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Say I have a rocky airless world with size and density to produce two gees orbiting around an old dim star.

Could I have a round(ish) lake with a high molar hydrochloric acid ice? It could be deposited there by collision or leftover from a long ago history. I would like this lake to rotate slowly, could be as slow as one turn per month or even one a year. Also would like the lake wobble. I am thinking a moon or a few to create the necessary tidal forces? Could a lake like this persist?

And if this lake was near a mineral deposit, could the acid leach away impurities and leave behind a near pure source of tantalum?

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  • $\begingroup$ I have answered the current and tidal parts of the question. I think the geochemistry probably needs a separate question but let's see. Maybe someone can answer that as well. $\endgroup$
    – chasly - supports Monica
    Commented Apr 13, 2021 at 16:02
  • $\begingroup$ @Allan Would the lake of high molar hydrochloric acid persist for a long time on an airless world, or would it either freeze solid or evaporate? Water in a vacuum tends to evaporate rapidly, so why would high molar hydrochloric acid be different? I also note that a planet with a surface gravity of 2 g would probably have an escape velocity much greater than that of Titan, Venus, or Earth, which all have significant atmospheres. Possibly the planet was in a giant collision which removed all of its atmosphere and has not yet reacquired one. $\endgroup$
    – M. A. Golding
    Commented Apr 13, 2021 at 16:23
  • $\begingroup$ @M. A. Golding it is to be frozen solid $\endgroup$
    – Allan
    Commented Apr 13, 2021 at 17:03

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Rotation

The basic answer about rotation is Yes. A large lake can be caused to rotate by a combination of (a) the Coriolis effect and (b) the prevailing wind being funnelled in such a way through the local geography that water currents form.

The direction of the Coriolis rotation will depend on which hemisphere the lake is in. For example, in the Northern hemisphere on Earth, Coriolis causes a clockwise rotation of currents. See first diagram https://theozonehole.com/coriolis.htm

enter image description here

Coriolis plus prevailing wind

enter image description here

http://www.geo.mtu.edu/KeweenawGeoheritage/Lake/Currents.html

Tidal forces

A moon isn't necessary for tidal forces provided that the planet is not tidally locked to the star. The star itself will cause the tides. If, by wobble, you mean that the bulk of the water moves back and forth along the lake according to the tidal forces, then yes. Without a moon, the oscillation will correspond with the length of the planet's day.

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  • $\begingroup$ Would there be rotation without wind? The world has no atmosphere. $\endgroup$
    – Allan
    Commented Apr 13, 2021 at 16:11
  • $\begingroup$ @Allan - You need a current for a current to be deflected. The wind can create the current. Otherwise, you need a tidal current but this would require a suitable narrowing of the lake or a suitable variation in the depth of the lake bed that would cause deflection of the tidal stream. I think this would cause the direction of spin to change according to the direct of the tide unless the lake bed has very unusual characteristics. $\endgroup$
    – chasly - supports Monica
    Commented Apr 13, 2021 at 16:21
  • $\begingroup$ There might be a way to arrange one way rotation but I think it will depend on the size and positioning of the lake on the globe as well as the shape. Probably you would need an ocean rather than a lake. $\endgroup$
    – chasly - supports Monica
    Commented Apr 13, 2021 at 16:24
  • $\begingroup$ NOTE - I forgot about the ice. How do you intend the ice to rotate? Does it float on the surface or is it solid? $\endgroup$
    – chasly - supports Monica
    Commented Apr 13, 2021 at 16:28
  • $\begingroup$ It could float of the lake could be solid. The main reason I am looking for rotation, or even just wobbling is to create a point of contact with movement and friction so that the acid could erode to cause the leaching. $\endgroup$
    – Allan
    Commented Apr 13, 2021 at 17:01

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