Earth Imaging Journal: Remote Sensing, Satellite Images, Satellite Imagery
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May 15, 2017
New USGS Maps of Mars Reveal Ancient Oases

A new set of high-resolution geologic maps reveal complex geologic processes that suggest a dynamic, wet environment once existed on early Mars, according to the U.S. Geological Survey.

“The major finding of this work is that the layers of rock exposed within what is called western Candor Chasma record a past environment where groundwater was abundant and occasionally seeped onto the ground surface, forming pools,” said USGS scientist Dr. Chris Okubo, lead author of the maps. “These pools would have been habitable for life, just as they are on Earth. Dust and sand blown into these pools may have buried and preserved evidence of past Martian life, which would be present as fossils within the rocks that we see today.”

These maps show that the western Candor Chasma region is an important location for future human and robotic exploration of Mars’ astrobiologic resources. The areas analyzed are in the northern, central, and southern portions of the western Candor Chasma, which is one of the largest branches of the continent-sized Valles Marineris canyon system. The results of the USGS mapping effort reveal possible distributions of past habitable sites and areas that have the potential to accumulate markers of any organisms that might have lived in them.

“This provides very specific new targets for continued scientific investigation,” said Okubo.

Flyover of the southeast Ceti Mensa map. Distinct groups of rock layers, called geologic units, are shaded in different colors, with dark browns representing the oldest rocks and green representing the youngest rocks. All of these rocks formed as wind-blown sand that became trapped in shallow, ephemeral lakes, similar to the wet playas of the desert southwest US. The irregularly-shaped green unit is a large landslide that brought rocks from higher up on Ceti Mensa down into this area.A new set of high-resolution geologic maps reveal complex geologic processes that suggest a dynamic, wet environment once existed on early Mars, according to the USGS. 

These three new maps are the products of an investigation of Martian rock layers, faults and landforms that explores the character of geologic processes, especially the influence of local groundwater and surface water that produced the present-day Valles Marineris, known as the “Grand Canyon of Mars.” The research aims to understand the shape and orientation of rock layers and sediments through producing maps that are comparable in scale and detail to those created using traditional geologic field methods on Earth.

“Among the many studies reporting water on Mars, this mapping effort stands out for its careful and detailed examination of a particularly interesting part of Mars,” said Lazlo Kestay, USGS Astrogeology Science Center Director. “The result is compelling evidence of how abundant groundwater was in this location, providing one of the essential ingredients for life.”

The highest resolution images available were used for the geologic and structural mapping effort. These orbiter-based images, from the High Resolution Imaging Science Experiment (HiRISE) camera on board the Mars Reconnaissance Orbiter, allow the scientific observations to record an extraordinary level of geologic detail. The fine-scale mapping techniques include measurements of the orientations of the rock layers, revealing not only flat-lying sedimentary rocks, but faults, unconformities and large landslides.

These landslides share key structural characteristics with water-saturated landslides on Earth, indicating abundant groundwater in the region and that strongly affected the way the rock layers deformed. The mapping reveals other areas of Candor Chasma where groundwater welled up onto the ground surface at springs and formed shallow pools. These pools helped to trap wind-blown dust and ultimately led to the formation of the rock layers we see today. This environment would have resembled the dunes and wet salt flats found in the desert southwestern U.S. On Earth these “eolian-dominated wet playa” environments can host habitable oases, or small wet areas in a desert region. Ancient playa deposits often contain fossils that can be used to understand past ecosystems.

Highly-detailed maps such as these serve as case studies that can be used as the basis for developing broader-scale astrobiologic resource assessments and geologic investigations throughout Valles Marineris.

The Martian surface has been the subject of scientific observation since the 1600s, first by Earth-based telescopes, and later by fly-by missions and orbiting spacecraft. The Mariner 9 and Viking Orbiter missions produced the first planet-wide views of Mars’ surface, enabling publication of the first global geologic maps (in 1978 and 1986-87, respectively) of a planetary surface other than Earth and its moon. Extremely high resolution images and data obtained by a new generation of sophisticated scientific instruments, such as those from the HiRISE camera, are allowing more complex, large-scale (zoomed-in) mapping of the Martian surface.  

The production of planetary cartographic products has been a focal point of research at the USGS Astrogeology Science Center since its inception in the early 1960s. USGS began producing planetary maps in support of the Apollo Moon landings, and continues to help establish a framework for integrating and comparing past and future studies of extraterrestrial surfaces. In many cases, these planetary geologic maps show that, despite the many differences between bodies in our Solar System, there are many notable similarities that link the evolution and fate of our planetary system together.

The project was funded by the NASA Planetary Geology and Geophysics Program.

Three-dimensional view of the west Ceti Mensa area looking toward the southeast.

Three-dimensional view of the west Ceti Mensa area looking toward the southeast. These rock layers formed as wind-blown sand that became trapped in shallow, ephemeral lakes. If present, past life on Mars living in these lakes or in water underground may have been incorporated into these layers as the wind-blown sand accumulated. Any such evidence of past life may now be preserved as fossils within the layers. (Public domain.)

Image of the east Candor Sulci area showing variations in color that help distinguish individual rock layers.

Image of the east Candor Sulci area showing variations in color that help distinguish individual rock layers. These differences in color may be due to variances in chemical composition, physical make up, and/or surface roughness. All of these layers were originally flat and horizontal, like pages in a book, as wind-blown sand became trapped in shallow pools and lakes. Sometime after their formation, these layers became crumpled and up-ended by a large landslide.(Public domain.)

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