Gullies on Mars

Gullies in the southern highlands of Mars, south of Argyre Planitia. 2014 image from the HiRISE camera on the Mars Reconnaissance Orbiter.

Martian gullies are small, incised networks of narrow channels and their associated downslope sediment deposits, found on the planet of Mars. They are named for their resemblance to terrestrial gullies. First discovered on images from Mars Global Surveyor, they occur on steep slopes, especially on the walls of craters. Usually, each gully has a dendritic alcove at its head, a fan-shaped apron at its base, and a single thread of incised channel linking the two, giving the whole gully an hourglass shape.[1] They are estimated to be relatively young because they have few, if any craters. A subclass of gullies is also found cut into the faces of sand dunes,[2] that are themselves considered to be quite young. Linear dune gullies are now considered recurrent seasonal features.[3]

Most gullies occur 30 degrees poleward in each hemisphere, with greater numbers in the southern hemisphere. Some studies have found that gullies occur on slopes that face all directions;[4] others have found that the greater number of gullies are found on poleward facing slopes, especially from 30° to 44° S.[5] Although thousands have been found, they appear to be restricted to only certain areas of the planet. In the northern hemisphere, they have been found in Arcadia Planitia, Tempe Terra, Acidalia Planitia, and Utopia Planitia.[6] In the south, high concentrations are found on the northern edge of Argyre basin, in northern Noachis Terra, and along the walls of the Hellas outflow channels.[6] A recent study examined 54,040 CTX images that covered 85% of the Martian surface found 4861 separate gullied landforms (e.g., individual craters, mounds, valleys, etc.), which totaled tens of thousands of individual gullies. It is estimated that CTX can resolve 95% of gullies.[7]

This article gives a history of the discovery and research on gullies. As research progresses, the cause of Martian gullies has shifted from recent liquid water to pieces of dry ice moving down steep slopes, but research continues. On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers think that the processes carving the gullies involve liquid water.[8][9] When the volumes of the aprons are compared to the rest of the gully, it appears that there is much less volume in the apron; hence, much of the material may have contained water and ice that disappeared.[10] However, this remains a topic of active research. Because the gullies are so young, this would suggest that liquid water has been present on Mars in its very recent geological past, with consequences for the potential habitability of the modern surface. On July 10, 2014, NASA reported that gullies on the surface of Mars were mostly formed by the seasonal freezing of carbon dioxide (CO2), and not by that of liquid water as considered earlier.[11]

  1. ^ Malin, M.; Edgett, K. (2000). "Evidence for recent groundwater seepage and surface runoff on Mars". Science. 288 (5475): 2330–2335. Bibcode:2000Sci...288.2330M. doi:10.1126/science.288.5475.2330. PMID 10875910.
  2. ^ G. Jouannic; J. Gargani; F. Costard; G. Ori; C. Marmo; F. Schmidt; A. Lucas (2012). "Morphological and mechanical characterization of gullies in a periglacial environment : The case of the Russell crater dune (Mars)". Planetary and Space Science. 71 (1): 38–54. Bibcode:2012P&SS...71...38J. doi:10.1016/j.pss.2012.07.005.
  3. ^ K. Pasquon; J. Gargani; M. Massé; S. Conway (2016). "Present-day formation and seasonal evolution of linear dune gullies on Mars" (PDF). Icarus. 274: 195–210. Bibcode:2016Icar..274..195P. doi:10.1016/j.icarus.2016.03.024. S2CID 124099612.
  4. ^ Edgett, K.; et al. (2003). "Polar-and middle-latitude martian gullies: A view from MGS MOC after 2 Mars years in the mapping orbit" (PDF). Lunar Planet. Sci. 34. Abstract 1038. Bibcode:2003LPI....34.1038E.
  5. ^ Cite error: The named reference 2007Icar..188..315D was invoked but never defined (see the help page).
  6. ^ a b Heldmann, J; Carlsson, E; Johansson, H; Mellon, M; Toon, O (2007). "Observations of martian gullies and constraints on potential formation mechanismsII. The northern hemisphere". Icarus. 188 (2): 324–344. Bibcode:2007Icar..188..324H. doi:10.1016/j.icarus.2006.12.010.
  7. ^ Harrison, T., G. Osinski1, and L. Tornabene. 2014. GLOBAL DOCUMENTATION OF GULLIES WITH THE MARS RECONNAISSANCE ORBITER CONTEXT CAMERA (CTX) AND IMPLICATIONS FOR THEIR FORMATION. 45th Lunar and Planetary Science Conference. pdf
  8. ^ Luu, K., et al. 2018. GULLY FORMATION ON THE NORTHWESTERN SLOPE OF PALIKIR CRATER, MARS 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2650.pdf
  9. ^ Hamid, S., V. Gulick. 2018. GEOMORPHOLOGICAL ANALYSIS OF GULLIES ALONG WESTERN SLOPES OF PALIKIR CRATER. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2644.pdf
  10. ^ Tyler Paladin, T., et al. 2018. INSIGHTS INTO THE FORMATION OF GULLIES IN ASIMOV CRATER, MARS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2889.pdf
  11. ^ Harrington, J.D.; Webster, Guy (July 10, 2014). "RELEASE 14-191 – NASA Spacecraft Observes Further Evidence of Dry Ice Gullies on Mars". NASA. Retrieved July 10, 2014.