Perseverance, Mars 2020 Rover : Updates

[djellison]

I don't think those huge chunks seen now on the twice the diameter size wheels can be explained as fine dust.

I've been looking at pictures of Mars rover wheels since 2004.  I've taken >30,000 images between Opportunity and Curiosity.  This happens loads.    It's just a kind of dust we're not particularly familiar with.   Most people look at it and think it has to have the mechanics of wet sand/mud to behave the way they see it.....but it just....isn't.   I don't know what to tell you.  You need to look at more Mars pictures, and play with different kinds of materials.   The environmental conditions preclude the sort of mechanism you're proposing.

You're certainly not the first person to see this clingy fine dry dust do this and be convinced it has to be damp to behave like that.  You certainy wont be the last.

[Holger Isenberg]

You're certainly not the first person to see this clingy fine dry dust do this and be convinced it has to be damp to behave like that.  You certainy wont be the last.

For an infinitely large surface, the theoretical maximum thickness for a flour-fine dust layer on a vertical rough aluminum surface on Mars is using a simple yield stress model (h = c / (ρ g)):
Cohesion c ≈ 500 Pa (mid-range for fine dust simulants)
Bulk density ρ ≈ 1200 kg/m³
Martian gravity g ≈ 3.71 m/s²

h ≈ 500 / (1200 × 3.71) ≈ 0.11 m (11 cm)

On Earth it would be: h ≈ 500 / (1200 × 9.81) ≈ 0.042 m

[djellison]

h ≈ 500 / (1200 × 3.71) ≈ 0.11 m (11 cm)

Given the diameter of the wheels is ~50cm....I think you just proved the point that this is entirely plausible without it being damp clay.

And I'll repeat my point.....go look at the phase diagram for water....look at the conditions at Jezero.

[Dalhousie]

Never before has this effect been observed on a Mars rover

Very fine grained soil does that all the time. It's been seen on Mars rover wheels for 20 years.  This article has a captioned image of it on the wheels of MER-B and MSL.

https://link.springer.com/article/10.1186/s40645-025-00725-3  ( specifically figure 4 - https://link.springer.com/article/10.1186/s40645-025-00725-3/figures/4 )


 'Wet' clay isn't possible on the Martian surface.   It would sublimate away in the heat of day and freeze solid any other time.  The 'liquid' corner of the phase diagram of water at Martian air pressure is miniscule.

https://en.wikipedia.org/wiki/Phase_diagram#/media/File:Phase_diagram_of_water_simplified.svg

See...
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023JE007880 where you'll see data showing the ambient pressure hovers right around that triple point at Jezero.

The 'looks like wet soil/mud' phenomenon has plagued those observing rover ops for two decades.   The behavior of VERY fine grained, VERY dry fines is quite unintuitive.  I'd suggest playing around with a tray of cornflower to understand just how clingy and clumpy it can be.

Perseverance is currently at an altitude of -1940 m, to liquid water is possible.  Especially in saline, which will shift the lower phase diagram boundary to the left.  It does not take much interstitial water to make a fine-grained material sticky.

[djellison]

Perseverance is currently at an altitude of -1940 m, to liquid water is possible 

Yes.  I said so earlier, citing the specific measured air pressure at the Jezero site.   Which is JUST high enough to get into the liquid wedge of the phase diagram.

Especially in saline, which will shift the lower phase diagram boundary to the left.

Such that every time it gets warm enough for liquid water, you're pretty much guaranteed to be hot enough to boil it off due to the low atmospheric pressure.  Moreover - the back of that rover is the hottest thing on the entire planet.  The wheels and suspension are anodized black to heat up in the sunshine - far warmed than the air temperature in the MEDA paper I cited earlier.

There is an incredibly narrow window where something might be 'damp' - so the question then becomes, where did the water come from and how did it get there given that every day the surface temperature is more than enough to boil it off.

If it were really sticky damp clay - it would stick around - it would happen all over the place.   It only happens when driving over incredibly fine dust, when the drive ends without leaving that dust, typically across ripple formations, and then is gone a drive later.

Once drive away from that find dust.....that wheel is CLEAN.   If it were damp and clingy...it would still be there.

https://mars.nasa.gov/mars2020-raw-images/pub/ods/surface/sol/01690/ids/edr/browse/ncam/NLF_1690_0816971842_895ECM_N0813608NCAM02690_10_195J01.png



Martian conditions are far less Earth like, and that material is far less familiar than I think you realize.

[Dalhousie]

Perseverance is currently at an altitude of -1940 m, to liquid water is possible 

Yes.  I said so earlier, citing the specific measured air pressure at the Jezero site.   Which is JUST high enough to get into the liquid wedge of the phase diagram.

Especially in saline, which will shift the lower phase diagram boundary to the left.

Such that every time it gets warm enough for liquid water, you're pretty much guaranteed to be hot enough to boil it off due to the low atmospheric pressure.  Moreover - the back of that rover is the hottest thing on the entire planet.  The wheels and suspension are anodized black to heat up in the sunshine - far warmed than the air temperature in the MEDA paper I cited earlier.

There is an incredibly narrow window where something might be 'damp' - so the question then becomes, where did the water come from and how did it get there given that every day the surface temperature is more than enough to boil it off.

If it were really sticky damp clay - it would stick around - it would happen all over the place.   It only happens when driving over incredibly fine dust, when the drive ends without leaving that dust, typically across ripple formations, and then is gone a drive later.

Once drive away from that find dust.....that wheel is CLEAN.   If it were damp and clingy...it would still be there.

https://mars.nasa.gov/mars2020-raw-images/pub/ods/surface/sol/01690/ids/edr/browse/ncam/NLF_1690_0816971842_895ECM_N0813608NCAM02690_10_195J01.png



Martian conditions are far less Earth like, and that material is far less familiar than I think you realize.

I am quite well aware, thank you, having spent 25 years working on Mars topics, and a few decades more working on terrestrial desert soils.

Perchlorate salts can expand the stability field of water at 600 Pa by over 100 K, from 180 K and up to at least 298 K. See https://pmc.ncbi.nlm.nih.gov/articles/PMC7191838/

If this is due to moisture, patchy frost may explain the discontinuous distribution is one possibility.  Equally, patchy distribution of relevant salts and their abundance is another.  Likewise you could eb right, and it is just very fine material, slightly cohesive through electrostatic forces.  Whatever the case may be, a degree of caution in interpretation is, I suggest, warranted.

[Star One]

Scientists Say These Small Electrical Discharges May Be the First Direct Evidence of Lightning on Mars

Rather than big bolts of lightning as seen on Earth, NASA’s Perseverance rover recorded audio of small zaps similar to those from static electricity

https://www.smithsonianmag.com/smart-news/scientists-say-these-small-electrical-discharges-may-be-the-first-direct-evidence-of-lightning-on-mars-180987766/

Paper linked to in the article.

[Dalhousie]

"Strangely bleached rocks on Mars hint that the Red Planet was once a tropical oasis"

Bleached clay rocks found on the Martian surface suggest that the Red Planet was once home to heavy rainfall and tropical conditions, new Perseverance observations hint.


https://www.livescience.com/space/mars/strangely-bleached-rocks-on-mars-hint-that-the-red-planet-was-once-a-tropical-oasis

Note that "tropical" here refers to the martian context, not to any equivalence to the terrestrial counterpart!

Link to paper: https://www.nature.com/articles/s43247-025-02856-3

What's interesting is that this is the first time AFAIK that we have imaged rocks on Mars with the familiar mottling that we see in strongly weathered rocks on Earth. Such rocks are generally fairly weak (though not aways) and are thus unlikely to be transported to Earth as meteorites. Hopefully the Perseverance team can find the source outcrop and sample it for eventual return to Earth.

[Blackstar]

https://www.jpl.nasa.gov/news/nasa-rover-detects-electric-sparks-in-mars-dust-devils-storms/

[Blackstar]

https://www.nasa.gov/missions/mars-2020-perseverance/perseverance-rover/nasas-perseverance-mars-rover-ready-to-roll-for-miles-in-years-ahead/

[Nomadd]

 "After nearly five years operating inside Mars Jezero Crater, NASA's Perseverance rover has logged almost 25 miles (40 kilometers) of driving while engineers certify that its mobility hardware and other subsystems can keep working for many more years.
Built and operated by NASA's Jet Propulsion Laboratory in Southern California, Perseverance is following up the long-running Curiosity rover and was designed from the outset for extended missions on the Martian surface. JPL teams have been running parallel tests of flight-spare hardware on Earth, recently confirming that the rotary actuators that steer and drive the rover's six wheels should perform optimally for at least another 37 miles (60 kilometers), with comparable brake testing in progress.
 Over the past two years, engineers have evaluated almost every major subsystem and concluded that Perseverance can operate through at least 2031 if supported. "These tests show the rover is in excellent shape," said Perseverance's deputy project manager, Steve Lee of JPL, who presented the results at the American Geophysical Union's annual meeting, describing how the systems can sustain a long-term campaign to examine this region of Mars."

https://www.marsdaily.com/reports/Perseverance_rover_cleared_for_long_distance_Mars_exploration_999.html

[Blackstar]

Until 2031:

https://www.nasa.gov/missions/mars-2020-perseverance/perseverance-rover/nasas-perseverance-mars-rover-ready-to-roll-for-miles-in-years-ahead/