Clicking on the small images above, and the links listed below, provides access to details about evidence, gathered by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC), that liquid water may have flowed on the surface of Mars during the past 7 years. These captioned materials accompany publication of results regarding present-day impact cratering and gully activity on Mars in the 8 December 2006 issue of Science.

The first two releases, regarding gullies in an unnamed crater in Terra Sirenum and another in the Centauri Montes region east of the Hellas Basin, give the details about the “smoking gun” evidence that change has occurred in two martian gully settings located in the southern hemisphere, nearly on opposite sides of the planet. In both cases, “before” and “after” images were acquired, documenting that these changes occurred between 2001 and 2005 in the Terra Sirenum case, and 1999 and 2004 in the Centauri Montes case.

• New Gully Deposit in a Crater in Terra Sirenum:
  Evidence That Water Flowed on Mars in This Decade?
  
  
• New Gully Deposit in a Crater in the Centauri Montes Region:
  Evidence That Water Flowed on Mars During the Past 7 Years?

The third release describes other examples of rare, light-toned deposits found in martian gullies elsewhere on the planet, but in these cases no “before” image is available to indicate when the light-toned material was emplaced. These cases, however, help identify sites that should be repeatedly imaged by cameras on current and future Mars orbiting spacecraft, to see if any new light-toned flows occur.

• Other Martian Gullies With Light-toned Deposits

The fourth release explains why the new light-toned gully deposits in the unnamed craters in the Terra Sirenum and Centauri Montes regions cannot be the product of downslope movement of dust. In other words, they are not the product of dry, granular flow, but instead must have involved a fluid that has the physical properties of liquid water. Key differences between light and dark slope streaks—generally considered to have formed by mass movement of dust—and the new gully deposits, are examined.

• Why the New Gully Deposits Are Not Dry Dust Slope Streaks

The fifth release centers on a related and important topic—the growing evidence that martian gullies generally formed by erosion caused by fluids that seeped from the ground. Evidence includes an important case in which a single gully formed at a site where a fault intersects a crater wall; on Earth, groundwater preferentially flows along cracks created by faulting and springs will result where the fault reaches the planet’s surface.

• Support for Hypothesis that Groundwater is Source for Fluid Responsible
  for Erosion in Martian Gullies

These releases concerning gullies are also accompanied by a set of materials regarding another subject of the Science paper of 8 December 2006, the present-day cratering rate on Mars.

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