# If mars had more density

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1. Aug 10, 2012

### willstaruss22

What would mars be like if it had 50% more density? Like what would be occuring inside, on the surface and the atmosphere? Would there be no water because of the extra density, hotter core, more atmosphere or any other processes?

2. Aug 10, 2012

### Simon Bridge

You want to speculate about a hypothetical planet with the same mass as Mars but in a smaller volume at Mars distance from a G2 star?

That would make the radius about 87% what it is now. The surface gravity would be higher and it could hang on to more lighter gasses.

Then the planet would have to have been made of denser materials ... more heavy metals etc. You'd need to find a mechanism for this to happen for such a large body. There are reasons for materials being found in particular ratios.

It'd have a smaller surface area - losing heat slower - but would generate more of it due to nuclear decays (heavier metals right?)

That should give you an idea of what sort of thinking is involved.

What's your specific interest? Or is it just idle curiosity apropos of nothing much?

3. Aug 10, 2012

### Chronos

Increasing the density of mars by 50% would increase its mass to nearly 20% of earth mass [compared to about 10% at present]. It would also imply a significant increase in heavy elements in the core, a hotter core, and probably a magnetosphere. These factors would contribute to a denser atmosphere, albeit still well short of the kind of atmospheric density on earth. A modest amount of surface water might be retained under such conditions and, in that case, the prospects for life on mars would be dramatically improved.

4. Aug 10, 2012

### willstaruss22

No i wanted to see what would happen if we upped the density of mars by 50% and kept its radius. Im also fasinated by how this might have theoretically occured and what this would mean for life on the surface?

Last edited: Aug 10, 2012
5. Aug 10, 2012

### Chronos

There is no good way for this to happen. A giant asteroid collision is a possibility, but, it would basically destroy the planet.

6. Aug 10, 2012

### willstaruss22

I was thinking of that to and came up with 2 possibles for exoplanets with the same density mass radius as the hypothetical mars.

1 The planet forms in the accrecian disk of a star that is much more iron rich than our sun.
2 the planet has the same impact as thea did with earth that formed the moon billions of years ago but again much more iron rich.

As now i know that there is no way mars would recieve all the iron to raise its density without destroying the planet. But maybe if it were still molten and #2 happened then the density would go up.

Would that make sense?

7. Aug 11, 2012

### Drakkith

Staff Emeritus
Keep in mind that adding material to a planet increases it's radius.
Edit: That is correct isn't it? I know that certain gas giants can decrease in radius if more material is added, but I don't think the terrestrial planets would.

8. Aug 11, 2012

### Simon Bridge

Yeah - it makes more sense to talk about the hypothetical Mars-similar planet than adding material to the actual Mars to up it's density by so much.

For sci-fi some mad scientist could just transport a high density material to Mars... a bucket of neutronium? (Yes I know.)

The added mass need not all appear all in one go - Mars could be intercepted by a very big cloud of dense-material micrometeorites that rain heavy dust down to the surface over A Long Time ... basically plating the planet.

Actually... that sounds like fun:

Back of envelope...
If we add new material density $\rho_n$ in a shell around the existing mars then the total radius would be given by:

$$\frac{3\rho_M}{2} = \frac{\rho_n R^3 - (\rho_n - \rho_M)R_M^3}{R^3}$$
...rearranging:
$$R^3 = \frac{2(\rho_n - \rho_M)}{2\rho_n - 3\rho_M}R_M^3$$

[note: I think something is wrong with this - if ρn→ρM the shouldn't R→∞ ? But it seems to behave itself for high densities...]

Some figures:
$R_M = 3397\text{km}$
$\rho_M = 3.93\text{g cm}^{-3}$

Iron:
$\rho_{Fe} = 6.96\mathbb{g cm}^{-3} \Rightarrow R = 4813\text{km}$
... which would be a 1500km iron shell.

Chengdeite:
$\rho_{Ir_3 Fe}=19.3\text{g cm}^{-3}\Rightarrow R = 3556\text{km}$
... for a mere 150km shell of quite pretty rock.

Osmium:
$\rho_{Os}=22.59\text{g cm}^{-3} \Rightarrow R = 3522\text{km}$
... 126km shell of the densest stable element.

Neutronium: (this should nail it!)
$\rho_{nu}= 3\times 10^{14}\text{g cm}^{-3} \Rightarrow R = 3397\text{km}$