Starship Asterisk*

http://www.planetary.org/blog/article/00002611/ wrote:

Hubble Space Telescope photo of Mars during its 2007 opposition. Credit: NASA, ESA, the Hubble Heritage Team, J. Bell and M. Wolff

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[size=140][b][color=#FF0000]3[/color][color=#0000FF]D[/color][/b] MRO view of the enigmatic Acidalia mounds.[/size] The whole image is about 25 kilometers wide by 40 kilometers tall. Credit: NASA / JPL / MSSS

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The Planetary Society Blog
The enigmatic mounds of Acidalia Planitia
Aug. 4, 2010 | By Emily Lakdawalla

<<Acidalia Planitia is a large basin in Mars' northern lowlands, a dark splotch visible even from Earth telescopes. Many of the greatest canyon systems on Mars -- from Valles Marineris to Kasei, Ares, and Tiu Valles -- can be followed into Chryse Planitia, which must have collected vast amounts of floodwaters that carried on northwards until they reached bottom in Acidalia Planitia. Chryse and Acidalia together make the wide dark splotch covering the top right side of this global view of Mars from Hubble, immediately adjacent to the seasonal north polar cap.

Zoom toward Acidalia Planitia from space and the first thing you'll notice is the occasional sharp-rimmed impact craters with splatty outlines. It's not a heavily cratered place -- its floor is generally smooth and relatively crater-free compared to Mars' southern highlands, evidence that something must have wiped out its ancient crater record. That something could be the deposition of vast amounts of sediment carried within all those great outflow channels, but it's important to remember that volcanism, too, has played a big role in resurfacing Mars, and both processes likely operated here.

Zoom in a bit more and that generally smooth floor begins to look a bit lumpy; it starts breaking up into very large polygons, five or ten kilometers wide, separated by sharp canyons. Here and there, isolated plateaus rise up out of the landscape; one such plateau is the infamous "Face on Mars." Zoom in a bit more and you begin to notice odd little pimples on the polygons. Here is a glorious 3-D view of the region, courtesy of Mars Reconnaissance Orbiter's Context Camera or CTX.

Those pimples are the Acidalia mounds. There are tens of thousands of them. They were first noticed in Viking images as being circular, low mounds with central pits, up to about a kilometer across, that looked brighter than the surrounding terrain. Their origin is mysterious; they've been interpreted as pseudocraters; cinder cones; tuff cones; pingoes; or ice-disintegration features. So they could have been caused from outside Mars, by impact cratering; from inside Mars, by active volcanism; or by surface processes on Mars, through the seasonal behavior of ground ice. So pretty much everything that could have been blamed, has been blamed!

More recently, they've been proposed to be mud volcanoes, and exploring that possibility is the subject of a paper recently published in Icarus by Dorothy Oehler and Carlton Allen titled "Evidence for pervasive mud volcanism in Acidalia Planitia, Mars."

http://apod.nasa.gov/apod/ap090330.html

http://asterisk.apod.com/vie ... 17&start=0

http://en.wikipedia.org/wiki/Mars wrote:

Opportunity photo of microscopic rock formed in water

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<<Geological evidence gathered by unmanned missions suggest that Mars once had large-scale water coverage on its surface, while small geyser-like water flows may have occurred during the past decade. In 2005, radar data revealed the presence of large quantities of water ice at the poles, and at mid-latitudes. The Phoenix lander directly sampled water ice in shallow martian soil on July 31, 2008.

* Noachian epoch (named after Noachis Terra): Formation of the oldest extant surfaces of Mars, 4.5 billion years ago to 3.5 billion years ago. Noachian age surfaces are scarred by many large impact craters. The Tharsis bulge, a volcanic upland, is thought to have formed during this period, with extensive flooding by liquid water late in the epoch.

Water flows in the grabens called the Cerberus Fossae occurred less than 20 Mya.>>

http://en.wikipedia.org/wiki/Athabasca_Valles wrote:

Athabasca Valles showing source of its water, [url=http://asterisk.apod.com/viewtopic.php?f=8&t=20204&p=127025#p127025][b]Cerberus Fossae[/b][/url]. Note streamined islands which show direction of flow to south.

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<<Athabasca Valles is a valley on Mars, and is one of the youngest known channels cut into its surface by catastrophic flooding. The flood produced distinctive "teardrop" landforms similar to those found in the channeled scabland region of the United States on Earth. It is thought that these landforms were produced though depositional processes wherein the floodwaters dropped sediment behind resistant bedrock outcroppings and craters. The source of water for the flood is thought to be Cerberus Fossae.

The very high spatial resolution images from the HiRISE camera onboard the Mars Reconnaissance Orbiter have revealed that all the flood features are draped by lava flows (Jaeger et al., 2007). Research, published in January 2010, described the discovery of a vast single lava flow, the size of the state of Oregon, that "was put in place turbulently over the span of several weeks at most." This flow, near Athabasca Valles, is the youngest lava flow on Mars. It is thought to be of Late Amazonian Age.

The floor of Athabasca Valles is peppered with thousands of small cones and rings formed as steam exploded through the lava flow. Because the flood-carved surface is now covered by lava, it is no longer easy to determine the age of the water floods that passed through Athabasca Valles. It is plausible that the flood was triggered by rising magma and hence the water flood and lava flows are essentially contemporaneous, but this has not been confirmed.

Images from HiRISE in the Athabasca Valles region show features formed by the expansion and contraction of ice. Because these features occur in a channel that was active only 2 million years ago, the features hint at a warmer climate existing later than generally thought. To make the features, ice melted to form liquid water, then refroze. The detailed images from HiRISE show features similar to common landforms on Earth where permafrost is melting (polygonally patterned surfaces, branched channels, blocky debris and mound/cone structures).>>

http://www.space.com/scienceastronomy/mars_water_031114.html wrote:
Mars Images Suggest Persistent Rivers Past
By SPACE.com Staff : 14 November 2003

Fan-shaped deposit discovered provide evidence that some ancient rivers on Mars flowed for a long time, not just in brief, intense floods : NASA/JPL/Malin Space Science Systems

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<<In a long-running debate over whether Mars ever had long-lasting rivers, the latest images supporting the "yes" side have been put forth. Pictures from NASA's Mars Global Surveyor orbiter show eroded ancient deposits of transported sediment long since hardened into interweaving, curved ridges of layered rock. Scientists interpret some of the curves as traces of ancient "meanders" made in a sedimentary fan as flowing water changed its course over time.

"Meanders are key, unequivocal evidence that some valleys on early Mars held persistent flows of water over considerable periods of time," said Michael Malin of Malin Space Science Systems, San Diego, which supplied and operates the spacecraft's Mars Orbiter Camera. "The shape of the fan and the pattern of inverted channels in it suggest it may have been a real delta, a deposit made where a river enters a body of water," Malin said. "If so, it would be the strongest indicator yet Mars once had lakes."

Most scientists now agree that Mars has abundant water ice, at both its poles and under the dusty surface across much of the rest of the planet. If Mars did have liquid water for lengthy periods, then conditions would might been favorable to the development of life.

The fan covers an area about 8 miles (13 kilometers) long and 7 miles (11 kilometers) wide in an unnamed southern hemisphere crater, downslope from a large network of channels that apparently drained into it billions of years ago, according to a NASA press release.

"This latest discovery by the intrepid Mars Global Surveyor is our first definitive evidence of persistent surface water," said Jim Garvin, NASA's Lead Scientist for Mars Exploration. "It reaffirms we are on the right pathway for searching the record of Martian landscapes and eventually rocks for the record of habitats. Such localities may serve as key landing sites for future missions, such as the Mars Science Laboratory in 2009."

No liquid water has been detected on Mars, although one of the previous discoveries from Mars Global Surveyor pictures suggests some gullies have been cut in geologically recent times by the flow of ephemeral liquid water. Some researchers, however, remain unconvinced what those features show. One aspect to the debate suggests some other substance, and not water, may have carved the canyons of Mars. Other scientists have argued the flows -- whatever material involved -- were brief and catastrophic rather than sustained.

Malin and his colleague, Ken Edgett based their analysis also on information from Mars Global Surveyor's laser altimeter and from cameras on Mars Odyssey and NASA's Viking Orbiter. "Because the debris in this fan is now cemented, it shows that some sedimentary rocks on Mars were deposited by water," Edgett said. "This has been suspected, but never so clearly demonstrated before.">>

kogelmans wrote:

Can anyone tell me if this is some kind of Martian river?