| Piú votate - Mars Reconnaissance Orbiter (MRO) |
PSP_010057_2040_RED.JPGUnnamed Crater with Ridges and DD Tracks (natural colors; credits: Lunexit)53 visiteThis image shows two features of interest on the floor of a large impact crater. The first is the set of roughly parallel ridges on the crater floor that point towards the crater center north of the image. These may be Inverted Stream Channels, where old streambeds became resistant to erosion due to cementation or simply deposition of large rocks. This is consistent with the slightly wavy, sinuous shape of the ridges, but these examples are not particularly well-preserved.
More recently, this site has become blanketed by dust, settling out after Global Dust Storms. This obscures much of the fine-scale geology, but allows HiRISE to see the effects of a recent process: Dust Devils. These have left the dark stripes across the surface by disturbing the dust cover. Most followed straight paths, but a few loops or turns are visible. Dust Devils may be an important factor in the Martian climate system because they lift dust into the atmosphere, helping to trigger larger Dust Storms.MareKromium
(6 voti)
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PSP_009942_2645_RED_abrowse-01.jpgSmall Crater on Planum Boreum (edm - natural colors; credits: Lunexit)63 visiteThis edm frame shows an example of a rare, small crater (approx. 115 meters, or 125 yards, in diameter). Scientists can count these shallow craters to attain an estimate of the age of the upper few meters of the Planum Boreum Surface.
The colors come from the presence of dust and of ice of differing grain sizes. The blueish ice has a larger grain size than the ice that has collected in the crater. The reddish material is dust. The smooth area stretching to the upper right, away from the crater may be due to winds being channeled around the crater or to fine-grained ice and frost blowing out of the crater.MareKromium
(6 voti)
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PSP_009942_2645_RED_abrowse-00.jpgSmall Crater on Planum Boreum (ctx frame - natural colors; credits: Lunexit)74 visiteImpact craters on the surface of Planum Boreum, popularly known as the North Polar Cap, are rare. This dearth of craters has lead scientists to suggest that these deposits may be geologically young (a few million years old), not having had much time to accumulate impact craters throughout their lifetime.
It is also possible that impacts into ice do not retain their shape indefinitely, but instead that the ice relaxes (similar to glass in an old window), and the crater begins to disappear.MareKromium
(6 voti)
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Psp_009619_1630_red.jpgDouble Impact Crater (natural colors; credits: Lunexit)92 visiteThis image shows a double impact crater in Syria Planum, and probably formed when a binary asteroid pair (two asteroids closely orbiting each other, while also orbiting the Sun) struck the Surface. The asteroids must have been about the same size, on the order of a few hundred meters across, to produce these craters.
How is it possible to say that the double crater is due to a binary asteroid, instead of two independent impacts? Neither crater shows signs of burial by ejecta from the other. More importantly, the ejecta (material thrown out of the craters) shows signs of interacting; the ridges extending to the southeast of the crater probably formed when ejecta from the craters collided in midair, causing more debris to pile up at certain points.
This means that the impacts occurred within moments of each other.
Ejecta interaction features like this can also form in association with “secondary” craters (craters made by debris from other impacts, rather than by asteroids), since many secondary craters form at once. In this case, however, a binary asteroid is the likely cause. The very large size is one indicator (secondary craters are generally much smaller than the “primary” crater), and there is not an obvious nearby source crater. While secondary craters are common, binary impacts are expected to occur as well, since binary asteroid pairs are observed.
This crater pair is also of geologic interest since it exposes a cross-section of the local rocks. Thin, flat layers are visible in the upper walls. Since this region has seen extensive volcanic activity, these may be a mix of old lava flows and other volcanic debris. Exposures like this provide evidence for the extent and thickness of these deposits. MareKromium
(6 voti)
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PSP_009696_2575_RED.JPGDunes and Translucent Ice-Spot in the Northern Plains (Saturated and Enhanced Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team) 54 visiteThis Terrain is located near the North Pole. The bright patch of material is ice, which might have been deposited in the previous Winter.
After ice in the form of surface frost is deposited from the Atmosphere, it experiences changes throughout the Martian Year. Some of the ice has a polygonal texture which probably formed when temperature variations created stress and cracks in the ice.
The dark features scattered throughout the scene are Dunes. The streaks emanating from the Dunes trending in the South/West direction indicate the dominant direction of the wind in recent times.MareKromium
(6 voti)
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PSP_006659_1460_RED_abrowse~0.jpgGullies in Dao Vallis (MULTISPECTRUM; credits: Lunexit)53 visiteGullies on the North-West side of Dao Vallis, a Martian outflow channel, are the focus of this observation. The outflow channels are thought to have been carved by gigantic, ancient floods.
Gullies are largely thought to be the result of water flow, but the origin of the water is much debated.
One theory proposes that melting snowpack, or a mantling (blanketing) unit, forms gullies. Such a mantling unit is visible here between some of the gullies, in the full high-resolution image. Some alcove-shaped features appear to have mantling material in them.
If the mantling unit is indeed related to gully formation, then gullies are potentially forming here.
MareKromium
(6 voti)
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Psp_009535_2240_red.jpgMerging Lobate Debris Aprons of Deuteronilus Mensae (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunar Explorer Italia)118 visiteThis image lies within the Deuteronilus Mensae Region, located on the Northern Edge of Arabia Terra and borders the high-standing, heavily cratered Southern Hemisphere and the low, relatively uncratered, plains of the Northern Hemisphere of Mars.
Deuteronilus Mensae is characterized by hills and mesas surrounded by broad debris aprons and this HiRISE image shows examples where lobate-shaped debris aprons appear to overlap.
There is zone of ridges that formed in an area where lobate debris aprons merged from different directions. A current hypothesis is that these ridges are expressions of compressional deformation between two lobes acting like a viscous fluid. One possibility, given the high latitude of the occurrence, is that the lobes of debris are ice-rich and flow somewhat like glaciers.
Recent results from the SHAllow RADar (SHARAD) instrument, also onboard the Mars Reconnaissance Orbiter, indicate that lobate debris aprons in Deuteronilus Mensae are composed of material dominated by ice [Plaut et al., 2008].
This supports the interpretation that these might be potential debris-covered glaciers or rock glaciers.
Some of the detailed textures on the surface of the debris aprons are commonly believed to be the result of ice loss due to sublimation (ice changing into water vapor). On Earth, debris-covered glaciers/rock glaciers typically develop wrinkles and fractures due to stresses in the ice as it flows. Where flows merge, they can buckle and push up ridges producing features similar to those visible here.MareKromium
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Psp_009650_1755_red.jpgCrater Floor and Central Mound in Gale Crater (natural colors; credits: Lunexit)53 visitenessun commentoMareKromium
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Psp_009505_1755_red.jpgThe Floor of Gale Crater (natural colors; credits: Lunexit)53 visitenessun commentoMareKromium
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Psp_009571_1755_red.jpgCrater Floor and Central Mound in Gale Crater (Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunar Explorer Italia)53 visitenessun commentoMareKromium
(6 voti)
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PSP_008214_2285_red.jpgPeriglacial Landscape in Northern Utopia Planitia (Saturated Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)69 visitenessun commentoMareKromium
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Psp_009474_1705_red.jpgWater Bearing Minerals in Noctis Labyrinthus (natural colors; credits: Lunexit)53 visiteNoctis Labyrinthus consists of a series of Pits on the western end of the large Valles Marineris Canyon System.
The HiRISE camera and the CRISM Spectrometer have revealed that the floors of some of these Pits exhibit layered rocks, or strata, that contain minerals with water. These Pits were formed several billion years ago, therefore the rocks and sediments on their floors record evidence of water during this period of Mars’ history.
The walls of the Pits are commonly covered with dust and other loose sediments that form dunes and dune-like forms, and in many cases the floors of the pits are also covered with these materials. This image shows an example of light-toned layers exposed beneath these sediments and dunes, and CRISM data show that these layers have hydrated minerals.
The dark-brown/orange tones in this natural color image correspond to areas with more Pyroxene, a mineral found in volcanic rocks and Martian Dust. Some Pits, such as this one, appear to have deposits associated with large landslides that are younger than the hydrated minerals and partially bury them.MareKromium
(6 voti)
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