Ancient ocean may have existed on Martian northern plainsResearch uses data from Nasa probe that orbited MarsScientists see a \u201ccoastal shelf\u201d where land met water<\/p>\n
WASHINGTON, April 17 \u2014 There is a lot of evidence from orbiting satellites and surface rovers indicating that liquid water was present long ago on the surface of Mars in the form of ponds, lakes and rivers. But the idea that Mars once had a huge and long-lived ocean on its northern plains has remained a matter of debate.<\/p>\n
Scientists have now detected what might be the contours of this putative ocean on Earth\u2019s planetary neighbour, using data collected by a Nasa probe that orbited Mars for a decade. Their research indicates the presence of the Martian equivalent of the continental shelf that defines the boundaries of Earth\u2019s oceans.<\/p>\n
They compared it to a huge \u201cbathtub ring\u201d showing where water may have once met land on Mars. Because Mars does not possess continents and lacks the geological process called plate tectonics that led to the formation of Earth\u2019s continents, the researchers are calling the Martian landforms a coastal shelf.<\/p>\n
Like Earth and the solar system\u2019s other planets, Mars formed roughly 4.5 billion years ago. Early in its history, Mars was warmer and wetter than the cold and arid place it is today.<\/p>\n
\u201cThe Martian ocean could have existed when the planet had an active hydrological cycle, with flowing rivers and lakes, nearly 3.7 billion years ago, and it likely disappeared as the planet became dry. Exactly where the water went remains highly debated,\u201d said University of Texas planetary scientist Abdallah Zaki, lead author of the research published on Wednesday in the journal Nature.<\/p>\n
A coastal shelf could have formed on Mars over millions of years due to rivers dumping sand and mud into an ocean, waves spreading those sediments around, and the sea level rising and falling over time. Looking from above, the sedimentary rock making up this shelf might superficially resemble the ring that remains after a bathtub has been drained.<\/p>\n
\u201cA \u2018bathtub ring\u2019 on Mars means that if an ocean filled the northern lowlands, it may have left behind a shoreline, or shelf-like boundary, marking the water level,\u201d Zaki said.<\/p>\n
\u201cIf we sent a rover, we would expect to see sedimentary rocks and structures similar to those found on Earth\u2019s continental shelves, including layering, sloping surfaces called clinoforms and textures produced by waves and currents,\u201d Zaki said.<\/p>\n
The researchers examined topographical data for Mars that was obtained by Nasa\u2019s Mars Global Surveyor, and identified a band suggestive of oceanic contours. Previous research has indicated that this hypothesised ocean in the Martian northern hemisphere covered approximately a third of the planet\u2019s surface, equivalent to about 13 per cent of the total area of Earth\u2019s oceans.<\/p>\n
The study builds on earlier evidence of a bygone Martian ocean including studies identifying features resembling an ancient shoreline. Ground-penetrating radar data obtained by China\u2019s Zhurong rover, described in a study published last year, detected evidence suggesting sandy beaches from a Martian shoreline now buried underground.<\/p>\n
Scientists also have identified multiple landforms that appear to be remnants of ancient river deltas, where rivers may have flowed into a larger body of water.<\/p>\n
\u201cThe northern ocean on Mars, if it existed, dried up a long time ago, and there have been billions of years of volcanic activity and wind abrasion on Mars, so interpreting ancient landforms is not straightforward,\u201d Caltech planetary scientist and study senior author Michael Lamb said.<\/p>\n
\u201cNonetheless, our study shows some telltale signs of a coastal shelf. And the shelf occurs in the same zone as the deformed shorelines and where scientists have previously mapped river deltas and other landforms and deposits characteristic of a land-ocean transition,\u201d Lamb said.<\/p>\n
Taken together, Lamb said, the evidence points toward a long-lived ancient ocean.<\/p>\n
\u201cThis means that Mars once looked much more like the Earth than it does today,\u201d Lamb said.<\/p>\n
The existence of an ocean would be an important factor in understanding whether Mars was ever able to give rise to life.<\/p>\n
\u201cIf Mars once had an ocean covering roughly one third of the planet over geologic timescales, that would suggest that a large part of its surface had sustained water, which is a key ingredient for habitability,\u201d Zaki said.<\/p>\n
\u201cThat does not mean Mars was inhabited, but it does suggest that potentially habitable environments may have been more widespread and longer-lived than if water had only existed briefly or locally,\u201d Zaki said. \u2014 Reuters<\/p>\n
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