The Geology of Jezero Crater, Observations & Findings Options

[Pando]

While these "holey" rocks appear light in color around the rover, the rocks that were blasted clean by the descent stage nozzles appear dark, just like the basalt example above. I'd say that's probably what they are.

[Marz]

Vesicular basalt can look a bit like the holey rocks:

Yes, I think the crater floor rocks in the vicinity of the rover are expected to be volcanic in origin (based on orbiter data) with the holes caused by gas bubbles. In the mastcam image, small rocks and sand can be seen inside the vesicles, which can act to abrade features much faster. Perhaps that debris is simply from the retro-rocket plume stirring stuff up though.

There's a chance the linear features on those rocks were not caused by wind and instead from how the igneous rock formed, but my hunch is they show an extremely long-term prevailing wind for Jezero.

[Blue Sky]

If the crater floor is covered by ash or other volcanic material, if Perseverence heads up the delta toward the inflowing river bed, would it be able to find any of the original river- or lake-bed shallow enough that its instruments can reach it? I suppose this area is a major destination for the helicopter.

[HSchirmer]

This image was cropped from the navcam pan. It appears the wind scouring of the "holey rocks" at the base of the rover show a prevailing direction occurred for a long period of time. If aeolian deflation of the delta occurred, then the sediments likely were deposited in that direction.

Very interesting- those grooves look VERY much like what you find in glacial till - rocks that were held in place by soil as ice was flowing over them, or small pieces of rock that were held in place by ice which flowed over other rocks. It should be fairly easy to determine, as the orientation of the grooves should quickly reveal if weather or wether is responsible.

If the hardness of the holey rocks and delta deposits can be assessed, then the total mass lost to erosion would have an estimate. I also wonder if the wind helped scour some of those holes larger?

The voids/vugs are fairly small, for aeolian 'pot holes" but most DO seem to have the signature of water-worn potholes, a single abrasive rock in each chamber. If should be easier to know what is happening after a few more rocks are imaged.

[JRehling]

It's virtually certain that some of the material from the lake – pebbles here and there – would be part of the regolith around Perseverance, but lacking context, they won't be as valuable to study as the rock in layers where the relative ordering is known.

The original lake bed is certainly not within reach soon. That said, the end of the lake was probably not a completely binary event, and there may have been some time near the end when the lake was first dry, and then later got a little bit of temporary recharge. The 2020 USGS publication about Jezero notes the possibility that the landing site had been reworked with later lacustrine environments. This would be of interest, but clearly secondary interest, as a place that was "habitable" for a few days or months would be much less interesting than a place that was "habitable" for a million years.

Remember, Spirit completely failed to access the original lakebed of Gusev, but surprisingly found evidence of aqueous evolution in the Columbia Hills. While we certainly don't see a Columbia Hills very close to Perseverance now, it would be hard to rule out later aqueous activity in the layer where it landed. But the actual delta layers are going to take a while to access.

Curiosity reached Yellowknife Bay on Sol 125. Perseverance has about twice that distance to go before reaching the delta, and it's possible that the morphology of the edge of the delta will keep us from touching that material without considerably longer traversals to the south (or north). I don't think we've had a chance yet to see the material – wherever it is – where Perseverance will first sample the delta layers. And we possibly will still be saying that in June and July.

[serpens]

..... I'm thinking of ashfall into a lake as sedimentary, I seems like you're considering ashfall as volcanic? ....

Ashfall has a volcanic provenance but I don't believe that the mafic floor unit was formed under such a process. I feel it is is probably effusive, pyroclastic maybe perhaps. Time and Perseverance will tell. The gap between the outlying remnants and the delta indicates that there was significant erosion with step back of the delta front measured in kilometres before the MFU was formed. This would support the assessment that the MFU formed some 300 million years after the lake dried up.

Andreas image (post #29) seems indicative of aeolian erosion with flutes / stretched vesicles.

[Andreas Plesch]

Yes, these lineations may have formed from aeolian erosion, indicating prolonged surface exposure (perhaps when there was still more of an atmosphere). The apparent stretching may be from obliquely cutting through vesicles. Since the holes seem to appear on all sides of imaged examples, I think it is less likely that they are potholes from scouring and milling. But it would be insightful to drill to see if there are similar holes in the interior of a large block.

I would also the envision the drying of the lake as a longer process, with wetter and drier periods. Are there thoughts on potentially multiple lake filling events ? After drying up substantially ?

Here is a cool new image of that outlier, first pointed out over in the general thread:

https://mars.nasa.gov/mars2020-raw-images/p...6_110085J01.png

There is nice stratigraphic layering, perhaps cyclic, and what appears to be a thick layer of foresets prograding outwards, above halfway up the slope or so. It may be possible to find the same sequence in the main delta (if and when the rover can get closer).

[JRehling]

Great look at the layering in the outlier, Andreas.

Another possibility would be to find a match between those layers and the ones in the crater wall, in case this is something that formed before the delta and remained intact through martian history.

[Andreas Plesch]

Great look at the layering in the outlier, Andreas.

Another possibility would be to find a match between those layers and the ones in the crater wall, in case this is something that formed before the delta and remained intact through martian history.

For convenience, reproduced here, with grey lines indicating potential foresets in a massive layer:

[Guest_Steve5304_*]

Vesicular basalt can look a bit like the holey rocks:



This example is from Hawaii and also has some Olivine in it. The texture is quite common in basalts and less common in pyroclastic deposits. The holes are trapped gas bubbles forming during degassing. Pumice would be an extreme example.

I think these holey rocks would make an attractive target for testing all the instruments. Not sure if similarly textured rocks had been observed before and they seem to be in-situ, eg. bedrock which would help with understanding the mapped unit as a whole.

If thats Vesicular basalt then isbit safe to say we havent landed in an area that was aquactic

[JRehling]

Opportunity and Curiosity both found rocks that were formed in aquatic environments. The shape of a rock isn't the only thing to know about it.

[MahFL]

If the crater floor is covered by ash or other volcanic material, if Perseverence heads up the delta toward the inflowing river bed, would it be able to find any of the original river- or lake-bed shallow enough that its instruments can reach it? I suppose this area is a major destination for the helicopter.

The helicopter is a demonstration mission, it's not flying anywhere to view stuff, it's only doing 3 short demo flights as far as I know.

[Marz]

this is a high-level description of the regional geology of Jezero with the relative ages:
https://phys.org/news/2021-02-geologists-pe...rance-site.html

[serpens]

For convenience, reproduced here, with grey lines indicating potential foresets in a massive layer:

This post correlates to Demko's post #392 in the Perseverance Lands In Jezero Crater thread. The direction of sediment flow raised by Tim's assessment has implications for the original size and configuration of the delta and potentially interactions between the two deltas.

[HSchirmer]

this is a high-level description of the regional geology of Jezero with the relative ages:

Good summary-
TLDR version- Exploring Mars is like "Russian Dolls with logarithmic crater sizes.
1) A lunar sized body obliterated the entire northern polar region of Mars leaving the "North Polar Basin." This impact is about the same class as the collision that created the Earth's moon.
2) At the southern edge of the "North Polar Basin" a smaller impact creates Isidris basin, roughly 950 miles across. This impact crater is about 7x the diameter of the 'dinosaur killer' crater at Chicxulub.
3) At the western edge of the Isidris impact basin, an impact created Jezro crater, about 30 miles across. This is roughly comparable to the size of the "Chesapeake Bay" impact crater on the US east coast.
4) Perseverance landed east of "Belva Crater" which is an impact crater on the delta deposits that is roughly the size of "Meteor Crater" in Arizona.