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MidnightPlatinum t1_iwvgkxh wrote

This is weird to think about. Does the planet lack enough mass to keep that much water and the atmosphere such evaporation would generate?

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ClarkFable t1_iwvhgv0 wrote

combination of lack of mass and lack of strong magnetic fields (also correlated with mass) which would shield it from some atmosphere stripping radiation.

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WontStopAtSigns t1_iwwbkwr wrote

Wouldn't the mass of 300m deep oceans have helped create a magnetosphere, cloud layers, ozone, etc?

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weristjonsnow t1_iwwhqyi wrote

300m of water is nothing compared to planetary mass. Mars lost it's core spinning

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WhiteAndNerdy85 t1_iwwj3j2 wrote

Yeah. If the Earth was shrunk down to the size of a bowling ball it would be completely smooth. The deepest oceans and tallest mountains wouldn't even register. Mars is the same way.

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Plinythemelder t1_iwxg63p wrote

Yo that bothered be for so long until I found out that not true. https://ourplnt.com/earth-smooth-billiard-ball/

A billiard ball scaled to earth size would be much smoother.

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x925 t1_iwxtxvs wrote

A marble sized earth would be smoother still.

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xSARGEx117x t1_iwxws0s wrote

If we shrink it down enough, does it curve right back around to being pointy again?

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PyramidBusiness t1_iwxpv7a wrote

The oceans really aren't that deep if you think about it. 2 or 3 minutes down the road from your house can be a further drive than the ocean is deep.

Fun fact: The meteor that wiped out the dinosaurs was almost as big in diameter as the ocean is deep on average.

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WontStopAtSigns t1_iwwhwol wrote

Interesting bc it sounds like a big amount.

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kldload t1_iwwsftt wrote

You might think 300 meters is a lot, but that’s just peanuts to Mars

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SqueakyKnees t1_iwwqfha wrote

Just Mars's mantel is 1,560,000 meters deep. The mantel material is also more dense than water. Problem is is size is relative. 300m of water is a crazy amount to us humans, but to a planet's mass, it's not that much.

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RunLoud6534 t1_iwz57q6 wrote

Equivalent to those little cups of water we hand out to people running a 5k.

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_-Event-Horizon-_ t1_iwyajxm wrote

For comparison the average depth of Earth's oceans is more than 3,000 meters with the deepest points going in excess of 10,000m and Earth has much bigger surface area. And Europa's oceans are theorized to be around 100Km deep.

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Crowbrah_ t1_iwya0kj wrote

Sounds like we gotta start it up again. All we need is a subterranean laser drill and a couple of nukes

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Zztrox-world-starter t1_iwyiny4 wrote

That's an extremely small amount of water on planetary scales. For comparison, Earth's ocean are more than 3700m deep on average, yet it's still insignificant compared to other materials.

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StrangeTangerine1525 t1_iwzvipv wrote

A magnetic field isn't the primary determination for an atmosphere, Earth is the only terrestrial object with an atmosphere that has a magnetic field. Venus is roughly the same size and has an atmosphere 2 orders of magnitude larger, and lacks any kind of intrinsic magnetosphere. Planetary mass matters much more in regards to atmosphere retention, as well as temperature and atmospheric composition. Titan is another good example, were it lacks both a magnetic field and mass, but the moon is so cold that it can maintain a relatively dense atmosphere.

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weristjonsnow t1_iwwhmbk wrote

Once a planetary core stops spinning you lose your em field. Em field protects atmosphere from floating away. Mars has a dead core

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Bensemus t1_iwyge56 wrote

This isn’t true. Venus doesn’t really have a magnetic field yet has an atmosphere so dense it would crush you. Planet mass is way more important.

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merkitt t1_iwy9or9 wrote

Can't we send in an impeller-driven craft to the core to restart the rotation with strategically placed nuclear charges?

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Crowbrah_ t1_iwyalfh wrote

That's crazy talk. What we actually need to restart its core is a giant electromagnetic pulse device to fire down into Mars's fault lines. Some sort of Deep Mars Seismic Trigger Initiative or something or other.

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merkitt t1_iwyhhdt wrote

Heh, I haven't watched that one

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Crowbrah_ t1_ix2ipf1 wrote

It's from the same film lol, The Core. 'DESTINI' was the mcguffin that caused the core to stop rotating in the first place.

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StrangeTangerine1525 t1_iwzvwe4 wrote

There are many other methods of atmospheric escape a magnetic field can't protect against. UV rays, thermal escape processes, 'freezing' of the atmosphere into a planets crust. A magnetic field isn't the "big factor" in terms of whether not a planet has an atmosphere or not. Look at Venus and Titan, the two other places in the solar system that aren't gas giants and have atmosphere's besides Earth (and Mars). Neither of them have an intrinsic magnetic field and they still have substantial atmospheres.

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NearABE t1_iwvrzgv wrote

UV light splits water into hydrogen and hydroxyl. Atomic hydrogen would quickly escape.

Earth does not have enough gravity to retain helium.

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LaunchTransient t1_iwwlwb3 wrote

>Earth does not have enough gravity to retain helium

Nor hydrogen, which is lighter still. Your mechanism is problematic, as the Earth is both 2/3rds the distance from the sun as Mars is (and so has 2 times the UV intensity) but it also has a relatively consistent quantity of water over the last two billion years despite being glared at by those same rays.

A more likely driver of ocean loss on Mars is pressure-driven boil off. With no magnetosphere to protect it, the atmosphere gets stripped away by solar winds, causing the oceans to evaporate at an increasing rate.

The one issue I have with this hypothesis of deep oceans that have evaporated away is the apparent lack of surface evaporite deposits. Where's the salt flats?Just look at anywhere on Earth where there has been an endorheic basin - The Utah salt flats, Lake Karum in Ethiopia, Salar de Arizaro in Argentina, etc. Even under the Mediterranean sea there are layers of salt 3 kilometres thick from the era of the Messianic salt crisis. The absence of evaporite deposits just doesn't add up.

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NearABE t1_iwwpge8 wrote

On Earth water condenses and forms clouds. There is very little of it at the top of the atmosphere. Instead we see atomic oxygen and ozone.

>The one issue I have with this hypothesis of deep oceans that have evaporated away is the apparent lack of surface evaporite deposits. Where's the salt flats?

https://en.wikipedia.org/wiki/Vastitas_Borealis

>"Results published in the journal Science after the Phoenix mission ended reported that chloride, bicarbonate, magnesium, sodium, potassium, calcium, and possibly sulfate were detected in the samples"

Not too far off from "salt flat".

Mars has extensive dunes and dust storms. The frost reworks water soluble material. It should not look exactly the same as Earth's salt flats.

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LurkerInSpace t1_iwwxjcv wrote

To nitpick; Earth is about 70% the distance Mars is - it gets roughly twice as much sunlight rather than four times as much. Venus in turn gets about twice as much as Earth and four times as much as Mars.

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LaunchTransient t1_iwwz0vf wrote

edited. I am tired, so my memory for orbital radii gets kinda crap. I should have checked.

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StrangeTangerine1525 t1_iwzw4m4 wrote

Earth has an ozone layer that causes a temperature inversion. Water can't readily reach the upper atmosphere like it can on Mars and Venus. Once Earth's temperature inversion in the middle atmosphere is gone, hydrogen and water vapor will readily escape like it does on Venus, magnetic field or not.

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rocketsocks t1_iwy6r68 wrote

One thing people forget about is that water permeates through "solid" soil as well as just sitting on the surface in the form of lakes, rivers, and oceans. These sub-surface aquifers and water tables still exist today on Mars in the form of permafrost and sub-surface glaciers. The water that exists on the surface is mostly in the form of a small amount of water vapor in the atmosphere and ice in the polar caps. The rest of the water that used to exist on Mars has mostly been lost to space along with a, likely, heavier atmosphere at some point. The lighter planetary mass and lack of a magnetic field means that it's comparatively easy for molecules in the atmosphere to directly evaporate to escape velocity or to get dragged away by the solar wind. The same thing happened with much of the water on Venus, even though the gravity is much stronger there (but the planet is also much hotter).

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Ok_Goal7960 t1_iwxw2f1 wrote

Mars somehow lost its magnetic field. Eventually the solar winds eroded Mars atmosphere away until it was no longer capable of supporting liquid water on the surface.

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Bensemus t1_iwyggg8 wrote

Not true. It’s due to Mars being tiny. Venus has basically no magnetic field while also being much closer to the Sun. It’s atmosphere melts lead.

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