by bystander » Wed Dec 18, 2013 7:57 pm
Matthew Chojnacki wrote:Sandstone Cliffs and Hematite Lag Deposits of Ophir Mensa (PSP_002208_1755) (HiClip)
This target was one of the first close HiRISE views of the enigmatic Valles Marineris interior layered deposits. These light-toned sedimentary deposits are of interest to scientists because they are partially composed of minerals like hematite that likely formed in the presence of liquid water.
The lighter-tone linear units to the north are called "
yardangs" and formed when downslope winds carved the fragile sandstone into channels. Over time, wind and gravity conspire to erode material downslope and
onto the canyon floor. The darker-toned sandy deposits at the cliff base contain
high concentrations of hematite (along with basaltic or volcanic sand) known from infrared orbital measurements.
HiRISE resolution can clearly show outcrops mass wasting finer materials out, and darker layers that are likely
hematite-bearing units. This is an excellent candidate for what's called a "hematite lag deposit," where more resistant iron-rich hematite concretions have weathered out of the brittle mesa driven by gravity and wind, similar to that observed at the Mars Exploration Rover Opportunity landing site.
Mike Mellon wrote:Linear Ridges (ESP_033902_2125) (HiClip)
Straight and meandering thin ridges are periodically found on Mars. Such ridges can form in a variety of ways.
Rivers beneath glaciers can deposit rocks and sand leaving a raised ridge, called an esker, when the glacier retreats. Sometimes sandy river beds can become cemented by minerals. Later when the river is gone and the uncemented soils next to the old river bed are eroded more easily, the old river bed itself is left standing.
In this observation, relatively straight and narrow ridges are found crisscrossing the slopes between rocky mesas and adjacent valleys.
That these ridges extend along steep slopes is unlike the water-born ridges mentioned above. Additionally, some ridges appear to connect through the mesa and extend also down the opposite slope. These features of the ridges suggest that they cut deep into the interior of the mesas.
A ridge of volcanic rock called a dike occurs when magma is squeezed into a deep fracture in the surrounding rock and upward to (or near) the surface. This magma cools and solidifies into a strong rock that resists erosion better than the fracture rock the magma squeezed into earlier. When erosion of these rocks occurs, the harder volcanic rock is left standing as a ridge and reveals the underground plumbing system of the volcanic vent.
HiRISE Science Team wrote:Crater with Trough in Utopia Rupes (ESP_033242_2315) (HiClip)
Does this observation show a possible proto-pedestal crater?
This crater has a ring trough, but the inner circle around the crater does not appear significantly elevated. Why did the ring around the crater collapse before anything else? Could it be an example of ice sublimating from below the surface?
A high resolution image shows us better details,
as we can see in this close-up.
Lazlo Kestay wrote:Rafts of Lava with Strange Infrared Properties (ESP_033556_1890) (HiClip)
This image covers part of the Athabasca Valles flood lava plain, the youngest large lava flow on the surface of Mars.
At this location, there are two rafted pieces of lava crust with strange infrared properties. Compared to the rest of the lava flow, these two raised areas are cold at night and warm in the day. This property of the surface, where the temperature changes quickly, is called "low thermal inertia." Rocks tend to have relatively high thermal inertia, so this is unexpected.
This image confirms speculation from earlier, lower resolution images. The rafts are composed of broken up (brecciated) lava, forming an extraordinarily rough surface. Normally, such a jagged pile of lava rocks would have high thermal inertia. But in this location, the rough surface has served as a trap for wind-carried dust. Thus in these rafts, and only in these rafts, is the lava covered by a thick pile of fluffy dust.
Such dust is extremely insulating, meaning that all the solar heating is deposited in a very thin layer near the surface. Therefore, dust gets relatively hot during the day. Because the heat is deposited so shallowly, it is easily lost at night. So, the trapped dust is the explanation for the low thermal inertia of these lava rafts.
Credit: NASA/JPL/University of Arizona
<< Previous HiRISE Update[quote="Matthew Chojnacki"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/PSP_002208_1755.jpg[/img3][/float][size=110][b][i][url=http://www.uahirise.org/PSP_002208_1755]Sandstone Cliffs and Hematite Lag Deposits of Ophir Mensa (PSP_002208_1755)[/url] ([url=http://www.youtube.com/watch?v=IpYkdopvkkQ]HiClip[/url])[/i][/b][/size]
This target was one of the first close HiRISE views of the enigmatic Valles Marineris interior layered deposits. These light-toned sedimentary deposits are of interest to scientists because they are partially composed of minerals like hematite that likely formed in the presence of liquid water.
The lighter-tone linear units to the north are called "[url=http://uahirise.org/images/2013/details/cut/PSP_002208_1755-1.jpg][b]yardangs[/b][/url]" and formed when downslope winds carved the fragile sandstone into channels. Over time, wind and gravity conspire to erode material downslope and [url=http://uahirise.org/images/2013/details/cut/PSP_002208_1755-1.jpg][b]onto the canyon floor[/b][/url]. The darker-toned sandy deposits at the cliff base contain [url=http://uahirise.org/images/2013/details/cut/PSP_002208_1755-2.jpg][b]high concentrations of hematite[/b][/url] (along with basaltic or volcanic sand) known from infrared orbital measurements.
HiRISE resolution can clearly show outcrops mass wasting finer materials out, and darker layers that are likely [url=http://uahirise.org/images/2013/details/cut/PSP_002208_1755-3.jpg][b]hematite-bearing units[/b][/url]. This is an excellent candidate for what's called a "hematite lag deposit," where more resistant iron-rich hematite concretions have weathered out of the brittle mesa driven by gravity and wind, similar to that observed at the Mars Exploration Rover Opportunity landing site. [/quote]
[quote="Mike Mellon"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_033902_2125.jpg[/img3][/float][size=110][b][i][url=http://www.uahirise.org/ESP_033902_2125]Linear Ridges (ESP_033902_2125)[/url] ([url=http://www.youtube.com/watch?v=1l-YvjXjPnA]HiClip[/url])[/i][/b][/size]
Straight and meandering thin ridges are periodically found on Mars. Such ridges can form in a variety of ways.
Rivers beneath glaciers can deposit rocks and sand leaving a raised ridge, called an esker, when the glacier retreats. Sometimes sandy river beds can become cemented by minerals. Later when the river is gone and the uncemented soils next to the old river bed are eroded more easily, the old river bed itself is left standing.
In this observation, relatively straight and narrow ridges are found crisscrossing the slopes between rocky mesas and adjacent valleys. [url=http://uahirise.org/images/2013/details/cut/ESP_033902_2125.jpg][b]That these ridges extend along steep slopes[/b][/url] is unlike the water-born ridges mentioned above. Additionally, some ridges appear to connect through the mesa and extend also down the opposite slope. These features of the ridges suggest that they cut deep into the interior of the mesas.
A ridge of volcanic rock called a dike occurs when magma is squeezed into a deep fracture in the surrounding rock and upward to (or near) the surface. This magma cools and solidifies into a strong rock that resists erosion better than the fracture rock the magma squeezed into earlier. When erosion of these rocks occurs, the harder volcanic rock is left standing as a ridge and reveals the underground plumbing system of the volcanic vent. [/quote]
[quote="HiRISE Science Team"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_033242_2315.jpg[/img3][/float][size=110][b][i][url=http://www.uahirise.org/ESP_033242_2315]Crater with Trough in Utopia Rupes (ESP_033242_2315)[/url] ([url=http://www.youtube.com/watch?v=0Y09QKwpkk4]HiClip[/url])[/i][/b][/size]
Does this observation show a possible proto-pedestal crater?
This crater has a ring trough, but the inner circle around the crater does not appear significantly elevated. Why did the ring around the crater collapse before anything else? Could it be an example of ice sublimating from below the surface?
A high resolution image shows us better details, [url=http://uahirise.org/images/2013/details/cut/ESP_033242_2315.jpg][b]as we can see in this close-up[/b][/url]. [/quote]
[quote="Lazlo Kestay"][float=left][img3=""]http://www.uahirise.org/images/wallpaper/800/ESP_033556_1890.jpg[/img3][/float][size=110][b][i][url=http://www.uahirise.org/ESP_033556_1890]Rafts of Lava with Strange Infrared Properties (ESP_033556_1890)[/url] ([url=http://www.youtube.com/watch?v=bySebAOH9Ag]HiClip[/url])[/i][/b][/size]
This image covers part of the Athabasca Valles flood lava plain, the youngest large lava flow on the surface of Mars.
At this location, there are two rafted pieces of lava crust with strange infrared properties. Compared to the rest of the lava flow, these two raised areas are cold at night and warm in the day. This property of the surface, where the temperature changes quickly, is called "low thermal inertia." Rocks tend to have relatively high thermal inertia, so this is unexpected.
This image confirms speculation from earlier, lower resolution images. The rafts are composed of broken up (brecciated) lava, forming an extraordinarily rough surface. Normally, such a jagged pile of lava rocks would have high thermal inertia. But in this location, the rough surface has served as a trap for wind-carried dust. Thus in these rafts, and only in these rafts, is the lava covered by a thick pile of fluffy dust.
Such dust is extremely insulating, meaning that all the solar heating is deposited in a very thin layer near the surface. Therefore, dust gets relatively hot during the day. Because the heat is deposited so shallowly, it is easily lost at night. So, the trapped dust is the explanation for the low thermal inertia of these lava rafts. [/quote]
[b][i]Credit: NASA/JPL/University of Arizona[/i][/b]
[url=http://asterisk.apod.com/viewtopic.php?t=32612][size=85][b][i]<< Previous HiRISE Update[/i][/b][/size][/url]