Mars today is a chilly desert. But ancient landscapes reveal a time when water may have flowed freely. Scroll to see how the red planet has evolved.
If Mars explorers could literally step back 3.8 billion years, they would be walking on a warmer, gray world. The iron-rich soil had not yet rusted, and the planet was blanketed in a thicker atmosphere. Geologic clues suggest that Mars back then was covered with crater lakes, river valleys, and maybe even a large ocean in the northern hemisphere.
Other evidence suggests that the planet was a glacial realm 3.8 billion years ago, with ice stretching from its poles and most liquid water trapped underground. Seasonal changes coupled with volcanic and geothermal activity could have caused sections of ice to melt periodically, but Mars overall was only a little warmer and wetter than it is today.
By about 3.5 billion years ago, oxygen in the atmosphere had reacted with the soil to give Mars its familiar ruddy hue. Volcanoes were also bursting with activity, and massive eruptions likely ejected tons of gases into the atmosphere. Gushing magma melted some reserves of ice, triggering catastrophic flooding.
A Waterlogged Crater
Some of our best evidence for water flows on early Mars comes from Gale Crater, a 96-mile-wide impact basin near the planet’s equator. The crater displays hydrated minerals, alluvial fans, remnants of lakes, and other features that paint a vivid picture of a wetter past about 3.5 billion years ago.
Today’s Dusty Basin
In August 2012, the Curiosity rover landed in Gale Crater, and it quickly found signs that the basin went through multiple episodes of wet conditions over millions of years. In one region, rounded rocks embedded in conglomerate rock tell of streams tumbling across the crater floor, while minerals in lakebed sediments suggest the water here would have been drinkable.
The Nili Fossae region lies just above the giant Isidis impact basin. Its curved troughs probably formed in the wake of that impact and exposed some of the planet’s most ancient materials, dating back 3.8 billion years. Valley networks crisscross the surface, while layers inside the troughs show that Mars had long-lived regional aquifers.
Modern Mineral Bonanza
Modern Nili Fossae showcases a dramatic, diverse landscape, enticing scientists with its layered cliff faces and chunks of ancient material tossed up by impacts. The rocks also hold olivine, a volcanic mineral that, when broken down by water, may have been useful to primordial life.
A Widening Gap
About 3.6 billion years ago, a giant crack started forming on Mars, and it quickly grew into a vast canyon system about 2,500 miles long, up to four miles deep, and at points more than 18 miles wide. While nearby volcanism probably did most of the work opening this rocky gash, the region also shows signs that it was shaped by groundwater seeps, isolated lakes, and intense flooding about three billion years ago.
Today’s Grandest Canyon
The extensive canyon system likely stopped growing around two billion years ago. As with the Grand Canyon on Earth, the well-preserved layers in the Valles Marineris walls could tell scientists even more about the geologic processes that have shaped Mars throughout its history.
An Enticing Orb
Global dust storms, landslides, and even “marsquakes” continue to sculpt the red planet’s surface. Since 1976, waves of landers and rovers have been exploring this alien terrain, gathering clues about the Martian past while setting the stage for future missions. And when the first people arrive on Mars, they will push human ingenuity further than ever before as they make this cold red world their new home.
Brian T. Jacobs, Matthew W. Chwastyk, Victoria Jaggard, Jason Treat, NG Staff. Art: Dana Berry. Sources: Bethany Ehlmann, California Institute of Technology; Caleb Fassett, NASA Marshall Space Flight Center; Tim Goudge, The University of Texas at Austin; Robin Wordsworth, Harvard University