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I'm new to this and my scientific knowledge is massively lacking in this area (so please take it easy on me!) I'm writing a historical science-fiction novel. Parts of it set in the past (1977) and some of it set in the not so distant future.

I need to create a planet that has a layer of silver dust (not necessarily the element/metal silver, but silver in appearance) that covers the entire planet's surface. From a distant solar system, does not need to be similar to our solar system. I would also like to include rivers/lakes of mercury on the surface of the planet. Is it possible for a planet like this to exist and what would its chemical make-up be? Humans do not need to be able to survive there or even visit. Just two metal robots/spacecrafts... one is from Earth (launched 1977, Voyager) and one is from another planet (Robot, very sophisticated).

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    $\begingroup$ reading this remind me of Emperor Qin Shi Huang Tomb and his Liquid River/Lake made of the so called "Pill of Immortality". $\endgroup$ – Li Jun Apr 5 at 13:11
  • $\begingroup$ human survival not necessary indeed..... $\endgroup$ – Li Jun Apr 5 at 13:20
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    $\begingroup$ Silver dissolves in mercury (technically it forms an amalgam, but the effect is the same), so your silver dust won’t last for long if there’s mercury flowing around. $\endgroup$ – Mike Scott Apr 5 at 18:43
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    $\begingroup$ Mercury is also heavier than most other metals (~20% heavier than lead). Unlike water, it will leak under the crust at first tectonic occasion. $\endgroup$ – fraxinus Apr 5 at 21:16
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    $\begingroup$ To be ultra-realistic, how do the rivers get refilled? Here, water easily sublimates into the atmosphere, forms clouds, and rains down. What's the mercury cycle that re-fills the rivers? $\endgroup$ – simon at rcl Apr 6 at 14:52
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A world with very large amounts of mercury seems improbable as mercury is so much less common than the lighter elements. Perhaps large amounts of mercury could have been gathered by an alien race for some unknown purpose, but rivers of mercury are sadly very unlikely to occur naturally in the vast quantities that you need.

Should such a world be hand waved into existence and remain intact I would expect the vast majority of the planet to be composed of metallic elements. Many non-metals would react with mercury forming a range of salts that would spoil the appearance with a white or coloured crust.

Many metals also form amalgams with mercury so there would be a great deal of erosion of any metallic landscape. That said some metals are more resistant to forming amalgams such as iron, platinum, tantalum and tungsten so these elements might be more useful in constructing any landscape on the surface.

As an additional issue a world the size of the Earth built from heavy metals would have a much stronger gravitational field than the Earth, so it would be necessary to accept the higher gravity or specify a smaller planet.

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    $\begingroup$ I think, while you don't mention, the atmosphere can't contain much, if any, oxygen as that will also play havoc with metals $\endgroup$ – elemtilas Apr 5 at 12:51
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    $\begingroup$ And lots of metals dissolve in mercury... $\endgroup$ – AlexP Apr 5 at 13:18
  • $\begingroup$ Hey Slarty, Thank you so much for response. I've done some more research, following on from your very helpful suggestions. Would this be possible?.. If a planet was primarily constructed from say a mixture of iron and other metals, but also had a natural element like Bromine at the surface. I think I'm right in saying a chemical reaction would take place with the mercury on the crust of the planet, creating a white salt, that could help give the surface a white/silver complexion? This is super fascinating, thank you so much for everyone's replies! RJ0001 $\endgroup$ – RJ0001 Apr 5 at 16:25
  • $\begingroup$ Also if I wanted the bromine to be a solid, the planet would have to be below -7.2 C... but not below -37.89 C as then the mercury would become a solid? Reasonable idea? - Thanks again $\endgroup$ – RJ0001 Apr 5 at 16:33
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    $\begingroup$ But bromine will react with the environment unless it is a very specially contrived planet. Excess bromine would lead to a very dense red brown atmosphere and no mercury on the surface just mercuric bromide, excess of mercury would lead to some mercuric bromide and perhaps just a little bromine in the atmosphere sounds like the planet from hell either way… $\endgroup$ – Slarty Apr 5 at 21:33
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Your planet is a construct.

CIRCUIT BOARD PLANET and moon

Liquid gallium rivers are its superficial circuits / arteries. The powdery surface is its skin, intended to slowly ablate as our skin does to protect from radiation and particle impacts.

This construct can be integrated into your story. Maybe it is of the same provenance as your advanced robot and they are part of a package. Maybe that robot built it, or found it and modified it for its own use.

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    $\begingroup$ Thank you so much for your response! The advanced robot is actually from another planet so it's not been constructed by him, but the idea of the protection from radiation is a great addition. However I love the composite/image of the planet you posted, did you make it?! $\endgroup$ – RJ0001 Apr 5 at 16:28
  • $\begingroup$ @RJ0001 - yes that is mine. Powerpoint! $\endgroup$ – Willk Apr 5 at 16:36
  • $\begingroup$ Amazing!! Really cool! $\endgroup$ – RJ0001 Apr 5 at 16:40
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    $\begingroup$ Credit where due: the circuit board is from this site - creativematerials.com/news/pr-fine-line-conductive-ink.php $\endgroup$ – Willk Apr 5 at 16:42
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    $\begingroup$ @justhalf - sphere tutorial. youtube.com/watch?v=W0CMo-U1x_Q. Then pattern fill from file (circuitboard jpg) for sphere w artistic render (at the bottom of effects slider), and radial gradient background for space. $\endgroup$ – Willk Apr 6 at 11:29
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I'm not sure of the viability of this:

Your planet started life as a jovian or superjovian world. It spiraled in towards it's parent, eating everything it encountered (and this was far more material than comprises our inner solar system), but then it got so close to it's parent that it was vaporized--but it's gravity was enough to hold onto the heaviest elements (at that temperature there are no compounds) anyway. It then moved back out and cooled. You're left with a cinder that's mostly heavy metals.

I do not know how to keep the mercury from reacting with the other heavy metals, though.

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