And all the low-lying terrain in this image was under water…

I am fascinated by Mars as it is. Even so, this amazing image really forces me to stop, and stare, and imagine this scene, imagine Mars, as it was. It’s artfully framed, yes, but I’m still stunned to visualize how those old, low, rounded-down ridges in the background would look entirely different if they were encompassing open water. Every time you think you’re starting to understand Mars…

Very late reply, Paul, hope you don’t mind:

I’d love to contribute here a lot more - I’ve been planning to do so for a while now - but I tend to write very long-winded posts (see above, again) which maybe doesn’t work on social media, and I’m also not one-tenth the geologist Steve Ruff is. If you think my somewhat inexpert posts are OK, though, I’m happy to oblige when I actually manage to find the time.

Wouldn’t we expect all the ground water to have no dissolved oxygen?

Very late reply - but your question is totally fair, so I hope you don’t mind:

On the face of it, you’d expect Martian groundwater to be pretty damned poor in dissolved oxygen, yes, and groundwater on Earth does get its oxygen almost entirely from the atmosphere, as you mentioned. (This would be easier on Earth than Mars due to the greater atmospheric pressure, among other things.) However:

If you’ve heard anything about recent discoveries of “dark oxygen” being generated on Earth’s deep seafloor, you might agree with me that nature often finds a way to create chemical niches where interesting stuff happens. In the just-discovered terrestrial case, metals on the seafloor are essentially acting as batteries, zapping water and splitting the oxygen off from the hydrogen. Obviously I can’t expect that this process was occurring at the Jezero Delta, but I’m cautious about saying that the groundwater there never had any dissolved oxygen, especially when we know that hot water can break down minerals and release the oxygen within.

So again, the question is a good one, but it’s already been partially answered by Curiosity, which found the following on the floor of Gale Crater:

Trace amounts of the element manganese typically exist in basalt. To get a rock with as much manganese as Caribou has, the manganese needs to be concentrated somehow. The rock has to be dissolved in liquid water that also has oxygen dissolved in it.

If conditions are right, the manganese liberated from the rock can then precipitate as manganese oxide minerals. On Earth, dissolved oxygen in groundwater comes from our atmosphere. We’ve known for some time now that Mars once had vast oceans, lakes and streams. If we could peer onto Mars millions of years ago, we’d see a very wet world. Yet we didn’t think Mars ever had enough oxygen to concentrate manganese—and that’s why we thought the data from Caribou must have been an error.

In the Earth’s geological record, the appearance of high concentrations of manganese marks a major shift in our atmosphere’s composition, from relatively low oxygen abundances to the oxygen-rich atmosphere we see today. The presence of the same types of materials on Mars suggests that something similar happened there. If that’s the case, what formed that oxygen-rich environment?

Good article to read if you have the time…

I’m already committing the cardinal sin of discussing redox states on social media, Paul, so forgive me for adding this note:

With all the groundwater that seemingly flowed within the rocks of this region, oxygen needn’t have been present at the time of deposition. Alteration/diagenesis seems to be pretty damned important here. (Further aside - non-geologists are always shocked to learn that oxygen is part of so many minerals and rocks to begin with. Maybe it’s easier to talk about free oxygen, the kind that isn’t already attached to the iron or magnesium of whatever…)

Not necessarily. Here comes another episode of Wide World of Iron Minerals…

The mineral that Prof. Ruff refers to - hematite - contains ferric iron, as opposed to the other kind, ferrous iron. The difference between the two is simple - ferric iron is missing 3 electrons, whereas ferrous is only missing 2. Some process has to strip the ferrous iron of that extra electron - it requires noticeably more energy to make ferric than ferrous. Mars has plenty of the ferrous kind, like you find in the rocks on the Jezero crater floor; it’s what you’d generally expect to find in the planet’s hard rock. So you want to pay attention when you get the ferric kind - especially when you find it in the “soft rock”, like Percy is exploring now. One way of making ferric is exposing it to free atmospheric oxygen and moisture, as on modern Earth, producing various “oxidized” minerals, which some casually call “rust”. But there are other ways for oxygen to do the job, as well - say, when it’s dissolved in groundwater. And this Neretva Vallis site evidently had plenty of groundwater. The oxygen content of that groundwater, however, is kind of a big question.

Thing of it is, hematite can also be produced without water and oxygen, purely by volcanic action, too. So hematite has a lot to say either way, it’s one of those minerals to watch.

The phenomenon of iron minerals on Mars has been a big deal, and will continue to be. Opportunity’s landing site was chosen because the variety of hematite that satellites detected there was unusual, and that led to the discovery of sandstone laid down by massive amounts of water - the first sedimentary rock ever discovered off Earth. Without that discovery, I’m not sure that Percy gets sent to Mars. And I haven’t even started to talk about other sources of ferric iron, like you find in the dust, or all the weird stuff that happens when sulfur and iron get together and have a baby…

EDITED to talk about hard and soft rocks. Don’t giggle, we’re geologists.

I know that the mission releases the proper calibrated images here, but only some months later, so neumast’s reply is the correct one for now.

Thanks for your detailed reply, Paul. It would definitely be worth compiling a set of NavCam images like the ones we’re talking about here. A casual review came up with this recent one, and Sol 1093 has another, so there should be a few.

Just to clarify, the very specific framing of the NavCam tile above is something I don’t remember seeing much since we landed. There are a few elements that make the shot perfect, like the ratio of rover suspension/wheels to surface, the shadows, alignment of the rover and so on. The sense of depth created by seeing parts of the rover at different heights from the camera is really important here. I realize that I’m getting into the weeds and thinking like a photographer and not a rover planner. I’m just trying to point out that this specific framing here is both informative and artistic - maybe even iconic - in a way that other regularly-planned shots don’t quite match.

I’ll see if I can compile a list in the next week or so.

I don’t want to be pedantic here in saying this: Mars experiences dust storms, rather than sand storms. That is a significant difference, because dust is light enough to stay aloft for much longer than sand, which has noticeable effects on climate. Today’s Martian atmosphere cannot loft sand very far. Keep in mind that sand storms would be much more effective at eroding rocks like the one Percy is investigating now - and doing damage to things like rovers and solar panels.

Imagery from today (sol 1084) shows that visibility is not great - parts of the Jezero rim are hazy or invisible - but it’s far from the worst we’ve seen on the planet (I’m thinking of what Opportunity saw in the great storm of '07). I would actually expect Ingenuity to survive this.

Potato-shaped??? I’d like to see Mars Guy’s figure after a few billion years…

Please. Some respect here for these two well-accreted ellipsoids with a few extra tera-tons. If you people want to swipe left on something, you can go straight to the Belt with all those charisma-free rubble piles and old boulder-faces. Sure, they’ve got the organic matter and the metals, but we’ll see who you come running back to when you remember who’s been lighting up every romantic Martian evening for all these eons…

Perseverance is deep within the ongoing Margin Unit campaign, where orbital signatures of carbonate minerals appear strongest.

Perseverance is approaching a small, ~50-m-wide impact crater that has created a natural cross-section of rock layers of the Margin unit, potentially providing new views of deeper bedrock. The team is eagerly awaiting images of the interior of this small crater, which could reveal information about the emplacement of the upper Margin Unit.

Based on orbital satellite images, rock layers near the Jezero Crater Rim are thought to be among the oldest rocks that could be explored by a rover on Mars. Therefore, the light-toned rock layers pictured here could represent much older strata than has yet been explored by Perseverance – possibly dating back to the Noachian (approximately 3.7 – 4.1 billion years ago). Exploration of these terrains could provide unprecedented insight into the climate and environmental habitability during earlier and possibly wetter periods in Mars’ history.