# Could you feel the wind on Mars?

The air pressure on Mars is about 1% that of Earth's at sea level. But wind speeds on Mars can be higher, up to maybe 60 mph sustained (actually I have come across several different figures, some going very high indeed.)

So if you hold your hand out in a 60 mph wind that is 1% the density of air, can you feel it? Would you feel the pressure against your back? Could it blow you over? Could it blow a landing vehicle over, as in Weir's book, The Martian? Thank you!

(edit) This question appears to be the same as the other question (asking what it would "feel like to be in a Martian dust storm"), but in the full post it is clear that question is really whether or not the sand in Martian windstorms would be abrasive. I am asking, literally and exactly, whether or not you could feel the wind as pressure on your body; my question has nothing to do with sand. The wind speed is often higher than on Earth, but the atmospheric density is far lower, making this a worthy question, I feel.

• Related question: space.stackexchange.com/questions/2621/… – Hobbes Jun 2 '15 at 8:25
• I would retract my close vote, if you could make the distinction to the question that Hobbes linked to clearer. What Martian wind feels like was already asked&answered. Maybe you should ask specifically with all the details given in the book, if that tipping scenario is realistic. (and btw: he would have certainly poisoned himself with the hydrazine). – Rikki-Tikki-Tavi Jun 2 '15 at 10:56
• Small point to add, but you'd weigh less on Mars, so you'd get blown over more easily, but, even so, the atmosphere on Mars likely couldn't do it. There's a cute article about astronauts losing their balance on the moon because the low gravity was confusing to them. Our bodies depend on gravity to know which way is up and down. Mars however, has enough gravity that this shouldn't be a problem, but on the moon, a light breeze might knock a person over. space.com/27029-moon-gravity-falling-astronauts.html – userLTK Jun 3 '15 at 9:57
• I've seen him talk, and Weir admits that the winds wouldn't have been strong enough. Too bad they kept it in the movie... – Mephistopheles Jan 4 '16 at 18:26
• I don't have an answer, but keep in mind that Martian "sand" is very, very fine, so it can certainly fly fast, and may be what you're feeling. – Mikey Jan 5 '16 at 21:52

Let's do some Maths!

The pressure exerted by wind is dynamic pressure, or velocity pressure and it is given by the formula,

${q}$ ${=}$ ${0.5{\rho}v^2}$

where ${q}$ is the pressure, ${\rho}$ is the density of the atmosphere & ${v}$ is the velocity (speed) of the wind.

From the NASA Mars Fact Sheet, the density of air on Mars is about ${0.020}$ ${kg/m^3}$ and from Wikipedia the density of air on Earth, at sea level is ${1.225}$ ${kg/m^3}$. A significant difference of densities.

Using your wind speed of 60 mph, this is 96.54 km/h or 26.817 m/s.

A wind on Earth with this speed would exert a pressure of:

${q_E}$ ${=}$ ${0.5(1.225)(26.817)^2}$ ${=}$ ${440.480}$ ${Pa}$

The pressure from such a wind on Mars would be:

${q_M}$ ${=}$ ${0.5(0.02)(26.817)^2}$ ${=}$ ${7.192}$ ${Pa}$

For a wind on Earth to exert the same pressure as that on Mars, its speed would need to be lower. By manipulating the dynamic pressure equation, the speed would be:

${v}$ ${=}$ ${[2q/{\rho}]}$${^1}$${^/}$${^2} {v} {=} {[2(7.192)/1.225]}$${^1}$${^/}$${^2}$ ${=}$ ${3.427}$ ${m/s}$ ${=}$ ${7.667}$ ${mph}$,

Wind on Earth, with a speed of ${7.7}$ ${mph}$, exerting a wind pressure of ${7.2}$ ${Pa}$ will not blow over a landing vehicle thus, a wind on Mars with a speed of ${60}$ ${mph}$, exerting the same pressure of ${7.2}$ ${Pa}$ would not blow over a landing vehicle.

• You are not taking into account the lower gravity. Also, if I remember correctly the wind was faster in the book. – Rikki-Tikki-Tavi Jun 3 '15 at 10:35
• @KokotheTalkingApe Welcome to the site. I've only been here about 4 or 5 months myself. I'm still getting to grips with the MathJax (or LaTEX) formating. The Engineering Meta site has a couple of questions which act as a guide to such formating. These are the links [How Can I Use MathJax Latex to Type Set Equations?] (meta.engineering.stackexchange.com/questions/307/…) & [When Should I Use Markup (meta.engineering.stackexchange.com/questions/178/…) – Fred Jun 6 '15 at 6:19
• @Rikki-Tikki-Tavi, I now see that your original comment was trying to say that the answer didn't account for Martian gravity ability to hold a landing vehicle upright on its surface, rather than Martian gravity's effect on martian atmospheric pressure. – Keith Reynolds Jan 18 '16 at 23:27
• @Rikki-Tikki-Tavi, Martian gravity is about 3.7 m/s² at the surface or 37.7% that of Earth's. If a lander is safe up to 60mph winds on earth with 440.48 Pa of force, then the same lander should be safe with martian winds pressure up to (440.48 Pa * (.377 of earths gravity)) or 166.06 Pa. Given the equation in the answer, 166.06 Pa = 0.5 * (martian atmospheric density of 0.02 kg/m^3) * (wind velocity of 128.865 m/s)^2. That means, given an earth safe limit of 60 mph winds and equations provided in the answer above, a lander should be safe with martian winds up to 128.8.65 m/s or 288.24 mph. – Keith Reynolds Jan 18 '16 at 23:39
• @Fred, when determining wind pressure, shouldn't one also consider the density of the atmosphere with wind blown dust suspended? – Keith Reynolds Jan 18 '16 at 23:46

Though I appreciate the thoroughness of Fred's answer, there is a simpler way to "smell-test" if the windo on Mars could be felt by a human observer.

The MER Rovers landed on Mars in January 2004 for 90-day missions. Spirit ended her mission in 2010 and Opportunity is still running. One of the mission limiting factors was expected dust buildup on the horizontal solar panels. It turns out that the Martian wind blows sand particles off the panels, keeping them clean. Now put some sand on a flat surface and check how gently you can blow on it to displace the sand. Put your finger there: can you feel that gust?

I therefore conclude, without math, that a human could feel the wind on Mars. K'Breel informs me that the rain is another matter, though.

• You neglect two things. First, Martian sand is extremely, extremely fine. Fine sand like this would dissolve in water on earth (because of the high surface to volume ratio). Secondly, Maritan surface gravity is 0,38g, so that is another reason why the sand is much easier to dislocate from the horizontal solar panels. – Rikki-Tikki-Tavi Jun 3 '15 at 15:54
• Indeed. I understand some Martian dust is finer than cigarette smoke. In fact it is so fine that it is very difficult to manufacture and handle on Earth, which makes it harder to test equipment designed for the Martian surface. Some dust may stay aloft in the atmosphere for months. – Koko the Talking Ape Jun 6 '15 at 4:43
• Tell me guys another aspect of that: are we able to produce electricity using vertical wind generators? – Dzianis Yafimau Nov 6 '15 at 12:13
• @DenisEfimov We can but that doesn't mean we should. For comparison, there is an aircraft design which, instead of using propellers with the axis of rotation parallel to the direction of travel, use a sort of reel-type thing like an old push lawnmower, along the front of the wings. Models seem to work, but there's no rush to convert the world's air fleets to them... – user12895 Jan 4 '16 at 3:57
• @DenisEfimov ... They're just less efficient. In the case of windmills, which have to survive out in all weathers for years, the constant vibration from the downwind blade moving through the turbulence behind the upwind blade shortens their life expectancy. For the same reason, nearly all horizontal-axis windmills have the blades in front of the tower, not behind it. – user12895 Jan 4 '16 at 3:57