Why did Mars die?




very little liquid surface water, temperatures fluctuating between -55 and 20 each day and most importantly no magnetic field that protects would be life from deadly radiation and keeps a nice dense atmosphere on a planet. We done?


No, not quite. Maybe we know this, but I am not aware of the answers.

Mars’ chemical composition and age are comparable to Earth’s so why the different geology (no magnetic field)?

Why no surface water? Is Mars just too small to hold a thicker atmosphere and liquid water/water vapor? A thicker atmosphere could also stabilize temperature, raising the average and narrowing the spread.


I think gravity is a major factor. Too little, and the gases just bleed off into space, including water vapor. Too much, and your planet captures every damn thing and turns into Jupiter.


Mars died in the 1940s, when Burroughs could no longer send John Carter to Barsoom to repair Helium’s 4-mile wide atmosphere plant. The good news: Mars will come back to life in 2084 when Doug Quaid (aka Hauser) manages to get it working again.

...the next Earth-like planet may be in the Tau Ceti system, seventy trillion miles away...
Tau Ceti is the nearest sun-like star, and although it doesn't have any known planets it does have a disk of smaller debris. But Epsilon Eridani is closer and just a bit smaller, with at least one gas giant and multiple asteroid belts.

What I’m saying is, I think there’s still hope that the next Earth-like planet is only sixty trillion miles away.

This is the most straightforward: the magnetic field isn’t just the result of composition, but relies on Earth’s dynamic interior. Mars has only a tenth the mass, and so its interior has cooled and solidified.

Atmospheric evolution is more complicated, but this probably plays a factor there too - some balance of less outgassing, less shielding, and less to hold it down.


As a god of war, he’s still very active.


True, yet a good part of the mission is to investigate if life could’ve gained a foothold, or still does.


well for starters, it’s only 10% the mass of Earth.
When you have something so much smaller it tends to cool much quicker and retain much less free floating gasses.


10% the mass assuming same density means about half the gravity, so not obviously enough to lose almost all atmosphere.

Heat loss is proportional to surface area per volume, so Mars should lose its initial heat a few times faster than Earth. But why should the heavy radioactive elements not sink to the Martian core and continue generating heat like they do on Earth?

And Mars being colder means free floating gases have less kinetic energy, which in terms of loss rate should at least partly compensate for the lower gravity.

I agree, at the end of the day gravity is the most likely culprit. I’m just saying it isn’t obviously so. Venus and Earth are very close gravitationally, yet Venus’ atmosphere is many times denser even though its higher temperature should increase loss rate. Venus also may be geologically active in a very different way than Earth - no plate tactonics, lots of volcanos, and occasional huge global eruptions. So if two very similar planets can be so different, it is plausible that a few accidents could have gone differently to make a more Earthlike Mars.


Sure there a ton of places on Earth that life has adapted to. But a lot of them are places that life wouldn’t start on its own. They had to be colonized.

Maybe Mars is a planet full of environments that life could eventually adapt to, but just never had any in which life could actually start.


…the next Earth-like planet may be in the Tau Ceti system, seventy trillion miles away…

It’s quite silly to quote galactic distances in miles and kilometres. Sort of like measuring terrestrial distances in inches. Light years, astronomical units and parsecs make more sense. And ignorance is no excuse, if anyone wants to they can look up what a light year is.


well of course Venus has a denser atmosphere, the atmosphere’s made out of sulfuric acid which on it’s worst day is 7 times the mass of our earthly atmosphere.

If Earth had an atmosphere of Sulfuric acid we’d be literally swimming in it… briefly.


Obviously, we need to mash Venus and Mars together, then tease them apart to make two planets, one in each of Earth’s trojan points.

By the time their surfaces cool off enough for rain to fall in a couple million years we should have a replacement to the Shuttle ready.


They should, but there are going to be much less of them in total. And there would be less initial heat to start off with, since it reflects gravitational potential energy from formation. So combined with the increased cooling, the interior is going to lose its activity relatively fast.

Like you say, being colder is going to make it harder to drive away atmosphere, although you reach a point where things start freezing out of it - water vapor being an important greenhouse gas and all. But that’s much more dependent on the sun than the geology.

Internal heat has more to do with getting those gases in the first place. Bombardment is expected to have blown away much of the original material, which then would have to be replaced by things like volcanism and outgassing. There’s going to be a lot less of those on a smaller planet.

Venus does have a little sulfuric acid in its atmosphere, and it’s important because it forms clouds. But the main component is carbon dioxide, plus a few percent nitrogen. That’s basically the same as Mars’s atmosphere.

Except the pressure on Venus is over 15000 times theirs, and a good 90 times ours. So it’s not a matter of the molecules being heavier, there’s still a lot more of it.

Which is a great way to convey just how hard it would be for an inchworm to travel.


Mars may have died due to the loss of its magnetic field. At one point, it had both a molten core and magnetic field - like Earth. Now, it’s cold all the way through, and no giant magnet. Our magnetic field is kept moving by our own molten core and it protects us from the solar wind.

One explanation for the total destruction on Mars is the impact of a very large object. The general idea is that the damage was so vast it was like an unrepairable wound in the planet’s surface - causing massive volcanic activity all over. With a rip in its side, the planet eventually lost its central heat and magnetic protection.

Past exploration of the Martian environs has proven that the planet had a magnetic field billions of years ago along with active tectonic plate action. It has also revealed the possibility of a a huge impact crater. The suspected crater is thought to be 10,600 km by 8,500 km. That seems to infer an impactor the size of Pluto hitting the surface about 4 billion years ago during the Late Bombardment period of the Solar System. It would be interesting to know if the core and tectonic action ceased as a result of the huge impact.


I thought that he died because we quit believing in him…


Which is a great way to convey just how hard it would be for an inchworm to travel.

We have been sending probes into space and reporting about them for the last 50 years, and the use of light years as a unit of measurement is not something obscure that the general public wouldn’t understand. Science news is quite mainstream now. More so when you can look up the term immediately on the net. At best they should add a footnote explaining that it’s the distance covered by light in one year at the velocity of 300,000 km/s.

You don’t after all see a headline saying ‘The Concorde could travel from New York to London, a distance of 219288960 inches, in a little over 5400 seconds’.


Well then, you’d better let NASA know that they’re doing it wrong.


That’s a weekly report of the Voyager probe, not a study on distant stars and galaxies. In galactic terms, Voyager 1 is about 19 light hours away from us after 36 odd years of travel. If it were leaving the house it’s barely got up from the sofa, let alone opened the front door, considering the closest star Proxima Centauri is 4 light years away. I’m referring to the breathless description of Tau Ceti being ‘trillions of miles’ away instead of just saying it’s 12 light years away.