Mars Society Switzerland
Source: Jet Propulsion Laboratory. Press release 2010-209 06/24/2010
New Clues Suggest Wet Era on Early Mars was Global: Hydrated Minerals Exposed at Stokes, Northern Mars
Stokes Crater, pictured here, is one of at least nine craters in the northern lowlands of Mars with exposures of hydrated minerals detected from orbit, according to a June 25, 2010, report. These minerals, including phyllosilicates, have previously been found in thousands of small outcrops in the southern highlands of Mars, but had not previously been identified in the northern lowlands, which cover nearly half of the planet. The numerous outcrops in the south have been interpreted as evidence that early Mars -- about 4 billion years ago -- had wet conditions necessary for producing phyllosilicates and possibly conducive to life. The exposures in some northern craters indicate these minerals are in an older layer underneath the younger surface of northern Mars and are made visible where crater-forming impacts have exposed the underlying material. The new report in the journal Science by John Carter of the University of Paris and his co-authors says that the northern finds suggest the ancient, wet conditions extended globally. Their report draws upon observations by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard NASA's Mars Reconnaissance Orbiter and the OMEGA spectrometer orbiting aboard the European Space Agency's Mars Express. Stokes spans 66 kilometers (41 miles) in diameter, centered at 55.6 degrees north latitude, 171.2 degrees east longitude. The image on the right shows an area near the center of the crater, with color coding for where CRISM observations have shown exposures of three types of hydrated minerals and nearby exposures of two volcanic minerals unaltered by water: pyroxene and olivine. The scale bar is 2 kilometers (1.2 miles). The context map on the left indicates the location of that CRISM footprint within Stokes Crater. It is a mosaic of images taken by the Context Camera on Mars Reconnaissance Orbiter and the High Resolution Stereo Camera on Mars Express. The scale bar is 25 kilometers (15.5 miles). NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, built the spacecraft. The Johns Hopkins University Applied Physics Laboratory led the effort to build the CRISM instrument and operates CRISM in coordination with an international team of researchers from universities, government and the private sector. Malin Space Science Systems, San Diego, provided and operates the Context Camera. The European Space Operations Centre in Darmstadt, Germany, operates the European Space Agency's Mars Express mission. The High Resolution Stereo Camera was developed by a group with leadership at the Freie Universitat Berlin. Image Credit: NASA/ESA/JPL-Caltech/JHU-APL/MSSS/FU-Berlin
PASADENA, Calif. -- Minerals in northern Mars craters seen by two orbiters suggest that a phase in Mars' early history with conditions favorable to life occurred globally, not just in the south. Southern and northern Mars differ in many ways, so the extent to which they shared ancient environments has been open to question. In recent years, the European Space Agency's Mars Express orbiter and NASA's Mars Reconnaissance Orbiter have found clay minerals that are signatures of a wet environment at thousands of sites in the southern highlands of Mars, where rocks on or near the surface are about four billion years old. Until this week, no sites with those minerals had been reported in the northern lowlands, where younger volcanic activity has buried the older surface more deeply. French and American researchers report in the journal Science this week that some large craters penetrating younger, overlying rocks in the northern lowlands expose similar mineral clues to ancient wet conditions. "We can now say that the planet was altered on a global scale by liquid water about four billion years ago," said John Carter of the University of Paris, the report's lead author. Other types of evidence about liquid water in later epochs on Mars tend to point to shorter durations of wet conditions or water that was more acidic or salty. The researchers used the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), an instrument on the Mars Reconnaissance Orbiter, to check 91 craters in the northern lowlands. In at least nine, they found clays and clay-like minerals called phyllosilicates, or other hydrated silicates that form in wet environments on the surface or underground. Earlier observations with the OMEGA spectrometer on Mars Express had tentatively detected phyllosilicates in a few craters of the northern plains, but the deposits are small, and CRISM can make focused observations on smaller areas than OMEGA. "We needed the better spatial resolution to confirm the identifications," Carter said. "The two instruments have different strengths, so there is a great advantage to using both. "CRISM Principal Investigator Scott Murchie of Johns Hopkins University Applied Physics Laboratory, Laurel, Md., a co-author of the new report, said that the findings aid interpretation of when the wet environments on ancient Mars existed relative to some other important steps in the planet's early history. The prevailing theory for how the northern part of the planet came to have a much lower elevation than the southern highlands is that a giant object slammed obliquely into northern Mars, turning nearly half of the planet's surface into the solar system's largest impact crater. The new findings suggest that the formation of water-related minerals, and thus at least part of the wet period that may have been most favorable to life, occurred between that early giant impact and the later time when younger sediments (lava) formed an overlying mantle. "That large impact would have eliminated any evidence for the surface environment in the north that preceded the impact," Murchie said. "It must have happened well before the end of the wet period. "The report's other two authors are Francois Poulet and OMEGA Principal Investigator, Jean-Pierre Bibring , both of the University of Paris. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for NASA. Johns Hopkins University Applied Physics Laboratory provided and operates CRISM, one of six instruments on that orbiter. For more information about the mission, see Guy WebsterJet Propulsion Laboratory, Pasadena, Calif.818-354-6278
Carbonates Northen Ice Cap LCROSS Nili Fossae Mud VolcanismWater