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

Politics

The Democrats’ War at Home

How can the president’s party defend itself from the president’s foreign policy blunders?

Congress’ Public Shaming of the Secret Service Was Political Grandstanding at Its Best

Michigan’s Tradition of Football “Toughness” Needs to Go—Starting With Coach Hoke

A Plentiful, Renewable Resource That America Keeps Overlooking

Animal manure.

Windows 8 Was So Bad That Microsoft Will Skip Straight to Windows 10

Politics

Cringing. Ducking. Mumbling.

How GOP candidates react whenever someone brings up reproductive rights or gay marriage.

Building a Better Workplace

You Deserve a Pre-cation

The smartest job perk you’ve never heard of.

Hasbro Is Cracking Down on Scrabble Players Who Turn Its Official Word List Into Popular Apps

Florida State’s New President Is Underqualified and Mistrusted. He Just Might Save the University.

  News & Politics
Politics
Sept. 30 2014 9:33 PM Political Theater With a Purpose Darrell Issa’s public shaming of the head of the Secret Service was congressional grandstanding at its best.
  Business
Moneybox
Sept. 30 2014 7:02 PM At Long Last, eBay Sets PayPal Free
  Life
Gaming
Sept. 30 2014 7:35 PM Who Owns Scrabble’s Word List? Hasbro says the list of playable words belongs to the company. Players beg to differ.
  Double X
The XX Factor
Sept. 30 2014 12:34 PM Parents, Get Your Teenage Daughters the IUD
  Slate Plus
Behind the Scenes
Sept. 30 2014 3:21 PM Meet Jordan Weissmann Five questions with Slate’s senior business and economics correspondent.
  Arts
Brow Beat
Sept. 30 2014 8:54 PM Bette Davis Talks Gender Roles in a Delightful, Animated Interview From 1963
  Technology
Future Tense
Sept. 30 2014 7:00 PM There’s Going to Be a Live-Action Tetris Movie for Some Reason
  Health & Science
Medical Examiner
Sept. 30 2014 11:51 PM Should You Freeze Your Eggs? An egg freezing party is not a great place to find answers to this or other questions.
  Sports
Sports Nut
Sept. 30 2014 5:54 PM Goodbye, Tough Guy It’s time for Michigan to fire its toughness-obsessed coach, Brady Hoke.