Author Topic: Earthquakes on Mars exposing ice? (Read 14805 times)

dunwich · « **on:** 01/20/2021 06:29 am »

Hi,

I've read that in the canyons of Mars sometimes fog is forming.
Now I wonder that if you were in a Martian canyon and a part of the canyon wall fell down after an earthquake exposing a lot of water ice to the near vacuum could it sublimate (violently) obscuring the canyon for weeks/months in a fog.

I also wonder how violent it could get?

My question is based on the book "The martian" by Andy Weir, in it a violent duststorm threatens to top the Mars ascent vehicle and obscures the area so Mark Whatney (the main character), body can't be found.

Would a cave in on ( a part of) the canyon wall be forceful enough the threaten to tip the MAV? Would this most likely be because of the tremors or a pressure blast from the nearby sublimating water, would the expanding water vapor be strong enough to potentially rip out the antenna and impale an astronaut.
Could the resulting fog linger for around 3 weeks obscuring the site from orbit?

small note in The martian the base is not located inside a canyon, but what if it was placed in Mawrth vallis in stead.

Anyway, thank you for your response. I hope the question can stand on itself, I did a search for the term fog but could not find anything. So feel free to expand on the original question.

the_other_Doug · « **Reply #1 on:** 01/20/2021 03:54 pm »

Alas, you selected one of the very few details in The Martian that Andy Weir himself admits is completely without scientific basis, i.e., is energetic arm-waving.

The atmosphere on Mars at the surface ranges from about 4 to 8 millibars. One bar is the Earth's average atmospheric pressure; a millibar is one-hundredth of that. At the bottom of the deepest canyons and basins, the air gets to be at most eight one-hundredths as dense as Earth's.

You see fog because the point at which pressure and average high-end temps on Mars that allow liquid water (i.e., in fog droplets) is right around 6 millibars. You can get that in the canyon floors and in the floors of some of the deeper basins, like Hellas. It has nothing to do with the wind; it has to do with those areas being lower, and therefore having slightly higher air pressure. That pressure varies seasonally, though, as CO2 moves from one pole to the other through a given hemisphere's spring/fall and enriches the overall atmosphere in CO2 gas as it does so, so the fogs come and go seasonally, as well.

Storms on Mars can pick up minute dust particles and the air can even suspend such particles, small as talc particles, for months. But an 80 km/hr gale on Mars would apply less pressure onto, say, a Mars Ascent Vehicle than I could likely apply with my hand.

So, wind movement of particles larger than the standard talc-sized grains suspended in the air on Mars is not capable of moving much of anything that is more massive than that. Even particles the size of small sand grains can only be scooted rather slowly across the ground by Martian winds in a process called saltation; wind erosion on Mars is an extremely slow, long-term thing. We just see lots of its effects because it's been going on for literally billions of years. Heck, we can even see the changes in climate, when prevailing wind directions changed for eons and then changed again, in the erosion patterns on the rocks.

Weir needed a way to strand Mark Watney on Mars, and couldn't come up with any other plot devices that would work. So, he admittedly had a Martian windstorm act as if the air was as thick as Earth's, when it's hundredths of that density and could never threaten the MAV, or pick up a radio antenna and fling it through a human body at tens of miles an hour.

Sorry to burst your bubble...

dunwich · « **Reply #2 on:** 01/20/2021 05:42 pm »

Hello and thank you for responding.

I'm aware of Andy Weir's position on the matter and I do loved The martian.
And I do agree with you, that the first storm would not be able to cause the problems that happend in the book (the second storm was more realistic).

But I'm afraid I did not make myself clear enough.

I suggested that their was no (dust) storm in the first place. The HAB or base would be placed not in acidalia planitia (open plain) but in Marwth Vallis (more boxed in) a location Mark travels trough in the book and what was a potential (not chosen) landing spot for the new mars rover perseverance.
https://mars.nasa.gov/mars2020/timeline/prelaunch/landing-site-selection/eight-potential-sites/

It was indeed a potential landing site, but more interestingly there is no obvious source of the water that carved it in the first place. In this scenario an earthquake would make a part of the canyon wall collapse, exposing buried water ice. Either the tremors from the earthquake and nearby collapsing rocks would damage the Mars Ascend Vehicle for it to need to depart in a hurry. Or an airblast of mostly sublimating water vapor from the exposed ice. The visibility would go down because of a combination of fog and snow.
Ice would keep sublimating for a long period filling the canyon and somewhat reducing the visibility. But not enough to impact his solar production or local visiblity. Mark assumes NASA can't see him in the fog but NASA figures it out long before he goes to the Pathfinder landing site. Mark doesn't harvest the water ice because the region is not stable enough. The weather clears up eventually.

No dust storms would appear until later in the story when mark is on his way to schiaparelli crater (the location of the next MAV).

So is this scenario somewhat more realistic? Could fog cover the entire canyon for weeks/months
again thank you for your input

PS the fog mentionend is no dust but actual water vapor
https://www.google.com/search?q=fog+mars

the_other_Doug · « **Reply #3 on:** 01/22/2021 02:43 pm »

Thanks for the clarification!

Yes, that's a somewhat more realistic scenario than the one Weir used to strand Watney in the first place, and while it's unlikely that there are any large buried seams of water ice near any canyon walls that haven't already sublimated away through cracks in the crust along canyon and chasm walls, it's theoretically possible.

The problem is that, while this could put the MAV in danger and cause the main crew to abandon the surface, it doesn't offer many ways by which Watney could get left behind. Just "lost in the fog" wouldn't likely be as believable.

Also, placing the base camp, and thus the hab, into a scenario where its own solar arrays are blocked pretty badly, you'd reduce Watney's chances of surviving his first couple of months of being stranded.

Honestly, the dangers you point out are things that would likely rule out landings on valley and chasm floors for the first couple of dozen landings. You want to land in places that don't limit your solar power on a regular basis, and just normal morning fogs in canyon floors can predictably limit your solar power for the entire length of a surface mission. Far better, for logistical purposes, to land in higher, flatter land like 50 km from one end of a valley system, and plan long-duration traverses into the valley floor regions. Which doesn't give you many ways you can use to strand Watney on Mars, alas...

I can certainly see why Weir had so many problems finding any other plot devices he could use to accomplish the stranding of Mark Watney, without which he couldn't tell the rest of his story. In fact, Weir actually posted in one of these online fora I participated in at the time, asking about other possible plot devices he could use to strand a guy on Mars, as the one he had thought up wasn't scientifically accurate. No one, of a large group of people like you and me, could come up with a scenario that resulted in Watney being abandoned, with a fully operable hab, on the surface. So, with regrets and apologies, Weir used the non-scientific plot device.

But, hey, good thinking...