes, we believe we've found evidence of that.

mosshillacademy: ***Thank you so much, Dr. Renee Weber! This was wonderful and our first time doing something like this!!! We learned a lot and hope to be more involved with NASA online! :)

Renee_Weber: You're so welcome - hope to see you again on future chats!

TitanMan: What would you tell a future NASA moon explorer?

Renee_Weber: Just to do as much science as possible - and pick up lots of rocks!

guest: If a wind were to suddenly develop on the moon and all the dust were swept away would there be solid rock over most of the surface.

Renee_Weber: I think so - but I'm not sure how it would look!

trialmix: what are the cuses of the shallow moonquakes ?? does it affect the moon surface??

Renee_Weber: The cause is currently unknown.

MoonMan: What is your favorite aspect or part of the moon to study?

Renee_Weber: I like learning about the deep interior of the moon because it was the least well constrained part in the Apollo era.

Alex: Would it be hard to deploy those 4? stations all over the near side far apart from each other or is that too logistically difficult?

Renee_Weber: The Apollo instruments were all deployed by the astronauts. We don't know what the future holds, so we have to plan on remote deployment - which is always a technological challenge.

(Moderator Jason): We've got time for a few more questions today...

spacegirl: What exactly does a planetary scientist do?

Renee_Weber: There's a wide range of topics to study in planetary science. Anything from rocky bodies, like Mercury, Venus, Earth, Mars, the Moon, to the gas giants, their satellites and many other things in the solar system. Anything you can think of, you can study!

trialmix: thanks dr weber.... its 5am now here... ive learned a lot from this chat!

Renee_Weber: Wow, you're up early - thanks for being here!

MoonInformation: Are the Appolo instruments still active?

Renee_Weber: Not today, unfortunately!

Alex: Do you think remotely deployed seismometers will record/be coupled as well as astronaut deployed instruments?

Renee_Weber: Some seismometers have been developed to withstand an impact with the surface, so would be deployed in a "penetrator" - others require semi-soft landing.

LJespersen: Thanks for answering all the questions, was very interesting!

Renee_Weber: This has been a great chat, and I appreciate the questions. Thanks for being here.

MoonMan: Thanks for the great insight and for anwsering my question. :D

Renee_Weber: My pleasure!

(Moderator Jason): Thanks Renee for the great answers to everyone's questions. We appreciate your taking time out of your day to sit down with us. Our chat is over! Thanks for participating. A transcript will be available within the next few days.

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