The artwork of the Martian landscape

The entire universe in blog form
Oct. 15 2009 11:28 AM

The artwork of the Martian landscape

It's been a while since I've sung the praises of the Mars Reconnaissance Orbiter's HiRISE camera, which takes incredibly hi-res images of the surface of Mars. Thanks to the HiRISE Twitter feed, I found this incredible picture:


Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

Advertisement

Can I get a Holy Haleakala! from the congregation?

Wow. I mean seriously, wow. You really really want to go look at the embiggened version. What you're seeing here are sand dunes on Mars. This region is in the center of a large crater at mid-north latitude on Mars, a couple of hours past local noon, and with a resolution of 50 cm (18 inches) per pixel. Sand dunes are common in crater beds, where the wind can blow steadily across the surface and sculpt the ever-present sand into those flowing sculptures.

But what this picture so spectacular are the graceful blue-gray swirls arcing across the dunes. These are caused by dust devils, which are a bit like mini-tornadoes. If the ground gets heated, rising air can punch through cooler air above it. This starts up a convection cell, with warm air rising and cool air sinking. If there is a horizontal wind the cell can start spinning, creating a vortex like a dust devil. I've seen hundreds of these on Earth, and they are wonderful and mesmerizing to watch.

The important thing to note here is that the sand in the craters of Mars is actually dark grey in color, since it's made of basalt. The reason it looks red in pictures is because covering the sand is a thin layer of much finer dust, and the dust is what's red. When a dust devil moves over the Martian surface, it can pick up the very light dust particles, but not the heavier sand grains. So those blue-grey swirls are tracks where the dust devil has vacuumed up the dust, revealing the darker sand underneath. If you look carefully in the tracks, you can see the sand dune ripples are undisturbed. Only the dust is gone.

There's more to see in the picture as well. There is a sloping dune peak cutting across from top left to lower right (it's more obvious in the larger context view of this region), and again more dark streaks, linear this time, probably caused by sand sliding down the dune face. When the sand moves, the dust covering it gets disturbed and once again you see the darker color of the sand itself. I also love the way the dune shapes change depending on where they are in the picture, caused by differences in the wind patterns across the floor of the crater.

When I look at pictures like this, I am smacked in the face with the cold, hard fact that Mars is a world. It's not just a dot in the sky, it's not just a set in a movie, it's not just pictures from a space probe. It's a planet, a vast complex system of interacting environments which produces climates, landscapes, vistas, weather.

And man oh man, does it produce beauty, awe, and wonder. Wow.

My thanks to Dr. Alfred McEwen of HiRISE for taking the time to explain to me the difference in color between the dust and the sand, and how that affects this image.

TODAY IN SLATE

Foreigners

The World’s Politest Protesters

The Occupy Central demonstrators are courteous. That’s actually what makes them so dangerous.

The Religious Right Is Not Happy With Republicans  

The XX Factor
Oct. 1 2014 4:58 PM The Religious Right Is Not Happy With Republicans  

The One Fact About Ebola That Should Calm You: It Spreads Slowly

The Feds Have Declared War on New Privacy Measures From Apple and Google

These “Dark” Lego Masterpieces Are Delightful and Evocative

Crime

Operation Backbone

How White Boy Rick, a legendary Detroit cocaine dealer, helped the FBI uncover brazen police corruption.

Politics

Talking White

Black people’s disdain for “proper English” and academic achievement is a myth.

Europe’s Next Digital Commissioner Thinks Keeping Nude Celebrity Photos in the Cloud Is “Stupid”

Piper Kerman on Why She Dressed Like a Hitchcock Heroine for Her Prison Sentencing

  News & Politics
Politics
Oct. 1 2014 7:26 PM Talking White Black people’s disdain for “proper English” and academic achievement is a myth.
  Business
Moneybox
Oct. 1 2014 2:16 PM Wall Street Tackles Chat Services, Shies Away From Diversity Issues 
  Life
Outward
Oct. 1 2014 6:02 PM Facebook Relaxes Its “Real Name” Policy; Drag Queens Celebrate
  Double X
The XX Factor
Oct. 1 2014 5:11 PM Celebrity Feminist Identification Has Reached Peak Meaninglessness
  Slate Plus
Behind the Scenes
Oct. 1 2014 3:24 PM Revelry (and Business) at Mohonk Photos and highlights from Slate’s annual retreat.
  Arts
Brow Beat
Oct. 1 2014 6:39 PM Spoiler Special: Transparent
  Technology
Future Tense
Oct. 1 2014 6:59 PM EU’s Next Digital Commissioner Thinks Keeping Nude Celeb Photos in the Cloud Is “Stupid”
  Health & Science
Science
Oct. 1 2014 4:03 PM Does the Earth Really Have a “Hum”? Yes, but probably not the one you’re thinking.
  Sports
Sports Nut
Oct. 1 2014 5:19 PM Bunt-a-Palooza! How bad was the Kansas City Royals’ bunt-all-the-time strategy in the American League wild-card game?