The Curiosity rover broke scientific ground in February 2013 when one of its instruments drilled into a rock and sent back images of gray rock powder. It was the first time a rover had sampled the interior of a rock from another planet.
Attention will remain focused on Mars in the coming months as Curiosity makes its way toward Mount Sharp, a large sediment pile in the center of Gale Crater. But to understand why Curiosity was sent to Gale Crater and Mount Sharp, you need to look at Earth and Cuatro Ciénegas Basin, a gypsum-rich area of northern Mexico’s Chihuahua Desert.
Gypsum is a mineral that, on Earth, forms when sulfate- and calcium-rich salt water evaporates. One of the key reasons Curiosity is working in Gale Crater is that scientists suspect the sediment mound at its center contains gypsum—the product of an ancient lake when Mars was a much warmer, wetter place. In 2005, the OMEGA instrument on ESA’s Mars Express orbiter detected gypsum at several locations on Mars, evidence suggesting that liquid water used to be much more common on the Red Planet. And in 2013, Curiosity bolstered the case by finding what appeared to be a series of gypsum veins in a part of Gale Crater known as Yellowknife Bay.
Trace amounts of gypsum are fairly common on Earth, but since the mineral dissolves readily in water, just a handful of locations have gypsum in large quantities. The Cuatro Ciénegas Basin, home to some of the purest gypsum dune fields in the world, is one of them. The Advanced Land Imager (ALI) on Earth Observing-1 (EO-1) acquired this view of Cuatro Ciénegas Basin on January 18, 2013.
Individual dunes are not visible at this resolution, but the gypsum dunes are concentrated just west of the Sierra San Marcos highlands within the bright white playa area of the image. Hundreds of springs and pools, many welling up mineral-rich waters from deep below the surface, flank the highlands to the north and east.
While vegetation is primarily cactus and yucca throughout much of the basin, the spring-fed wetlands are lush with mesquite trees and creosote bushes that paint the surface dark brown. In addition to the vegetation, the springs support an unusually broad range of microbial and animal life, much of which has adapted to the basin and exists nowhere else in the world.
The blue pool in the upper right is an artificial lake used for swimming. It is one of a number of water-intensive activities that are drawing ever-larger quantities of groundwater from the area and threatening the unique ecosystems within and around the springs.
The springs of Cuatro Ciénegas are interesting to astrobiologists because they are home to colonies of blue-green algae similar to some of the oldest forms of life on Earth. Colonies of the bacteria—which thrive in the sulfate-rich environments that promote gypsum formation—create distinctive reef-like structures called stromatolites. If scientists find evidence of life on Mars, they think will be something similar to the bio-signatures present in the stromatolites of Cuatro Ciénegas Basin.
“Between the gypsum and the stromatolites, Cuatro Ciénegas is simply one of the best analogs we have for what Mars might have been like earlier in its history,” said Valerie Souza, a scientist at the National Autonomous University of Mexico. “Going there is bit like stepping into a time machine.”
NASA Earth Observatory image by Jesse Allen and Robert Simmon, using EO-1 ALI data provided courtesy of the NASA EO-1 team and the U.S. Geological Survey. Caption by Adam Voiland with information from Valerie Souza and Jan Siefert.
Along Tunisia’s southeastern coast is a flat plain of about 150 square kilometers (58 square miles) that lies below sea level. Known as Sebkhat El Melah (or Sebkha El Melah), it is in an evaporite basin.
The Uvs Nuur Basin sits on the northern edge of the Central Asian steppes, bounded on all sides by mountains. Though largely arid, the basin is dotted with water. A large salt lake, the Uvs Nuur Lake, sits at the center of the basin, and several smaller lakes are scattered across the 600 kilometers east to west and 120 kilometers north to south that make up the basin.