IAL 14: Mars: the Red Planet

Don't Panic


  1. Introduction
  2. Mars Facts
  3. Mars Geography
  4. Mars Geology, Except for Water Geology
  5. The Martian Atmosphere
  6. Water on Mars
  7. Life on Mars

  1. Introduction

  2. Mars is the most fascinating---in general opinion---and sometimes the most ominous of the unearthly planets.

    See the image of full Mars in the figure adjacent/below (local link / general link: mars_full.html).

    1. Mars in Myth and Early History:

      Mars has been known since prehistory, of course.

      The ancient Babylonians associated Mars with their war and pestilence god Nergal. The ancient Greeks with their war god Ares---of whom few amusing stories are told.

      Mars is, of course, also associated with the Roman war god Mars who was identified with Ares.

      Mars has always been a favorite with astrologers---Mars in your sign is pretty easily interpreted by the Art. With artists less so---they've generally preferred Venus---but Botticelli managed to combine the twain. See the figure below (local link / general link: botticelli_venus_and_mars.html).

      Mars has a memorable symbol: ♂. See the figure below (local link / general link: alien_mars_symbol.html).

      As a scientific object,
      Mars came to the fore in the early 17th century. Johannes Kepler's (1571--1630) study of the orbit of Mars led him to discover that the planets had elliptical orbits.

      The nature of Mars itself began to be elucidated by the telescope. Using a telescope, Christian Huygens (1629--1695) identified the largest dark region on Mars, Syrtis Major.

      In the 18th century, it was discovered that Mars has polar caps and sooner or later that they decrease in the summer hemisphere and increase in the winter hemisphere ???.

      In the 19th century???, it was noted that the dark areas on Mars also seemed to increase in springtime suggesting increasing vegetation.

      Alas, this effect is really due to spring??? winds blowing lighter colored Martian dust off darker surfaces (HI-183).

      Maps of Mars were produced in the 19th century, but really how good they were by modern standards, I don't know---probably so-so for the largest features and rotten for anything smaller. See Giovanni Schiaparelli (1835--1910) map of Mars in the figure below.

    2. The Martian Canals:

      In 1877 during a FAVORABLE opposition of Mars, Italian astronomer Giovanni Schiaparelli (1835--1910) concluded the Martian canals were a major feature (Ka-293). The canals were apparent linear markings on Mars.

      Actually in calling them canali (singular canale) in Italian, Schiaparelli was NOT necessarily implying that they were artificial: his meaning may have been probably closer to the English channels---but Schiaparelli made no effort to correct the English translation---he may NOT have noticed it much (Wikipedia: Martian canals: History of canals).

      Canale does have canal as its primary meaning in Italian.

      Two images in the figure below (local link / general link: martian_canals.html) show the Martian canals in the imagination of the artist.

    3. The Martians:

      The Martian canals they became in popular conception and some people became convinced they were constructions of intelligent beings: the Martians.

      The most prominent of the believers in Martians was Percival Lowell (1855--1916)---who founded the Lowell Observatory in Flagstaff, Arizona. See Lowell in the figure below (local link / general link: percival_lowell.html).

      Lowell did a lot of Mars observations by himself. Three of his less elaborate drawings of Mars are shown in the figure below (local link / general link: percival_lowell_mars_map.html).

      Because of the popular interest in
      Martians, they invaded fiction---most famously in H. G. Wells' (1866--1946) The War of the Worlds (1898)---see the two figures below (local link / general link: h_g_wells.html; local link / general link: h_g_wells_war_of_the_worlds.html).

      Also famously,
      Orson Welles (1915--1985) presented a radio play version of The War of the Worlds (1898) in 1938--- for young Orson and an explication of the Martian invasion scare, see the figure below (local link / general link: orson_welles.html).

    4. The Truth About Martians:

      Many/most astronomers never believed in the Martian canals and always thought they were optical illusions---and all the talk about Martians was vastly premature.

        In his day, Percival Lowell refuted his critics who said his Martian canals were just optical illusions, by saying that at the Lowell Observatory in Flagstaff, Arizona he had the world's best observing site---for his day, you understand---and so could see what others couldn't.

        Lowell was right about having a good observing site, but he was still just seeing optical illusions.

      However, even up to the 1950s, Martians and Martian canals were considered plausible at least in scifi and in scifi illustrations---like those of Chesley Bonestell (1888---1986) and in the figure below (local link / general link: alien_prototype_martian.html).

      But the final
      nail in the Martians' coffin was provided by the images from the Mariner 4 flyby of Mars in 1965.

      The Mariner 4 images and other work showed Mars was a cratered world with a very low density atmosphere.

      It was a quite disappointment to young scifi fans like me in the 1960s. No Martian canals, no Martians, no Thuvia, Maid of Mars. See the figure below (local link / general link: thuvia_maid_of_mars.html).

      Nowadays, we see
      Mars as a world intermediate between the large rocky planet Earth and small, airless rocky bodies like the Moon.

      But mysteries remain.

      1. Mars has water today in vapor and solid form and clearly it has had liquid water in the past, but when and how much?

        Is there sub-surface liquid water today?

      2. The Mars ocean hypothesis---did Mars ever have an ocean? The hypothesis is that a vast ocean covering about a third of Mars existed in the northern hemisphere. It's NOT established or dismissed.

      3. Was there ever life on Mars in an earlier warmer, wetter time?

        Is there life today below the surface in a deep biosphere: perhaps like the Earth's deep biosphere.

        We've know since circa 1990 that there is a deep biosphere on Earth and microbial life can be found down to several kilometers in the crust (HI-196).

        Question: In what temperature range can liquid water exist when the atmosphere has Earth surface pressure?

        1. 273 K to 373 K.
        2. 0 C to 100 C.

        Both answers are right.

        Just checking on who is awake.

        To be more exact at standard 1 atmosphere pressure the freezing temperature is 0.00 C and 273.15 K. The boiling point is 99.975 C and 373.125 K (HRW-429)

        Some microbial life can live at somewhat higher temperatures than 100 C when the water is kept liquid by high pressure (Wikipedia: Biosphere: Extent of Earth's biosphere).

  3. Mars Facts

  4. Just some basic Mars facts---which, of course, beg for an explanation---and there is some explanation, but also some "Just So."

    1. A Mars Fact Table:

      Below we give a table of some Mars facts.

      Table:  Mars Facts
      Quantity                            Value
      Mean distance from the Sun    1.5237 astronomical units
      Eccentricity of orbit         0.0934 :   which is the much larger than 
                                               Earth's 0.0167
                                               but much smaller than 
                                               Mercury's 0.206.
      Mean inclination to Ecliptic  1.85061° 
      Axis tilt to orbital pole     25.19°
      Orbital period                686.95 days = 1.88071105 years
      Rotational Period             1.02595675 days : This is the sidereal period
      Martian day                   1.02749 days : just a bit longer than 
                                                   the rotational period 
                                                   for the same that Earth's day 
                                                   is longer than its rotational period.
      Equatorial radius             3,397 km = 0.53 R_Earth_equatorial
      Mass                          6.424*10**23 kg = 0.1075 Earth masses
      Mean density                  3.94 g/cm**3 : significantly less than
                                                    mean Earth density
      Uncompressed mean density     3.3 g/cm**3 : significantly less than
                                                   uncompressed mean Earth density 
                                                   and about same as the Moon's 
                                                   uncompressed and compressed mean
      Surface gravity               0.379 Earth gravities
      Surface temperature           about -80 C (190 K) at night to -30 C (240 K)
                                      in the day on a summer day.  This is 
                                      surface air temperature.  On a hot day
                                      in summer the ground temperature can rise
                                      above freezing (HI-187).
      Moons                          The Martian moons are
                                     Phobos with mean radius 11.1 km
                                     Deimos with mean radius 6.2 km.
                                     They are both irregular in shape and 
                                     may be captured asteroids,
                                     but there are rival theories.

      Sources: Cox-294,295; Se-418,479; HI-187.


    2. The Martian Moons:

      The Martian moons are two: Phobos (mean radius 11.2667 km) and Deimos (mean radius 6.2 ± 0.18 km).

      They were discovered by Asaph Hall (1829--1907) in 1877 during a favorable Mars opposition---the same one that led old Giovanni Schiaparelli (1835--1910) to concluded that the Martian canals were a major feature of Mars.

      The most common theory is that the Martian moons are captured asteroids, but rival theories exist (see Wikipedia: Moons of Mars: Origin).

      Both Martian moons are tidally locked to Mars, and so turn the same face to Mars all the time (see Wikipedia: Moons of Mars: Characteristics).

      The tidal force on Phobos is causing it to inspiral and it will break up and impact in fragments on Mars probably in 30--50 Myr (see Wikipedia: Phobos: Predicted destruction). On the other hand, the tidal force on Deimos is causing it to outspiral. See Wikipedia: Moons of Mars: Characteristics and Caleb A. Scharf, 2015, SciAm.

      For the Martian moons, see the two figures below (local link / general link: martian_moons_phobos.html; local link / general link: martian_moons_to_scale.html).

      We don't have more to say on the Martian moons.

    3. The Density, Iron Core, and Magnetic Field of Mars:

      Oddly the uncompressed density of Mars is similar to that of the Moon.

      This suggests that Mars doesn't have a large iron core relative to Earth???.

      A molten iron core is probably necessary for a large dipole magnetic field. Electrical currents generated in the iron core by convection and rotation generate the dipole magnetic field---somehow he said while handwaving.

      Since Mars has no large dipole magnetic field now, its iron core is NOT sufficiently large and/or sufficiently molten.

      The Earth's magnetic field and the magnetic field of Mars are illustrated in the figure below.


        Caption: A cartoon comparing Earth's magnetic field and Mars's magnetic fields.

        Earth's magnetic field is a global dipole field like a bar magnetic. It is believed to be caused by a dynamo effect of conducting liquid iron in the Earth's iron outer core.

        Mars's iron core may no longer be liquid even in part. In any case, it is NOT generating a global field. There are small local fields due to permanently magnetized rock????. These are fossil magnetic fields.

        Credit/Permission: NASA, Mario Acuna, Jack Connerney, Chris Meaney, 1999 / Public domain.
        Download site: Views of the Solar System by Calvin J. Hamilton: The image is public domain, but CJH does NOT to give a download site.
        Image link: Itself.

      The Earth's magnetic field protects the Earth's atmosphere from the blasting effect of the solar wind: i.e., solar wind sputtering atmospheric escape The solar wind tends to blow away an exposed atmosphere.

      The lack of strong global magnetic field means that the Martian atmosphere is directly exposed to the solar wind (see Wikipedia: Martian atmosphere: History). This seems to be a major factor Mars evolving to have a very low the density atmosphere compared to Earth's atmosphere. The average atmosphere pressure on the Martian surface is about 0.006 that of the average atmosphere pressure at Earth's sea level. Roughly speaking the Martian atmosphere is 100 times thinner than the Earth's atmosphere.

      However, the low gravity of Mars (about 0.4 of Earth) and thermal atmospheric escape is probably the main reason for the relatively thin Martian atmosphere.

      For more on atmospheric escape, see the figure below (local link / general link: solar_system_atmospheric_escape.html).

  5. Mars Geography

    1. All Mars Maps:

      As a first glance at Martian geography see the all Mars maps in the figure below (local link / general link: nasa_mars_map_000.html).

    2. The Western Hemisphere of Mars:

      For an image of the western hemisphere of Mars, see the figure below (local link / general link: mars_full.html).

      Valles Marineris is compared to the United States in the figure below.

    3. A Topographic Map of Mars:

      The collage-image map (see figure above: local link / general link: nasa_mars_map_000.html) and western hemisphere image (see figure above: local link / general link: mars_full.html) do NOT directly reveal the strong distinctions between the northern and southern hemispheres of Mars, except for more cratering in the southern one.

      A topographic map reveals the elevation distinction. See the figure below.

  6. Mars Geology, Except for Water Geology

  7. Nowadays there's just too much known about the Martian geology.

    Too much for us.

    So we'll skim.

    1. Mars in the Middle:

      Because of its intermediate size between Earth and the Moon, we expect Mars to be intermediate in geological drivers.

      Recall the bigger the rocky body, the more primordial-radiogenic heat geology (see also Wikipedia: Earth's internal heat budget: Radiogenic heat: Primordial heat) it has.

      The upshot is that Earth and Venus have a lot of primordial-radiogenic heat geology. The Moon virtually none.

      Mars is in the middle in size---about 1/10 of the Earth in mass, but about 8 times the Moon. So Mars has some primordial-radiogenic heat geology: much less than Earth and Venus, but a lot more than the Moon.

      Also like Earth and Venus, Mars' primordial-radiogenic heat geology has been slowing down since the Formation of the Solar System 4.6 Gyr ago.

    2. The Geological Evolution of Mars:

      Like Earth and the Moon, just after formation, Mars 4.6 Gyr ago went through chemical differentiation and cratering under the heavy bombardment and probably had massive lava flows in giant basins---any trace of this on Earth has been erased if it ever happened.

      On the Earth, the impact craters of the heavy bombardment have been erased; on the Moon, many of them remain except where erased by subsequent impactors (leaving newer impact craters) and by the formation of the maria.

      Mars retains a lot of Earth, the impact craters probably many??? from the heavy bombardment (circa 4.6--3.8 Gyr ago) in the southern hemisphere. See the topographic map of Mars below.

      Hellas Planitia in the southern hemisphere may be a remnant of the early lava flooding of an impact basin (HI-185). So it may be a sort of a lunar mare.

      The northern hemisphere is much less cratered and probably impact craters there are from after the heavy bombardment, but still relatively long ago. The northern hemisphere seems to have been resurfaced by lava flows.

      We discuss
      water on Mars in section Water on Mars, but here we can say there is water on Mars has been more in the past, probably intermittantly, but that in any case erosion by water has been far less than on Earth.

      So water erosion has also been much less important on Mars than on Earth. This is another reason for the surface of to be generally much older than that of Earth, but still less old than that of the Moon.

      Also, it was once thought (circa 2005) that primordial-radiogenic heat geology was actively melting water ice periodically to the present day. But this is now doubtful. There may have been no flowing liquid water on Mars for a long time. Nothing is settled on this issue. See the section Water on Mars below.

      Recall Mars' primordial-radiogenic heat geology has been slowing down since the Formation of the Solar System 4.6 Gyr ago.

      So Mars' volcanism has been slowing down, but unlike that of the Moon and other small rocky body without tidal-flexing-heating geology, Mars still has slightly volcanoes it is thought. we take up the subject of Mars' volcanism in the next subsection.

    3. Volcanoes on Mars:

      Mars has volcanoes most notably the four big ones of the Tharsis region.

      The biggest of the four and biggest known in the Solar System, in fact, is Olympus Mons---see the figure below.

      Olympus Mons is a shield volcano. See cartoon of ashield volcano in the figure below (local link / general link: volcano_shield_cartoon.html).

      shield volcanoes are formed by repeated lava flows and have gentle slopes (SWT-572)---as illustrated in the diagram to the right.

      Shield volcanoes occur on Venus, Earth, and Mars.

      Below is another image of Olympus Mons.


        Caption: Olympus Mons in the Tharsis region of Mars.

        This is Mars Orbital Camera (MOC) approximately true color image from 1998apr25.

        Olympus Mons is the largest known volcano in the Solar System.

        It is a shield volcano with shallow slopes of 2° to 5° grade. You could walk up it The base is about 500 km across, the height above the lower deserts is 24 km, and the summit caldera is about 65 km across (HI-190).

          Calderas on Earth anyway form when a chamber near the summit is partially emptied by the outflow of lava and ash collapse to form a broad flatish depression with steep walls (SWT-573).

        The image was taken in winter in the northern hemisphere. East is to top and west is to the bottom. The east is actually cloudy and the clouds form a whitish haze that I think I can pick out.

        The clouds are water ice clouds (such as we have on Earth) I think (FMW-200--201).

        There are also dust clouds and carbon dioxide (CO_2) ice clouds, but the former might look dustier and the latter are supposed to be high altitude whatever that means for Mars.

        Anyway water ice clouds are supposed to often form near mountains.

        Credit/Permission: NASA, Malin Space Science Systems, 1998 / Public domain.
        Download site: Views of the Solar System by Calvin J. Hamilton: The image is public domain, but CJH does NOT give a download site.
        Image link: Itself.

      See the video Vuela sobre el monte Olympus de Marte | 0:1:55 (an animation of a flight over Olympus Mons) in Mars videos below (local link / general link: mars_videos.html):


    4. Mars Lives---Geologically Speaking:

      It was once thought that Mars's primordial-radiogenic heat geology was dead, like the Moon's---but only more recently deceased.

      But now there are lava flows judged to be less than 100 Myr old from crater counts (HI-189).

      Less than 100 Myr is almost nothing on the time-scale of internal heat loss for a Mars-size body.

      Thus, Mars has primordial-radiogenic heat geology and volcanism today---although at a much lower level of activity than Earth or Venus.

      Of course, we may have to wait millennia or millions of year for the next volcanic eruption.

    5. Plate Tectonics on Mars?

      Does Mars have plate tectonics?

      Apparently, NOT.

      There is no solid evidence for divergent boundaries or convergent boundaries.

      It is theorized that Valles Marineris (see below local link: mars_videos.html) is large rift valley where the Martian crust is being pulled apart (see Wikipedia: Valles Marineris: Formation). On Earth, rift valleys can be divergent boundaries between tectonic plates (see Wikipedia: Rift valley), but Valles Marineris does NOT seem to fall into that class.

      Valles Marineris may be plate-tectonics feature of Martian plate tectonics that never developed very far.

      There are no real continent or terra formations. (Terras are the continent-like features on Venus.)

      Volcanism on Mars may be all hotspot volcanism. The Tharsis region may have been formed by a giant hotspot and may be similar to the coronas on Venus (HI-191).

      See Valles Marineris in Mars videos below (local link / general link: mars_videos.html):


    6. The Future of Mars:

      In the future, of course, primordial-radiogenic heat geology must slow on Mars as primordial heat from formation and past radioactive decay decreases. It must turn off eventually.

      But probably this won't happen until long after the Sun becomes a white dwarf.

      Mars probably won't be vaporized by the red giant phases of the Sun and may continue to orbit the white dwarf Sun in some orbit for hundreds of gigayears into the future????.

      The orbit of Mars will certainly be different in that far future since the Sun will lose a lot of mass in becoming a white dwarf, and thus its gravitational force will be weakened. Probably the orbit will be much larger.

  8. The Martian Atmosphere

  9. The Martian atmosphere is thin.

    1. The Thinness of the Martian Atmosphere:

      Below is an image showing the Martian atmosphere.

      The surface pressure that is about 1 % of Earth's.

    2. The Existence of Liquid Water on Mars:

      The low pressure of the Martian atmosphere means that liquid water CANNOT exist on the surface for any length of time.

      Under low enough pressure, the liquid phase doesn't occur for most (all?) substances: they condense from gas to solid and sublimate (or evaporate in loose astro jargon) from solid to gas.

      The figure below (local link / general link: co2_ice.html) gives an example of a substance that under standard temperature and pressure (STP) has NO liquid phase.

      Water below 0.01 atmospheres does NOT have a liquid phase. See the phase diagram of water in the figure below (local link / general link: phase_diagram_water.html).

      Qualification: The liquid phase doesn't exist in thermodynamic equilibrium if the pressure is too low. If you suddenly inject the liquid into a low pressure environment, it is out of the thermodynamic equilibrium and will persist as liquid for some time---how long depends on the conditions---which for Mars, yours truly doesn't know.

      The figure above (
      local link / general link: phase_diagram_water.html) suggests that at Martian surface pressure (about 0.06 of Earth's pressure or about 0.600 kPa) that liquid water could exist if the temperature rose above 0° C.

      It may be that on the warmest days on the Martian equator or in the Martian summer hemisphere in the deepest valleys that liquid water could persist---but there's no evidence that there is any under such conditions.

    3. The Composition of the Martian Atmosphere:

      The Martian atmosphere is CO_2 dominated like the atmosphere of Venus---but there is VERY LITTLE greenhouse effect because of the low density.

      The table below shows the composition of the Martian atmosphere.

        Table:  Martian Atmospheric Composition by Number 
        Gas                      Percentage
        CO_2                     95
        N_2                       2.7 
        Ar                        1.6
        CO                        0.6
        H_2O                      0.03     variable due to condensation & sublimation 
        References: HI-187.

      There is some water vapor which can condense in the air to make white water ice clouds as we maybe??? saw with the Olympus Mons picture above.

      CO_2 ice clouds can make clouds at high altitudes too (FMW-200--201).

      Probably early on, Mars had a significant CO_2 and water vapor atmosphere from volcanic outgassing like the early Earth and early Venus are thought to have had.

        There is a theory that comets brought significant volatile material, particularly water, to the Earth in some early phase---"a hard rain fell".

        If this was so for the early Earth, then it is also likely so for the early Mars.

        The theory has had its ups and downs in acceptance.

        At present, theory that comets from the Kuiper belt brought most water to Earth seems to be gaining ground.

        We won't discuss the hard comet rain theory further for Mars---but it should be kept in mind.

      In fact, Mars may have had several intervals of such an atmosphere as we will discuss below in the section Water on Mars.

      But because of the the low gravity of Mars and probably solar wind in the absence of a global magnetic field, much of this early thick Martian atmosphere has undergone atmospheric escape over the gigayears.

      The fractionation of the argon isotopes in the Martian atmosphere provides direct evidence of atmospheric escape. See the figure below.

      Probably the molecules of CO_2 and H_2O were broken up at high altitudes and the C and H escaped mostly.????

      Credit/Permission: NASA/Jet Propulsion Laboratory (JPL)-Caltech, 2013 (uploaded to Wikipedia by User:Drbogdan, 2013) / Public domain.
      Image link: Wikipedia: File:PIA16818-MarsCuriosityRover-Argon-AtmosphericLoss.jpg.

    4. O_2 on Mars:

      Any oxygen in the form of O_2 did NOT stay, and there may never have been much build of it in the Martian atmosphere if Mars never had biological production.

      The reddish color of much of the soil and rocks of the Martian surface is due to to iron(III) oxide.

      Mars really is the Red Planet or reddish planet viewed from most of the Martian surface. This is illustrated in the figure below.


        Caption: The terrain around the Pathfinder landing site. 1997dec.

        Pathfinder was the first lander since the Viking 1 and 2 landers in the 1976. It landed in 1997 (HI-183--184).

        The image is a 360° panorama.

        In order to study the surroundings in detail with the SOJOURNER ROVER (near Yogi at 320° in the image), it was necessary to map the landscape.

        For mnemonic reasons names were given to quite small features: names were evidently derived from a variety of pop-cultural sources.

        As one can see the sand is reddish and so are some of the rocks. The red color is due to iron oxide and is typical of Mars (PF-118).

        Mars is the Red Planet after all.

        Credit/Permission: NASA, US Geological Survey (USGS), 1997 / Public domain.
        Download site: Views of the Solar System by Calvin J. Hamilton: The image is public domain, but CJH does NOT to give a download site.
        Image link: Itself.

    5. The Colors of Mars:

      Actually Mars's colors are tricky.

      From Earth, it looks reddish-orange with the naked eye??? (PF-118).

        This coloration may well have been the original reason associateing war gods as mentioned in the Introduction.

      Telescopic observers see a mix of colors including red and orange and dark.

      Close up orbiter images often show the bright areas as more yellowy-browny than red.

      The reddish surface, as discussed above, is because of the high amount of iron(III) oxide (see Wikipedia: Martian surface: Albedo and Color).

      The dark or blackish regions (like Syrtis Major) are because of a high amount of iron(II) oxide or ferrous oxide (FeO) Wikipedia: Martian surface: Albedo and Color.

      Then there is the problem of the Martian sky color.

      Images typically use filters to bring out features, NOT show true color as seen by the human eye.

      The Martian sky color does vary, but the daytime color seems to be mainly a bright yellow-brown. See the figure below.

      Near sunrise and sunset the color is mainly rose, but just near the Sun the color is blue.


        Caption: "The Martian sky color at noon is yellow-brown, which contrasts with its pinkish-red color at sunset. The true color of Mars based upon three filters with the sky set to a luminance of 60. The color of the Pathfinder landing site is yellowish brown with only subtle variations. These colors are identical to the measured colors of the Viking landing sites reported by Huck et al. [1977]. This image was taken near local noon on Sol 10. A description of the techniques used to generate this color image from IMP data can be found in Maki et al., 1999. Note: a calibrated output device is required accurately reproduce the correct colors."

        Credit/Permission: NASA, 1999 (uploaded to Wikipedia by User:Liftan, 2007) / Public domain.
        Image link: Wikipedia: File:Mars sky at noon PIA01546.jpg.

    6. Climate on Mars:

      Because of its low pressure and hence lack of liquid water, Mars today is essentially a cold desert.

        Recall from above that summer day time temperatures in the air only get up to about -30 C.

      Mars does have seasons because of its axial tilt (and secondarily its orbital eccentricity) and weather.

    7. Seasons on Mars:

      The Martian seasons somewhat mimic Earth's and are most noted through the variations in the Martian polar ice caps. See figure below.

      The Martian polar caps are coated in a layer CO_2 ice (dry ice) over a much thicker layer of water ice.

      In a Martian summer hemisphere, some of the CO_2 evaporates (properly speaking sublimates) and goes into the Martian atmosphere. So the summer Martian polar cap shrinks.

      At the same time, the winter Martian polar cap in the other Martian hemisphere (the winter hemisphere) grows as CO_2 from the Martian atmosphere condences (properly speaking deposits) on it.

      So the north polar cap and south polar cap alternatively grow and shrink with the Martian seasons.

      The figure below shows a simplified version of the behavior of Martian volatiles which implies the seasonal cycle of the Martian polar caps.

      Besides the Martian polar cap, CO_2 gas condences at other places on Mars too as a CO_2 frost as illustrated in the figure below.

    8. Weather on Mars:

      The weather on Mars is most notable through the winds blowing Martian dust and dust storms.

      These dust storms can be global, but I've never seen an image where it was easy for me to notice that a dust storm was happening---it must take a trained eye.

      A smaller Martian dust phenomena are the Martian dust devils.

      Dust devils are little whirlwinds which we have on Earth too including in Arizona and Nevada---there was one in my parking lot once. See the figure below.

      See Martian dust devils in Mars videos below (local link / general link: mars_videos.html):


      Wind erosion and wind building of dunes is a common feature of Mars too---but we leave it at that for now---except for the image of Martian sand dune shown in the figure below.

      The Martian atmospheric dust is reddish in color (or yellowish-brown, but it's in the eye of the beholder) and its magnetic component is due to magnetite (iron oxide Fe_3O_4) (a black iron oxide) (see Kerr, R. A. 2005, Science, 308, apr08, 192).

      Magnetite is NOT formed in water and that it is in the Martian dust suggests much of Mars has been mostly dry for a long time.

      Martian dust and other evidence is pointing to Mars having had a dry surface for maybe 3.7 Gyr, except perhaps for brief episodes (see Kerr, R. A. 2005, Science, 308, apr08, 192).

  10. Water on Mars

  11. The subject of water on Mars has been heavily investigated.

    There is more than yours truly can say.

    So we skim?

    1. Liquid Water on the Surface of Mars:

      There is significant Water on Mars---but there is no continuous liquid water on the surface.

      And it is liquid water that is needed for life as we know it and liquid water erosion.

        There is water ice and glacial erosion too as we noted on Earth. See below.

    2. A Catalog of Water on Mars:

      Let's do a little catalog of water and possible water on Mars.

      1. In the atmosphere, there is about 0.03 % water vapor by number as noted above.

        This is much lower than the 0.1--2.8 % range on Earth (CW-296), and recall Earth's atmosphere is about 100 times denser than Mars's atmosphere.

      2. There is water in the soil in the form of isolated molecules embedded in the crystal structure of rock grains. This was discovered by the Viking landers (HI-188).

      3. There is substantial water ice. The polar caps as noted above probably have 1 to 3 km of water ice in places (HI-187).

      4. Although NOT proven absolutely, it is considered highly likely that there is water ice in the soils at higher latitudes (HI-188).

          I'd like to say permafrost above, but permafrost, apparently, means soil below freezing for two or more years whether water ice is present or NOT.

      5. At deep enough depths where pressure and temperature are sufficiently high, there well may be liquid water in aquifers (HI-195).

      6. There is solid evidence now for Martian glaciers on that formed within millions to tens of millions of years ago as one can tell by cratering on them (Kerr, R. A. 2005, Science, 308, apr08, 192). One is at the base of Olympus Mons for example.

        The glaciers are rock-and/or-dust-coated, and so hidden. It has taken detailed imaging by the NASA Mars Global Surveyor and the ESA Mars Express Orbiter (first operational 2004) and radar mapping by the NASA Mars Reconnaissance Orbiter to find their signatures.

        They are NOT like most terrestrial glaciers, but rather like those in the McMurdo dry valleys in Antartica---they ooze over things rather than slide on a wet layer.

        Probably the Martian glaciers formed from straight vapor to solid transitions. There was no liquid water involved.

        They probably are NOT growing now, but are relics of a time when Mars's axial tilt was larger and more water could be sublimated from the polar caps and spread to other regions. The axial tilt seems to vary because of some effect???.

    3. Martian Gullies:

      As noted in the section The Martian Atmosphere, liquid water CANNOT exist now on the surface for any length of time because of the low pressure and low temperature.

      It can exist for short times before it evaporates or freezes.

      But does it?

      It's very uncertain.

      In the last few years the Mars Global Surveyor's Mars Orbiter Camera (MOC) has been finding evidence of fairly recent gullies on Mars.

      The figure below shows Martian gullies and gives some description.

      Where is the liquid water---if there is any on the surface ever---coming from?

      Well you don't need to go far down into the ground before the pressure rises high enough for liquid water to exist.

      Since we argued above that Mars has still modest internal heat, at some depth beneath the ground it is probably warm enough as well as high enough in pressure for liquid water.

      Thus, it's possible, as noted above, that underground water reservoirs (i.e., aquifers) exist today (HI-195).

      Subsurface events may sometimes squeeze liquid water to the surface where it flows out of canyon or crater walls and forms gullies in the brief time before it evaporates or freezes.

        I imagine that water ice, except near the poles, likely sublimes quickly in the summer weather.

      BUT a recent theory says the "gullies" may be slumping of the powdery surface, and thus a purely dry phenomenon. See Nature: Shinbrot et al. Just when you think you understand something, some crazy scientist comes along and ...

      There has been a nugget of evidence from chemical deposits for the presence of liquid water on maybe a yearly or millennial basis, but it's NOT very exciting (Nature: Liquid Water Found on Mars, But It's Still a Hard Road for Life, 2010oct29). In any case, it's NOT on the surface, but below CO_2 ice layers.

    4. A Wetter Mars in the Past:

      Was Mars wetter in the past? Did it have continuous surface water?

      Well ever since the Viking orbiters of the 1970s these questions have been hotly debated.

      Images from the Viking orbiters showed many striking channel features---dry of course.

      Some of them may be flood channels due to a sudden melting of water ice and release of liquid water by a volcanic eruption or an impactor.

      But some channels look very much like rain-fed runoff channels such as we find on Earth.

        Question: What do extensive rain-fed runoff channels look like on Earth as viewed from above?

        1. Like parallel straight lines.
        2. They form a dendritic (i.e., tree-branching) pattern.

        Answer 2 is right.

      For rain and surface liquid water to exist, Mars's atmosphere would have had to have been substantially denser and warmer than today.

      There is evidence for this as discussed in the figure below.


        Caption: A network of channels on Mars.

        This is a Viking Orbiter image showing a region just west of the Viking 1 Lander site in Chryse Planitia. Probably the coordinates are about 25 N, 50 W.

        The image is about 300 x 300 km.

        The network of channels strongly suggests rainfall and surface runoff: i.e., they could be rain-fed runoff channels.

        But they could have been formed by groundwater sapping.

        In groundwater sapping, liquid groundwater eats away at a cliff face. One images the water as frozen until some geothermal event temporarily melts it and this leads to groundwater sapping.

        Whether or NOT this network is due to rain-fed surface runoff, I don't know.

        But in fact, the current thinking is that the some channels are Mars do indicate some persistent flow and rain.

        But rain and run-off rivers were probably very intermittent.

        It has been suggested that major impacts may somehow ??? have heated Mars for a few decades every few million years and thus brought about an intermittent wet Mars (publicized by Kerr, R. A., 2003jun06, Science, 300, 1496).

        On the other hand, periods of intense volcanism may have temporarily given Mars a thickish CO_2 atmosphere that in turn gave Mars's enough greenhouse effect for surface liquid water and rain (HI-194).

        Current thinking is that Mars was always too cold to be continuously wet (publicized by Kerr, R. A., 2003jun06, Science, 300, 1496).

        But the story could change again---it keeps doing that, you know.

        Credit/Permission: NASA, Viking 1 Orbiter (1976--1980), before or circa 1980 / Public domain.
        Download site: NASA: GEO_PLATE_P-8.HTML. Alas, a dead link.
        Image link: Itself.

      There are in fact a huge number of gully images and other images from the Mars Global Surveyor's Orbiter Camera (MOC). See Malin Space Systems: Mars Global Surveyor Mars Orbiter Camera Captioned Image Releases.

      But was there ever continuous running water on Mars?

      Even before the Mars Exploration Rovers (Spirit, active 2004--2010, and Opportunity, active 2004--, there was confirming evidence that Mars had continuous running water for some significant periods of time: years? decades? centuries? megayears? I havn't found any estimates yet.

      The confirming evidence came from the Mars Global Surveyor and is shown in the figure below.

      So yes, Mars, had at least rivers and bodies of water of some size.


        Caption: A distributary fan on Mars. From the Mars Global Surveyor's Mars Orbiter Camera (MOC), 2003nov13. Image MOC2-543a.

        The fan is 24.3 S, 33.5 W. The image is 14 x 19.3 km. The fan is located in a partially destroyed impact crater of diameter 64 km.

        A distributary fan is a river delta or similar alluvial feature.

        The fan is important for 3 reasons:

        1. It proves there was persistent water flow on Mars.

          Water channels have been long identified on Mars, but they it is argued that they could be due to flood events due sudden heating of frozen water: volcanic or impact heat would be the cause.

          But to form a fan with typical fan features like oxbows (see below) takes time.

        2. The fan is marked out by sedimentary rock. The fan channels are now raised above the surroundings. The sedimentary rock must have been cemented harder than the surroundings. Probably wind erosion has worn away the surroundings.

        3. It seems likely that the fan flowed into a body of water: perhaps a small lake.

        The boxes mark out especially decisive features:

        1. Box c shows an oxbow is a loop in a meandering river typical of the Mississippi River for example.

          A cut-off meander has pinched off the oxbow: this is typical of meandering Earth rivers and requires persistent flow.

          Note the impact crater to the east of box c. This crater is superimposed on the fan and so came later.

        2. Box d shows crossed channels with one clearly lower than the other. This indicates the fan persisted long enough to reform and cut new channels.

        As impressive as this fan discovery is, one must keep in mind that MOC was imaging Mars in high resolution from 1997dec and this is the first most definite evidence it found after 6 years.

        Clearly, Mars didn't have a lot of water channels and lakes or else the evidence has been destroyed by long ago volcanism and cratering.

        Credit/Permission: NASA, Malin Space Science Systems, 2003 / Public domain.
        Downlaod site: MGS MOC Release No. MOC2-543, 13 November 2003.
        Image link: Itself.

    5. The Mars Ocean Hypothesis:

      Did Mars ever have oceans?

      This topic has been hotly debated for years with different groups coming to different conclusions based on the studies of basin shapes and rock formations.

      The 800 lb gorilla of an idea is the Mars Ocean Hypothesis that posits that virtually the whole blue region in the topographic map in the figure below was an ocean about 3.8 gigayears ago.

      We won't go into the full evidence for the
      Mars Ocean Hypothesis---cause I've NOT had time to bone up on it.

      However, the Mars Exploration Rovers (Spirit (2004--2010) and Opportunity (2004--)) have added some evidence in favor of oceans and have proven that there were at least desert basin salt lakes.

      Some images illustrating the mission of the Mars Exploration Rovers are shown in the three figures below.

      And the evidence from the Mars Exploration Rovers for oceans and at least desert basin salt lakes is shown in the dramatic figure below. These kind of images just make geologists go wild.


        Caption: A view of a cross-laminated, sedimentary rock. Opportunity, 2004mar05.

        The fine layers (laminae) in this rock are ``truncated, discordant and at angles to each other.''

        I assume that these layers are the cross-laminae and there appearance means the rock is cross-lamination.

        The BLACK LINES trace the cross-lamination and the BLUE LINES possible boundaries between sets of cross-laminae. Possibly the sets were laid down at different times???.

        Cross-lamination indicates that these sediments were laid down by flowing water. The water flow was perpendicular to the plane of the image either inward or outward.

        The water was 5 cm deep or so or much deeper and the flow speed was about 10 to 50 cm/s.

        Chlorine and bromine in the rock suggests that the sediments were laid down in salty water where the concentrations of salts exceeded the saturation due to evaporation.

        The formation enviromment may have been a sea shore or desert basin.

        Credit/Permission: NASA, JPL, Cornell University, USGS, 2004 / Public domain.
        Download site: NASA: Standing Body of Water Left Its Mark in Mars Rocks. See also NASA/JPL/Cornell/USGS: Standing Body of Water Left Its Mark in Mars Rocks.
        Image link: Itself.

      It seems that Opportunity in the Meridiani Planum was the lucky landing site with lots of water evidence. Spirit in Crater Gusev has come up dry it seems.

      The Curiosity Mars rover also found evidence of water. See the figure below.


        Caption: "Where Water Flowed Downslope.

        This image shows the topography, with shading added, around the area where NASA's Curiosity rover landed on Aug. 5 PDT (Aug. 6 EDT). Higher elevations are colored in red, with cooler colors indicating transitions downslope to lower elevations.

        The black oval indicates the targeted landing area for the rover known as the "landing ellipse," and the cross shows where the rover actually landed.

        An alluvial fan, or fan-shaped deposit where debris spreads out downslope, has been highlighted in lighter colors for better viewing. On Earth, alluvial fans often are formed by water flowing downslope. New observations from Curiosity of rounded pebbles embedded with rocky outcrops provide concrete evidence that water did flow in this region on Mars, creating the alluvial fan. Water carrying the pebbly material is thought to have streamed downslope extending the alluvial fan, at least occasionally, to where the rover now sits studying its ancient history. Elevation data were obtained from stereo processing of images from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter."

        Perhaps Curiosity Mars rover's greatest discovery is that a of minerals showing the presence of liquid water once---hundred of millions of years ago? or billions?---that was chemically safe for life---NOT too acidic or alkaline.

        The previous minerals showing water formation showed unsafe conditions for life.

        Credit/Permission: NASA/Jet Propulsion Laboratory (JPL)-Caltech/University of Alabama, 2012 (uploaded to Wikipedia by User:Drbogdan, 2012) / Public domain.
        Image link: Wikipedia: File:PIA16158-Mars Curiosity Rover-Water-AlluvialFan.jpg.

      There are lots more Mars Exploration Rover images and results, but that's enough for now.

      The site Views of the Solar System: Mars offers a good selection of rover and other images of Mars.

      See also Mars videos below (local link / general link: mars_videos.html):


  12. Life on Mars

  13. Is there or has there ever been life as we know it on Mars (i.e., Martian life)?

    Life as we don't know it is harder to debate. There is no evidence of it existing at all. But who knows.

    1. Martian Life Possibly:

      From the discussion above in the section Water on Mars, it seems that Mars was sometimes warmish and wet.

      In other respects, early Mars was also probably like early Earth with a CO_2 and water vapor atmosphere.

      We think that microbial life first appeared on Earth 3.465 Gyr ago at least and perhaps 4.28 Gyr ago (see Wikipedia: Earliest known life forms; Wikipedia: Abiogenesis). But we don't know how exactly it arose. But somehow:

      If the 3.465 Gyr value is correct, it didn't take long---geologically speaking---for life to arise after the HEAVY BOMBARDMENT was over.

      Thus, it is possible that microbial life arose quickly on early and sometimes warm and wet Mars.

    2. Transpermia:

      It is also possible that life originated once on either Earth or Mars and was transferred to the other by impact events. Or perhaps some more complex multiple origins and transfers happened.

      The process of life spreading through impactor-ejected rock has been called transpermia. See P.C.W. Davies: How bio-friendly is the universe.

      The cartoon in the figure below illustrates transpermia in action.

      An impactor throws rocks containing microbes into space.

      The microbes stay in some kind of suspended animation and then re-animate if the rock impacts on a hospitable planet.

      The rocks have to stay below about 100° C and be relatively unshocked, but calculations show that some material will stay this cool and unshocked both through ejection and impact.

      Significant transfers of materials between planets do happen this way and it is believed that some kinds of microbial life would survive the journey.

      Biological contamination back and forth between Earth and Mars may even have happened repeatedly in the early solar system.

      Reading about transpermia has given me more confidence in the possibility of Martian life---but Martian life affected by transpermia will probably NOT be independent of Earth life.

    3. Famous, But Largely Dismissed, Evidence for Life on Mars:

      And there is some famous, but largely dismissed, evidence for microbial life on early Mars.

      The evidence is meteorite Allan Hills 84001 show and described in the figure below.

    4. Life on Mars Today?

      Could life still exist on Mars today?

      Well there can't be life as we know it on the surface---unless it can carry its own liquid water supply and shield itself from ultraviolet (UV) light.

        Recall life on Earth is protected from dangerous UV radiation our atmosphere, particularly the ozone layer 25 km above the surface (Se-439). Mars doesn't have this shielding and the surface life (unless it had its own shielding) could NOT survive there even if it were warm enough and had water.

      Also the Viking landers did tests for organic compounds in Martian topsoil which would have been some evidence for Martian life and found nothing (HI-157).

      But that evidence has been recently disputed. A re-analysis of Viking lander tests suggests that they did find organic compounds after all (Washington Post: New Mars tests find possible life ingredients, 2010sep03). It's all very uncertain though.

      We need fresh tests for organic compounds in Martian soil and remarkably none of the landers since Viking have done those tests.

      So far the Mars Exploration Rovers and all other probes have found no signs of life either.

      But microbial life could exist in the aquifers that probably exist below the surface or in other moist subsurface environments? Recall it seems likely that aquifers exist today (HI-195).

      Earth provides us with evidence by analogy.

      Since circa 1990, we have known microbial life on Earth reaching down to 3 km or more below the surface. This deep life has been collectively called the deep biosphere.

      Additionally, microbial life discovered 3.5 km below the Antarctic ice. This life has been isolated from the surface for more than 1 Myr.

      It has also been claimed that some terrestrial microbes can be dormant for 100 Myr or more (HI-157). So its possible that Martian life could endure long periods of poor conditions and resurrect in better times.

      So it seems possible that something like Earth microbes could live on Mars below the surface today.

      But do they?

    5. Probes for Martian Life:

      So we have both possibilities: life in the past on Mars and life today.

      To find out we need probes.

      The Mars Exploration Rovers (Spirit and Opportunity first operational 2004) did NOT find evidence of life: e.g., fossil remains.

      The European Space Agency's (ESA's) Mars Express Orbiter (first operational 2003) found a bit of evidence consistent with life as we know it.

      Mars Express Orbiter is shown in the figure below.

      The evidence?

      Mars Express Orbiter has spectroscopically confirmed the existence of methane (CH_4) in the Martian atmosphere (see ESA Press Release: Mars Express confirms methane in the Martian atmosphere ; Wikipedia: Atmosphere of Mars: Methane).

      The amount detected is tiny: 0.01 ppm = 10 ppb.

      Methane is a main component of natural gas.

      But methane CANNOT last in the Martian atmosphere for more than a few centuries because it breaks up to form CO_2 and water using oxygen present in some form.

      Therefore methane must be continually produced on Mars.

      Volcanic or hydro-thermal activity on Mars could produce methane.

      If this is the source, then it confirms our believe of continuing primordial-radiogenic heat geology.

      On the other hand, methane can be produced biologically (e.g., by fermentation).

      So the possibility of subsurface microbial life is raised.

      Further studies of the abundance and distribution of methane might yield more insight.

    6. Earth Invades!

      In the search for Martian life, we may get lucky.

      Spirit (out of touch since 2010mar22) can't, but Opportunity (still active as of 2018 maybe) could find fossils tomorrow---though NOT likely now after all the years since 2004 it's been aroving.

      But I suspect that the search will have to go on for a long time.

      It would be a pity if there were no Martians (see the figure below: local link / general link: alien_prototype_are_here.html) to observe our slow-motion invasion.

      It is The War of the Worlds (1898)---first, we send our monster robots, then ...