Hmm...Anyone with enough chemistry kmowledge to guess why some scientists think Mars water broke down into....

[electric_blue68]

hydrogen and oxygen and vanished?

Reccent news I just read.

Could a thinning atmisphere contribute to that with stronger sunlight hitting the then waters?

[erronis]

1. It doesn't really need that type of very strong reaction (splitting H2O) to cause water to disappear

Just enough heat for enough time. Those little molecules will dissipate into the very thin atmosphere and eventually make their way out into space.

[Bernardo de La Paz]

2. Mars is smaller, has substantially less gravity, hence the escape velocity for molecules is much smaller

I think that is the main mechanism.

[ProfessorGAC]

3. The Only Thing I Can Think Of...

...is uV & the presence of abundant metal oxides on Mars.
I'd still like to see the data though, because there is a lot of light energy required, even catalyzed, to split the water.
The fact that the atmosphere is nearly nonexistent means a lot of uV, even at 50 million miles farther from the sun.
I don't see a thermal route (requires over 1,500 degrees & metal oxides).
I suppose I can buy the uV route after the vast bulk of any water would have vaporized due to the very low pressure on Mars. I've used vacuum ovens with a 2 stage pump still have more pressure than the atmosphere on Mars.
I'm not, however, understanding how the metal come into contact with such a tiny mass of water diluted over such a huge volume. The mass transfer barriers seem insurmountable.
It's also highly endothermic, even with catalysis.
I'm dubious, but willing to be shown how they think it works.

[John1956PA]

4. On earth, hydrolysis creates oxygen and hydrogen by applying an electrical charge through water.

Perhaps pools of water on Mars were exposed to electrical charges which caused a hydrolysis effect.

As far as molecules of water dissipating into space is concerned, I do not know of the process by which that would occur.

Mars does have a thin atmosphere. The helicopter Ingenuity which NASA sent to explore the planet utilized the planet's atmosphere as a medium to keep it aloft.

https://wikipedia.org/wiki/File:Mars_helicopter_on_sol_46.png

[electric_blue68]

8. In our JHS Science Class we had a Hydrolysist machine!

So cool. Attached balloons to the separate release valves for the separated Oxygen, and Hydrogen.

So the hydrogen balloon filled up twice as large.
For non sciencey people: it's why the water chemical symbol is H2O. Two hydrogen atoms vs one oxygen.

[John1956PA]

10. Did the teacher allow you to transfer some of the gases to test tubes?

If a wooden match is struck, and if the resulting flame is blown out, the head of the match will remain glowing for about five seconds. If the glowing match head is inserted into the test tube containing the oxygen gas, the match head will reignite into a flame. If the glowing match head is inserted into the test tube containing the hydrogen gas, there will be a quick "pop" sound, but the match head will not reignite.

Your school's hydrolysis machine was a great teaching device.

[electric_blue68]

11. Interesting! No, we didn't do that. It was very cool to have that demonstration.

The only "bad" thing was the time she opened up a container of "Swamp Water".
Most of us went to huddle in the back third of classroom bc of the smell!
.
She put a dropperful on a slide, and we when up to look at the parameciums under the microscope.

[sl8]

5. Hubble Helps Solve The Mystery of Mars' Escaping Water (NASA video)

Last edited Thu May 15, 2025, 08:11 PM - Edit history (1)

Hubble Helps Solve The Mystery of Mars’ Escaping Water

NASA Goddard
Sep 5 2024

Mars was once a very wet planet. Scientists know that over the last 3 billion years, some of the water went underground, but what happened to the rest?

Now, NASA’s Hubble Space Telescope and the Mars Atmosphere and Volatile Evolution (MAVEN) mission are helping unlock that mystery. To understand how much water there was and what happened to it, scientists need to understand how the atoms escape into space.

A team combined data from Hubble and MAVEN to measure the current rate of these atoms escaping into space. This information allowed them to extrapolate the escape rate backwards through time to understand the history of water on the Red Planet.

For more information, visit https://nasa.gov/hubble.

Credit: NASA's Goddard Space Flight Center
Paul Morris: Lead Producer
Dan Gallagher: Producer for Assorted Mars Animations

Music Credit:
"Cosmic Overture" by Sergey Azbel [BMI] via Nova Production Music Ltd [PRS], and Universal Production Music.

[...]

[Bernardo de La Paz]

6. Thing is, scenarios based on a thin atmosphere don't explain how it got thin in the first place; except

... except that I think the gravity / escape velocity does explain how a thick earth-like atmosphere got thin.

[Chemical Bill]

7. I would expect...

oxygen would stick around in the atmosphere even if hydrogen didn't, but I would also expect to find hydrocarbons, either in the atmosphere or in solid form.

However, I have not read any research or hypotheses about this, and I reserve the right to be wrong.

[electric_blue68]

9. Thanks, everyone! 👍 🔭 ⚗️

[eppur_se_muova]

12. Short-wavelength UV, particularly before there was enough O2 to form an ozone shield, is all that's needed.

H atoms and H2 molecules are sufficiently low in mass to escape from Earth's gravitational field at the temperatures available. H2O and O2 are heavier and escape much more slowly. So escaping H and H2 allowed some of Earth's early water to vanish.

As long as the ozone is in place (and we banned CFCs to ensure that is) the rate of photodissociation is very unlikely to ever regain the importance it once had, since the ozone absorbs UV very effectively -- that's why it's called the ozone "shield", and why severe sunburn and skin cancer were expected to increase if we didn't ban CFCs. Of course most plants and animals would have been affected as well, but even that impact if due to less energetic UV than is required to photodissociate H2O. In the very outer reaches of Earth's atmosphere, some photodissociation still takes place, but it involves very small amounts of material. Really short UV never makes it to the surface.