Edge of Mars' Great Dichotomy Eroded Back By Hundreds of Kilometers (arstechnica.com) 12
Ars Technica's John Timmer reports: In Monday's issue of Nature Geoscience, a team of UK-based researchers tackle a big one: Mars' dichotomy, the somewhat nebulous boundary between its relatively elevated southern half, and the low basin that occupies its northern hemisphere, a feature that some have proposed also served as an ancient shoreline. The new work suggests that the edge of the dichotomy was eroded back by hundreds of kilometers during the time when an ocean might have occupied Mars' northern hemisphere. [...] The new work focuses on an area called Mawrth Vallis, which sits at the edge of the dichotomy. Relative to the northern basin, it's a kilometer-high plateau cut by a major outflow channel that seems to have been caused by one or more massive floods. The slopes surrounding the plateau feature different types of clay-derived minerals, suggesting the area had been subject to interactions between the original materials and water.
Rather than focusing on the plateau itself, the work focuses on the neighboring lowlands, which include a large region dotted with thousands of buttes and mesas that rise roughly a kilometer above the surrounding plains. Using data from the ESA's Mars Express mission, they determine that these features tend to top out at the same height as the nearby plateau. And, using data from NASA's Mars Reconnaissance Orbiter, they determined that the clays present along the slopes match those found on the plateau as well. Their conclusion from this is that the mesas and buttes are the remains of what was once a far larger plateau, which was largely eroded away on the side facing the northern basin. And that erosion took place across a pretty significant distance, as the buttes extend hundreds of kilometers away from the present highlands. And, just as at the highland plateau, these mounds hint at a water-based process that modified the rocks from the top down. That's because the deeper clays are often magnesium-rich, which tends to happen when water comes in contact with volcanic rocks or material with similar chemistry. Closer to the surface, things transition to aluminum- and iron-rich clays. These clays can occur when the water source is acidic or can be simply due to longer exposure to water, as the magnesium clays are a bit more soluble.
The huge area covered by these mounds gives a sense of just how significant this erosion was. "The dichotomy boundary has receded several hundred kilometers," the researchers note. "Nearly all intervening material -- approximately 57,000 cubic kilometers over an area of 284,000 square kilometers west of Ares Vallis alone -- has been removed, leaving only remnant mounds." Based on the distribution of the different clays, the team argues that their water-driven formation took place before the erosion of the material. This would indicate that water-rock interactions were going on over a very wide region early in the history of Mars, which likely required an extensive hydrological cycle on the red planet. As the researchers note, a nearby ocean would have improved the chances of exposing this region to water, but the exposure could also have been due to processes like melting at the base of an ice cap. Complicating matters further, many of the mounds top out below one proposed shoreline of the northern ocean and above a second. It's possible that a receding ocean could have contributed to their erosion. But, at the same time, some of the features of a proposed shoreline now appear to have been caused by the general erosion of the original plateau, and may not be associated with an ocean at all.
Rather than focusing on the plateau itself, the work focuses on the neighboring lowlands, which include a large region dotted with thousands of buttes and mesas that rise roughly a kilometer above the surrounding plains. Using data from the ESA's Mars Express mission, they determine that these features tend to top out at the same height as the nearby plateau. And, using data from NASA's Mars Reconnaissance Orbiter, they determined that the clays present along the slopes match those found on the plateau as well. Their conclusion from this is that the mesas and buttes are the remains of what was once a far larger plateau, which was largely eroded away on the side facing the northern basin. And that erosion took place across a pretty significant distance, as the buttes extend hundreds of kilometers away from the present highlands. And, just as at the highland plateau, these mounds hint at a water-based process that modified the rocks from the top down. That's because the deeper clays are often magnesium-rich, which tends to happen when water comes in contact with volcanic rocks or material with similar chemistry. Closer to the surface, things transition to aluminum- and iron-rich clays. These clays can occur when the water source is acidic or can be simply due to longer exposure to water, as the magnesium clays are a bit more soluble.
The huge area covered by these mounds gives a sense of just how significant this erosion was. "The dichotomy boundary has receded several hundred kilometers," the researchers note. "Nearly all intervening material -- approximately 57,000 cubic kilometers over an area of 284,000 square kilometers west of Ares Vallis alone -- has been removed, leaving only remnant mounds." Based on the distribution of the different clays, the team argues that their water-driven formation took place before the erosion of the material. This would indicate that water-rock interactions were going on over a very wide region early in the history of Mars, which likely required an extensive hydrological cycle on the red planet. As the researchers note, a nearby ocean would have improved the chances of exposing this region to water, but the exposure could also have been due to processes like melting at the base of an ice cap. Complicating matters further, many of the mounds top out below one proposed shoreline of the northern ocean and above a second. It's possible that a receding ocean could have contributed to their erosion. But, at the same time, some of the features of a proposed shoreline now appear to have been caused by the general erosion of the original plateau, and may not be associated with an ocean at all.
If only it had slighty greater gravity... (Score:5, Insightful)
.. maybe 0.5G instead 0.3G , it may well have held onto most of its atmosphere and its water. Would be a true alternative to earth once we had the technology to get there instead of the almost airless, UV irradiated desert with toxic soil it is today which will never be a viable habitat for humans despite what Musk and other may think.
Re:If only it had slighty greater gravity... (Score:5, Funny)
He could sign an executive order increasing the gravity of Mars, but he can't backdate it, sorry.
Re: EO to increase gravity (Score:1)
He already declared Mars "objectively male".
Re: (Score:2)
Re: If only it had slighty greater gravity... (Score:3)
Yes it would have taken longer, much longer, that's the point. Venus doesnt have a global magnetic field either but it has one hell of an atmosphere despite being only 70% of the distance from the sun. Gravity matters.
Re: (Score:2)
Whether a 40% increase in planetary mass would do "enough", I can't say - it'll be a complex, 2
Re: (Score:2)
It would also be a lot cheaper to fix up Earth. That would affect everyone, not just those rich enough to evacuate.
Great Dichotomy eroded by hundreds of kilometers. (Score:2)
Wafer thin (Score:3)
Re: (Score:2)
I disagree, Mars is hollow. It's where all the martians are hiding.
Re: (Score:1)
Where's the "Gelsack troll" when you need them? I miss the Gelsack troll.