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willstaruss22
2012-Sep-19, 05:55 AM
Can a planet be coreless and if so how would it get that way?

Shaula
2012-Sep-19, 06:08 AM
Only very small objects could be - for larger objects the temperature and pressure due to overlaying layers pushing down would cause the planetary material to deform and fill in any gap at the core.

Ara Pacis
2012-Sep-19, 06:22 AM
Or does the OP mean that there's no differentiation of material into core, mantle, crust, etc.?

korjik
2012-Sep-19, 06:30 AM
Or does the OP mean that there's no differentiation of material into core, mantle, crust, etc.?

Technically it is the same either way. Once you get up over the size of around Ceres it is pretty much inevitable.

chornedsnorkack
2012-Sep-19, 06:54 AM
Technically it is the same either way. Once you get up over the size of around Ceres it is pretty much inevitable.

Moon is suspected of having very small core. So are the inner big satellites of Saturn.

You could avoid differentiation if you form the planet from material of homogenous composition - nothing to differentiate and thus the composition remains unaltered at all depth. Inevitably all substances are subject to elastic compression, but a homogenous body with no changes with depth save continuous and fully reversible elastic compression can fairly be described as coreless.

eburacum45
2012-Sep-19, 07:45 AM
To have a rocky planet that has very little or no core requires a process that reduces the iron in the composition of the planet to a minimum. The creation of the Moon is one such process; after the collision the Moon was formed mostly from material spashed up from Earth and the impacting body, which means that the iron at the Earth's Core was not included in the mix. If a planet were created by a collision between two larger bodies, which coalesced into one even larger body and a smaller, lighter body, then this second body could have a very low core mass fraction. If you want it to be a separate planet rather than a moon you would probably need to imagine a second encounter with yet another planet which could rip the moon out of orbit.

I think that some outer system bodies might be mostly composed of ice and rock, with little iron; this might be the case if there is some sort of differentiation in the protoplanetary cloud, so that heavier metals are concentrated in the inner system. If an icy body were displaced into the inner system the result might be a watery world with very little core, but possibly a large rocky mantle.

willstaruss22
2012-Sep-19, 07:49 AM
Yes thats what i was thinking a ice world in the outer solar system with very little iron migrating to the inner solar system. I just didnt realize that was possible because it would need something big enough to displace its orbit.

Ivan Viehoff
2012-Sep-19, 12:27 PM
Can a planet be coreless and if so how would it get that way?
Given that planets are not believed to form with cores already present, but rather form a core when their interiors are sufficiently able to flow to allow differentiation to form one, what you really mean is, "how would it avoid forming a core". The answer is "by being cold enough". Usually, to be cold enough, it has to be small enough, so that the heat of accretion does not melt the interior. In principle a larger-than-usual coreless planet could form if accretion happened sufficiently slowly for it to lose heat as it formed to remain cold inside. It would also have to avoid heating up inside through radioactive decay. This could only happen if the population of material forming the planet was depleted in heavy elements.

quotation
2012-Sep-19, 06:04 PM
Given the right circumstances, such as the combination of elements, energy (heat), etc., why couldn't the process (linked below) scale up to produce a hollow "planet-oid"?

http://www.ysxbcn.com/upfile/soft/20091127/36-p0718.pdf
Si3N4 nano-microsphere synthesized by cathode arc plasma and heat treatment

Abstract: The Si3N4 microcrystals with a hollow sphere structure were prepared by using the simple heat treatment of the Si3N4 flakes, which were prepared by using the cathode arc plasma. The products were characterized by XRD, SEM and TEM. The photoluminescence (PL) spectrum of the Si3N4 nano-microsphere was studied. The obtained Si3N4 microcrystals, which show a hollow sphere structure, are up to several nanometers in diameter. During the process, the heat treatment and Ni catalyst play a key role in the forming structure and morphology. This result provides a possibility for mass producing Si3N4 microcrystals.

Noclevername
2012-Sep-19, 08:34 PM
Given the right circumstances, such as the combination of elements, energy (heat), etc., why couldn't the process (linked below) scale up to produce a hollow "planet-oid"?

http://www.ysxbcn.com/upfile/soft/20091127/36-p0718.pdf
Si3N4 nano-microsphere synthesized by cathode arc plasma and heat treatment

Gravity. The mass increases with size, the expansive force does not, or at least not nearly as much.

Ara Pacis
2012-Sep-20, 09:44 AM
Technically it is the same either way. Once you get up over the size of around Ceres it is pretty much inevitable.

I thought Shaula was referring to a planet with a hollow center.

Shaula
2012-Sep-20, 11:31 AM
I thought Shaula was referring to a planet with a hollow center.
I was - but from what the OP has said afterwards that was not what they meant. So I shut up out of embarrassment at misinterpreting them!

publiusr
2012-Sep-22, 08:11 PM
I think an asteroid might be shoved towards the sun after having it pass near Jupiter, similar to the solar probe plus (sent there to cancel the orbital angular momentum so it might fall more directly to the sun)

The asteroid would have a nuke or even some water at its core to cause it to expand into a hollow shape when molten.