This pair of images covers one of many sites on Mars where researchers use the
HiRISE camera on NASA's Mars Reconnaissance Orbiter to study changes in gullies
on slopes. Changes such as the ones visible in deposits near the lower end of this
gully occur during winter and early spring on Mars.
Image Credit:
NASA/JPL
Repeated high-resolution observations made by NASA’s Mars Reconnaissance Orbiter (MRO) indicate the gullies on Mars’ surface are primarily formed by the seasonal freezing of carbon dioxide, not liquid water.
The first reports of formative gullies on Mars in 2000 generated excitement and headlines because they suggested the presence of liquid water on the Red Planet, the eroding action of which forms gullies here on Earth. Mars has water vapor and plenty of frozen water, but the presence of liquid water on the neighboring planet, a necessity for all known life, has not been confirmed. This latest report about gullies has been posted online by the journal Icarus.
"As recently as five years ago, I thought the gullies on Mars indicated activity of liquid water," said lead author Colin Dundas of the U.S. Geological Survey's Astrogeology Science Center in Flagstaff, Arizona. "We were able to get many more observations, and as we started to see more activity and pin down the timing of gully formation and change, we saw that the activity occurs in winter."
Dundas and collaborators used the High Resolution Imaging Science Experiment (HiRISE) camera on MRO to examine gullies at 356 sites on Mars, beginning in 2006. Thirty-eight of the sites showed active gully formation, such as new channel segments and increased deposits at the downhill end of some gullies.
Using dated before-and-after images, researchers determined the timing of this activity coincided with seasonal carbon dioxide frost and temperatures that would not have allowed for liquid water.
Frozen carbon dioxide, commonly called dry ice, does not exist naturally on Earth, but is plentiful on Mars. It has been linked to active processes on Mars such as carbon dioxide gas geysers and lines on sand dunes plowed by blocks of dry ice. One mechanism by which carbon dioxide frost might drive gully flows is by gas that is sublimating from the frost providing lubrication for dry material to flow. Another may be slides due to the accumulating weight of seasonal frost buildup on steep slopes.
The findings in this latest report suggest all of the fresh-appearing gullies seen on Mars can be attributed to processes currently underway, whereas earlier hypotheses suggested they formed thousands to millions of years ago when climate conditions were possibly conducive to liquid water on Mars.
Dundas's co-authors on the new report are Serina Diniega of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, and Alfred McEwen of the University of Arizona, Tucson.
"Much of the information we have about gully formation, and other active processes, comes from the longevity of MRO and other orbiters,” said Diniega. “This allows us to make repeated observation of sites to examine surface changes over time."
Although the findings about gullies point to processes that do not involve liquid water, possible action by liquid water on Mars has been reported in the past year in other findings from the HiRISE team. Those observations were of a smaller type of surface flow feature.
An upcoming special issue of Icarus will include multiple reports about active processes on Mars, including smaller flows that are strong indications of the presence of liquid water on Mars today.
"I like that Mars can still surprise us," Dundas said. "Martian gullies are fascinating features that allow us to investigate a process we just don't see on Earth."
HiRISE is operated by the University of Arizona, Tucson. The instrument was built by Ball Aerospace & Technologies Corp. of Boulder, Colorado. JPL manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate in Washington.
This pair of before (left) and after (right) images from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter documents formation of a new channel on a Martian slope between 2010 and 2013.
Image Credit:
NASA/JPL-Caltech/Univ. of Arizona
For more information about HiRISE, visit:
Additional information about MRO is online at:
For recent findings suggesting the presence of liquid water on Mars, visit:
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Guy Webster
Jet Propulsion Laboratory, Pasadena
818-354-6278
el dispensador dice:mientras estás ocupado en tus cosas,
mientras el universo vibra y oscila sin que lo percibas,
mientras el espacio late y la Tierra gira,
mientras sueñas con una esperanza viva,
cosas suceden,
realidades cambian,
sin que te involucren,
sin que las conozcas,
sin que tu consciencia participe,
todo lo que existe...
más allá de tu persona,
más allá de tus tiempos respirables,
más allá de tu mañana necesario,
ése que esperas... mientras otros andan viajando...
todo lo que existe...
tal te digo,
deja en evidencia que el Verbo es testigo,
de que todo funciona,
prescindiendo de tus manos...
prescindiendo de tus ojos...
sin necesidad de prestar tu abrigo...
sapiencias...
de espacios sin veranos,
de lejanías sin inviernos,
de otoños sin hojas secándose,
de primaveras sin flores brotando...
otras comarcas,
otros duendes,
otras hadas,
otros órdenes "ordenados",
prolijamente funcionando,
sin historiar ningún pasado,
sin atestiguar ningún presente,
sin un futuro vendido... ni ningún otro comprado...
¿te das cuenta del valor que rige en el espacio?,
todo lo que existe es una ofrenda,
un regalo...
nadie es dueño de la creación,
ni siquiera la ha patentado,
no hay propiedad intelectual,
en lo que el Verbo ha concedido,
a través del Espíritu Santo...
por lo tanto no huyas de tu destino,
ya que siempre,
siempre,
éste te estará alcanzando.
JULIO 12, 2014.-
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