Is there a forum where people can share and discuss features on Mars?

[russ_watters]

I don't get where you are coming from with this kind of aggression and projection. I stated from the beginning that I was looking for scientific explanations. I've instead gotten aggressively interrogated about why I would want to do such a stupid thing in the first place.

You're coming up with excuses for why they wouldn't investigate an interesting rock and apparently not listening to being told repeatedly that "investigate an interesting rock" is most of the purpose of the mission. It's frustrating - you seem to be putting your effort into avoiding learning.

 

[Jarvis323]

You're coming up with excuses for why they wouldn't investigate an interesting rock and apparently not listening to being told repeatedly that "investigate an interesting rock" is most of the purpose of the mission. It's frustrating - you seem to be putting your effort into avoiding learning.

I'm not interested in arguing, and despite what it seems like, I am interested in learning. I'll concede this one to you, I guess they would go investigate. And maybe I read the mission statements too literally.

 

[russ_watters]

How is speculation about what they would choose to get a closer look at relevant anyways? We can see what they looked at. If I see something that they didn't get a closer look at, it could be be because they didn't notice it, or it wasn't compelling enough, or whatever. If they noticed it, and analyzed the image, and made a conclusion about what they think it is or might be, then great. That's what I'm curious about. And obviously everything needed to find this is available. So why is what I'm looking for impossible to get?

Big picture understanding should be easier to find and learn and more useful than specifics about a single rock of the thousands a rover took pictures of. I'm not sure if that granular level of detail is available online, but there is probably an archive somewhere, where a scientist wrote a short analysis about every significant rock in every photo the rovers took. It'd be a million pages of analysis, and there's probably a few sentences about that specific rock. But finding it would be a daunting challenge.

Heck, did you look at the first link I posted? In it is a photo that looks very much like your "petrified wood" to me...

...someone in a geology forum could probably confirm.

 

[russ_watters]

And maybe I read the mission statements to literally.

Well, what mission statements have you read? Maybe we can fix that.

 

[Jarvis323]

Well, what mission statements have you read? Maybe we can fix that.

I read the wikipedia page on the spirit rover and Gusev crater, and I skimmed this paper.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2002JE002026

 

[Jarvis323]

I read the wikipedia page on the spirit rover and Gusev crater, and I skimmed this paper.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2002JE002026

There is a section about specific hypotheses:

4. Testable Hypotheses for MER
[35] Spirit's suite of sensors and imaging systems are anticipated to provide insight into the depositional and soil formation processes that have occurred in Gusev Crater [Squyres et al., 2003]. Integrated observations that will be key for assessing the nature of past and present geological processes and environments include geochemistry, mineralogy and microtextural information obtained from rocks and soils. While lacustrine processes may have supplied significant material to Gusev, volcanic, fluvial [Kuzmin et al., 2000], aeolian [Greeley et al., 2003], and glacial processes [Grin and Cabrol, 1997] are likely to have contributed material too. The basic rock and soil characteristics that may be addressed with the Athena instrument payload in testing the various depositional hypotheses are reviewed in the following section.

4.1. Main Hypotheses
[36] Data from the Viking, MGS, and MO missions have allowed several main hypotheses (Table 2) to emerge that attempt to explain the spectral and albedo characteristics of surface material and the geomorphology observed in Gusev. Each main hypothesis carries a set of subhypotheses that require in situ measurements for either accepting or rejecting the subhypotheses. The variations of each subhypotheses are not mutually exclusive and in some cases overlap each other.

Table 2. Main and Subhypotheses on the Origin of the Sediments and Material in Gusev Landing Ellipsea

Main Hypotheses for Sediments Origin	Subhypotheses	Origin
1. Lacustrine	1.1. perennial lake 1.2. episodic lake	1.1.1/1.2.1. precipitation 1.1.2/1.2.2. groundwater 1.1.3/1.2.3. hydrothermal water 1.1.4/1.2.4. glacial meltwater 1.1.5/1.2.5. combination of two or more of the above sources due to changing conditions through time
2. Fluvial	2.1. runoff 2.2. outflow from intravalley lake	2.1.1/2.2.1. precipitation 2.1.2/2.2.2. groundwater 2.1.3/2.2.3. hydrothermal water 2.1.4/2.2.4. glacial meltwater 2.1.5/2.2.5. combination of two or more of the above sources due to changing conditions through time
3. Glacial	3.1. glacier	3.1.1. local snow and ice packs 3.1.2. regional glaciation
3.2. ice‐covered stream	3.2.1. free water underneath the ice until the water supply ceased 3.2.2. progressive complete freezing down of the water
4. Volcanic	4.1. plastic flowb	4.1.1. hyperfluid lava 4.1.2. viscuous lava 4.1.3. pyroclasts and ashes are filling Gusev basin
5. “Exotic” fluid	5.1. CO2 flowc	5.1.1. liquid CO2reservoir
5.2. clathrate flowc	5.2.1. clathrate reservoir
6. Aeolian	6.1. regional to local windsd	6.1.1. wind regimes
6.2. global air falle	6.2.1. global atmosphere circulation.
7. Subsurface hydrothermal	7.1. hydrothermal minerals	7.1.1. impact‐generated 7.1.2. crustal magma sources

• a The subhypotheses shown reflect discussions about processes that have been presented in the literature over the years, either for the formation of the Ma'adim Vallis/Gusev crater system or for channels in general on Mars.
• b Hyperfluid lava carved Ma'adim Vallis and deposited material in Gusev. Viscuous lava generated a landform that mimics a delta at the outlet of Ma'adim. Pyroclasts and ashes are filling Gusev basin.
• c Obliquity changes provided temperature conditions for CO2 or clathrates release at the latitude of Ma'adim and Gusev. The surface pressure is still problematic.
• d Wind regimes following climate changes have driven the deposition and exhumation of material in Gusev.
• e Sediments in Gusev are made of material extracted over the planet and deposited in the basin by global atmosphere circulation.

4.2. Soil Formation and Sedimentary Processes
[37] The main hypotheses can be associated with specific soil and/or sediment types that may be detected by the Athena instrument payload which include: (1) global soil; (2) soils formed in a nonaqueous environment; (3) soils formed in an aqueous environment; (4) volcanic materials; (5) lacustrine sediments; (6) fluvial sediments; (7) aeolian sediments; and (8) glacial sediments. Soil and sediment profiles may be observed in the form of ejecta blocks from impact events, outcrops, and aeolian exposures (e.g., yardangs, see Figure 10). Excavation by spinning a rover wheel while the rover remains stationary is also anticipated to access soil and sediment 5–10 cm below the surface.

Figure 10
Open in figure viewerPowerPoint
Caption
[38] This discussion cannot touch on all possible signatures of all sediment and soil formation processes that could be detected by the Athena instruments. Moreover, we do not presume to have identified every possible type of soil or sediment that could conceivably occur within Gusev. This is meant as a guide, and attempts to demonstrate what the Athena instruments may detect and what hypotheses could be identified if presented with certain evidence of a geologic or pedogenic process. Table 3 summarizes what results from the Athena instruments would suggest a particular geologic or pedogenic process listed above and is supported by the following discussion.

Table 3. Possible Results From Athena Instruments of Hypothetical Soils and Sediments in Gusev Cratera

Hypothesis	Panoramic Camera	Microscopic Imager	Alpha Particle X Ray Spectrometer	Mini‐Thermal Emission Spectrometer	Mössbauer Spectrometer
Global soil	Similar multispectral characteristics as MPF soil.	No uniquely identifiable characteristics.	Similar elemental chemistry as MPF and VL 1, 2 soil.	No uniquely identifiable characteristics.	No uniquely identifiable characteristics.
Soils from physical weathering of local rock	No uniquely identifiable characteristics.	Angular soil grain morphology.	Soil elemental chemistry similar to local rock chemistry.	Soil spectra similar to local rock spectra. No secondary mineralogy.	Soil Fe mineralogy similar to local rock Fe mineralogy. No secondary Fe‐oxyhydroxides.
Volcanic ash	Sedimentary deposit that conforms to topography.	Glass shards cupsate, blocky, platy <250 μm.	Any range of Si content. Chemistry may be different than local rock.	Poorly crystalline to crystalline material (e.g., plagioclase, pyroxene, hornblende).	Ilmenite, titanomagnetite, titanomaghemite, magnetite, Fe‐pyroxene.
Maar base surge deposit	Massive, planar sedimentary deposits. Soft sediment deformations, vesicles, bedding sags.	Glass shards, blocky. Fine‐grained material <1 mm.	Any range of Si content.	Poorly crystalline to crystalline material (e.g., plagioclase, pyroxene, hornblende).	Ilmenite, titanomagnetite, titanomaghemite, magnetite, Fe‐pyroxene.
Soil from aqueous weathering (e.g., melting snow)	Soil structure. Columns, wedge, blocky, platy. Vesicular porosity near soil surface.	Vesicular porosity near soil surface.	Loss or accumulation of Ca, Mg, K, Na relative to local surface rock.	Phyllosilicates, carbonates, sulfates, secondary Fe‐oxyhydroxides.	Secondary Fe‐oxyhydroxides.
Fluvial deposit	Conglomerate facies;sheet, tabular cross stratified, lateral, channel fill, rounded/subrounded clasts up to 30 cm.	No visible grains.	No uniquely identifiable characteristics.	Primary minerals with cementing mineralogy; Fe‐oxyhydroxide, carbonate, or phyllosilicates.	Detect mineralogy of Fe‐cementing mineral if present. Possible siderite (FeCO3) Fe2+‐smectite if outer oxidized layer on sedimentary rock is removed by the RAT.
	Sandstone facies; tabular and trough cross bed and ripple bed.
	Shale facies; planar bed.
Lacustrine deposit	Alternating planar layers of light‐colored layers with darker layers. Layer thickness few cm to 10s cm.	Sand and gravel grains at lake's margin; clay/silt grains toward lake's center.	High levels of Ca, Mg, K, Na, S, Cl, N in basin.	Mineralogy variation from lake margin to lake center (e.g., carbonate → sulfate); phyllosilicates.	Possible siderite (FeCO3) Fe2+‐smectite if outer oxidized layer on sedimentary rock is removed by the RAT.
	Lake's margin: sandstone facies; possibly similar to fluvial facies.	Rounded sand grains.
	Lake's middle: shale facies; planar layers of silt/clay.	No visible grains.
Aeolian deposit	No particles larger than can be moved by creeping.	Grain size <4 mm.	Sediment chemistry differing from local rock chemistry.	Comparisons of sediment and local rock spectra suggest differing mineralogies.	Comparisons of sediment and local rock Mössbauer spectra suggest differing Fe mineralogies.
	Sandstone facies: planar, laminar cross bedding or ripple bedding. No trough cross bedding.
	Presence of global soil (see above).
	>20 m thick deposits with little stratification (loess).	Grain size not easily discernable (loess).
Glacial deposit (glacial till/moraine)	Poorly sorted material; cm to large boulders, striated rocks, gravel, boulders. Flattened rocks and gravel.	Striated rocks and gravels.	No uniquely identifiable characteristics.	Primary minerals.	Primary Fe minerals.
Glacial lake	Varves, rain‐out debris in planar layered sediments.	No visible grains.	High levels of Ca, Mg, K, Na, S, Cl, N	Phyllosicates.	Possible siderite (FeCO3) Fe2+‐smectite if outer oxidized layer on sedimentary rock is removed by the RAT.

• a Bold text of instrument analytical results suggest a positive identification of an individual hypothesis.

4.2.1. Global Soil
[39] The Viking and Mars Pathfinder (MPF) sites show widely similar bulk soil elemental compositions, suggesting a soil that has been globally distributed by aeolian activity [Rieder et al., 1997]. The presence of global soil in Gusev will be indicated by alpha particle X‐ray spectrometer (APXS) bulk chemical analyses reporting elemental concentrations similar to the Viking and MPF sites. Further support for global soil in Gusev may be established if Pancam multispectral imaging shows spectra similar to what was obtained by MPF [Bell et al., 2000].

4.2.2. Soil Formation in a Nonaqueous Environment
[40] The APXS data of soils derived from local rocks will be expected to have total elemental composition similar to the local rock. Furthermore, Mini‐TES and Mössbauer spectrometer (MB) spectra would show that the rocks and soils have similar spectral properties. Soils that show no evidence of secondary mineralogy (e.g., clay minerals, iron‐oxyhydroxides, carbonates, and sulfates) would suggest that the soils were not affected by postdepositional aqueous activity. The Microscopic Imager (MI) data may show soil particles with angular morphology suggesting that they were derived locally.

4.2.3. Volcanic Ash/Maar Base Surge Deposits
[41] Apollinaris Patera is 250 km north [Robinson et al., 1993] and may have deposited volcanic ash and pyroclasts in Gusev [Kuzmin et al., 2000]. The detection of blocky, platy, and/or cupsate glass shards by MI will support the idea that volcanic ash is component of the soil [Orton, 1996]. Mini‐TES spectra of an ash deposit may show a basaltic or andesitic signature if the ash has significant lithic component. Ash deposits with a significant vitric component would tend to show a poorly crystalline Mini‐TES spectra. If the volcanic ash is not altered by water, the MB may detect Fe phases such as ilmenite, titanomagnetite, titanomaghemite, and magnetite and Fe containing pyroxene [Fischer and Schmincke, 1984; Gunnlaugsson et al., 2002].

[42] While craters in Gusev are presumed to be of impact origin, it is conceivable that some craters could be maars or tuff rings (Figure 11). Maar or tuff ring volcanoes can produce base surge deposits that resemble fluvial deposits (e.g., planar to wavy layering) as shown in Figure 12. However, unlike fluvial deposits, base surge deposits may contain soft sediment deformations (i.e., folded layering between undeformed layer), vesicles (gas bubbles) and bedding sags that may be observable with Pancam [Cas and Wright, 1987; Fischer and Schmincke, 1984].

Figure 11
Open in figure viewerPowerPoint
Caption

Figure 12
Open in figure viewerPowerPoint
Caption4.2.4. Soil Formation in Aqueous Environment
[43] The observation of platy, blocky, prismatic, and/or columnar, soil structures in an exposed soil profile by the Pancam would suggest that the soil may have been affected by water. Extensive leeching of base cations from the soil profile would have occurred regardless of whether Mars had a reducing or an oxidizing environment. Soil levels of Ca, Mg, K, and Na as detected by the APXS may be lower relative to local rocks. Mini‐TES may detect clay minerals (e.g., kaolinite, vermiculite, chlorite, and smectite), gibbsite, Fe‐oxyhydroxides [e.g., ferrihydrite (5Fe2O3·9H2O), goethite (FeOOH), or hematite (Fe2O3)], and calcite (CaCO3). MB could detect the presence of any Fe‐oxyhydroxides.

[44] Arid soils experiencing low or episodic water activity can develop structure as discussed above. Vesicular porosity is prevalent near the soil surface in arid soils [Dunkerley and Brown, 1997] and may be observable by the Pancam and MI. Arid aqueous activity would be indicated by the APXS detecting elevated levels of Ca, Mg, K, Na, S, Cl, and/or N in the soil relative to local rock. Mini‐TES may detect calcite (CaCO3), gypsum (CaSO4· 2H2O), annhydrite (CaSO4), and possibly nitratite (NaNO3) [Eriksen, 1981; Clark et al., 1982; Amit and Yaalon, 1996; Li et al., 1996; Böhlke et al., 1997]. Smectite is usually the prevalent clay mineral formed in arid environments [Allen and Hajek, 1992] and could be detected by Mini‐TES.

[45] The above discussion of aqueous weathering assumed Earth oxidizing conditions. Reducing conditions could well have prevailed during aqueous mineral weathering on early Mars [Catling, 1999]. Siderite (FeCO3) may have formed in greater abundance than calcite [Catling, 1999]. Under reducing conditions magnetite (Fe3O4), siderite, and pyrite (FeS2) would have the potential to precipitate rather than goethite, ferrihydrite, or hematite. The prevalence of the apparent oxidizing conditions on Mars today may obscure any evidence of reducing mineralogy. The abrasion of a sedimentary rock or indurated soil blocks with the RAT to analyze material not directly exposed to the past and/or present Martian oxidizing conditions should allow MB and Mini‐TES to test the existence of reducing mineralogy.

4.2.5. Lacustrine Sediments
[46] Pancam could detect soil profiles of a lake deposit showing alternating layers of light colored salts and darker colored clay/silt layers [Li et al., 1996]. However, complex mixtures of evaporites and clay mineralogies can occur in lacustrine soils and may not be discernable by Pancam. Soil structure in lacustrine soils may also be observable by the Pancam. Evaporite and clay minerals may also be detected by Mini‐TES. The APXS may show elevated levels of Ca, Mg, K, Na, S, Cl and possible N relative to local rock. Pancam and MI could detect a lake's margin because of the presence of beach sands and gravels relative to clays and silts that occur toward the center of the lake. Some of the precipitation sequence of (carbonates → sulfate) → halite could be detected as Mini‐TES and APXS sample from the outer reaches of the lake and moves toward the center of the lake [Eugster and Kelts, 1983; Shaw and Thomas, 1997]. Within a 600 m traverse, the spectrometers and cameras onboard the rover are likely to observe chemical transition. Soils with abundant evaporite minerals could be indurated, and clay mineral deposits may become shale‐like. Any shale‐like material with planer layering or indurated evaporites may occur as ejecta blocks large enough to be examined with the Athena instruments.

4.2.6. Fluvial Sediments
[47] Evidence of past fluvial activity in Gusev crater may occur as ejecta blocks or outcrops of conglomerate, sandstone, or shale at the surface. Any material exhibiting layered morphology (e.g., cross bedding, ripple bedding and trough cross bedding) [Collinson, 1996] observed by Pancam are candidates for fluvial deposition. Rounded soil grains observed by MI would suggest fluvial activity. Mini‐TES would detect the primary mineralogy of the sand or conglomerate particles and may detect their cementing agents (e.g., silica, carbonate, clay, iron oxyhydroxides) [Klein and Hurlbut, 1993]. The color of the sandstone may reflect the cementing agent with silica and carbonate agents producing a light color and the iron oxyhydroxides producing a red to reddish brown color. If an iron‐oxyhydroxide or siderite is the primary cementing agent, then MB may indicate the iron mineralogy of the cementing agent. PanCam images of a rock or outcrop material showing planar layering with no MI identifiable sand‐sized grains would suggest shale‐like material. Mini‐TES would produce spectra with primary mineralogies and clay mineralogies. Shale‐like material containing a significant vitric component derived from volcanic ash would tend to produce poorly crystalline Mini‐TES spectra.

4.2.7. Aeolian Sediments
[48] Detection of the global soil would suggest aeolian deposition of soil. MI will detect aeolian sedimentary deposits that show planar cross bedding and rippled bedding if the aeolian grains are large (>30 μm. However, trough cross bedding that occurs in fluvial environments typically does not occur in aeolian environments. Furthermore, layering of materials coarser than 4mm would suggest only fluvial and not aeolian activity [Greeley et al., 1992].

[49] Loess deposits on Earth tend to be 20–30 m thick but have been known to be as thick as 60 m and usually are derived from fluvial and glacial sediments [Pye, 1987; Dunkerley and Brown, 1997]. Loess particle sizes range from 10 to 50 μm and are usually deposited in weakly stratified accumulations. Any Pancam and MI observations of deposits that appear to have little or no stratification with particle sizes barely or not visible by the MI may indicate loess.

4.2.8. Glacial Sediments
[50] Soil profiles or outcrops containing glacial till or material deposited at the terminus (moraine material) of a glacier will be poorly sorted and contain all grain sizes ranging from clay‐sized grains to meter‐sized boulders. The layering observed with glacially deposited material could look similar to fluvial material. However, closer examination of rock fragments (>2 mm) in glacial till could show indications of striations resulting from the abrasion of the rock, which is characteristic of the grinding action of glaciers on rock against another rock or bedrock surface. Some striated pebbles or rock may be elongated or flattened and would lie in the direction of glacial movement. “Rain‐out” debris from rafted ice that is deposited in the lake's sediment may indicate a glacial lake [Bennett and Glasser, 1996]. Varves are usually indicative of glacial activity and, if so, consist of alternating layers of clay and silt/sand in the lake's sediment. Varving also occurs in temperate climates with seasonal fluctuation in precipitation. All of the above indicators of glacial activity may be observed with Pancam or MI.

[51] It is important to note that the key indicators for each of the described hypotheses could all be identified in situ within the range of the rover traverse as they are strongly based on the mineralogy of sedimentary exposures and grains and their morphology. In situ observations from the rover will be then complemented by larger‐scale orbital data surveys (MGS and MO) during the mission in order to fully understand the significance of the observation and the results of the measurements.

 

[Jarvis323]

No, they have a low concentrations of silica. The link discusses rocks that are unusual, precisely because they are rich in silica. Compared to other Mars rocks.

Ahh, I didn't notice that.

Anyways, if you have more to share about how we can tell if the conditions necessary for petrification had existed, that would be interesting. I didn't know about this issue before.

I think that the specific image I shared P294 may be from the Columbia Hills in Gusev crater, which is one of those places where more silica was found.

https://www.sciencedirect.com/science/article/abs/pii/S0019103509001638

Towards the middle of the six-year mission (a mission that was supposed to last only 90 days), large amounts of pure silicawere found in the soil. The silica could have come from the interaction of soil with acid vapors produced by volcanic activity in the presence of water or from water in a hot spring environment.[15]

After Spirit stopped working scientists studied old data from the Miniature Thermal Emission Spectrometer (Mini-TES) and confirmed the presence of large amounts of carbonate-rich rocks, which means that regions of the planet may have once harbored water. The carbonates were discovered in an outcrop of rocks called "Comanche."[16][17]

https://en.m.wikipedia.org/wiki/Columbia_Hills_(Mars)

 

[russ_watters]

I read the wikipedia page on the spirit rover and Gusev crater, and I skimmed this paper.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2002JE002026

It's not bad -- it doesn't have the concise list of overall objectives, but a deep dive into the details. It does specifically discuss searching for/potentially finding fossils...

 

[Jarvis323]

This one is odd. I don't know, I guess the wind blew this thing over maybe. Must be something fairly lightweight?

https://mars.nasa.gov/mer/gallery/all/2/n/1833/2N289093752EFFB074P1985R0M1.JPG
https://mars.nasa.gov/mer/gallery/all/2/n/1836/2N289363474EFFB0A1P1985R0M1.JPG
https://mars.nasa.gov/mer/gallery/all/2/n/1843/2N289976994EFFB0EOP0675R0M1.JPG

 

[Motore]

All I can see is common rocks (they are expected to have different shapes!). What I surmise is that the OP has a vivid pattern recognition (see post #12).

 

[sophiecentaur]

What? We're talking about a NASA mission here, not a ballistic missile submarine. The mission plan is public knowledge for anyone who chooses to google it!

Oh yes. No conspiracy theory intended. I was simply stating a fact that most people ('we') haven't read the mission statement and that most comments here are very much based on personal opinions.

 

[sophiecentaur]

This one is odd. I don't know, I guess the wind blew this thing over maybe. Must be something fairly lightweight?

Could it just be a parallax effect? There are not many clues about distances in those pictures but the viewpoints look different. You have to look for the most reasonable solution in these cases.
The viewpoint for the first image is very different.

 

[Jarvis323]

Could it just be a parallax effect? There are not many clues about distances in those pictures but the viewpoints look different. You have to look for the most reasonable solution in these cases.

Yeah, I think it might be the parallax effect. But I don't know how to work that out. It's quite displaced looking. I guess it could be because it's further back than it looks.

 

[russ_watters]

This one is odd. I don't know, I guess the wind blew this thing over maybe. Must be something fairly lightweight?

I can't tell if you're joking or not; the atmosphere on Mars is very thin (about 1/60th that of earth); the wind can't blow over/move a rock.

Yeah, I think it might be the parallax effect. But I don't know how to work that out. It's quite displaced looking. I guess it could be because it's further back than it looks.

In the wide view it is fairly clear that the nearby rocks are on a small hill and the further rock is on the ground well behind them.

Where is the archive you are accessing and what documentation is provided? I would be fairly shocked if they didn't provide all the necessary geometric information to draw a map of where all the objects are in the photos. All you need is the location of the rover when it took the photos and the direction the camera was pointed (for 2 photos).

 

[russ_watters]

Oh yes. No conspiracy theory intended. I was simply stating a fact that most people ('we') haven't read the mission statement and that most comments here are very much based on personal opinions.

"we" really should if "we" want to speculate if any given investigation is within the scope of the mission! Here's a concise statement for one of the rover missions (looks like a dead/archived page):

1. Search for and characterize a variety of rocks and soils that hold clues to past water activity. In particular, samples sought will include those that have minerals deposited by water-related processes such as precipitation, evaporation, sedimentary cementation, or hydrothermal activity.
2. Determine the distribution and composition of minerals, rocks, and soils surrounding the landing sites.
3. Determine what geologic processes have shaped the local terrain and influenced the chemistry. Such processes could include water or wind erosion, sedimentation, hydrothermal mechanisms, volcanism, and cratering.
4. Perform "ground truth" -- calibration and validation -- of surface observations made by Mars orbiter instruments. This will help determine the accuracy and effectiveness of various instruments that survey Martian geology from orbit.
5. Search for iron-containing minerals, identify and quantify relative amounts of specific mineral types that contain water or were formed in water, such as iron-bearing carbonates.
6. Characterize the mineralogy and textures of rocks and soils and determine the processes that created them.
7. Search for geological clues to the environmental conditions that existed when liquid water was present. Assess whether those environments were conducive to life.

https://www.webcitation.org/61AZSknZA?url=http://marsrovers.nasa.gov/science/objectives.html

Most of these can be summarized as "go and investigate an interesting rock".

 

[sophiecentaur]

"go and investigate an interesting rock"

That includes Point 7 "Search for geological clues to the environmental conditions that existed when liquid water was present. Assess whether those environments were conducive to life." to which examples of fossilised life forms would contribute pretty good evidence. So it's in the brief but they were not obsessed with the possibility of anything as direct as that.
That's pretty reasonable use of the money they spent.

 

[Jarvis323]

In case anyone is interested, I've spotted a bunch of (I think) intriguing objects. Here are a few of them.

Navigation Camera Sol 90. https://mars.nasa.gov/mer/gallery/all/2/n/090/2N134357490EFF2600P1846R0M1.HTML

From Navigation Camera Sol 76
https://mars.nasa.gov/mer/gallery/all/2/n/075/2N133028174EFF2200P1827R0M1.JPG

Navigation Camera Sol 1830
https://mars.nasa.gov/mer/gallery/all/2/n/1830/2N288828136EFFB000P0625L0M1.JPG

Navigation Camera Sol 1837
https://mars.nasa.gov/mer/gallery/all/2/n/1836/2N289363525EFFB0A1P1985L0M2.JPG

Navigation Camera Sol 65
https://mars.nasa.gov/mer/gallery/all/2/n/065/2N132143812EFF1600P1835L0M1.JPG

Navigation Camera Sol 77
https://mars.nasa.gov/mer/gallery/all/2/n/077/2N133199118EFF2224P1845L0M1.JPG

Navigation Camera Sol 87
https://mars.nasa.gov/mer/gallery/all/2/n/087/2N134089197EFF22FKP1883R0M1.JPG

 

[Jarvis323]

There has been a pretty groundbreaking discovery that seems relevant.

Reinterpretation of weak basin magnetizations on Mars
Our results demonstrate that the martian dynamo was active 4.5 and 3.7 Ga ago. The existence of a dynamo field before and after the large basins Hellas, Utopia, Isidis, and Argyre requires an explanation for the general absence of magnetic fields over those basins. The impact demagnetization hypothesis is based on the argument that magnetization is absent within, but present around, the basin. Although this is true, unexplained observations worth noting are as follows: (i) Large tracts of Noachian crust surrounding the basins Hellas and Argyre are also unmagnetized or very weakly magnetized (fig. S7). Shock demagnetization can affect the basin exterior (27) but fails to explain the heterogeneity of magnetization around the basin or the extensive Noachian aged areas in the southern hemisphere with similarly weak or no magnetization. (ii) Short-wavelength signatures may be present in the interior of the basins (fig. S7) (16, 17), although lower-altitude tracks or surface measurements are necessary to confirm this.
Can the absence of magnetic field signatures over the basins be explained if a dynamo was operating during basin formation? At least two possibilities exist: (i) The giant impacts excavated large fractions of the crust, possibly removing material capable of carrying strong magnetizations. For crater diameters, D, up to ~500 km, the excavation depth, d, is ~0.1D, i.e., up to 50 km (37). Transient crater diameter estimates for Argyre, Isidis, and Hellas range from 750 to 1400 km (38). Although the d/D ratio for such large basins is uncertain, the depths would exceed 50 km, effectively penetrating and removing magnetized crust. The observations of very weak fields over the BB, cf. the surrounding southern highlands, suggest that this is plausible. Weak, small-scale signals may exist within the Argyre, Isidis, Hellas, and Utopia basins but require more lower-altitude observations for definitive identification. Material excavation, with only weak or small-scale subsequent magnetization, would produce a magnetic field signature at MGS and MAVEN altitudes barely distinguishable from basin-localized demagnetization. (ii) We also cannot exclude a fortuitous scenario in which a dynamo field at the time of basin formation was substantially weakened or intermittent, as a result of a reversing dynamo field (39). (iii) Alternatively, the dynamo was inactive during the time of basin formation, for example, because of inherently changing dynamo processes (i.e., from a thermally to a compositionally driven dynamo).
Implications of a dynamo 4.5 and 3.7 Ga ago
Evidence for a dynamo both ~4.5 and ~3.7 Ga ago has major implications for Mars’ evolution. Assuming a thermo-chemically driven magnetic dynamo, Mars must have sustained sufficiently vigorous core convection at its very earliest times and at the time of LP flow emplacement. Furthermore, the observations at LP suggest that a substantial fraction of the magnetization is carried in a thin, shallow magnetized unit. The resulting magnetizations are consistent with magnetization of pyroclastic flows in a 3.7-Ga old surface field with a strength similar to that of Earth’s present field. Excavation during large impacts may have played a key role in establishing a heterogeneous distribution of magnetic carriers in the martian crust, particularly removing magnetic minerals from the interior of major basins. This scenario allows a dynamo to plausibly persist from 4.5 to 3.7 Ga ago, thereby opening the possibility for a range of new magnetization processes to affect the martian surface, including depositional and crystallization remanence. For example, morphological evidence for water in the form of valley networks at the surface of Mars is dated between the Noachian and the Early Hesperian (3), before and overlapping with the timing of formation of LP and hence the dynamo. Water circulating in the martian crust in the presence of a field could have resulted in hydrothermal alteration facilitating magnetization or remagnetization of magnetic minerals (40).
Furthermore, the results link to current and planned missions’ e.g., the interior structure is a primary goal of the InSight mission currently operating on the martian surface (41). The dynamo timing results presented here provide a major step forward in understanding Mars’ thermal evolution, especially when combined with existing constraints on heat flow, mantle temperature, interior composition, and physical models of structure of the martian core. Also, if a global magnetic field protects the atmosphere from solar wind energetic particles, a prolonged dynamo would delay the effects of some of the atmospheric removal processes and hence have implications for martian atmospheric loss rates (42). This is important for addressing one of the main MAVEN goals of atmospheric escape rates through time (42). The collection of martian samples and their return to the Earth will finally be underway with sample collection by the Mars 2020 rover to be launched next year. An extended dynamo, consistent with the new results here, is of key importance for the Jezero landing site selected for Mars 2020, because units that could be sampled might have formed at a time of an active dynamo field (43). Future laboratory investigation of return samples will be the next major step in Mars exploration and, if magnetized, for planetary paleomagnetism.

https://advances.sciencemag.org/content/6/18/eaba0513/tab-article-info

It's hard for me to tell what the full implications are. But it seems that the previous evidence we had for the disappearance of a magnetic field on Mars might have been mistaken. Most arguments why complex life is unlikely to have developed on Mars are based on that evidence. I guess there might be a significantly new story to piece together, in terms of the history of Mars and its past habitability? Or does this discovery leave the previous views mostly unchanged?

 

[DaveC426913]

Since we (including the OP) agree that this thread is not about fossils, but about things on Mars that simply look tantalizingly unrocklike, maybe we could set the tone of it by changing the thread title to "The Mars Pareidolia Thread" or some such.

 

[Jarvis323]

I think what I intended is more along the lines of, "How can we analyze Mars rover images for signs of life? Or "Is it possible to...?" Or "What methods do scientists use to determine whether a rock on Mars could be a macroscopic fossil?"

 

[eskergold]

I have been impressed with the fact that Mars really does have an "unworldly" look to it. I think this must be related to the fact that the air is so thin it can only carry fine dust particles - even when blowing at high speed. The erosion produced by this "dust-blasting", especially on layered sedimentary rock, teases out fine scale features to a degree we are not used to seeing. Lower gravity, non-earth normal turbulent flow regime at boundary, etc.. I would very much like to know more. Not to change the topic, but any space suit will need to be pretty tough to provide explorers with adequate protection.

 

[russ_watters]

I think what I intended is more along the lines of, "How can we analyze Mars rover images for signs of life? Or "Is it possible to...?" Or "What methods do scientists use to determine whether a rock on Mars could be a macroscopic fossil?"

I had hoped that the thread would head in that direction and tried to steer it there, but it seems to keep coming back to seeing a bunny-rabbit in the clouds. While superficially it may seem similar, "wandering around looking for interesting rocks to investigate" means something very different to a trained geologist than to a layperson. I encourage you to read up on the actual methods and tools the scientists/rovers are using for that investigation, including links provided in this thread and your own additional research.

Otherwise, this thread is drifting aimlessly and hasn't shown signs of becoming productive, so it is now locked.