Mars was once much like Earth. It had an atmosphere and flowing water. But it was so small that it froze through to the core, and that stopped the protection it got from its magnetic field, which allowed the solar wind to strip the planet. So now it has very little atmosphere and very little water.
The Earth gains something like 50- to 100-thousand metric tons each year from dust and rocks falling from space. It loses about 100-thousand metric tons from atmospheric loss. I assume that Mars is similar, though both the gains and the losses are smaller.
Will enough of that random space matter collect on Mars to eventually increase its mass and cause the mantle to re-melt and create a new magnetic field? Or is there just not enough stuff still out there to make a difference?
The first problem you have is that Mars is so small that it doesn’t have enough gravity to hang on to its atmosphere. The solar wind pushes harder than Mars can pull. This means that the losses are much greater than you’d expect if you are just scaling things down from Earth. Proportionally, Mars loses a LOT more of its atmosphere to the solar wind than Earth does just because of its reduced gravity.
The second problem is that Mars is far enough away from the Sun that it gets cold enough for atmospheric gases like oxygen and carbon dioxide to freeze at the poles.
The long and short of it is that a lot of your potential new atmosphere either gets stripped away or frozen. Instead of gaining atmosphere, Mars continues to lose atmosphere, and that trend shows no sign of changing at any time in the near future (the next few billion years or so).
The OP mentioned atmospheric loss, and part of what hits the Earth are ice balls (comets and such), which bring water and CO2 into the equation. I guess my mind focused too much on that and didn’t answer the actual question being asked. Sorry for that.
One of the things that defines a planet is that it basically clears its neighborhood. So yeah, there is stuff like dust and meteors and ice balls that land on Earth (and Mars, and every other planet), but there isn’t anywhere near enough of it to significantly change the mass of any of the planets. If there was that much stuff in the neighborhood of a planet that it could run into, then it would not have cleared its neighborhood and would no longer be defined as a planet.
It’s not impossible, but for Mars to gain that much mass it’s going to have to collide with something big, like a rogue planet that happened to find its way into our solar system or a couple of big asteroids that somehow got perturbed out of their orbits.
Mars’ surface temperature will increase a couple billion years from now when the Sun starts to expand, but it doesn’t have the gravity to have a full-fledged atmosphere like Earth does.
The mass of Mars is around 6.4 x 10[sup]23[/sup] kg. The mass of the entire asteroid belt is around 3.6×10[sup]21[/sup] kg. So every asteroid put together would barely nudge the mass of Mars upward.
Undermine the core? That sounds like word salad to me. The core is located at the centre of the planet; you can’t get any lower than that to undermine it.
Elon Musk has been talking about excavating volatiles from the crust using nuclear bombs to increase Mars’ surface pressure; recent estimates show that there isn’t enough ice on the planet to make a respectable atmosphere. If we were ever going to form an atmosphere on this little world we would need to import vast amounts of material from elsewhere. Not impossible, but very, very difficult.
I would note that, although the rate of atmospheric loss on Mars is quite high, even the low gravity of this world could hang on to an atmosphere for tens or hundreds of millions of years. It might be worth doing, so long as we don’t expect to live there for ever.
We just fire up the ol’ global alchemistry set to match our Mars-rock-to-atmosphere production to Mars’ natural size-based losses. I mean if we are fathoming a reality that can **create **a habitatal Mars, we are probably fathoming a reality that could **also sustain **it.
OP states Earth gains about 50,000-100,000 kg per year. Earth’s mass is stated as 5.9x10^24 kg. Even though Mars is a lot smaller its mass is still ~6.0x10^23 kg. What each planet gains or loses in a year is a rounding error.
Earth’s atmosphere isn’t just held down by its gravity, the planet’s magnetic field shields it from being blasted away by solar wind. Mars has no magnetosphere at all, so any attempt to give it some sort of substantial atmosphere would be constantly fighting that.
No, that’s a trivial amount of mass gained. Also, it’s not going to help them wrt a spinning core, regardless of how much mass you dump on the surface.
That said, in another, oh, say 500 million to a billion years, Mars probably will have a brief period of thicker atmosphere when the sun starts to transition to it’s red giant phase. Not sure Mars will exactly be earth like, but it will not be the frozen desert it is today…probably more like a hot desert, but it might have a period with an atmosphere thick enough that liquid water can briefly be on the surface anyway.
This all assumes that in that time period we don’t try to terraform it of course. We could probably mitigate some of the issues mentioned if we really, really wanted too, though it will be a lot easier to build space habitats than to terraform Mars.
K, so I’m seeing that there’s just not enough stuff left for Mars to clear to make much of a difference in its overall mass.
Thanks for the answers, everybody.
Follow-up question, if you’d all be so kind. Is the solar wind acting on a low-mass unshielded planet strong enough to strip dust away from the planet and into space? If so, once the atmosphere is gone, will Mars start dissolving?
Firstly because it’s not our mantle that’s molten, it’s our core. They are two different things. The mantle is mostly a plastic solid with only localized partial melting.
And second because the heat in our core and mantle isn’t *primarily *because of gravitic pressure, it’s because of the residual heat of formation of the planet, radioactivity (the biggest source), and latent heat from the inner core expansion.
Adding a few million tons of micrometeorites to Mars isn’t going to do much *unless *it’s all U, Th and K[sub]40[/sub] and you manage to get it into the Martian mantle and core without the active tectonics Mars lacks.
Nice Catch-22 there. Even if quite a few asteroids hit Mars and they happen to contain a decent amount of radioactive material, since their debris will be sitting on the surface their heat will radiate off. They’d only get sucked down by geological processes if Mars already had the heat to generate such processes.
OTOH, that’s warm stuff on the surface. Great. Now you just have to fight off the mutants.