New Gullies Found on Mars That Are Less Than a Year Old

The entire universe in blog form
March 29 2013 8:00 AM

New Gullies Found in a Young(ish) Crater on Mars

My first two science loves are, in order, astronomy and geology. If you combine the two your options are limited. You can observe the Earth from space, you can collect meteorites, or you can soak in the beauty of landscapes on other worlds provided by spacecraft.

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!  

I have a deep affection for all three, and which one I like best depends on when you catch me. For example, today, I’m fond of that last one, due to this gorgeous picture taken of ridges and gullies on Mars:

gullies on Mars
Gullies run down the rim of a crater on Mars, as seen here in an image by the HiRISE camera in orbit around the red planet. Click to enaresenate.

Image Credit: NASA/JPL/University of Arizona

Advertisement

This shot shows some of the terrain (or aresain or whatever term you use for Mars) inside Gasa crater, a 7 kilometer (4 mile) wide crater in the southern mid-latitude of the red planet. Weirdly, Gasa sits inside a larger 20-km-wide crater; whatever impact formed it happened in the same place as a larger impact a long time before. Gasa is young, probably less than two million years old.

The edge of Gasa is heavily scalloped, clearly caused by the rim eroding away. There’s a lot of carbon dioxide ice in this location, much of it beneath the surface. Every summer the ground warms up, the ice sublimates (turns directly into a gas) and some of the crater rim collapses inward.

Over time this forms gullies, erosional channels. They’re not terribly hard to find in some craters, since they look like, well, gullies: nearly straight channels in the crater wall dug out by material flowing downhill. There are fan-shaped regions surrounding them, and in the top image, which has been color enhanced, the fans are bluish, showing fresh deposits of carbon dioxide.

How fresh? This picture was taken in the austral spring of Mars, and those deposits weren’t there the year before! So the CO2 ice was laid down last winter in the Martian southern hemisphere, just months ago.

Mars is not a dead planet, at least not geologically. It changes year by year, even month by month.

Here’s a close-up, taken from the full-res image:

close up of the crater rim
Close-up of the crater rim showing the gullies better.

Image Credit: NASA/JPL/University of Arizona

You can see how sharp the ridges are. The Sun is shining down from the upper left, and the tops of the ridges look like a knife’s edge. You can also see boulders dotting the landscape as well, casting long shadows. That’s convenient, since the size of the boulders can be directly measured, and the angle of sunlight is known. That means the slope of the ridges can be determined, too. It’s amazing what you can squeeze out of an image like this.

It gets better, too. Here is a wider shot, showing more of the crater rim:

wide view of Gasa crater on Mars
A wider view of the Gasa crater showing more of the rim. Click to impactenate.

Image Credit: NASA/JPL/University of Arizona

See how the scalloped region with gullies is on the right? That’s the northern rim of the crater. Now think this through: In the southern hemisphere summer, when it’s warmer, the Sun will be shining more directly into the northern rim of the crater (just like having southern exposure in a house in the northern hemisphere on Earth gets you more sunlight). That’s why there’s more erosion there on the northern rim; the ground gets warmer and frees more carbon dioxide. As you look around the crater rim in both directions (east and west, heading south) the scalloping gets weaker, because the ground doesn’t get as much direct sunlight, and so is somewhat cooler.

That’s evidence of seasonal variation in the erosion, just like you’d see on Earth!

Mars is such an odd place. Thick gray basaltic sand is everywhere, covered itself by fine dust (tinged red due to iron oxide: rust). Cratered, battered, barely holding an atmosphere, yet it still has ways of reminding us of home. Comparative planetology is a fascinating field.

Huh. I may have to make that Number 3 on my list.

TODAY IN SLATE

Foreigners

More Than Scottish Pride

Scotland’s referendum isn’t about nationalism. It’s about a system that failed, and a new generation looking to take a chance on itself. 

What Charles Barkley Gets Wrong About Corporal Punishment and Black Culture

Why Greenland’s “Dark Snow” Should Worry You

Three Talented Actresses in Three Terrible New Shows

Why Do Some People See the Virgin Mary in Grilled Cheese?

The science that explains the human need to find meaning in coincidences.

Jurisprudence

Happy Constitution Day!

Too bad it’s almost certainly unconstitutional.

Is It Worth Paying Full Price for the iPhone 6 to Keep Your Unlimited Data Plan? We Crunch the Numbers.

What to Do if You Literally Get a Bug in Your Ear

  News & Politics
Weigel
Sept. 16 2014 7:03 PM Kansas Secretary of State Loses Battle to Protect Senator From Tough Race
  Business
Moneybox
Sept. 16 2014 2:35 PM Germany’s Nationwide Ban on Uber Lasted All of Two Weeks
  Life
The Vault
Sept. 16 2014 12:15 PM “Human Life Is Frightfully Cheap”: A 1900 Petition to Make Lynching a Federal Offense
  Double X
The XX Factor
Sept. 15 2014 3:31 PM My Year As an Abortion Doula
  Slate Plus
Slate Plus Video
Sept. 16 2014 2:06 PM A Farewell From Emily Bazelon The former senior editor talks about her very first Slate pitch and says goodbye to the magazine.
  Arts
Brow Beat
Sept. 16 2014 8:43 PM This 17-Minute Tribute to David Fincher Is the Perfect Preparation for Gone Girl
  Technology
Future Tense
Sept. 16 2014 6:40 PM This iPhone 6 Feature Will Change Weather Forecasting
  Health & Science
Science
Sept. 16 2014 1:39 PM The Case of the Missing Cerebellum How did a Chinese woman live 24 years missing part of her brain?
  Sports
Sports Nut
Sept. 15 2014 8:41 PM You’re Cut, Adrian Peterson Why fantasy football owners should release the Minnesota Vikings star.