Streaks at Martian crater suggest a watery flow

This is the upper edge of the Newton crater on Mars, imaged my the Mars Reconnaissance Orbiter (MRO). The dark streaks extending downslope are very interesting; they are only seen in spring and summer, and fade away during the colder seasons. These streaks might be due to a flow of subsurface water that is likely a salty brine due to long-term contact with the martian rocks. Salt lowers the freezing point, which might allow subsurface ice to melt and seep down the crater's slope. This might be the cause for the seasonal stains that are seen in the crater's soil. Additional details can be found at the MRO website, including this nice movie of streaks forming and then fading. If these streaks are in fact watery seeps, they will be of great biological interest because wet soil will be a natural place to look for microbial life on Mars.

3D model of Mojave Crater, Mars

This image is a rendering of a 3D model of the Mojave Crater on Mars. The image was crafted from stereo images acquired by the Mars Reconnaissance Orbiter, and spans about 4km. This is just a small portion of the crater's edge, since the crater itself is 60km across. This image also has its vertial relief enhanced 3x over that in the horizontal direction. Note that this part of the crater appears filled in, like a pond. This ponding is thought to occur when melt generated by an impact is captured behind mountainous walls. The dearth of additional smaller craters tells us this feature is relatively young for Mars, only 10 million years old. Note also the flows into and out of this region. They suggest that the impact event might have melted underground ice that also flooded this region.

Recent impacts on Mars exposes subsurface ice

The Mars Reconnaissance Orbiter (MRO) took these images of a 6m crater on Mars in October 2008 (left) and again in January 2009; see this press release for more details. This crater is absent from images acquired in 2007, so it must be due to a relatively recent impact. Note also the bright material in the crater that fades over time. This is to be expected if this were subsurface ice that was suddenly exposed to the surface. Water ice is not stable at the surface of Mars, and will sublimate (vaporize) over time. The MRO spacecraft has discovered several new craters where fresh ice appears to fade over time. This particular crater has a latitude of 43 degrees, which indicates that subsurface ice on Mars extends all the way from from the poles to Mars' mid-latitudes.

Martian gullies at crater's edge

Gullies are often spotted in sloped terrain on Mars, like the ones seen here at the edge of Hale crater on Mars. This image was acquired by the Mars Reconnaissance Orbiter August 3, 2009; that spacecraft has been observing Mars since March 2006. Martian gullies are of great interest, since their dendritic appearance suggests that groundwater might be seeping out and flowing downhill. However, after many years of study, it is still unclear whether wet or dry processes are responsible for sculpting these gullies. Dry processes include boulders or avalanches that might carve out these gullies as rocks and gravel tumble downhill. Also keep in mind that the martian surface is too cold for liquid water to exist there. Nonetheless, any groundwater would absorb salts from the surrounding rock, which might lower its freezing point enough to exist in liquid form. And where there is liquid water, there is also the possibility for microbial life. For more details, see this press release.