Mars

All posts tagged Mars

Brian Jackson’s Press Conference Presentation

Contact Info

Ash devil near Great Sand Dunes National Park in Colorado. From https://www.youtube.com/watch?v=DIWWeARqOj0.

Summary

An key source of dust, dust devils help drive weather and climate on Mars. With a sophisticated suite of meteorological instruments, the Mars 2020 Perseverance rover can detect when a dust devil passes nearby — the instruments can see the pressure and dust perturbations from the dust devils. (Wind data were not available by the time of our work, so we didn’t include any — oh, well, next time.)

(a) The pressure perturbation from passage of a dust devil near Mars 2020. (b) The dustiness of the vortex – Mars 2020 has several dust sensors, and depending on how the dust devil blows over the rover, some of them will see a dust shadow (down dip) and some will see reflected light (up blip). From https://iopscience.iop.org/article/10.3847/PSJ/ac4586.

In a two new studies, my research group used data from Mars 2020 to look for passing dust devils and spotted almost 1000 encounters over the missions first 178 days. We confirmed previous weather predictions that Mars 2020 would see more than other recent missions, including InSight and Curiosity. We also found out that there were lots of whirlwinds that passed by Mars 2020 that actually didn’t raise any dust — only about a quarter of whirlwinds showed any signs of dust-lifting.

These kinds of studies are important for understanding the martian dust cycle and the contribution from dust devils. Scientists know Mars’ dust cycle strongly affects climate, and increases in atmospheric dust increase the rate of water loss into space. Martian dust may even be toxic, so dust devils could pose a big hazard for humans on Mars.

Research Publications

  • Jackson, B. (2022) “Estimating the Heights of Martian Vortices from Mars 2020 MEDA Data.” in review with Planetary Science Journal.
  • Jackson, B. (2022) “Vortices and Dust Devils as Observed by the Mars Environmental Dynamics Analyzer Instruments on Board the Mars 2020 Perseverance Rover.” Planetary Science Journal.

Jackson’s AAS Science Presentation

NASA has sent missions to Mars since the mid-60s, but Mars’ interior has remained hidden from view. The InSight mission has begun to lift the veil to reveal a world with active quakes, shedding light on Mars’ ancient history, but the grand successes have also come with frustrating failures.

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The presentation will be live-streamed on this website from YouTube on Friday, starting at 7:30p. Participants will be able to ask questions via YouTube’s chat feature. Stay tuned.

Boise State Physics – First Friday Astronomy Event – Friday, Apr 3rd
“Rivers Across the Solar System”
Prof. Devon Burr, Astronomy & Planetary Sciences, Northern Arizona University
Online lecture begins 7:30pm – http://www.astrojack.com/ffa-rivers
Donate at http://give.boisestate.edu/astronomy

There were lots of great things about the movie “The Martian” (and a few inaccurate things), but one of the best things, for aeolian scientists like myself anyway, was the depiction of ubiquitous, enormous dust devils.

Mark Watney survery the desolate martian landscape.

Mars loves to make dust devils. It’s relatively easy for sunlight to heat the atmosphere and get it churning, and thick dust deposits blanket enormous regions on Mars.

A map of dust deposits on Mars. From https://sci.esa.int/web/mars-express/-/51861-mars-dust-map.

Dust devils on Mars help keep the atmosphere dusty, which warms the climate and helps drive weather. However, as surprising as it might be, we don’t totally understand how dust devils actually lift dust.

Sure it’s true that dust devils are windy, but when you actually plug the windspeeds measured in dust devils into the dust-lifting equations, the amount of dust they *should* lift can be much less than what they *do* lift. So some other mechanism besides just wind must help lift dust in devils.

A dust devil on Mars. From https://en.wikipedia.org/wiki/Dust_devil.

One possibility is that dust devils act like vacuum cleaners and actually suck dust up off the martian surface. See, a lot of the dust sitting on the surface of Mars has been sitting there for a long time, not moving. As a result, the dusty surface can become vacuum-packed, trapping some gas in between the dust grains.

The vacuum cleaner effect illustrated. The sub-surface pressure p2 is greater than the pressure at the center of the dust devil p1. From Bila et al. (2020).

At the center of a dust devil is a small dip in the atmospheric pressure (created by the convecting air inside the dust devil). So when a dust devil skitters over the hermetically sealed dust surface, the trapped gas pressure can launch the dust into the air, where the devil can pick it up.

But this vacuum cleaner effect is still just a hypothesis, so to test this idea, the Experimental Astrophysics group at University of Duisburg-Essen, experts in astrophysical dust experiments, set up a test chamber to mimic the martian surface under a low-pressure (1% of Earth’s) martian atmosphere.

The experimental set-up. The dust dispenser poured dust particles onto a fine mesh membrane, with ambient pressure p1 on one side, and higher pressure p2 on the other. From Bila et al. (2020).

They created a thin layer of small dust grains on a membrane, with a pressure differential across the membrane, to see if a small pressure differential could really lift the dust grains up. The answer is yes!

Dust grains of different sizes lofted by a pressure differential.

Now whether this experiment accurately replicates conditions on Mars is not totally clear, but some of the measurements made by the soon-to-be-launched and recently named Mars 2020 rover Perseverance may help to test the idea.

In addition to collecting geological samples for later return to Earth, Perseverance will collect high-resolution imagery of dust and mineral grains on the surface of Mars. It will also continuously measure meteorological conditions, which we know from past missions can reveal the presence of dust devils. So in addition to telling us about the possibility of past life on Mars, Perseverance may also help us test whether there are dust devil vacuum cleaners on Mars.

Naming the Mars 2020 rover. From https://www.youtube.com/watch?v=Muj4s7BCiMI.

Map of Mars’ south polar ice. The colors show how thick the ice is, and the black rectangle shows the location of the newly discovered sub-surface lake. From Orosei et al. (2018).

As summer winds down and we prepare for the fall semester, I finally found the time to read the recent announcement about finding sub-surface water on Mars using the MARSIS radar onboard Mars Express.

Although evidence for liquid water on Mars has been reported for a long time, these reports are almost always about ancient flows or very modest, salty trickles (and the presence of water often turns out to be illusory). By contrast, if this most recent report holds up to scrutiny, there could be 10 billion liters of liquid water under the martian south pole.

That’s not much on the scale of the Great Lakes (the smallest one, Lake Erie, contains 10,000 times more water), but it’s more than a thousand times the volume of tanks at the Georgia Aquarium, which hosts more than 100,000 aquatic animals. So the martian lake could easily host a microbial zoo (although no direct evidence for that as of now).

As is common in polar regions on Earth, the martian water lies under kilometers of polar ice and is probably so cold it requires some kind of geological anti-freeze to keep from freezing solid (the kinds of mineral salts that can do the job are actually pretty common on Mars). The overburden pressure from all the ice also helps keep the water liquid.

But the fact that the lake sits underneath so much ice raises an obvious question: how did the scientists spot it in the first place? The answer is related to why the recent wildfires in the west, in addition to fouling the air, have given us very lovely sunsets.

Preferential scattering of blue light by the atmosphere.

When it first leaves the surface of the Sun, sunlight is colored white. But as it passes through the atmosphere, the light (which is a wave of electric and magnetic fields, after all) interacts electromagnetically with the atmospheric gas molecules, which themselves contain electric charges.

The closer the wavelength of the light ray is to the sizes of the molecules, the stronger this electromagnetic interaction and the more the ray can be diverted from its straight path.

Since blue light has a wavelength (500 nanometers) closer to the size of the atmospheric molecules than red light (700 nanometers, it is more readily diverted or scattered. At dusk, as the sun sets, its light has to pass through more and more of the Earth’s atmosphere. So more and more blue light is scattered away, leaving behind more red light and making the Sun look red. If you sprinkle in lots of smoke from a wildfire, you can enhance the coloration.

What does all this have to do with martian lakes? The MARSIS instrument used to find the subsurface lake uses very red radar light, with wavelengths tens to hundreds of meters long. Similar to red sunlight, such long wavelengths can easily pass through even solid rock since they’re much larger than the rocky molecules that make up the martian surface.

Reflectivity of radar light from beneath the martian south pole. The bright patch at the bottom marked with “Basal reflection” is from the sub-surface lake. From Orosei et al. (2018).

This explanation simplifies things a lot, but the upshot is that MARSIS could see the lake as a very unusual bright patch underneath all that polar ice.

What’s next? It’s possible that continued data collection and analysis will turn up other subsurface lakes on Mars. If Mars’ south pole is brimming over with these icy lakes, it could be an especially good habitat for martian microbes. So maybe the effort to find martian life should explore using the same ice drilling technology being considered for exploring the oceans of Jupiter’s moon Europa.

I’m sitting in the hotel lobby at the Woodlands Marriott, waiting for my supershuttle to IAH and recouperating from my second Lunar and Planetary Sciences Conference, LPSC. Before I’m whisked away back to Boise, I thought to write about a few of the fascinating and mind-blowing things I saw this week.

First of all, LPSC is an annual conference that focuses on the geology, geochemistry, and geophysics of planetary science. There’s a lot of focus on solar system bodies with solid surfaces, as opposed to the annual DPS meeting, which has a bit broader focus.

I arrived on Sunday evening and dove immediately in, helping with the First-Timers’ presentation review, an opportunity for new-comers to the meeting to have more senior folks provide feedback on their posters or oral presentations.

Monday dawned cloudy, and I sat through several talks about our sister planet Mars. One that stuck out for me was one about field experiments to explain the perennially mysterious gully formations found on martian slopes with sleds of dry ice.

Tuesday saw me in a session on Saturn’s moon Titan, a cornucopia of geology and atmospheric physics. One particularly impressive talk discussed work to understand how methane deluges on Titan modified the surface.

Tuesday evening, I presented our group’s work flying drones through active dust devils.

Wednesday was packed with talks on sediment transport experiments and analyses, attempting to decipher the martian aeolian cycle, including a neat study of time-lapse imagery of martian dunes.

Thursday was packed with Pluto and results from New Horizons. One talk that stuck in my mind was an analysis of landslides on Pluto’s moon Charon, which, frankly, was a little bit of a tear-jerker. Hard to believe that not one hundred years ago, we didn’t even know Pluto existed. Now we’re trying to understand the system’s geology.

Friday morning wrapped up the meeting with a series of talks about glacial geology on Mars, including a fabulous presentation on mysterious geomorphic features on Mars. Even though these features look for all the world like glacial flow, they appear on totally flat ground, where flow shouldn’t be possible.

And now to catch the shuttle.