Was there Ever Liquid Water on Mars?

People love to speculate that Mars was once a great place for life to form, and claim that there is plenty of evidence that there used to be oceans and rivers there. But this isn’t true. People used to claim there were big Canal-like features on Mars, and used this as evidence that Mars was very wet.

It was later realized that these weren’t canals, but rather geological features caused by impact craters from astroids. But more recently, people have been claiming that images like the one above are examples of dried-up riverbeds.

But this turns out not to be the case. When we take a closer look, we find that these aren’t riverbeds, but are rather sand dunes, most likely formed by a very dry surface eroded by wind:

So it looks like there really isn’t evidence for Mars having a wet past, except for this fact: there are icecaps at the Martian Poles. Also, there are ice clouds found in Mars’ atmosphere. Take a look at the picture below:

So let’s ask the big question: even if there’s isn’t any water on Mars now, was there ever a lot of liquid water on Mars?

The quick answer: probably not very much, and if so, not for very long.

How do we know this? The atmosphere of Mars is too thin for liquid water to last for very long. We see Martian sand dunes frozen, and we see them dry (two pictures up), but we never see them wet. On Earth, the atmospheric pressure is high enough that water will be a liquid anywhere between 273 Kelvin and 373 Kelvin, and it happens that the average temperature of the Earth falls in between these two numbers (somewhere in the 280s and 290s for most places), so water is abundant. But on Mars, the atmospheric pressure is somewhere in between 0.6% and 1.0% of that on Earth, or between 100 and 150 times smaller. Mars is also much colder than Earth, so that these two factors combined means that there’s either never liquid water on Mars, and it goes from solid ice straight to water vapor when it gets warm (and back again when it gets cold), or it can be liquid water for a very narrow temperature range that only occurs very infrequently on Mars. Take a look at the phase diagram of water below.

There will never be liquid water on Mars if the atmospheric pressure is less than 0.7% that on Earth, and there’s only rarely liquid water there if the pressure is greater than that number. The phase diagram for water is shown above, with the letters M, E, and V showing where the average temperatures are for Mars, Earth, and Venus. While the temperature of Earth is pretty stable, temperatures on Mars can range from a minimum of -140 Celcius at the coldest to 20 Celcius at the warmest. While the Earth has a difference of about 20 degrees Celcius between the hottest and coldest parts of the day in any one place, the typical difference on Mars is 100 degrees Celcius.

So these two factors:

  1. A tiny, tiny atmosphere, and
  2. a temperature that is mostly very cold and varies a lot over short times,

makes it impossible for liquid water to exist on Mars for more than a few hours, maximum, at a time. While the average temperature of Mars may have been different in the past, there was never a larger atmosphere and the temperature was never stable. So while plenty of reputable-looking sources will tell you why we think there might have once been water on Mars, you now know why Mars could never have had a stable ocean or river; the best it could have had was an ice-bed that melts during the day, is lucky enough not to boil or evaporate (and if you know how that’s possible, because I don’t think it is, please leave a comment!), and then re-freezes for the night! So don’t believe the hype, Mars is dry and cold, and it doesn’t have the atmosphere to sustain liquid water! And if you liked this post, digg it!

UPDATE: After reading Briony’s comment and doing some research into Mars and the Martian surface, I must amend my conclusion — it was too strong. It is unfair to say there has never been liquid water on Mars. While the evidence is not completely conclusive as to the presence of liquid water at some point (e.g., the deposits we expect are often not found, but they could be simply covered), there is strong evidence that Mars did have a liquid past. See http://phoenix.lpl.arizona.edu/mars151.php, for example. It means, instead, that never is too strong a word, and instead I should say that, for the last three billion years, there hasn’t been liquid water on Mars. But there may have been prior to that. The how is still extremely speculative, but the evidence is too strong to say with any certainty that there was never any liquid water on Mars.

(But there hasn’t been for billions of years.)


  1. #1 HenkZw
    March 4, 2008

    Wouldn’t volcanism have increased greenhouse gases in Mars’ early atmosphere and hence the pressure ? And wouldn’t an early magnetic field
    have protected much of the atmosphere from being
    blown off by the solar wind ?
    If all volcanism on earth shut down suddenly(ignoring other side effects) wouldn’t the atmosphere become thinner, and contain less greenhouse gases (like water vapour and methane) ?
    Although it wouldn’t have that much of an effect on a bigger planet like earth…

  2. #2 ethan
    March 4, 2008

    Volcanism can, indeed, increase the amount of gas present in the atmosphere. You’re asking if the atmosphere could have been much thicker back when Mars was younger, and then have lost much of that atmosphere when magnetism and volcanic activity stopped, I don’t know enough to tell you that what you’re suggesting is impossible, but I can tell you it isn’t likely. This website, which sounds a lot like what you’re saying: http://humbabe.arc.nasa.gov/mgcm/HTML/FAQS/thin_atm.html is way out of date. Arguments like the ones you’re making were invented, however far-fetched that scenario might have been, to explain these “dried up riverbeds.” And now we know that there are no dried-up riverbeds. So rather than invent this complicated history for Mars, where it was very different in the past, had an atmosphere, and then lost that atmosphere, we could just go off of the evidence we have, which suggests Mars never had any water. As it goes, volcanism, core formation, and an early magnetic field on Mars doesn’t have much evidence going for it. Like I said, it isn’t impossible, but there isn’t any evidence for it.

  3. #3 Briony
    March 6, 2008

    While Mars scientists don’t claim that Mars was ever Earth-like, there is tons and tons of evidence that liquid water has flowed and even sat at the surface. For example, in the riverbed close up you show above, the evidence for flowing water is the meander in the river – the oxbow shape can only be produced by a liquid (but not lava) flowing in a streambed for a significant amount of time. The sand dunes are formed by material that was trapped in the trough but by the river. There are many other geologic features on Mars that are extremely difficult to explain without liquid water.

    Of course, we still don’t know how liquid water was able to stay at the surface. The current theory is that Mars once (3 billion years ago) had a much thicker atmosphere, either carbon dioxide (like Venus) or sulfur dioxide, which was rapidly stripped by the solar wind after the magnetic field shut down.

    There’s a huge amount of literature on this subject, much of it written in the last 10 years.

  4. #4 ethan
    March 6, 2008

    Thanks for your comments; I spoke too firmly. Why are there no carbonate deposits in these riverbeds? Is it possible they were formed by other processes, such as glaciation? The flowing liquid hypothesis seems reasonable, but how do we explain Mars having gotten such a thick atmosphere as compared to Earth’s in the first place? Mars must have been very different in the past to have had flowing water on its surface.

  5. #5 armando
    March 7, 2008

    Our beautiful planet was a thief on the past.
    Mars had a very close orbit to us and once it comes closer.
    Our gravity bigger stole the water, the air, and life, from our neighbor.
    Mars lost it forever.
    We get the water and our Moon also.
    Wath you think?

  6. #6 ethan
    March 7, 2008


    That’s not how orbits or gravity work. It’s a nice idea, but physics tells us that definitely wasn’t true. If there were a close orbital interaction at some point between Mars and Earth, their orbits would be very elliptical instead of nearly perfect circles. Thanks for your thoughts, though; it’s great to see the creative ideas you come up with!

  7. #7 baley
    March 8, 2008

    It is possible that the atmosphere of mars got strip away from the solar wind as the planet cools down (and the magnetic field reduces). The
    ESA Mars Express and Venus Express may be soon be able to determine the rate of atmospheric loss:

  8. #8 Brian
    March 8, 2008

    I agree with the comments that you were too harsh on saying Mars never had liquid water. It is widely accepted in the planetary geology community that Mars was once warmer and wetter than it is today. There is even some evidence of relatively recent surface water in a few places.

  9. #9 Neville van Wyk
    October 29, 2008

    NASA scientists did not base their theory of a wet mars on photography as mentioned here but rather on the discovery of various minerals or chemical compounds by the Rovers and now also by Phoenix Lander.

    The challenge ahead is rather to explain what happened to the heavy atmosphere that must have existed before. Loss of magnetic field is unlikely to be the reason. Earth magnetic has switched many times and must have been severyl reduced during switchover. The atmosphere remained nevertheless. Venus with little magnetic field and even closer to the sun boasts an retained its heavy atmosphere. Why?

  10. #10 Robert L. H
    January 3, 2009

    I am not a scientist but I do have common sense and my common sense tells me that if Mars ever had an ocean\oceans, then evidence of it would still be present today for what I believe is a very simple reason, the temperature of Mars. I read somewhere that the temperature on Mars ranges from 32 degrees to -180 degrees. If that is the case then whatever water on Mars would still be there because at those temperature the water is the oceans would be like it is on earth at the north and south poles. At minus 180 degrees the oceans of Mars would have been in a solid state most of the time and since Mars is considerably further from the sun than earth the strength of the sun would be greatly reduced.

    But I guess some of you a lot smarter than I am and with common sense will tell me why that don’t matter.

    The south pole have ice masses that are thousands of feet thick and at some places maybe even a mile or so thick.

    There have been proof that at one time the south pole was green with trees and plant life. So it has not been that long since the ice formed as far as geological time is concerned.

    I also assume that the temperature on Mars have been that way from the beginning so Mars would have started out with ice. Most of this ice would be in the poles which means that the Martian poles should be larger than they are now because the ice would not melt like it does on earth. Granted the volcanoes on Mars might trap C02 gases at the surface and help retain heat and melt the ice. But the earth is closer to the sun and we have active volcanoes, forest fires that were cause by lighting strikes and other means millennium before man was created, and earth still has it ice caps and sheets at the poles.

    Since none of you or I was around when and Mars had or did not have oceans full of water your opinion is as much a guess as mine.

    Care to prove me otherwise?

    In this solar system and perhaps thought this galaxy and beyond, earth is the ONLY planet with life….but there is a reason for that which I do know.

  11. #11 Gabor Pokoradi
    March 5, 2009

    Hello there,

    I studied physics. Astronomy is my hobby. I’m not a specialist in the subject, but I’m following Mars stories closely. (Sorry for my far not perfect English.)

    Let me suggest a solution for the water problem.

    Most scientist accept the fact that Mars has been much warmer after formation
    Mars could have a molten core and mantle just like Earth has nowadays. (Core could be molten in these days too)
    The planet cooled rapidly as 1) much smaller 2) did not experience an impact as big as Earth when the Moon was formed
    Most of Earth’s water came from the solar system’s outer regions well after it’s formation in a so called “late bombardment” era when most probably large planets like Jupiter has changed it’s path and routed many frozen watery objects towards the centre of the solar system. Why would has Mars missed this watery bombardment? Most probably is has not.

    My problem with all the “where is the water, we cannot se lakes and rivers, so there is non” opinions is that most of them are based on Earth’s nearly 2 dimensional example.

    What is the most important difference between Mars and Earth? I think is is very simple, you have to only think in 3 dimensions, instead of 2.

    On Earth water is on the surface, it’s everywhere. Why? Because if it travels down (eg. with continental crusts) it’s heated up, becomes a vapour and travels back up. It simply cannot sink down more than a few 10 kilometres. Absolutely insignificant distance compare to Earth’s radius.

    The story is completely different on Mars. It has cooled and the mantle has solidified. Probably the mantle is frozen down up to 50-60% of it’s radius.

    As the mantle has solidified it must have shrunk significantly. Most probably giant cracks and holes have formed under this process.

    (Could a geologist please calculate for me, how much volume the mantle could have lost while it has cooled from an average 1200 degree Celsius to a much milder 200-300 degree Celsius. Let’s calculate with only a 2000 km thick mantle. I would be very surprised if the shrinkage would have not been significant. Could you please calculate how much water could have disappeared in the deeps through crack and holes, in the volume of space which were created in this shrinkage process? )

    My suggestion is that the water has party escaped by solar wind, but most probably most of it has just simply travelled down alongside huge cracks and holes. As it has been travelling down pressure and temperature have risen so it could easily be kept in a liquid state.

    My guess is that there can be truly giant water reservoirs in the depths of Mars. Liquid water could be found a few 100 kilometres above the limit between molten and non molten crust / mantle. This limit on earth is from a few kilometres to a few ten kilometres. On Mars it can be a few hundreds or few thousands of kilometres.


    I think to search for life on Mars’ surface is nearly pointless.

    Is there anyone, who can imagine that life has once existed on the planet, but has simply travelled down with the water? Is there anyone who knows life forms not dependent on sunlight but chemical processes?

    Is there anyone, who can imagine a warm water reservoir 200 kilometres deep filled with microbiological like feeding on sulphurs, hydrogen or other gases and minerals?

    For me, it’s a very easy task to imagine.

    Best Regards,

    Gabor Pokoradi, London