MadSci Network: Astronomy

Re: Would it be possible for a planet to have an ocean of liquid mercury?

Date: Fri Mar 24 23:16:12 2000
Posted By: Matthew Buynoski, Senior Member Technical Staff,Advanced Micro Devices
Area of science: Astronomy
ID: 953785306.As

Well, it's a very big universe and science fiction is not limited by what we 
know today, but..... is *really* hard for this Mad Scientist to come up with anything 
that could even come close to providing any justificqation for such an 
incredible concentration of that element.

Mercury is probably made by two methods. The first is slow neutron capture. 
This can occur in a fair number of heavy stars and can make elements up to 
about the atomic mass of bismuth.  The second method is creation in 
supernovae; there is some argument as to exactly how this occurs, but the 
books I read seem to agree that the heaviest elements are made in these 
stellar catastrophes. However, in both cases, mercury will be only a tiny 
fraction of the total metals produced. 

Moreover, metallic mercury is only produced in reducing (no free oxygen) 
conditions. So your planet must have a reducing atmosphere and thus is 
likely to be a pretty large one, probably a gas giant with a rocky core. It 
is possible that it could be Earth sized, but somewhat unlikely because 
we're more or less saying the concentration of heavy metals is much higher 
in this particular planetary system and thus it seems reasonable (this is
guesswork on my part) that the protoplanets are likely to be exceptionally
heavy as well, thus more able to grab hydrogen and helium.

Worse, I just don't see how that much mercury (which is quite dense) will 
stay above the main bulk of the planet, which is almost certainly going to 
be iron/nickel/cobalt and some lighter elements. The mercury, even if it 
were there, is very likely to sink down into the center of the accreting 
planet and thus be swallowed into its core.  (In some vague sense, this 
comes close to your metallic ocean, that is, the Earth has a liquid outer
core...which  can be considered an 'ocean' of molten metal overlain with the
mantle of silicates. I suppose one could posit a catastrophe that stripped
a protoplanet of its silicates, leaving a naked core that might have, if not 
oceans, at least large lakes of molten metal at its surface...but that's
really stretching things).  

I'd like to recommend a book to you; "From Stone to Star" is a good 
introduction to the formation of the Earth from the original stellar nebula
that collapsed to form the solar system.  It will give you a pretty good
background against which to test your ideas for your imaginary planet.

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