PATTERNS IN MARS CRATER FLOORS GIVE PICTURE OF DRYING LAKES
Networks of giant polygonal troughs etched across crater basins on Mars have been identified as desiccation cracks caused by evaporating lakes, providing further evidence of a warmer, wetter martian past. The findings were presented today at the European Planetary Science Congress by PhD student Mr M Ramy El Maarry of the Max Planck Institute for Solar System Research.
The polygons are formed when long cracks in the surface of the martian soil intersect. El Marry investigated networks of cracks inside 266 impact basins across the surface of Mars and observed polygons reaching up to 250 metres in diameter. Polygonal troughs have been imaged by several recent missions but, until now, they have been attributed to thermal contractions in the martian permafrost. El Maarry created an analytical model to determine the depth and spacing of cracks caused by stresses building up through cooling in the martian soil. He found that polygons caused by thermal contraction could have a maximum diameter of only about 65 metres, much smaller than the troughs he was seeing in the craters.
“I got excited when I saw that the crater floor polygons seemed to be too large to be caused by thermal processes. I also saw that they resembled the desiccation cracks that we see on Earth in dried up lakes. These are the same type of patterns you see when mud dries out in your back yard, but the stresses that build up when liquids evaporate can cause deep cracks and polygons on the scale I was seeing in the craters,” said El Maarry.
El Maarry identified the crater floor polygons using images taken by the MOC camera on Mars Global Surveyor and the HiRISE and Context cameras on Mars Reconnaissance Orbiter. The polygons in El Maarry’s survey had an average diameter of between 70 and 140 kilometres, with the width of the actual cracks ranging between 1 and 10 metres.
Evidence suggests that between 4.6 and 3.8 billion years ago, Mars was covered in significant amounts of water. Rain and river water would have collected inside impact crater basins, creating lakes that may have existed for several thousand years before drying out. However, El Maarry believes that, in the northern hemisphere, some of the crater floor polygons could have been formed much more recently.
“When a meteorite impacts with the martian surface, the heat can melt ice trapped beneath the martian crust and create what we call a hydrothermal system. Liquid water can fill the crater to form a lake, covered in a thick layer of ice. Even under current climatic conditions, this may take many thousands of years to disappear, finally resulting in the desiccation patterns,” said El Maarry.
IMAGES
Desiccation patterns on Earth (left) and Mars (right). Credit: Google/NASA/JPL
Detailed image of large-scale crater floor polygons, caused by desiccation process, with smaller polygons caused by thermal contraction inside. The central polygon is 160 metres in diameter, smaller ones range 10 to 15 metres in width and the cracks are 5-10 metres across. Credit: NASA/JPL
Wide view of polygonal cracks on the floor of impact crater on Mars. Credit: JPL/NASA
Cracks in mud on Earth. Credit El Maarry
FURTHER INFORMATION
European Planetary Science Congress (EPSC) 2009
EPSC 2009 is organised by Europlanet, a Research Infrastructure funded under the European Commission’s Framework 7 Programme, in association with the European Geosciences Union. It is the major meeting in Europe for planetary scientists. The programme comprises 37 sessions and workshops covering a wide range of planetary topics.
EPSC 2009 is taking place at the Kongresshotel am Templiner See, Potsdam, Germany from Sunday 13 September to Friday 18 September 2009.
For further details, see the meeting website:
http://meetings.copernicus.org/epsc2009/
Europlanet Research Infrastructure (RI)
Europlanet RI is a major (€6 million) programme co-funded by the European Union under the Seventh Framework Programme of the European Commission.
Europlanet RI brings together the European planetary science community through a range of Networking Activities, aimed at fostering a culture of cooperation in the field of planetary sciences, Transnational Access Activities, providing European researchers with access to a range of laboratory and field site facilities tailored to the needs of planetary research, as well as on-line access to the available planetary science data, information and software tools, through the Integrated and Distributed Information Service. These programmes are underpinned by Joint Research Activities, which are developing and improving the facilities, models, software tools and services offered by Europlanet.
Europlanet Project website: http://www.europlanet-ri.eu/
Europlanet Outreach and Media website: http://www.europlanet-eu.org//
Networks of giant polygonal troughs etched across crater basins on Mars have been identified as desiccation cracks caused by evaporating lakes, providing further evidence of a warmer, wetter martian past. The findings were presented today at the European Planetary Science Congress by PhD student Mr M Ramy El Maarry of the Max Planck Institute for Solar System Research.
The polygons are formed when long cracks in the surface of the martian soil intersect. El Marry investigated networks of cracks inside 266 impact basins across the surface of Mars and observed polygons reaching up to 250 metres in diameter. Polygonal troughs have been imaged by several recent missions but, until now, they have been attributed to thermal contractions in the martian permafrost. El Maarry created an analytical model to determine the depth and spacing of cracks caused by stresses building up through cooling in the martian soil. He found that polygons caused by thermal contraction could have a maximum diameter of only about 65 metres, much smaller than the troughs he was seeing in the craters.
“I got excited when I saw that the crater floor polygons seemed to be too large to be caused by thermal processes. I also saw that they resembled the desiccation cracks that we see on Earth in dried up lakes. These are the same type of patterns you see when mud dries out in your back yard, but the stresses that build up when liquids evaporate can cause deep cracks and polygons on the scale I was seeing in the craters,” said El Maarry.
El Maarry identified the crater floor polygons using images taken by the MOC camera on Mars Global Surveyor and the HiRISE and Context cameras on Mars Reconnaissance Orbiter. The polygons in El Maarry’s survey had an average diameter of between 70 and 140 kilometres, with the width of the actual cracks ranging between 1 and 10 metres.
Evidence suggests that between 4.6 and 3.8 billion years ago, Mars was covered in significant amounts of water. Rain and river water would have collected inside impact crater basins, creating lakes that may have existed for several thousand years before drying out. However, El Maarry believes that, in the northern hemisphere, some of the crater floor polygons could have been formed much more recently.
“When a meteorite impacts with the martian surface, the heat can melt ice trapped beneath the martian crust and create what we call a hydrothermal system. Liquid water can fill the crater to form a lake, covered in a thick layer of ice. Even under current climatic conditions, this may take many thousands of years to disappear, finally resulting in the desiccation patterns,” said El Maarry.
IMAGES
Desiccation patterns on Earth (left) and Mars (right). Credit: Google/NASA/JPL
Detailed image of large-scale crater floor polygons, caused by desiccation process, with smaller polygons caused by thermal contraction inside. The central polygon is 160 metres in diameter, smaller ones range 10 to 15 metres in width and the cracks are 5-10 metres across. Credit: NASA/JPL
Wide view of polygonal cracks on the floor of impact crater on Mars. Credit: JPL/NASA
Cracks in mud on Earth. Credit El Maarry
FURTHER INFORMATION
European Planetary Science Congress (EPSC) 2009
EPSC 2009 is organised by Europlanet, a Research Infrastructure funded under the European Commission’s Framework 7 Programme, in association with the European Geosciences Union. It is the major meeting in Europe for planetary scientists. The programme comprises 37 sessions and workshops covering a wide range of planetary topics.
EPSC 2009 is taking place at the Kongresshotel am Templiner See, Potsdam, Germany from Sunday 13 September to Friday 18 September 2009.
For further details, see the meeting website:
http://meetings.copernicus.org/epsc2009/
Europlanet Research Infrastructure (RI)
Europlanet RI is a major (€6 million) programme co-funded by the European Union under the Seventh Framework Programme of the European Commission.
Europlanet RI brings together the European planetary science community through a range of Networking Activities, aimed at fostering a culture of cooperation in the field of planetary sciences, Transnational Access Activities, providing European researchers with access to a range of laboratory and field site facilities tailored to the needs of planetary research, as well as on-line access to the available planetary science data, information and software tools, through the Integrated and Distributed Information Service. These programmes are underpinned by Joint Research Activities, which are developing and improving the facilities, models, software tools and services offered by Europlanet.
Europlanet Project website: http://www.europlanet-ri.eu/
Europlanet Outreach and Media website: http://www.europlanet-eu.org//
