In Fact It’s Cold As Hell: Mars Isn’t As Earthlike As It Might Look

The slopes of Gale Crater as seen by Curiosity are reminiscent of the American southwest (NASA/JPL-Caltech)

“Mars ain’t no kind of place to raise your kids; in fact it’s cold as hell” sang Elton John in “Rocket Man”, and although the song was released in 1972 — four years before the first successful landing on Mars — his weather forecast was spot-on. Even though the fantastic images that are being returned from NASA’s Curiosity rover show a rocky, ruddy landscape that could easily be mistaken for an arid region of the American Southwest one must remember three things: this is Mars, we’re looking around the inside of an impact crater billions of years old, and it’s cold out there.

Mars Exploration Program blogger Jeffrey Marlow writes in his latest “Martian Diaries” post:

Over the first 30 sols, air temperature has ranged from approximately -103 degrees Fahrenheit (-75 Celsius) at night to roughly 32 degrees Fahrenheit (0 Celsius) in the afternoon. Two factors conspire to cause such a wide daily range (most day-night fluctuations on Earth are about 10 to 30 degrees Fahrenheit). The martian atmosphere is very thin; with fewer molecules in the air to heat up and cool down, there’s more solar power to go around during the day, and less atmospheric warmth at night, so the magnitude of temperature shifts is amplified. There is also very little water vapor; water is particularly good at retaining its heat, and the dryness makes the temperature swings even more pronounced. 

In that way Mars is like an Earthly desert; even after a blisteringly hot day the temperatures can plummet at night, leaving an ill-prepared camper shivering beneath the cold glow of starlight. Except on Mars, where the Sun is only 50% as bright as on Earth and the atmosphere only 1% as dense, the nighttime lows dip to Arctic depths.

“Deserts on Earth have very extreme temperature ranges,” says Mars Science Laboratory Deputy Project Scientist, Ashwin Vasavada. “So if you take a desert on Earth and put it in a very thin atmosphere 50% farther from the Sun, you’d have something like what we’re seeing at Gale Crater.”

And although the afternoon temperatures in Gale may climb slightly above freezing that doesn’t mean liquid water will be found pooling about in any large amounts. Curiosity’s in no danger from flash floods on Mars… not these days, anyway.

With atmospheric pressure just above water’s thermodynamic triple point, and temperatures occasionally hovering around the freezing point, it is likely that local niches are seeing above-zero temperatures, and Vasavada acknowledges, “liquid water could exist here over a tiny range of conditions.” But don’t expect a Culligan water plant in Gale Crater any time soon. “We wouldn’t expect for Curiosity to see liquid water, because it would evaporate or re-freeze too quickly,” explains Vasavada. “With so little water vapor in the atmosphere, any liquid water molecules on the surface would quickly turn to gas.”

So when on Mars, drink your coffee quickly. (And pack a blanket.)

“Gale Crater may look like the dusty, basaltic basins of the American southwest, but one look at the thermometer will send you running for the winter coat.”

– Jeffrey Marlow, Martian Diaries

Read Marlow’s full article here.

Image: Sunset on Mars seen by the MER Spirit from Gusev Crater in 2005 (NASA/JPL-Caltech)

18 Replies to “In Fact It’s Cold As Hell: Mars Isn’t As Earthlike As It Might Look”

  1. Well compared to Earth Mars is of course cold, but if you were to plot the temperature ranges of various solar system destinations (planets, moons, asteroids) you’ll find that the temperature range on Mars is very close to that of Earth. We haven’t gotten to other solar systems, but I suspect that if we ever do, a Mars-like planet will be considered quite a rare find.

    Lunar surface temperature swing from -200 to +100C, and the total absence of atmosphere means that even at the poles, vertical surfaces that face the sun are boiling hot, and 10 feet away, vertical surfaces that are in the shade are cryogenic.

    Venus will literally melt you, mercury will alternate between melting and freezing you, and everything else (which is past Mars) gets awfully cold awfully fast.

    In short – Mars is only “as cold as heck”. I’ll keep “Hell” for other, more deserving places.

    1. Though at around 50km above the surface of Venus, the temperatures and pressure are quite earth-like. One researcher suggest a balloon/aerosat filled with breathable air, (buoyant in CO2) to live in. It begins to feel like Star Wars.

      1. Given how close to Earth Venus is (very short trip, even with current rockets), I’ve thought for a long time it made a better target for human occupation than Mars. Using the floating colony idea that you mentioned of course. Couldn’t be on the surface:).

  2. The familiar look is mostly caused by the adjustment of the images to look like Palm Springs sunlight, which I find slightly annoying, albeit it has a purpose. When I want to get the real feel of the Red Planet I turn out the lights, get a big monitor on full screen and stare at the moody sepia cast of the raw pictures.

  3. “What I really need is a rover that understands the binary language of moisture vaporators.”

    “Vaporators? Sir, my first job was programming binary skycranes – very similar to your vaporators in most respects.”

  4. The temperature swing would tend to keep any extant life buried in the regolith. A few cm makes a huge difference in temperature swing.

    Extremophiles can, I believe, survive huge temperature swings if the environment forces them. Hydrothermal vents is an example where a few centimeters in distance makes a difference in tens of degrees Celsius.

    However we have other factors here, UV irradiance and low water activity of the surface. (The low water activity, effective vapor pressure, comes from having salts and UV produced oxidants at the surface but little water vapor due to evaporation and sublimation.)

    Curiosity can, I believe, drill and sample 5 cm below the surface. For deeper samples recent meteorites have to do the digging. That would not be likely to give us any living microbes, but perhaps something detectable as complex organics.

    1. Heat capacity is important, and atmosphere holds heat energy E =
      C_pT, and if the heat capacity C_p is small or zero then you have no heat
      energy in that region of space. At
      10^{-2} the pressure of Earth’s atmosphere what thermal energy exists in the
      atmosphere during the day is small, even if the temperature is above 0C, and is
      not enough to last probably more than a few minutes after “sol-set” on Mars.

      On the other hand, a vacuum is a good insulator, and the Martian atmosphere
      has enough pressure to keep H_2O near it triple point, but can act as an
      insulator that keeps the ground temperature above 0C. It might mean that while the thin atmosphere
      might plummet to below -50C after sol-set, the ground which was warmed up during
      the day to above 0C (up to 20C as I understand) can hold that thermal energy
      for a while, and that energy can conduct deeper into the ground. So there might be sufficient thermal energy a
      meter under ground to maintain water, at least for intermittent periods, in the
      liquid state.


      1. Another thing that can help is phase change. If there’s liquid water underground, it will start freezing from the top down, and a) have a lot of latent heat capacity, and b) once frozen, can insulate against further heat loss, just like on lakes on earth.

      2. Latent heat of fusion might also serve to warm deeper layers. It depends upon how much water is in a liquid form.


  5. The sky in the first picture is awfully blue compared to past pics we’ve seen. Did someone miss colorizing it? 🙂

  6. I thought that Mars received 25% as much sunlight as Earth. It’s twice as far away from the sun, and light decreases at the square of the distance.

    Am I misinformed?

  7. The pictures of Mars over the years make you almost think the temperature is near Earth’s. You don’t really sense it is cold there.

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