APOD: The Gator-back Rocks of Mars (2022 Apr 15)

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APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by APOD Robot » Fri Apr 15, 2022 4:06 am

Image The Gator-back Rocks of Mars

Explanation: Wind-sharpened rocks known as ventifacts, cover this broad sloping plain in the foot hills of Mount Sharp, Gale crater, Mars. Dubbed gator-back rocks their rugged, scaly appearance is captured in these digitally stitched Mastcam frames from the Curiosity rover on mission sol 3,415 (March 15, 2022). Driving over gator-back rocks before has resulted in damage to the rover's wheels, so Curiosity team members decided to turn around and take another path to continue the rover's climb. Curiosity has been on an ascent of Gale crater's central 5.5 kilometer high mountain since 2014. As it climbs, it's been able to study layers shaped by water on Mars billions of years ago.

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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by orin stepanek » Fri Apr 15, 2022 11:34 am

PIA25175.jpg
Interesting rock types on Mars!
8313_msl-rover-wheel-damage-pia21486-full2.jpg
Where's a tire store when you need one? :lol2:
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by De58te » Fri Apr 15, 2022 1:26 pm

Maybe this is counterintuitive but I recall in science class that rocks shaped by a water ocean over billions of years are usually worn smooth. So why is it if there was an ocean in that basin that the rocks higher up in the climb are expected to be worn smooth by water but yet the rocks on the bottom plain are jagged and sharp?

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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by Chris Peterson » Fri Apr 15, 2022 2:33 pm

De58te wrote: Fri Apr 15, 2022 1:26 pm Maybe this is counterintuitive but I recall in science class that rocks shaped by a water ocean over billions of years are usually worn smooth. So why is it if there was an ocean in that basin that the rocks higher up in the climb are expected to be worn smooth by water but yet the rocks on the bottom plain are jagged and sharp?
They are ventifacts, not rocks formed by water erosion. Ventifacts are the product of natural sand-blasting, and typically have sharp edges and flat surfaces due to prevailing wind patterns.
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by MarkBour » Fri Apr 15, 2022 7:42 pm

Wow, nearing 10 years son the surface! Not moving very fast, just about 2.7 km covered per year.

It has achieved some great science objectives.
(https://mars.nasa.gov/msl/mission/science/results/)
  1. Detected all kinds of signs of the presence of water in the past (and the evident scarcity of it today, indicating that most of it has disappeared over time).
  2. Found other of the base elements needed for Earth-like life to form (S, N, O, P, and C).
  3. Found methane in the atmosphere, and some wide variations in the methane concentration over time (the concentration actively changes in the atmosphere over time, having spikes for unknown reasons).
  4. Found larger organic molecules: chlorobenzene (150–300 parts per billion by weight (ppbw)) and C2 to C4 dichloroalkanes (up to 70 ppbw) in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay.
  5. Noted levels of radiation that occur enroute to Mars and on the Martian surface.
  6. Provided confirmation that some rock samples on Earth are of Martian origin.
As far as the search for life or evidence of ancient life, I find the organic molecule findings so far to be not very encouraging. Any planet like Mars is highly likely to at least have occurrences of some of the smaller organic molecules. But if any biological activity took off, we should expect to find some more convincing evidence of other byproducts. On the other hand, the environment is pretty inhospitable to preserving evidence, and has had a vast amount of time to wipe away any signs, so if it happened, any evidence of it might take some more determined searching and maybe a lot of luck to ever find. (I'm imagining some lakebed region that became buried, so as to trap fossil remains and that we could happen to find and get into.) The region of Mount Sharp, where Curiosity is roving, is a good choice, but I think it might take something more than Curiosity to actually unearth any remains. Unless one day its drill hits a jackpot.
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by Chris Peterson » Fri Apr 15, 2022 7:49 pm

MarkBour wrote: Fri Apr 15, 2022 7:42 pm Wow, nearing 10 years son the surface! Not moving very fast, just about 2.7 km covered per year.

It has achieved some great science objectives.
(https://mars.nasa.gov/msl/mission/science/results/)
  1. Detected all kinds of signs of the presence of water in the past (and the evident scarcity of it today, indicating that most of it has disappeared over time).
  2. Found other of the base elements needed for Earth-like life to form (S, N, O, P, and C).
  3. Found methane in the atmosphere, and some wide variations in the methane concentration over time (the concentration actively changes in the atmosphere over time, having spikes for unknown reasons).
  4. Found larger organic molecules: chlorobenzene (150–300 parts per billion by weight (ppbw)) and C2 to C4 dichloroalkanes (up to 70 ppbw) in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay.
  5. Noted levels of radiation that occur enroute to Mars and on the Martian surface.
  6. Provided confirmation that some rock samples on Earth are of Martian origin.
As far as the search for life or evidence of ancient life, I find the organic molecule findings so far to be not very encouraging. Any planet like Mars is highly likely to at least have occurrences of some of the smaller organic molecules. But if any biological activity took off, we should expect to find some more convincing evidence of other byproducts. On the other hand, the environment is pretty inhospitable to preserving evidence, and has had a vast amount of time to wipe away any signs, so if it happened, any evidence of it might take some more determined searching and maybe a lot of luck to ever find. (I'm imagining some lakebed region that became buried, so as to trap fossil remains and that we could happen to find and get into.) The region of Mount Sharp, where Curiosity is roving, is a good choice, but I think it might take something more than Curiosity to actually unearth any remains. Unless one day its drill hits a jackpot.
I don't see how life could form on Mars in its current state. But it's not difficult to imagine it forming as it was a few billion years ago. And life is remarkably resilient. I believe that life which was present early on could persist today. But almost certainly not where the probes we have sent so far could find it or detect it. The best chance would involve detecting something in the atmosphere. But like you say, the surface is not conducive to preserving evidence of life (other, perhaps, than outright macroscopic fossils... assuming life ever got that far).
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by johnnydeep » Fri Apr 15, 2022 8:39 pm

Chris Peterson wrote: Fri Apr 15, 2022 2:33 pm
De58te wrote: Fri Apr 15, 2022 1:26 pm Maybe this is counterintuitive but I recall in science class that rocks shaped by a water ocean over billions of years are usually worn smooth. So why is it if there was an ocean in that basin that the rocks higher up in the climb are expected to be worn smooth by water but yet the rocks on the bottom plain are jagged and sharp?
They are ventifacts, not rocks formed by water erosion. Ventifacts are the product of natural sand-blasting, and typically have sharp edges and flat surfaces due to prevailing wind patterns.
I took the question to be about how rocks higher up could be water worn, but rocks lower down be wind sharpened? Wouldn't the gradually ebbing water level leave the upper rocks with more time to be wind-sharpened? Unless there is a lot up upheaval involved causing what was once on top to now be lower. Or maybe it depends on the hardness of the particular rocks involved...
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by johnnydeep » Fri Apr 15, 2022 8:41 pm

I note from one of the links that the treads on the wheels of Curiosity are made of aluminum. Why wouldn't they have made them out of something harder and/or tougher? Was brittleness more of a concern than softness?
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by MarkBour » Fri Apr 15, 2022 9:00 pm

johnnydeep wrote: Fri Apr 15, 2022 8:41 pm I note from one of the links that the treads on the wheels of Curiosity are made of aluminum. Why wouldn't they have made them out of something harder and/or tougher? Was brittleness more of a concern than softness?
This was a fun article you inspired me to find:
https://www.sciencefriday.com/education ... -for-mars/
In particular, its section on "Reinventing the Wheel".

They were optimizing for low weight, traction, stability, and durability (and note that Mars is very cold).

Also, Perseverance changed the design based on the experience with Curiosity: Perseverance's wheels are narrower than Curiosity's, but bigger in diameter and made of thicker aluminum. (Still with Aluminum, but they ended up weighing more.)

Here's another great engineering take on it: https://llis.nasa.gov/lesson/22401
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by johnnydeep » Fri Apr 15, 2022 9:25 pm

MarkBour wrote: Fri Apr 15, 2022 9:00 pm
johnnydeep wrote: Fri Apr 15, 2022 8:41 pm I note from one of the links that the treads on the wheels of Curiosity are made of aluminum. Why wouldn't they have made them out of something harder and/or tougher? Was brittleness more of a concern than softness?
This was a fun article you inspired me to find:
https://www.sciencefriday.com/education ... -for-mars/
In particular, its section on "Reinventing the Wheel".

They were optimizing for low weight, traction, stability, and durability (and note that Mars is very cold).

Also, Perseverance changed the design based on the experience with Curiosity: Perseverance's wheels are narrower than Curiosity's, but bigger in diameter and made of thicker aluminum. (Still with Aluminum, but they ended up weighing more.)

Here's another great engineering take on it: https://llis.nasa.gov/lesson/22401
Ah yes, the cold. I take it that aluminum (or at least certain alloys of it) are more durable at Mars temps than titanium is.

It's also surprising to me that the article said that each of the 6 wheels was to contribute no more than 6% of the total weight. That means all 6 wheels could be up to 36% of the total weight?! The wheels don't LOOK like they're very heavy. I wonder if even the humongous wheels on those massive strip mining dump trucks are anywhere close to that. See http://cathincanada.blogspot.com/2012/0 ... world.html :

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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by Pilgrim36 » Fri Apr 15, 2022 10:23 pm

Are those wheel tracks in the small crater at the lower left of the image?

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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by Chris Peterson » Fri Apr 15, 2022 10:54 pm

johnnydeep wrote: Fri Apr 15, 2022 8:39 pm
Chris Peterson wrote: Fri Apr 15, 2022 2:33 pm
De58te wrote: Fri Apr 15, 2022 1:26 pm Maybe this is counterintuitive but I recall in science class that rocks shaped by a water ocean over billions of years are usually worn smooth. So why is it if there was an ocean in that basin that the rocks higher up in the climb are expected to be worn smooth by water but yet the rocks on the bottom plain are jagged and sharp?
They are ventifacts, not rocks formed by water erosion. Ventifacts are the product of natural sand-blasting, and typically have sharp edges and flat surfaces due to prevailing wind patterns.
I took the question to be about how rocks higher up could be water worn, but rocks lower down be wind sharpened? Wouldn't the gradually ebbing water level leave the upper rocks with more time to be wind-sharpened? Unless there is a lot up upheaval involved causing what was once on top to now be lower. Or maybe it depends on the hardness of the particular rocks involved...
Right. There are no exposed rocks on the steep slopes, only exposed rock. Which shows a layered face. All of the loose rock is at the bottom, and there hasn't been any flowing water there for billions of years. So those rocks have been weathered by blowing dust. They might have been river pebbles once upon a time. Not easy to tell anymore. Would need to dig down a bit.
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by johnnydeep » Sat Apr 16, 2022 8:57 pm

Chris Peterson wrote: Fri Apr 15, 2022 10:54 pm
johnnydeep wrote: Fri Apr 15, 2022 8:39 pm
Chris Peterson wrote: Fri Apr 15, 2022 2:33 pm

They are ventifacts, not rocks formed by water erosion. Ventifacts are the product of natural sand-blasting, and typically have sharp edges and flat surfaces due to prevailing wind patterns.
I took the question to be about how rocks higher up could be water worn, but rocks lower down be wind sharpened? Wouldn't the gradually ebbing water level leave the upper rocks with more time to be wind-sharpened? Unless there is a lot up upheaval involved causing what was once on top to now be lower. Or maybe it depends on the hardness of the particular rocks involved...
Right. There are no exposed rocks on the steep slopes, only exposed rock. Which shows a layered face. All of the loose rock is at the bottom, and there hasn't been any flowing water there for billions of years. So those rocks have been weathered by blowing dust. They might have been river pebbles once upon a time. Not easy to tell anymore. Would need to dig down a bit.
Thanks. So, what happens to loose water-rounded rocks higher up in locally flat places? What does several billion years of wind erosion do to them?
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by Chris Peterson » Sat Apr 16, 2022 9:16 pm

johnnydeep wrote: Sat Apr 16, 2022 8:57 pm
Chris Peterson wrote: Fri Apr 15, 2022 10:54 pm
johnnydeep wrote: Fri Apr 15, 2022 8:39 pm

I took the question to be about how rocks higher up could be water worn, but rocks lower down be wind sharpened? Wouldn't the gradually ebbing water level leave the upper rocks with more time to be wind-sharpened? Unless there is a lot up upheaval involved causing what was once on top to now be lower. Or maybe it depends on the hardness of the particular rocks involved...
Right. There are no exposed rocks on the steep slopes, only exposed rock. Which shows a layered face. All of the loose rock is at the bottom, and there hasn't been any flowing water there for billions of years. So those rocks have been weathered by blowing dust. They might have been river pebbles once upon a time. Not easy to tell anymore. Would need to dig down a bit.
Thanks. So, what happens to loose water-rounded rocks higher up in locally flat places? What does several billion years of wind erosion do to them?
Well, ventifacts form under the right conditions. But I'm sure there are plenty of places that don't have those conditions, so the rocks in those places will weather much more slowly.
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by MarkBour » Sun Apr 17, 2022 6:55 am

Pilgrim36 wrote: Fri Apr 15, 2022 10:23 pm Are those wheel tracks in the small crater at the lower left of the image?
I don't see any wheel tracks in the image. Just some ridges in the dust that I think are wind-sculpted and some very interesting rocks, some of which appear long, skinny, and linear.
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by MarkBour » Sun Apr 17, 2022 7:26 am

johnnydeep wrote: Fri Apr 15, 2022 9:25 pm ...
It's also surprising to me that the article said that each of the 6 wheels was to contribute no more than 6% of the total weight. That means all 6 wheels could be up to 36% of the total weight?! The wheels don't LOOK like they're very heavy. I wonder if even the humongous wheels on those massive strip mining dump trucks are anywhere close to that. See http://cathincanada.blogspot.com/2012/0 ... world.html :
I was struck with that number, too. It doesn't sound like much of a design restriction, since wheels on Earth vehicles are probably almost never that much of the weight! Let's see, Curiosity: 899 Kg, Perseverance: 1025 kg. So, in the vicinity of 1000 kg total weight, 6% is about 60 kg.
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by johnnydeep » Sun Apr 17, 2022 12:58 pm

MarkBour wrote: Sun Apr 17, 2022 7:26 am
johnnydeep wrote: Fri Apr 15, 2022 9:25 pm ...
It's also surprising to me that the article said that each of the 6 wheels was to contribute no more than 6% of the total weight. That means all 6 wheels could be up to 36% of the total weight?! The wheels don't LOOK like they're very heavy. I wonder if even the humongous wheels on those massive strip mining dump trucks are anywhere close to that. See http://cathincanada.blogspot.com/2012/0 ... world.html :
I was struck with that number, too. It doesn't sound like much of a design restriction, since wheels on Earth vehicles are probably almost never that much of the weight! Let's see, Curiosity: 899 Kg, Perseverance: 1025 kg. So, in the vicinity of 1000 kg total weight, 6% is about 60 kg.

Comparing.png
Yeah, and 60 kg is 132 lb, which is more than I weigh! There's no way in hades that each of the 6 wheels is anywhere near that. And I doubt that even including the drive train and axels would approach that weight.
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Re: APOD: The Gator-back Rocks of Mars (2022 Apr 15)

Post by MarkBour » Sun Apr 17, 2022 7:47 pm

johnnydeep wrote: Sun Apr 17, 2022 12:58 pm
Yeah, and 60 kg is 132 lb, which is more than I weigh! There's no way in hades that each of the 6 wheels is anywhere near that. And I doubt that even including the drive train and axels would approach that weight.
Hmmm ... That 6% figure, I can't seem to find it anywhere now that I look back, except in the first article that was describing it as a "student science/engineering project". I did find out that the actual wheels on Curiosity have a mass of only about 2.1 kg each, totalling something like 12.6 kg, if we're just talking about the outer "barrel-shaped" aluminum portion. Beyond the outer skin, though, there is the inner structure which is surely much beefier than the wheel surface, then each wheel has its own drive motor. As you're suggesting, perhaps the 6% limit, if it was a real specification, included all of that, and maybe also the rocker-bogie suspension. I have not seen mass measurements for any of the other parts.

It is kind of scary how things can get so quickly harmed and become a huge problem. It's been a long time, but the "mileage on those tires" is only 27km to date. I'd say they really did skimp on the wheels to save as much weight as they possibly could, using super-thin machined aluminum of just 0.75 mm thickness. (And why not? They had Spirit and Opportunity experience to go on.) Then, when some very nasty rocks started tearing them up, it could become the thing that halts a 2.5 billion dollar machine. Given enough time on Mars, something will eventually give! I suppose each engineering team secretly hopes it's somebody else's subsystem?
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