Mars weather

[J.Random]

I've just finished reading The Martian by Andy Weir, it's a great story and I highly recommend it. Very technical, very immersive. It's awesome, really. One thing that bugs me though is the very reason the hero was stranded on Mars. The MAV in the novel is qualified for up to 150kph wind speed, more than that and it starts tipping (it's not Saturn V heavy, but still, 10+ tons heavy). What I don't get is... how? Mars has what, 0.5, maybe 1% of Earth's pressure? Wouldn't this "super storm" be 100 times less powerful than on Earth? I think I've read somewhere that Opportunity withstand such "storms" annually and most they can do is to clean its solar panels. Maybe there's some Beufort's scale analogue for Mars? Maybe I don't get it? In every other aspect the story seems plausible. Or is it just a plot device to get the story started?

[deadshot462]

Maybe the novel was set in a time period in Mars' past? It's speculated that Mars had a much thicker atmosphere millions of years ago and slowly lost it due to solar wind.

[Scotius]

Tornadoes, or rather "Dust devils" were observed on Mars surface. Maybe locally such freak winds can occur?

[Nibb31]

It's just science fiction. Maybe the writer was ignorant or maybe the book was written before we had much detailed information about Martian atmospheric conditions. Bradbury's Martian Chronicles are particularly bad for this.

Many folks, including science fiction writers, are influenced by pictures of Mars surface that, to the untrained eye, looks a lot like desert regions on Earth. Our brain functions by associating what we see with what we already know. That's where the dreams of living on Mars come from, although it is just as uninhabitable as the Moon. Mars is totally alien and sterile. The atmosphere, the chemical and radiation environment, and the temperatures, are nowhere near anything we can experience on Earth.

We also don't know much about the weather, but judging from how erosion doesn't seem to have as much effect as on Earth and from the low atmospheric pressure, weather conditions don't seem too violent.

[Winter Man]

The dust storms can get thick enough to block out the sun almost entirely, but off the top of my head I don't think that'd add enough 'oomph' (to use the technical term) to push over a rocket.

[J.Random]

Maybe the novel was set in a time period in Mars' past? It's speculated that Mars had a much thicker atmosphere millions of years ago and slowly lost it due to solar wind.

No, it's set more or less in present time. The mission is basically "Mars (almost) Direct tier 2", with separate Hab and MDV (as I remember, initial Mars Direct had them as a single vehicle) and with ion-powered transfer vehicle (which has acceleration capability measured in mm/s/s, so, not Star Wars ion-powered).

It's just science fiction. Maybe the writer was ignorant or maybe the book was written before we had much detailed information about Martian atmospheric conditions. Bradbury's Martian Chronicles are particularly bad for this.

Many folks, including science fiction writers, are influenced by pictures of Mars surface that, to the untrained eye, looks a lot like desert regions on Earth. Our brain functions by associating what we see with what we already know. That's where the dreams of living on Mars come from, although it is just as uninhabitable as the Moon. Mars is totally alien and sterile. The atmosphere, the chemical and radiation environment, and the temperatures, are nowhere near anything we can experience on Earth.

We also don't know much about the weather, but judging from how erosion doesn't seem to have as much effect as on Earth and from the low atmospheric pressure, weather conditions don't seem too violent.

That's the point. The novel is written in 2012, and as far as my knowledge goes, it's very accurate from scientific point of view. The episode with the wind force is the only exception which I don't understand.

The dust storms can get thick enough to block out the sun almost entirely, but off the top of my head I don't think that'd add enough 'oomph' (to use the technical term) to push over a rocket.

That's what I'm wondering myself.

[Albert VDS]

There is nothing stopping the winds from reaching 150 km/h, in fact the average recorded wind speed by the Viking lander were almost 100 km/h.

The atmosphere might not be thick enough to create a strong wind, but you also have to consider how big the MAV is.

[lajoswinkler]

The energy of those winds is very low simply because there isn't enough actual matter being thrown around. The problem is with dust particles. They can, and will erode a lot of stuff.

[Motokid600]

150km/h would just feel like a breeze on Mars, no?

[lajoswinkler]

Probably, although your helmet would be sandblasted.

[cantab]

However weak the wind is, it can blow over a sufficiently unstable structure or object. For the rocket to be so unstable that it can be thus blown over is a pretty serious engineering mistake, but then engineers do make mistakes. I believe the strongest recorded Martian winds are around 100 kph (60 mph), so it's plausible that the engineers might think "Ah, more than 150 kph is never going to happen anyway".

Also bear in mind that wind load goes with the square of wind speed. So a 150 kph martian wind would be comparable to a 12 kph Earth one. Maybe stronger, since I think wind load depends on atmospheric density rather than pressure and I believe the Martian air will be denser at a given pressure. That's still pretty weak, but you'd feel it, and I can see how a rocket on a poor footing, perhaps already sitting at an angle, might be knocked over by it.

[Nibb31]

I believe the strongest recorded Martian winds are around 100 kph (60 mph), so it's plausible that the engineers might think "Ah, more than 150 kph is never going to happen anyway".

But we don't really have any extensive weather records other than our experience with the MERs in two very specific areas and orbital observations. It's like extrapolating Earth's climatology model from a weather station in Venezuela and another in Germany.

[RenevB]

Mr. Random, you have an interesting question and my physics instincts say that a wind of that speed at Mars's atmospheric pressure and density would not be enough to keep a rocket grounded.

The energy of those winds is very low simply because there isn't enough actual matter being thrown around. The problem is with dust particles. They can, and will erode a lot of stuff.

What approximately is the mass of Martian dust particles and what's the kinetic energy? Does this cause any problems for current and historic rovers and landers on Mars? And now I realise you'll likely have the same on the ground as well as while taking off with this rocket. Hmm...

[mrfox]

An answer from Andy himself:

http://youtu.be/gMfuLtjgzA8?t=32m30s