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When it comes to Mars, the hot topic of study is water – a prerequisite for life.
While liquid water is currently not stable on the surface of Mars, there is extensive evidence that it may have been in the past. Astronomers have discovered dried up riverbeds, lake deltas, and evidence of widespread glaciers – to name but a few examples.
However, evidence for a massive standing body of water, such as an ocean, is hard to come by. Early climate models struggle to create circumstances under which liquid water would be stable at all. Nonetheless, an ocean spanning the northern lowlands (approximately one third of the planet) has been long hypothesized.
Scientists at Caltech may have just now confirmed this long-held hope in finding recent evidence for a vast Martian ocean.
The region under investigation is known as Aeolis Dorsa – a plain located at the border between the northern lowlands and the southern highlands. This plain contains many ridges, which are interpreted as ancient river channels.
“These ‘inverted’ channels are now elevated because the coarse sand and gravel carried by the channels is more resistant to erosion than the surrounding mud and silt making up the floodplain material,” Dr. Roman DiBiase, lead author on the study, told Universe Today.
Satellite images of Aeolis Dorsa were collected using the HiRISE camera aboard the Mars Reconnaissance Orbiter. The resolution was so precise scientists could distinguish features as small as 25 centimeters – an impressive feat even when compared to images of the Earth.
For certain locations “repeat pictures taken with a slight offset enable the creation of stereo-images from which we can determine the relative elevations of features on the planet’s surface,” explains DiBiase. This impressive technique led to high-resolution topographic models, allowing the team to analyze the geometry and patterns of these inverted channels in unprecedented detail.
Not only do the channels spread out toward the end, they also slope steeply downward, forming a delta – a sedimentary deposit that forms where rivers flow into lakes or oceans.
While deltas have been identified on Mars before, all lie within distinct topographic boundaries, such as an impact crater. This is the most compelling evidence for a delta leading into an unconfined region – an ocean.
Final proof of a Martian ocean will advance our knowledge of the intricate interplay between water, climate, and life. “The history of water on Mars has implications not only for the evolution of Martian climate, but also for learning about the early evolution of Earth and Earth’s climate,” explains DiBiase.
As always, further research is needed. Perhaps in the nearby future the Mars Reconnaissance Orbiter and Curiosity will compliment each other quite well – the orbiter taking images from above while Curiosity plays in the dirt, gathering samples in the riverbed.
The study was published in the Journal of Geophysical Research and may be found here.