Gullies on the Moon formed by dry-granular flows

Posted by Dr P. Senthil Kumar, National Geophysical Research Institute, Council of Scientific & Industrial Research, Hyderabad 500007, India.

Gullies are well-known geomorphic features on Earth where they are mainly formed by erosion due to flow of liquid water. They are also detected on Mars and the Moon and their origin on those bodies are under discussion (Malin and Edgett, 2000; Senthil Kumar et al., 2010). The gullies consist of alcoves (erosional features), channels (features indicating transportation) and fans or debris aprons (depositional structures). These features are clearly observed on the interior walls of impact craters on Mars and widely on the mountain slopes of Earth. Hence, geomorphologists use these features to examine the characteristics of liquid water flow either in the present or past geological records.

Image 1: (a) The Chandrayaan-1 terrain mapping camera image showing the ~7.2-km-diameter fresh crater (centred at 72º12'S, 133º12'E) emplaced in the peak-ring material of Schrödinger basin. The topographic profiles along A-A' and B-B' are shown in Figure 1d. A 6860-m-diameter circle fits perfectly to the crater rim from the western to the northern sides of the crater, while the crater rim recedes in other parts due to enhanced crater wall erosion. (b) The shadow-enhanced TMC image reveals the presence of arcuate ridge and the pond material on the crater floor. Note the pond is oriented toward the prominent landslide surface. (c) The TMC image showing the presence of concentric faults along the northwestern crater rim. (d) The topographic profiles along A-A' and B-B'. The interior wall that contains the landslides (B-B') is gentler and shallower than the interior wall with the gullies (A-A'). The ridge material is characterized by a higher topographic relief than the surrounding crater floor. The pond material has a flat surface that embays the ridge and other floor materials. See Senthil Kumar et al. (2013) for more details.

Image 1: (a) The Chandrayaan-1 terrain mapping camera image showing the ~7.2-km-diameter fresh crater (centred at 72º12’S, 133º12’E) emplaced in the peak-ring material of Schrödinger basin. The topographic profiles along A-A’ and B-B’ are shown in Figure 1d. A 6860-m-diameter circle fits perfectly to the crater rim from the western to the northern sides of the crater, while the crater rim recedes in other parts due to enhanced crater wall erosion. (b) The shadow-enhanced TMC image reveals the presence of arcuate ridge and the pond material on the crater floor. Note the pond is oriented toward the prominent landslide surface. (c) The TMC image showing the presence of concentric faults along the northwestern crater rim. (d) The topographic profiles along A-A’ and B-B’. The interior wall that contains the landslides (B-B’) is gentler and shallower than the interior wall with the gullies (A-A’). The ridge material is characterized by a higher topographic relief than the surrounding crater floor. The pond material has a flat surface that embays the ridge and other floor materials. See Senthil Kumar et al. (2013) for more details.

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Unexpected variety among small inner satellites of Saturn

Post by Peter Thomas, Cornell University, Ithaca, New York

 Small satellites (< 150 km mean radius) usually resemble potatoes. Their irregular shapes are formed by a history of impact cratering without the benefit of internally-driven processes of volcanism, tectonics, or atmospheric effects (Castillo-Rogez et al., 2012).  During its 9 years orbiting Saturn, the Cassini spacecraft has shown that the small satellites orbiting close to Saturn have a variety of shapes, most of which deviate from the expected familiar battered potato appearance.  These objects are likely dominated by water ice as determined from mean densities and spectroscopy (Thomas et al., 2010; Buratti et al. 2010).  Satellites within rings have equatorial ridges (Charnoz et al. 2007; Porco et al., 2007).  Others, such as Janus and Epimetheus, the “co-orbitals” are almost lunar-like in appearance, close to the expected potato variety.

Image 1: Best available view of Helene. N1687119756, UV3 filter, phase = 97°, sub-spacecraft point is 2.7°N, 124.8°W.  North is down in this presentation.  Taken June 18, 2011.

Image 1: Best available view of Helene. N1687119756, UV3 filter, phase = 97°, sub-spacecraft point is 2.7°N, 124.8°W. North is down in this presentation. Taken June 18, 2011.

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Unconsolidated Gravels on Asteroid Itokawa

Posted by Dr. Hirdy Miyamoto,    

(Re-posted from IAG Image of the Month, November 2007)

In November 2005, the Hayabusa spacecraft performed touchdown rehearsals, imaging navigation tests, and two touchdowns on Itokawa, which is by far the smallest asteroid ever studied at high resolution.

Asteroid Itokawa

Image courtesy ISAS/JAXA and University of Tokyo

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