HiRISE: New Spotlighted Captioned Images (2010 Aug 04)

[bystander]

Exposed Ice in Fresh Crater (ESP_018273_2245)


Enigmatic Sinuous Features in Louth Crater Ice Mound (ESP_018301_2505)


Rayed Crater in Elysium Planitia (ESP_018352_1805)


Climate Change Recorded within North Polar Layers (ESP_018482_2790)

Credit: NASA/JPL/University of Arizona

HiRISE: PDS Release: August 2010 (orbit 18,100 - 18,499) 314 images

[Beyond]

In the first photo - exposed ice in fresh crater - the sides of the crater are so smooth that it took me a while to get this ole' brain to reconize that it IS a crater and not an orb of some kind hovering just above the surface. I suppose that if you are used to looking at many of these kinds of photo's daily, you would not have this problem.

[canopia]

After reading Beyond's post, I started to see not only the icy crater but also the smaller craters as hovering balls. They look equally interesting that way.

[bystander]

The same illusion that makes you see hovering balls makes the Rayed Crater in #3 look like a mound instead of a crater.

Meanwhile, #4 is the NASA Image of the Day

North Polar Layers of Mars

Click to view full size image

The north polar layered deposits are layers of dusty ice up to 2 miles thick and approximately 620 miles in diameter. We can see the layers exposed on the walls of troughs and scarps cut into the deposits, such as the trough wall imaged here.

The bright region at the top is the flat surface above the trough wall; it is higher than the terrain underneath. The wall exposing these layers has a vertical relief of about 1970 feet.

It is thought that the north polar layered deposits likely formed recently (i.e., millions of years ago) as rhythmic variations in Mars' orbit changed the distribution of water ice around the planet. As ice moved to and from the polar region in response to a changing climate, layers of ice and dust built up at the poles. By studying the history of these deposits, we hope to understand how the Martian climate has changed, similar to how scientists on Earth study ice cores from the North and South Poles.

Three things are immediately apparent about the layers exposed on this trough face. First, individual layers have different surface textures, which some scientists believe could reflect changing physical properties (such as dust content or ice grain size) of the underlying layer. Second, there are several unconformities, or places where one layer is interrupted and overlain by another layer. These unconformities are due to periods where layers were eroded or removed, followed by times when new layers were deposited. Mapping the locations of unconformities can tell us how the deposit shrank and grew over time, and tell us where large changes in climate occurred, causing water ice to be removed from the polar regions. Finally, the dark and bright streaks are due to recent winds blowing surface frost around, and can tell us about wind patterns in the current polar climate.

Credit: NASA/JPL/University of Arizona