NASA MARS RECONNAISSANCE ORBITER MISSION (2005-2015)
Hale Crater Mountains (150 kms diameter - 93 mile diameter)
Planet Mars (Argyre quadrangle)
1 & 2. Hale crater mountains slope seeping waters
3. Hale crater mountains gullies.
The "mountains"
Hale is a 150 km x 125 km (93 mi x 78 mi) crater located at 35.7°S, 323.4°E, just north of Argyre basin on Mars, the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury, often nicknamed "The red planet" because the iron oxide prevalent on its surface. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth.
On 28 September 2015 NASA confirmed the seasonal existence of liquid water in Hale crater. The salts in the water (magnesium perchlorate, magnesium chlorate, sodium perchlorate,...) lower its freezing and melting point to 203 K (−70 °C or −94 °F), which is near the average summer night temperature.
Hale was created by an asteroid roughly 35 km (22 mi) across that impacted at an oblique angle about 3.5–3.8 billion years ago. The rim and ejecta are eroded and show smaller impacts, but subsequent deposits have covered up small craters within it. On the southern rim of Hale, parts of the crater wall have moved downslope towards the crater's centre. The surface shows a network of fluvial channels which may have been caused by running water.
It is named after George Ellery Hale, an astronomer from Chicago who determined in 1908 that sunspots are the result of magnetic activity.
The wall of Hale Crater has a large number of gullies. Some are pictured below in an image from HiRISE. Unlike, some other gullies on Mars, these are in light-toned materials. Research published in the journal Icarus has found pits in Hale Crater that are caused by hot ejecta falling on ground containing ice. The pits are formed by heat forming steam that rushes out from groups of pits simultaneously, thereby blowing away from the pit ejecta.
Gullies occur on steep slopes, especially craters. Gullies are believed to be relatively young because they have few, if any craters, and they lie on top of sand dunes which are young. Usually, each gully has an alcove, channel, and apron. Although many ideas have been put forward to explain them, the most popular involve liquid water either coming from an aquifer or left over from old glaciers.
There is evidence for both theories. Most of the gully alcove heads occur at the same level, just as one would expect of an aquifer. Various measurements and calculations show that liquid water could exist in an aquifer at the usual depths where the gullies begin. One variation of this model is that rising hot magma could have melted ice in the ground and caused water to flow in aquifers. Aquifers are layer that allow water to flow. They may consist of porous sandstone. This layer would be perched on top of another layer that prevents water from going down (in geological terms it would be called impermeable). The only direction the trapped water can flow is horizontally. The water could then flow out onto the surface when it reaches a break, like a crater wall. Aquifers are quite common on Earth. A good example is "Weeping Rock" in Zion National Park Utah.
On the other hand, much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust. This ice-rich mantle, a few yards thick, smoothes the land, but in places it has a bumpy texture, resembling the surface of a basketball. Under certain conditions the ice could melt and flow down the slopes to create gullies. Because there are few craters on this mantle, the mantle is relatively young.
Changes in Mars's orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas. During certain climate periods water vapor leaves polar ice and enters the atmosphere. The water comes back to ground at lower latitudes as deposits of frost or snow mixed generously with dust. The atmosphere of Mars contains a great deal of fine dust particles. Water vapor will condense on the particles, then fall down to the ground due to the additional weight of the water coating. When ice at the top of the mantling layer goes back into the atmosphere, it leaves behind dust, which insulates the remaining ice.
The camera
The image above, has been captured by the HiRISE (High Resolution Imaging Science Experiment) camera aboard NASA’s Mars Reconnaissance Orbiter. The 65 kg (143 lb), $40 million USD instrument was built under the direction of the University of Arizona's Lunar and Planetary Laboratory by Ball Aerospace & Technologies Corp. It consists of a 0.5 m (19.7 in) aperture reflecting telescope, the largest so far of any deep space mission, which allows it to take pictures of Mars with resolutions of 0.3 m/pixel (about 1 foot), resolving objects below a meter across.
HiRISE has imaged Mars landers on the surface, including the ongoing Curiosity and Opportunity rover missions.
HiRISE was designed to be a High Resolution camera from the beginning. It consists of a large mirror, as well as a large CCD camera. Because of this, it achieves a resolution of 1 microradian, or 0.3 meter at a height of 300 km. (For comparison purposes, satellite images on Google Mars are available to 1 meter). It can image in three color bands, 400–600 nm (blue-green or B-G), 550–850 nm (red) and 800–1,000 nm (near infrared or NIR).
HiRISE incorporates a 0.5-meter primary mirror, the largest optical telescope ever sent beyond Earth's orbit. The mass of the instrument is 64.2 kg.
Red color images are at 20,048 pixels wide (6 km in a 300 km orbit), and Green-Blue and NIR are at 4,048 pixels wide (1.2 km). These are gathered by 14 CCD sensors, 2048 x 128 pixels. HiRISE's onboard computer reads out these lines in time with the orbiter's ground speed, meaning the images are potentially unlimited in height. Practically this is limited by the onboard computer's 28 Gbit (3.5 GByte) memory capacity. The nominal maximum size of red images (compressed to 8 bits per pixel) is about 20,000 × 126,000 pixels, or 2520 megapixels and 4,000 × 126,000 pixels (504 megapixels) for the narrower images of the B-G and NIR bands. A single uncompressed image uses up to 28 Gbit. However, these images are transmitted compressed, with a typical max size of 11.2 Gigabits. These images are released to the general public on the HiRISE website via a new format called JPEG 2000.
To facilitate the mapping of potential landing sites, HiRISE can produce stereo pairs of images from which the topography can be measured to an accuracy of 0.25 meter.
The HiRISE camera is designed to view surface features of Mars in greater detail than has previously been possible. It has provided a closer look at fresh martian craters, revealing alluvial fans, viscous flow features and ponded regions of pitted materials containing breccia clast. This allows for the study of the age of Martian features, looking for landing sites for future Mars landers, and in general, seeing the Martian surface in far greater detail than has previously been done from orbit. By doing so, it is allowing better studies of Martian channels and valleys, volcanic landforms, possible former lakes and oceans, and other surface landforms as they exist on the Martian surface.
The general public is allowed to request sites for the HiRISE camera to capture (see HiWish). For this reason, and due to the unprecedented access of pictures to the general public, shortly after they have been received and processed, the camera has been termed "The People's Camera".
The pictures can be viewed online, downloaded, or with the free HiView software.
