PDA

View Full Version : Mercury is Soft in the Middle



Fraser
2007-May-03, 07:40 PM
A team of astronomers has discovered that tiny Mercury has a molten core, just like our own planet. The discovery was made using three ground-based radio observatories that bounced radio waves off the planet, and then analyzed the return signals. ...

Read the full blog entry (http://www.universetoday.com/2007/05/03/mercury-is-soft-in-the-middle/)

trinitree88
2007-May-03, 11:08 PM
A team of astronomers has discovered that tiny Mercury has a molten core, just like our own planet. The discovery was made using three ground-based radio observatories that bounced radio waves off the planet, and then analyzed the return signals. ...

Read the full blog entry (http://www.universetoday.com/2007/05/03/mercury-is-soft-in-the-middle/)

Fraser. Thank you. Surprising result to some. Piece of the puzzle to others. Pete.

EDG
2007-May-04, 02:36 AM
Very interesting! So the question is, how is still molten after all this time? Just because of impurities in it, or could Mercury still be experiencing tidal heating in its eccentric orbit around the sun (seems unlikely to me, given the distances involved).

I'm guessing some suggestions for its continued molten state are in the original Science article...

John Mendenhall
2007-May-04, 02:46 AM
Very interesting! So the question is, how is still molten after all this time? Just because of impurities in it, or could Mercury still be experiencing tidal heating in its eccentric orbit around the sun (seems unlikely to me, given the distances involved).

I'm guessing some suggestions for its continued molten state are in the original Science article...

Radioactive heating?

EDG
2007-May-04, 03:07 AM
Well, radioactive heating is always going to be there in a rocky body anyway - that's generally what's keeping planetary interiors hot.

I just read the original paper, and the authors say that the implication is that the core (a) isn't necessarily entirely molten, just that there is at least a molten outer core that decouples the mantle/crust from the interior (a fully molten core would require a LOT more sulphur than thought, and also would probably knock out any dynamo magnetic field because with that much S it'd be stable to convection), and (b) that it's most likely molten because it has a high percentage of sulphur impurities. But according to our models of the protosolar nebula, sulphur can't condense at Mercury's distance, so the implication is that more of it came from elsewhere (further out, where more volatile rich planetesimals have more sulphur) - this in turn implies greater mixing of planetesimals with distance than previously supposed. I'm not too surprised by this myself, given what Sean Raymond has been saying in his excellent extrasolar system modelling papers (see http://lasp.colorado.edu/~raymond/research.html ).

Very interesting stuff.

RUF
2007-May-05, 03:45 AM
My impression was that sulfur has a lower melting point, so even with the amount of heat radiated away from Mercury over the eons, there would still be enough heat to melt sulfur.

EDG
2007-May-06, 03:38 PM
My impression was that sulfur has a lower melting point, so even with the amount of heat radiated away from Mercury over the eons, there would still be enough heat to melt sulfur.

Yes, but that's not what's going on here :). The sulphur isn't there in a pure state, it's chemically bound to the iron and nickel in the core. FeS (iron sulphide) has a lower melting point than pure iron or nickel-iron - that means the temperature has to drop further for the core to freeze, so the core remains molten or partially molten for longer.

RUF
2007-May-07, 06:51 PM
Excellent EDG. Now I understand

Walker59
2007-May-10, 11:22 PM
Radioactive heating?

Last I checked ESA was launching probes to map the planet in a variety of spectrums. Those results might be interesting, but for the most part it is a blasted lump of heavy metals. Mars or even Venus would be better to focus on as useful lifeboats for the future. But that's another story.

Nick4
2007-Jun-07, 01:45 AM
Could it be because its so close to the sun?

Nick4
2007-Jun-07, 01:46 AM
Could it be because its so close to the sun? Maybe mercury compensates for not having an extremly hot surface by having a molting inside...maybe the surface of mercury is like a thin greenhous like skin that holds in the heat and melts everything.

m1omg
2007-Jul-15, 09:23 AM
Could it be because its so close to the sun? Maybe mercury compensates for not having an extremly hot surface by having a molting inside...maybe the surface of mercury is like a thin greenhous like skin that holds in the heat and melts everything.

???
Mercury's avg. daily temperature based on it's dist. from Sun is 300 deg. Celsius, far cry from anything required to melt rock/metal.

3488
2007-Jul-16, 02:27 PM
Mercury's super thick silicate rich crust will insulate the care to quite a high degree. If sulphur is there in large quantities it will lower the molten point of the iron (I have heard similar with Jupiter's Ganymede, an Iron Sulphide core that is maybe partially molten).

The insulating effect of a mega thick crust & a iron sulphide core, is probably enough to keep it at least partially molten.

Not aware if Mercury still has active volcanism? I doubt it very much. We'll see when MESSENGER arrives.

During next January's encounter, we will get to see 45% of the unimaged hemisphere, by Mariner 10.

Andrew Brown.