APOD: Five Meters over Mars (2023 Aug 10)

[APOD Robot]

Five Meters over Mars

Explanation: On mission sol 872 (Earth date August 3) Ingenuity snapped this sharp image on its 54th flight above the surface of the Red Planet. During the flight the Mars Helicopter hovered about 5 meters, or just over 16 feet, above the Jezero crater floor. Tips of Ingenuity's landing legs peek over the left and right edges in the camera's field of view. Tracks visible near the upper right corner lead to the Perseverance Mars Rover, seen looking on from a distance at the top right edge of the frame. Planned as a brief "pop-up" flight, Ingenuity's 54th flight lasted less than 25 seconds. It followed Ingenuity's 53rd flight made on July 22 that resulted in an unscheduled landing.

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[Ann]

Rocks on Mars. Image Credit: NASA, JPL-Caltech, Ingenuity

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A sailing stone of Death Valley. Image credit: Lgcharlot of Wikimedia Commons

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I'm slow to process things (good thing I haven't got a driver's licence) so when I first saw today's APOD, my initial thought was, "Yes, that must be a picture of Death Valley and the sailing stones."

Or not. But because the APOD made me think of the sailing stones, I'll talk a little about them here!

Stones move in Death Valley when ponds have formed and then frozen on the flat surface of Racetrack Playa. In the daytime, when sunlight is breaking up the ice into large "panes" which start moving, these large ice panes are able to push the rocks. The rocks move at a leisurely pace until the ice moves away and leaves the rocks in a new position.

I recommend the Youtube video showing how the sailing stones were caught ni action!

Tracks of sailing stones in Death Valley. Image credit: Norris RD et al.

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Click to play embedded YouTube video.

So if we ever find sailing stones on Mars, that would be irrefutable evidence that there is still water on Mars capable of forming ponds, and the sunlight reaching Mars is warm enough to melt the ice and set large "panes" of it in motion, pushing rocks in front of them on a flat surface (which got so flat because the area is a dried-out lake bed from the past?).

Ah. I guess not.

Ann

Edit: Of course it's amazing that the picture that is today's APOD was taken by the Mars Helicopter. I don't mean to be disrespectful or "un-amazed" about that.

[Cousin Ricky]

What little sky is visible looks very Earth-like.

[Joe MOXIE]

Note the neat circle at the bottom of the frame where the rotor downwash cleared small dust that was darker than the underlying material.

[orin stepanek]

Wow; amazing!

[Roy]

That they can get anything to fly is interesting, because atmosphere is thin- six tenths of a percent of earth. On the other hand, low gravity of 38 percent of earth helps. Plus, controlling it at this distance is a noteworthy feat.

[Joe MOXIE]

Nominal pressure is about 6.5 mbar or about the 0.6% of earth sea level pressure, but there are two other factors. Most of the time it is much colder than the earth standard atmosphere which increases the atmospheric density. Also the Mars atmosphere is mostly CO2 so the molecular weight ratio to air on earth is 44/29 or about 50% higher. Combined you'd have about 1.5% of sea level air density (1.225 kg/m3) but it varies widely with time of day and time of year on Mars. I think Perseverance has seen from 0.013 kg/m3 to 0.023 kg/m3 since landing. The day night shift is about 0.004 kg/m3 and I think Ingenuity only flies in daytime so it will be on the lower range of the density say 0.015 kg/m3 average over the year. That's about 1.2% of earth sea level density.

Ingenuity's rotors are larger diameter and turn at higher rpm. Lift increases with the square of diameter for the same tip speed, and lift also increase with the square of the tip speed. Since as you point out gravity is 38% the combined diameter and rpm effect (both having a squared response) only need to increase a factor of 6 or so.

[johnnydeep]

Per the total Ingenuity "flight log" stats, it has flown a total of about 8 miles, which is respectable, and a bunch of the 54 flights so far were over 2 minutes in duration, also respectable. But the highest Ingenuity has ever flown was just under 60 feet. Is there any particular reason, such as quickly diminishing atmospheric density, that prevents a higher flight? I would think one test flight should simply be trying to get as high as possible. And is there no value added by observing the ground from a more expansive vantage point?