Western hemisphere of Mars with wry smile of Valles Marineris.
Credit:
NASA.
Western hemisphere of Mars with wry smile of Valles Marineris.
Credit:
NASA.
Sections
It has been known since prehistory, of course.
The ancient Babylonians associated MARS with their plague god Nirgal???. The Greeks with their war god ARES (of whom few amusing stories are told).
MARS is, of course, the Roman war god who was identified with Ares.
Mars' traditional symbol: note the spear.
In the 17th century using a telescope, Christian Huygens 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 (Sh-ch3).
Mars' orbit is considerably more eccentric than Earth's and this must also affect the seasons more than Earth's eccentricity affects Earth's seasons.]
Alas this affect is really due to spring??? winds blowing lighter colored dust off darker surfaces (HI-183).
Then in 1877 during a FAVORABLE OPPOSITION of Mars Italian astronomer Giovanni Schiaparelli (1835--1910) concluded the the MARTIAN CANALS were a major feature (Ka-293). The canals were apparent linear markings on Mars.
The most FAVORABLE OPPOSITION is PERIHELION OPPOSITION.
Question: What is a PERIHELION OPPOSITION?
Answer 3 is right.
PERIHELION means closest approach to the Sun and OPPOSITION means opposite the Sun.
At PERIHELION OPPOSITION, Mars is as close to the Earth as it ever gets.
Mars in perihelion opposition.
1877 was only a FAVORABLE OPPOSITION, not a PERIHELION OPPOSITION.
There was a PERIHELION OPPOSITION in 2003aug as you may recall.
See Seds on Mars oppositions and Primer on Mars Oppositions by J. Laskar, IMCCE/CNRS, Observatoire de Paris
The most prominent of these was PERCIVAL LOWELL.
Percival Lowell (1855-1916).
Lowell a member of the famous Massachusetts Lowell family was one of the last great astronomer magnates. He was an enthusiastic promoter of the Martian canal theory and did many observations from his own Lowell Observatory in Flagstaff, Arizona.
He drew many maps of Mars detailing the canals that he thought he could make out. In reality, they were almost entirely optical illusions caused by the eye trying to make out shapes out of variations in color at the verge of visibility.
Only one ``canal'' feature, a giant canyon he named Agathodaemon turned to be real: now called VALLES MARINERIS after the Mariner probe that really discovered it (No-578).
Lowell did believe that the canals were artificial and a product of intelligent Martians.
Credit: late-19/early-20th century photographer; download site: Eric Hutton's site Mars by Percival Lowell, 1895.
Plate I and frontispiece from Percival Lowell's Mars (1895).
This image is one of Lowell's less elaborate drawings. The canals are not real, of course.
The dark regions may be real. Lowell certainly could make out real dark regions on Mars as did earlier observers going back to Huygens in the 17th century. But without more information I can't identify Lowell's dark regions with anything I can see on a modern map. I suppose I could look up what features Lowell was trying to represent.
Credit: Percival Lowell; download site: Eric Hutton's site Mars by Percival Lowell, 1895.
H.G. WELLS in The War of the Worlds portrayed the Martians as faceless invaders. See John Walker's Fourmilab web The War of the Worlds.
The Martian Canals.
In 1938 ORSON WELLES caused a famous invasion scare with his Halloween radio play of the The War of the Worlds (Se-478).
But many astronomers never believed in the MARTIAN CANALS and always thought they were optical illusions---and all talk about Martians was premature.
In the 20th century, this view prevailed long before the first up-close pictures of Mars in the 1960s from the Mariner probes.
These Mariner pictures and other work showed Mars was a cratered world with a very low density atmosphere.
But mysteries remain.
Is there sub-surface LIQUID WATER today?
Is there LIFE today below the surface in a DEEP BIOSPHERE?
We know now that there is a DEEP BIOSPHERE on Earth and microbial life can be found down to several kilometers in the crust (HI-196).
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)
______________________________________________________________________________
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
but much smaller than Mercury's.
Mean inclination to Ecliptic 1.85061 degrees
Axis tilt to orbital pole 25.19 degrees
Orbital period 686.95 days = 1.88071105 years
Rotational Period 1.02595675 days
Martian day 1.02749 days : just a bit longer than
the 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
density.
Surface gravity 0.379 Earth gravities
Surface temperature about -80 C or 190 K at night to -30 C or 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).
_________________________________________________________________________
Sources: Cox-294,295; Se-418,479; HI-187.
_________________________________________________________________________
Oddly the uncompressed density of Mars is similar to that of the Moon.
This suggests that Mars doesn't have a large iron core???.
Certainly, it has no global magnetic field now. Perhaps, it's small iron core is solid now, but still hot.
A cartoon comparing Earth's and Mars' 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 core.
Mars' 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: NASA, Mario Acuna, Jack Connerney, Chris Meaney; download site Views of the Solar System by Calvin J. Hamilton. The image is public domain, but CJH declines to give a download source.
A Mercator Mars map in true color???.
For feature names refer to HI-185.
Zero longitude is in the center.
The large dark region in the eastern hemisphere is Syrtis Major which is the most prominent dark region seen from Earth and was first identified by Huygens in the 17th century.
Crater Schiaparelli is on the equator just east of zero longitude. This crater is named for Italian astronomer Giovanni Schiaparelli who in 1877 concluded that the Martian canals were a major feature of Mars.
The western hemisphere can most easily be identified by spotting VALLES MARINERIS.
West of VALLES MARINERIS are three volcanoes in a row and to the west of that is OLYMPUS MONS, the largest known volcano.
These volcanos are all in the THARSIS REGION: this is a giant dome or bulge that is, perhaps, above a giant mantle plume that has forced it up and given rise to the region's strong volcanism (HI-190--191).
The THARSIS REGION may be something like coronas of Venus (HI-191).
HELLAS PLANITIA is a basin centered at about 40 S, 70 E. It is low, circular region probably formed by a giant impactor similar to the ones that formed the Orientale Basin on the Moon and the Caloris Basin on Mercury???? (HI-199).
Note the southern hemisphere looks more heavily cratered than the northern hemisphere.
Answer 1 is right.
A Viking 1 Orbiter mosaic image of the western hemisphere of Mars.
1980feb22.
The ``wry smile'' at the center is Valles Marineris, the largest canyon on Mars. It extends about 5000 km (almost a quarter way around the equatorial region), is about 7 km deep, and is up to 100 km wide (FMW-198).
The two most northern of the Tharsis region triplet of volcanoes are visible to the west of Valles Marineris.
Some impact craters, channels, and dark regions can also be seen.
Credit: NASA.
The image map and western hemisphere image do not directly reveal the strong distinction between the northern and southern hemispheres, except for more cratering in the southern one.
A topographical map reveals the elevation distinction.
A Mercator topographical Mars map showing elevation.
For feature names refer to HI-185.
Note the southern hemisphere is generally higher than the northern hemisphere. The southern hemisphere is believed to be 2--4 Gyr and is ancient heavily cratered plains.
The northern hemisphere covered by younger lava flows, perhaps, on average 1 Gyr old (HI-189).
Note that the THARSIS REGION is the highest region on Mars.
HELLAS PLANITIA, a probable impact basin flooded by lava, is just about the lowest region at least at mid-latitudes (HI-185) .
The ``wry smile'' of Valles Marineris is clear on the east side of the Tharsis dome.
Credit: NASA Goddard Space Flight Center, image #PIA02031; download site Views of the Solar System by Calvin J. Hamilton.
EARTH geology is mainly RESIDUAL/RADIOACTIVE-HEAT GEOLOGY coupled with erosion principally by water. Earth is little affected by impacts.
The MOON has has pretty much lost its RESIDUAL/RADIOACTIVE-HEAT GEOLOGY and slowly evolves mainly due to impacts including micrometeoritic impacts.
MARS has more craters than the Earth, particularly in the old southern hemisphere, but is not saturated by craters like the lunar uplands.
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 is OLYMPUS MONS.
Olympus Mons in the Tharsis region of Mars.
This is an approximately true color mosaic image from Viking Orbiter 1 from 1978jun01.
Olympus Mons is the largest known volcano in the solar system.
It is a shield volcano with shallow slopes of 2 to 5 degree 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).
Credit: NASA.
Recall SHIELD VOLCANOES are formed by repeated lava flows and have gentle slopes (SWT-572).
Shield volcanoes occur on Venus, Earth, and Mars.
A cartoon of a shield volcano.
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 degree 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).
The clouds are water ice clouds (such as we have on Earth) I think (FMW-200--201).
There are also dust clouds and CO_2 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: NASA/Malin Space Science Systems; download site Views of the Solar System by Calvin J. Hamilton. The image is public domain, but CJH declines to give a download source.
We can go to an animation of a flight into Olympus Mons from Views of the Solar System.
It was once thought that Mars' RESIDUAL/RADIOACTIVE-HEAT GEOLOGY was dead, like the Moon's---but only more recently deceased.
But now there 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 RESIDUAL/RADIOACTIVE-HEAT GEOLOGY and volcanism today---although probably 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.
It probably can be said that Mars is somewhere in between having its geology dominated by impacts and having it dominated by RESIDUAL/RADIOACTIVE-HEAT GEOLOGY.
Does Mars have PLATE TECTONICS?
Apparently, not.
There is no evidence for divergent and convergent boundaries (i.e., rifts and subduction zones) although VALLES MARINERIS may be a rift-like feature???.
There are no real continent or terra formations.
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).
At formation, Mars must have gone through chemical differentiation and cratering under the heavy bombardment and perhaps massive lava flows in giant basins.
Some of the heavy bombardment cratering may remain in the southern hemisphere. Hellas Planitia may be a remnant of the early lava flooding of an impact basin (HI-185).
But continuing RESIDUAL/RADIOACTIVE-HEAT GEOLOGY and impactors have erased much of the early Martian surface especially on the northern hemisphere.
In the future, of course, RESIDUAL/RADIOACTIVE-HEAT GEOLOGY must slow as residual heat from formation and past radioactive decay decreases. It must turn off eventually.
The pressure varies with weather, season, and altitude, of course (HI-187).
This low pressure means that liquid water cannot exist on the surface for any length of time.
Water below 0.01 atmospheres doesn't have a liquid phase.
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.
A cartoon of water phase diagram.
See a more accurate water phase diagram.
The Martian atmosphere is CO_2 dominated like Venus---but there is VERY LITTLE greenhouse effect because of the low density.
_______________________________________________________________________
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 ice water clouds as we maybe??? saw with the Olympus Mons picture above.
CO_2 ice clouds can make clouds too at high altitudes too (FMW-200--201).
Probably early on Mars had a significant CO_2 and water vapor atmosphere from outgassing like the early Earth and early Venus are thought to have had.
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 low gravity of Mars, much of this atmosphere has leaked away over the gigayears.
Probably the molecules of CO_2 and H_2O were broken up at high altitudes and the H and C escaped mostly.
This iron oxide then survived the molten phase of the planet.
On Earth temperatures were higher in the molten phase and iron oxide may have dissociated at great depths with more iron sinking to the core.
Any abundant iron oxide left on the very surface would have been subducted and spread thin in subsequent surface renewal????.
See Rubie, D. C., Gessmann, C. K., & Frost, D. J. 2004, Nature, 429, 58.]
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 degree panorama.
In order to study the surroundings in detail with the SOJOURNER ROVER (near Yogi at 320 degrees 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: NASA/USGS; download site Views of the Solar System by Calvin J. Hamilton. The image is public domain, but CJH declines to give a download source.
Actually Mars' colors are tricky.
From Earth it looks reddish-orange with the unaided eye??? (PF-118).
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.
Of course, the Red Planet could have been red historically mainly because of its association with the god of war.
Because of its low pressure and hence lack of liquid water, Mars today is essentially a cold desert.
The seasons mimic Earth's and are most noted through the polar caps.
A Viking Orbiter image of the southern polar cap in the southern summer.
The cap is about 400 km across and this is about as small as it gets.
The northern polar cap has a larger residual size of 1000 km across (FMW-201).
Because it is mid-summer, the pole is in constant daylight with the night side of the planet here at the bottom of the picture.
The polar caps consist of water ice perhaps up to several kilometers thick covered by a layer of CO_2 ice that may be centimeters to several meters in thickness (HI-188).
Both kinds of ice tend to be white when they have a rough surface.
The water ice never evaporates much, but much of the CO_2 ice evaporates with the summer and condenses again in the winter.
Credit: NASA; download site Views of the Solar System: Mars by Calvin J. Hamilton. The image is public domain, but CJH declines to give a download source.
The terrain around the Viking 2 Lander site. 1979may18.
The Viking 2 Lander was in the northern/eastern hemisphere Utopia Planitia lava plain. It landed 1976sep03 (HI-184), and so must have operated a long time.
The time of the image is the northern winter???.
The image is true color. The red rock and dust is due to iron oxide (and rust) mineral content.
Whitish covering is CO_2 frost. It is thought that dust grains covered with a bit of water ice serve as condensation sites for CO_2.
When it gets cold enough (below 150 K: FMW-201), the CO_2 condenses out on the grains and the grains fall to the ground.
Credit: NASA: image #P-21873.
The weather on Mars is most notable through the winds blowing 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.
Wind erosion and wind building of dunes is a common feature of Mars too---but we leave it at that for now.
The DUST is yellowish brown in color and its magnetic component is MAGNETITE (a black iron oxide, Fe_3O_4) (Kerr, R. A. 2005, Science, 308, apr08, 192).
MAGNETITE is NOT formed in water and that it is in the DUST suggests much of Mars has been mostly dry for a long time.
DUST and other evidence is pointing to Mars having had a dry surface for maybe 3.7 Gyr, except perhaps for brief episodes (Kerr, R. A. 2005, Science, 308, apr08, 192).
Answer 2 is right, but answer 1 is almost right too.
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.
There is substantial water ice. The polar caps as noted above probably have 1 to 3 km of water ice in places (HI-187).
But there is also water in the soil in the form of molecules embedded in the crystal structure of rock grains. This was discovered by the Viking landers (HI-188).
There is also evidence now for glaciers on Mars 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 dust-coated, and so hidden. It has taken detailed imaging by the NASA Mars Global Surveyor and the ESA Mars Express to find their signatures.
They are not like most terrestrial glaciers, but rather like those in the Antarctic Dry Valleys: they ooze over things rather than slide on a wet layer.
See ESA Mars glacier images. Apparently, these images are NOT public domain.
Probably the 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' 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???.
As noted in the section Mars' Atmosphere, liquid water cannot exist now on the surface for any length of time because of the low pressure.
It can exist for short times before it evaporates or freezes.
But does it?
Probably.
In the last few years the Mars Global Surveyor's Mars Orbiter Camera (MOC) has been finding evidence of fairly recent gullies on Mars.
An approximately true color image of a Martian gully.
The MOC image is from 1999sep28. The image is 9 x 6.7 km. We are viewing the south-facing inner rim of the crater. There is a sand dune on the crater floor. The location is 54.8 S, 342.5 W (or 17.5 E).
The gullies are eroded into the rim of impact Crater Noachis Terra. The image is an approximate true color, high resolution image from the Mars Global Surveyor's Mars Orbiter Camera (MOC).
One sees the channels and apron of debris. It seems that there must have been groundwater seepage and surface runoff leading to the apron.
The feature is very similar to gullies seen in the American south-west.
There are no superimposed craters indicating that the gullies are geologically young. How young?
There may be liquid water in the Martian subsurface today.
Other images suggest water seepage within tens of years which is the same as saying it is ongoing ( Views of the Solar System by Calvin J. Hamilton.
Mars' atmosphere is too rarefied to allow liquid water to exist in THERMODYNAMIC EQUILIBRIUM. Only the solid and gas phases of water can persist.
Perhaps the liquid water in the subsurface is sometimes squeezed to the surface by a sudden geothermal event or an impact could melt ice near the surface.
If something like that happen, water could flow for awhile until it evaporated or froze.
Credit: NASA/JPL/Malin Space Science Systems. An alternative download site is Views of the Solar System by Calvin J. Hamilton. The image is public domain, but CJH declines to give a download source.
Where is the liquid water 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.
It seems very likely that underground water reservoirs (i.e., aquifers) exist today (HI-195).
Subsurface events sometimes probably 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.
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 ...
But 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 water channel features---dry of course.
Some of them may be flood channels due to a sudden melting of ice and release of liquid water by a volcanic eruption or an impactor.
But some channels look very much like rain-fed run-off channels such as we find on Earth.
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.
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 run-off: i.e., they could be RUN-OFF CHANNELS.
But they could have been formed by SAPPING.
In sapping, liquid ground water eats away at a cliff face. One images the water as frozen until some geothermal event temporarily melts it and this leads to sapping.
Whether or not this network is due to run-off 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' enough greenhouse effect for liquid surface 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: NASA.
There are in fact a huge number of gully images and other images from the Mars Global Surveyor Mars 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 of 2004, there was solid 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 evidence came from the Mars Global Surveyor.
A distributary fan on Mars. From Mars Global Surveyor
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:
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.
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.
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: NASA/JPL/Malin Space Science Systems.
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 Mars Exploration Rovers of 2004 have added some evidence in favor of oceans or at least desert basin salt lakes.
A Mercator topographical Mars map showing elevation and
lander sites through 2004.
There have only been 5 successful landers on Mars through 2004:
Credit: NASA/JPL.
Parachute descent.
Bouncing on airbags
Airbag encased and at rest on Mars.
Artist conceptions of how the Mars Exploration Rovers of 2004 (Spirit and Opportunity) landed.
Credit: NASA/JPL.
Mars Exploration Rover, artist conception, 2004.
Credit: NASA/JPL.
Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images
of Opportunity landing site. 2003aug24, 2004feb01.
The Mars Exploration Rover Opportunity landed 2004jan25 on Meridiani Planum near 2.0 degrees S, 5.6 degrees W.
North is at the top, east is at the right, and the lower image is about 1.4 km wide.
Opportunity came to rest in a small crater of approximately 20 m in diameter.
Credit:
NASA/Malin Space Science Systems
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: NASA/JPL/Cornell/USGS. See also the full press release NASA: Standing Body of Water Left Its Mark in Mars Rocks.
It seems that OPPORTUNITY in the Meridiani Planum was the lucky landing site with lots of water evidence.
SPIRIT in Gusev Crater has come up dry it seems.
There are lots more Mars Exploration Rover images and results, but it will take awhile for data to all analyzed and summarized.
The site Views of the Solar System: Mars offers a good selection of rover and other images of Mars.
In other respects early Mars was also like early Earth with a CO_2 and water vapor atmosphere.
We think that microbial life first appeared on Earth as early as 2.7 Gyr ago and perhaps 3.5 Gyr ago (NewScientist, 2004may01, 12). But we don't know how exactly it arose.
If the 3.5 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.
It is also possible that life originated once on either Earth or Mars and was transferred to the other by impact events.
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 transpermia hypothesis.
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 degrees 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.
And there is some direct, but controversial, evidence for MICROBIAL LIFE on early Mars.
A microscopic image of the interior of meteorite Allan Hills 84001.
Allan Hills 84001 is meteorite found in Antarctica. It impacted about 13,000 years ago and left Mars about 16 Myr ago when an impactor knocked into space (Se-589).
Analysis of gas bubbles inside confirm that it is a Mars rock.
The rock itself is very old and formed about 4.5 Gyr ago (HI-196).
An analysis by NASA scientists in 1996 suggested that this meteorite contained fossils of microscopic Martian life that entered it long after formation.
They suggested elongated structure in this picture was Martian microbe.
To say the least this suggestion has been controversial. There has been a lot of back and forth and it seems no unanimous answer has been reached.
But I think the majority view is strongly against the structures being fossilized life.
Credit: NASA; download site On the Question of the Mars Meteorite at the Lunar and Planetary Institute site.
Could life still exist on Mars today?
Well there can't be life on the surface---unless it can carry it's own water supply and shield itself from ultraviolet (UV) light.
So far the Mars Exploration Rovers have found no signs of life either.
But MICROBIAL LIFE could exist in the aquifers that probably exist below the surface. Recall it seems likely that aquifers exist today (HI-195).
Earth provides us with evidence by analogy.
In the last decade we have found MICROBIAL LIFE on Earth reaching down to 3 km or more. 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).
It seems possible that something like Earth microbes could live on Mars below the surface today.
But do they?
So we have both possibilities: life in the past on Mars and and life today.
To find out we need probes.
The SPIRIT and OPPORTUNITY rovers did not find evidence of life: e.g., fossil remains.
Additionally, the European Space Agency's (ESA's) MARS EXPRESS ORBITER
reached Mars 2003dec25
(
Space.com: Mars Express Arrives in Orbit, No Word Yet from Beagle 2).
The MARS EXPRESS also sent down a lander, Beagle 2, which alas failed.
The projected landing site of the Beagle 2 lander.
The European Space Agency's (ESA') Mars Express probe sent down the Beagle 2 lander to land on Isidis Planitia (11.6 N, 90.75 E) on 2003dec25.
The Beagle 2 lander was specifically designed to test for life signs.
Alas it went down on Mars and was never heard from again: this is the fate of many landers.
It could not, of course, directly test for the Martian deep biosphere, but it can test a likely place on the surface for signs of life. Perhaps micro-fossils or biological compounds were to be looked for.
The landing site seems to be a sedimentary basin and thus date from an epoch of surface water.
The ellipses on the image presumably mark out the landing target area.
Note the half-seen crater. The impact apron around it seems at bit thick to me.
It may be one of those aprons that is interpreted as having been made out thick slurry of material from an impact on ice-laden soil (HI-190). But I don't really know. See ESA Beagle 2 site and The University of Leicester Space Research Centre's Beagle 2 site).
Credit: NASA.
The MARS EXPRESS ORBITER, however, is operational and doing imaging and spectroscopy.
European Space Agency (ESA) Mars Express Orbiter. From 2003 on.
Mars Express has imaging and spectroscopic capability.
Credit: ESA 2001, Illustration by Medialab. ESA gives permission for educational use and reproduction.
The most interesting result so far from the MARS EXPRESS is that it has spectroscopically confirmed the existence of METHANE (CH_4) in the Martian atmosphere ( ESA Press Release: Mars Express confirms methane in the Martian atmosphere ).
The amount detected is tiny: 0.01 ppm.
METHANE is a main component of natural gas recall.
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 RESIDUAL/RADIOACTIVE-HEAT GEOLOGY.
On the other hand, METHANE can be produced organically (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.
In the search for life on Mars we may get lucky.
SPIRIT or OPPORTUNITY could find fossils tomorrow.
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 to observe our slow-motion invasion.
