Nili Patera dune field

File:Nili Patera Dune Field wide angle.jpg

File:Sand Dunes in Nili Patera Caldera.jpg

Over a period of 35 years, starting with Mariner 9 and ending with Mars Odyssey, there had been no detection of sand movement on Mars. Up to that point, scientists had speculated about the static or dynamic nature of Martian dunes. To answer that question, the Nili Patera dunes were examined by HiRise at different times and the results were analysed using software designed to analyse movement of the dunes by examining the differences between the photographs over time. It was discovered that the Patera dunes changed their morphology over time, and, therefore, the Nili Patera dune field has very dynamic formation characteristics. In addition it was discovered that there was a velocity difference between the top and bottom strata of the dune, with the top layer ripples moving at a higher velocity than the ripples of the bottom one. This indicates that the dune is moving as a unit across the Martian landscape.

File:Ripple Movement on Sand Dune in Nili Patera, Mars.gif of the Nili Patera dune field, over a three-year period (2007–2010), indicating movement of the ripples of the dunes]]

The flux rates of the migrations of the ripples versus the whole dune were determined, and from that calculation, the relative proportion of low-energy sand grains, primarily responsible for ripple migration, called the "reptons", versus the higher energy grains, the "saltons", was determined. The saltons are primarily responsible for the movement of the dune as a unit.{{cite book|title=Treatise on Geophysics|url=https://books.google.com/books?id=Rg6dBAAAQBAJ&pg=RA2-PA420|date=17 April 2015|publisher=Elsevier Science|isbn=978-0-444-53803-1|pages=2}} Such movement mechanism is called saltation and it has been determined that the dunes at Nili Patera, under the existing wind conditions, are active and moving as a unit.{{cite news|author1=S. Silvestro, L. K. Fenton, D. A. Vaz, N. Bridges and G. G. Ori1|title=RIPPLE MIGRATION ON ACTIVE DUNES IN NILI PATERA (MARS).|url=http://www.lpi.usra.edu/meetings/dunes2010/pdf/2003.pdf|publisher=1 International Research School of Planetary Sciences, Viale Pindaro, Pescara, Italy, 2 SETI Institute, NASA Ames Research Center, CA, USA, 3 Centre for Geophysics, University of Coimbra, Portugal, 4 Applied Physics Laboratory, Laurel, MD, USA, 5 Ibn Battuta Centre, Universitè Cadi Ayyad, Marrakech, Morocco.}} Due to the thinner atmosphere of Mars, winds have to be approximately 10 times faster than those on Earth to cause sand movement. These high winds occur very rarely on Mars, but because of the thinner atmosphere and lower gravity of the planet, sand grains, once in motion, can move faster and to a longer distance than on Earth.

It is theorised, that on Mars, once high winds initiate the movement of the sand particles, weaker winds can sustain the motion of the dune, due to the lower gravity of the planet and the lower resistance of the thinner atmosphere. The lighter-coloured surface under the dunes of the Nili Patera Dune Field is ancient lava which has cooled. The cracks in the lava surface are filled with dark sand, of probable volcanic origin. However, it is not known if the volcanic sand originates from the local caldera, or has blown from another volcanic site.{{cite web|title=Sand Dunes in Nili Patera Caldera|url=https://hirise.lpl.arizona.edu/PSP_005684_1890|website=hirise.lpl.arizona.edu}}

The sand flow rate, known as flux, of the Nili Patera dunes is approximately equal to the flux of the dunes in Victoria Valley,{{cite web|author1=Nola Taylor Redd|title=Sand Dunes on Mars Are Surprisingly Speedy|url=https://www.space.com/15611-mars-sand-dunes-discovery.html|website=Space.com|date=9 May 2012}} Antarctica.{{cite web|title=Advancing Dune in Nili Patera, Mars|url=https://www.nasa.gov/mission_pages/MRO/multimedia/pia15295.html|publisher=NASA}} The Nili Patera dune movement can be used to predict rock erosion rates due to sand blasting the rocks. Based on the gathered evidence, rock erosion rates are predicted to be close to the ones in Antarctica.{{cite web|title=NASA Spacecraft Detects Changes in Martian Sand Dunes Advancing Dune in Nili Patera, Mars|url=https://mars.jpl.nasa.gov/mro/news/whatsnew/index.cfm?FuseAction=ShowNews&NewsID=1220|publisher=NASA|date= 9 May 2012}} In a paper published in the journal Nature, NASA scientists report that they have detected motion of Nili Patera dunes up to a height of {{convert|200|ft|m}} as "coherent units across the Martian landscape".{{cite journal|title=Threshold for sand mobility on Mars calibrated from seasonal variations of sand flux|journal=Nature|volume=5|pages=5096|date=30 September 2014|doi=10.1038/ncomms6096|pmid=25268931|bibcode=2014NatCo...5.5096A|last1=Ayoub|first1=F.|last2=Avouac|first2=J.-P.|last3=Newman|first3=C.E.|last4=Richardson|first4=M.I.|last5=Lucas|first5=A.|last6=Leprince|first6=S.|last7=Bridges|first7=N.T.|doi-access=free}} These discoveries have led to increased understanding of the role the wind plays in erosion phenomena of the Martian landscape. This, in turn, can lead to better planning of future Mars expeditions, both human and robotic.{{cite web|author1=Nathan Bridges|title=Topography of Moving Dunes in Nili Patera|url=https://hirise.lpl.arizona.edu/ESP_017762_1890|publisher=NASA|date=7 November 2012}}

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File:Dark sand dunes on Nili Patera.jpeg |Dark sand dunes on Nili Patera of probable volcanic origin. The lighter-coloured surface is ancient lava, which has cooled. The cracks on the lava floor are filled with dark, volcanic sand.

File:Dunes and Ripples in Nili Patera.jpg|Dunes in Nili Patera, showing wind-created ripples and an avalanche on the lee side of the centre dune

File:Barchan dunes at Nili Patera.jpg |Barchan dunes at Nili Patera

File:Nili Patera Dune Field anaglyph.jpg|Nili Patera dune field anaglyph 3D

• Classical albedo features on Mars
• Abalos Undae
• Hagal dune field
• Olympia Undae
• Hyperboreae Undae
• Siton Undae
• Aspledon Undae
• Ogygis Undae

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Category:Dunes on Mars

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