The Mars Global Digital Dune Database
Published 5/30/2018 in Lori Fenton's Blog Author lfenton
There are a lot of dune fields on Mars. Over the last ten years I've been part of a group that's mapped out the big dark dunes on the planet to see where they form, and to understand the sedimentary and meteorological processes that control their formation. We compiled a database showing their locations and various physical characteristics. Wait, why do piles of sand form in the first place? On Earth, it's because: 1. There's a lot of sand (not a surprise). 2. There's a lot of strong wind (also not a surprise). 3. The sand is free to be moved by the wind. That is, it's not held down by vegetation, or covered by a lake, or paved over. That mostly amounts to dune fields piling up in arid places, where there's not a lot of vegetation or rainfall to stop the wind from moving sand around. And even then, you don't see piles... read more ❯

Published 5/9/2018 in Lori Fenton's Blog Author lfenton
Here's a grand dune, making its stately way northward under winds blowing mainly from the south-southeast (bottom to top), with a secondary wind blowing from the southwest (lower left to upper right). There are two rippled and sharp-crested slip faces on this dune -- can you identify both of them (hint: each wind creates one slip face on the downwind side)?   The dune is ~750 m (2,460 ft) long. It's made of dark sand the wind blows along the ground until it piles up into these big mobile hills we call dunes. But the dune isn't alone. Trailing behind the dune, like a veil, is an entourage of smaller, paler ripples. These are coarse-grained ripples, made partly of larger grains that are too heavy to move as quickly as the finer dark sand that makes up the bulk... read more ❯

Wild & dark lacy dunes on twisty bright layers
Published 4/30/2018 in Lori Fenton's Blog Author lfenton
Some windblown dunes on Mars are just beyond words. Take these beasts in this 0.95x0.95 km (0.59x0.59 mi) scene: These are a peculiar type of bedform called a transverse aeolian ridge, or TAR for short, with a spacing of about 50 m (164 ft). Nobody really understands these things: are they dunes or ripples or something totally different? They're common on Mars but unusual (maybe even nonexistent) on Earth. They're also pretty dark-toned here, whereas on most of Mars they tend to be lighter than the surrounding rocks. The TARs mostly cover the surface, but you can see bright bits poking through in places. You can see layers sweeping around - this is a place where stuff (either sediment or volcanic rock) was deposited in successive layers. It may then have been tilted or deformed, and then it was eroded away to expose the... read more ❯

Reusing old canvases
Published 4/23/2018 in Lori Fenton's Blog Author lfenton
The wind on Mars is an artist, or at least it tries really hard to be one. It flutters up and down mountains, winding along valleys, dragging its wings in the sand and building up really amazing structures that could win any sand sculpture award. Well okay maybe I'm a little biased. Like this 0.92x1.325 km (0.57x0.82 mi) view (click to see the detail, it's worth it): HiRISE ESP_054171_1605, NASA/JPL/Univ. of Arizona A while back (maybe a million years or so), the wind blew sediment from the lower right to upper left, leaving behind some long, thin ripple-like things we call TARs. It even managed to pile up some little ones on the hilltops, which is pretty wild. But the wind kept blowing, pushing the TARs downwind towards the left. At some point, the area ran out of new sand to pile up into new TARs (the loose stuff exited stage right),... read more ❯

An Update on the Potential Habitability of TRAPPIST-1. No Aliens yet, but We’ve Learned a lot.
Published 4/20/2018 in Franck Marchis Blog Author Franck Marchis
One year ago, I wrote an article about the remarkable discovery of the TRAPPIST-1 planetary system, a system of seven temperate terrestrial planets orbiting an ultra-cool red dwarf star. This was an enormous astronomical discovery because these low-mass stars are the most numerous ones in our galaxy, and the discovery of potentially habitable planets around one of them led many people to speculate about the existence of life there and elsewhere in our galaxy around similar stars. This announcement also inspired a lot of additional studies by astronomers worldwide, who have used additional instruments and run complex models to better understand this planetary system and its potential for hosting life. One year later, it seems to me that the time is right to give you an update on what we’ve learned about this planetary system, which is located only 41 light-years from Earth. Better Understanding of the Planetary System Between December 2016 and March... read more ❯

Squish! ????
Published 4/20/2018 in Lori Fenton's Blog Author lfenton
This isn't a full blog post. Just something I saw while looking around for other things on Mars. And for once it's (probably) not related to the wind. But it's cool enough to share. I saw something that went "squish" ???? . This is a ~1.2 km (0.75 mi) wide crater in the northern mid-latitudes of Mars. I don't know much about this region geologically (haven't done my homework, as this is just a quick look). This crater has a set of layers in it that have partially eroded away. And underneath those layers on the crater floor are what look like the remnants of something that got 'sploded from underneath those layers. Judging from the direction of the 'sploded rays, it came from under that beak-shaped part of the layers. And I can sort of convince myself that maybe the squishing event happened once the layers got to the shape they're in now... read more ❯

Flow. Lots of flow.
Published 4/16/2018 in Lori Fenton's Blog Author lfenton
Over the years, many things have flowed across the surface of Mars: lava, ice, water, and wind. Two things have flowed in this image (the view is 0.75x0.6 km or 0.47x0.37 mi): Image credit: HiRISE ESP_026541_1840, NASA/JPL/Univ. of Arizona If you know my blog at all, then you might recognize the big structures as yardangs. They are part of an enormous set of yardangs on Mars called the Medusa Fossae Formation. At some point in the past, probably a few billion years ago, the wind kicked up a bunch of sand that carved out these structures, blowing from the lower left to the upper right. That's cool. But the thing to notice is the stuff around the yardangs. As the wind carved them out, it also created ripples. It's fairly normal to find ripples, especially coarse-grained ripples, in the troughs between yardangs, because a wind strong enough to carve out bedrock is also strong... read more ❯

My 2018 paper on recent climate change in Meridiani Planum, Mars (Part 3)
Published 4/13/2018 in Lori Fenton's Blog Author lfenton
This is the 3rd (and final) entry in a blog series describing a paper I recently published with colleagues in JGR Planets. Here are links to the previous two entries: Part 1, Part 2. Wow, I didn't think this would take 3 entries. Science is weird. You start a project feeling out of your depth, not knowing exactly where it will take you. You stumble around, read a bunch of papers to absorb the wisdom of others, and work up the courage to do things. You struggle mightily in doing those things: making the model run, keeping access to the computer system, making sure the model output is what you think it is, figuring out what you need to calculate and the best way of doing so. And then a bunch of refining and reworking and throwing out old ideas and trying new things, sometimes based on precious conversations with colleagues... read more ❯

My 2018 Paper on Recent Climate Change in Meridiani Planum, Mars (Part 2)
Published 4/12/2018 in Lori Fenton's Blog Author lfenton
In a previous post, I set the stage for my recently published paper in JGR Planets. A recap: we've got good evidence for a change in Mars's climate. Widespread ripples in Meridiani Planum formed >200,000 years ago, last migrated westward more than ~50,000 years ago, had their crests reformed into little dunes by a slightly different wind sometime after that, but have been dormant ever since. Meanwhile, we know that over that same time period, Mars' orbit and axial tilt have varied, which can affect wind patterns. Moreover, over this period, those same planetary changes led to a stepwise sequestration of atmospheric CO2 into the south polar ice cap, so that we know the air pressure was once higher than it is today. This too can affect wind patterns. All of these parameters can be plugged into a Mars global climate model (MGCM) to see if the model thinks the wind directions... read more ❯

My 2018 paper on recent climate change in Meridiani Planum, Mars (Part 1)
Published 4/11/2018 in Lori Fenton's Blog Author lfenton
Today a big thing happened: a paper I've spent a year or so working on has finally been published in the Journal of Geophysical Research: Planets (which we just call "JGR Planets"). Scientists write a lot of papers, so it's not as momentous as, say, graduating (or watching a student graduate), but it's still a really nice feeling. I can now download a PDF of the paper, look at all the pretty formatting, lovely figures and tables, pages of analysis and what I hope will turn out to be insightful discussion, and say "Yeah, I did that, and with some great colleagues. It's awesome". I'm going to try to explain what we did. If you can access the paper itself, you'll see that JGR now includes a "Plain Language Summary", the journal's attempt to reach a wider audience. It's not a bad idea in this era of ever-deepening specialization, so that... read more ❯

Wind-exposed layers
Published 3/26/2018 in Lori Fenton's Blog Author lfenton
On Earth, layers comprising the geological record of an area are most often exposed by fluvial erosion, as a river cuts through rock (a typical example is the Grand Canyon). On Mars, fluvial channels are not so common (especially in the past few billion years). But the wind has relentlessly worked away at the surface, sometimes revealing strata laid down long ago. Click on the image for more detail. This is a tiny bit (0.5x0.375 km, or 0.31x0.23 mi) of the side of an "Interior Layered Deposit" in the middle of Candor Chasma, called Juventae Mensa. Wind blowing from the upper left and upper right has eroded the whole area, eroding and exposing a bunch of layers. For some reason a bit of those layers is a little more resistant to erosion, where the wind has left behind a tiered hill (technically it's a sort of yardang). Each step on the... read more ❯

Dune trails deep in Hebes Chasma, Mars
Published 3/19/2018 in Lori Fenton's Blog Author lfenton
A few weeks ago I wrote about dunes leaving behind trails near the north pole of Mars. They do this in a few other places as well, but it's not very common. Below is a rare example, this time on the floor of Hebes Chasma (one of the Valles Marineris), which is a tectonically-opened hole in the ground that's about 6 km deep. I don't mean to repeat the same topic, but geologists are usually drawn to terrain that so plainly lays out the geological story of an area, and obvious dune-generated layers are pretty rare. (Also pretty.) (HiRISE ESP_045586_1585, NASA/JPL/Univ. of Arizona) What's going on? A wind has blown sand from the left to right in this image, forming crescent-shaped "dome" dunes. As they migrate to the right, they've left behind their lowest bits (like a snail's slime trail). That trail is also being eroded away, slowly, which is why it... read more ❯

Athena Coustenis, Professional Status
Published 3/16/2018 in Athena Coustenis Author Athena Coustenis read more ❯

Wind on Mars and the Huygens-Fresnel Principle
Published 3/12/2018 in Lori Fenton's Blog Author lfenton
How about some basic physics? It'll be easy, I promise. Just look at the pretty picture below (click on it to see it better): The big crater is ~400 m (1/4 mile) across. Wind blows sediment from the top to the bottom of the view, making some dune-like features (TARs, really) at the top and inside the crater. The rim at the top of the crater has a set of hills with a dip inbetween them, which allows wind and sediment to be funneled into the crater through a narrow valley. Once inside the crater, the wind expands laterally, so that some of the dune-like features form arcs, like ripples that form after you throw a rock into a pond. This is a demonstration of the Huygens-Fesnel principle: that waves do their best to travel spherically outward in all directions. Most of... read more ❯

AI as a Tool for Planetary Defense: How a Computer Could Help Us Make the Right Decisions When Facing An Asteroid Threat
Published 3/8/2018 in Franck Marchis Blog Author Franck Marchis
Last May, a diverse group of astronomers, space agency executives, government representatives, and theorists who study tsunamis and asteroid impacts met for a week in Tokyo to discuss the state of planetary defense.  This group also included a few members of the NASA’s Frontier Development Lab (FDL), an applied research accelerator, aims to foster collaboration between AI experts  and planetary researchers expressly for the purpose of finding solutions to NASA global challenges, including Planetary Defense. The conference took place at Japan’s Miraikan (literally, “Future Museum”), which seemed highly appropriate given that our topic was the threat posed by asteroids and comets, and the actions we might take to address it. After listening to talks by several experts, attendees began a role-playing game which simulated the threat of a ~200m asteroid that might—or might not—strike Earth in ten years. Over the course of a week, we took on the role of government... read more ❯

"Baby" dunes on Mars are big
Published 3/5/2018 in Lori Fenton's Blog Author lfenton
Baby dunes on Mars are pretty big compared to those on Earth. In this 885x512 m (0.55x0.32 mi) frame, there are four dunes of roughly the same size, all of which are about as small as dunes can get on Mars. They're ~180 m (590 ft) across, several times bigger than similar "elementary" dunes on Earth. There's another key difference between Earth and Mars dunes. The avalanching lee slope (the slip face) comes to a point in these dunes. That's because there are two winds forming these dunes, one from the upper right and one from the upper left. On Earth, as winds alternate, they erode the older slip face and create a new one directly downwind, so you wouldn't typically see two crisp slip faces meeting at a point, like they do here. There's something about sand or the movement of sand on Mars that makes slip face creation faster... read more ❯

Dune trails
Published 3/1/2018 in Lori Fenton's Blog Author lfenton
There's so much going on in this 0.75x0.75 km (0.47x0.47 mi) image. You're looking at a broad dune migrating toward the upper right. It's early summer, but this is close enough to the north pole that some winter ice lingers (pale blueish white), amid slumps that have shed down from the dune. The slumps probably form as ice weighs down the dune sand -- they are not seen on dunes at lower latitudes, where ice is less common. The upwind side of the dune is interesting as well. The dark dune slowly migrates forward, leaving behind bits of itself (sort of like how a snail leave a trail of slime). Those left-behind bits have somehow formed into a bright surface -- I'm not sure why it's bright, but it is being slowly being broken into a polygonal shapes and eroded by wind scour, both of which are processes that are common... read more ❯

Ius Chasma dunes: they move
Published 2/20/2018 in Lori Fenton's Blog Author lfenton
Many dunes on Mars are actively migrating, like these dunes (view is 0.4x0.5 km, 0.25x0.31 mi). These are found deep in Ius Chasma, one of the Valles Marineris. These dunes slowly migrate toward the right, pushed by winds blowing from the lower and upper left.       Comparing this recent image with the first HiRISE image taken ~10.5 years ago (that's ~4.4 Mars years) shows development of a crest linking these two dunes, indicating the wind from the upper left has been most active over the last few years. Click on the grayscale image to the left to see an animation of this change. If you want to learn more about Valles Marineris dunes, you can read about them in this paper by Chojnacki et al. (2014). (HiRISE ESP_053595_1725, NASA/JPL/Univ. of Arizona) read more ❯