# What if mars had more mass

willstaruss22
Lets say Mars has a density of 6 g cm/3 instead of its current density and kept its radius.
What would the effects of this increased mass be?
Im curious on the interior like the core and mantle.
Im curious about the surface like mountain height, rate at lava flow, geologic activity.
Also am curious about the icreased effects on the atmosphere and what it would mean for the jetstream flow and air pressure and if it would be enough to heat the core to a molten state.

Homework Helper
If Mars increased it's (mean?) density and kept it's volume, then it's mass will go up.
This increases gravity - which makes volcanoes steeper ... they'd be taller too except there would more likely be a molten mantle promoting continental drift - so the volcanoes will grow and die as the hot-spot moves on ... and so on and on.

Mars would also have a different orbital speed (to have the same mean orbit-radius) or would be in a different orbit. It's moons would have different orbits too.

In short: the effect could be profound.

What you are asking about - especially with regard the weather - is very complex and I could write a book on the subject. I little out of the scope for an online forum.

Is there a particular reason for choosing that specific density? It's about 3/2 the current one.

willstaruss22
Well i would think a density like that would be profound for mars, that's all. So i basically Mars would be more geologically active. So basically what you mean with the orbit is it could move out or be closer to the sun?

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Mars would also have a different orbital speed (to have the same mean orbit-radius) or would be in a different orbit.
That seems incorrect. Orbital characteristics are independent of the mass of the orbiting body, insofar as the central body is much more massive than the orbiting one. (look at the Kepler's third law)
E.g. an astronaut and a space station need exactly the same orbital velocity to stay in the same orbit.

The only actual difference would be in moving the barycentre of the Sun-Mars system closer towards Mars. But, as mentioned before, the difference should be negligible.

Also, I've read somewhere(not much of a citable source, I know) that the maximum height of mountains is dependent on the gravity of a planet. I.e.the stronger the gravity, the lower the mountains, as the rigidity of the crust is unable to sustain all that weight protruding outwards. Somebody can verify this?

Homework Helper
That seems incorrect. Orbital characteristics are independent of the mass of the orbiting body, insofar as the central body is much more massive than the orbiting one. (look at the Kepler's third law)
That is correct - my bad. Though a higher mass would affect how it interacts with other bodies... that's a bit subtle for this discussion.

Also, I've read somewhere(not much of a citable source, I know) that the maximum height of mountains is dependent on the gravity of a planet. I.e.the stronger the gravity, the lower the mountains, as the rigidity of the crust is unable to sustain all that weight protruding outwards. Somebody can verify this?
Lets see Maat Mons (Venus) is 8km high, Olympus Mons clocks in at 22km, and Moana Kea at 4.2kms (Everest goes to 8.8km above sea level though).

Venus surface gravity is 8.87m/s^2 vs Earth's 9.81m/s^2
... It looks like there would be some justification.

For very soft worlds like Io, the big volcanoes are basically big holes.
But notice, with this example, that high surface gravity does not have to go with a soft crust.

What we want is something like:
Scheuer P. A. G. How High can a Mountain be J. Astrophys. Astr. (1981) 2, 165–169

willstaruss22
Do you think with the increased gravity and gelological activity it could hold a thick enough atmosphere for there to be liquid H2O on the surface?

rbj
Do you think with the increased gravity and gelological activity it could hold a thick enough atmosphere for there to be liquid H2O on the surface?

if Mars was bigger, like the mass of the Earth, it likely would not yet have cooled to become a solid block of planet. because the Earth is bigger, it has a smaller surface area to volume ratio. stored thermal energy is proportional to volume ($\frac{4}{3} \pi r^3$) and the rate of heat loss is proportional to surface area ($4 \pi r^2$). because the Earth has not yet cooled off completely, the core is still molten, we have a fairly strong planetary magnetic field, that magnetic field creates the Van Allen radiation belt that traps charged particles sending them into loops, and that shields our atmosphere from being blasted off the planet by the solar winds.

when Mars cooled off millions or billions of years ago, it lost that shield and whatever atmosphere it had before gotten blowed off by the solar wind.

willstaruss22
Yes i know Mars cooled off. I am just wondering what the increase in density with keeping the radius would do for the core and if it would have a thicker atmosphere because of gravity perhapse for liquid h20?
Dont forget It is said Mercury has a molten core and it is way smaller than Mars. So is Titan but its farther away so its colder.

Homework Helper
rbj is pointing out that the ratio of surface area to volume is important to work out if a dense Mars would have had time to cool off ...

In comparison with the Earth, a denser Mars (Mars is smaller than the Earth) may be hotter at the early stage and cool faster ... the higher surface area to volume ratio also indicates faster cooling.

Mercury's molten core is besides the point - Mars also has a molten core... and by a similar mechanism: the sulfur mixed in with the iron lowers the melting point.
http://www.newscientist.com/article/dn11962-lab-study-indicates-mars-has-a-molten-core.html

Don't know what Titan has to do with anything.

willstaruss22
i would think that this denser Mars having more mass would cool slower from all the excess heat being produce by the core under presure. So if a denser planet with a higher surface area to volume ratio would cool faster. Why is mercury still molten? I would think it would be solid.

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Homework Helper
.. but it is closer to the Sun and it's core has a low melting point.

willstaruss22
Ohhh so the sulfur comes into play. So basicallyif this new Mars had more sulfur it would be active for longer?