GRANITO SU MARTE (come avranno fatto gli Shardana a portarcelo?)

Evidence found for granite on Mars

dimostrata la presenza di granito su Marte: lo portarono i Shardana?

Researchers now have stronger evidence of granite on Mars and a new theory for how the granite -- an igneous rock common on Earth -- could have formed there, according to a new study. The findings suggest a much more geologically complex Mars than previously believed.

NASA's Mars Reconnaissance Orbiter is providing new spectral "windows" into the diversity of Martian surface materials. Here in a volcanic caldera, bright magenta outcrops have a distinctive feldspar-rich composition [Credit: NASA/JPL/JHUAPL/MSSS]

Large amounts of a mineral found in granite, known as feldspar, were found in an ancient Martian volcano. Further, minerals that are common in basalts that are rich in iron and magnesium, ubiquitous on Mars, are nearly completely absent at this location. The location of the feldspar also provides an explanation for how granite could have formed on Mars. Granite, or its eruptive equivalent, rhyolite, is often found on Earth in tectonically active regions such as subduction zones. This is unlikely on Mars, but the research team concluded that prolonged magmatic activity on Mars can also produce these compositions on large scales.

"We're providing the most compelling evidence to date that Mars has granitic rocks," said James Wray, an assistant professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology and the study's lead author.

The research was published November 17 in the Advance Online Publication of the journal Nature Geoscience. The work was supported by the NASA Mars Data Analysis Program.

For years Mars was considered geologically simplistic, consisting mostly of one kind of rock, in contrast to the diverse geology of Earth. The rocks that cover most of Mars's surface are dark-colored volcanic rocks, called basalt, a type of rock also found throughout Hawaii for instance.

But earlier this year, the Mars Curiosity rover surprised scientists by discovering soils with a composition similar to granite, a light-colored, common igneous rock. No one knew what to make of the discovery because it was limited to one site on Mars.

The new study bolsters the evidence for granite on Mars by using remote sensing techniques with infrared spectroscopy to survey a large volcano on Mars that was active for billions of years. The volcano is dust-free, making it ideal for the study. Most volcanoes on Mars are blanketed with dust, but this volcano is being sand-blasted by some of the fastest-moving sand dunes on Mars, sweeping away any dust that might fall on the volcano. Inside, the research team found rich deposits of feldspar, which came as a surprise.

"Using the kind of infrared spectroscopic technique we were using, you shouldn't really be able to detect feldspar minerals, unless there's really, really a lot of feldspar and very little of the dark minerals that you get in basalt," Wray said.

The location of the feldspar and absence of dark minerals inside the ancient volcano provides an explanation for how granite could form on Mars. While the magma slowly cools in the subsurface, low density melt separates from dense crystals in a process called fractionation. The cycle is repeated over and over for millennia until granite is formed. This process could happen inside of a volcano that is active over a long period of time, according to the computer simulations run in collaboration with Josef Dufek, who is also an associate professor in the School of Earth and Atmospheric Sciences at Georgia Tech.

"We think some of the volcanoes on Mars were sporadically active for billions of years," Wray said. "It seems plausible that in a volcano you could get enough iterations of that reprocessing that you could form something like granite."

This process is sometimes referred to as igneous distillation. In this case the distillation progressively enriches the melt in silica, which makes the melt, and eventual rock, lower density and gives it the physical properties of granite.

"These compositions are roughly similar to those comprising the plutons at Yosemite or erupting magmas at Mount St. Helens, and are dramatically different than the basalts that dominate the rest of the planet," Dufek said.

Another study published in the same edition of Nature Geoscience by a different research team offers another interpretation for the feldspar-rich signature on Mars. That team, from the European Southern Observatory and the University of Paris, found a similar signature elsewhere on Mars, but likens the rocks to anorthosite, which is common on the moon. Wray believes the context of the feldspar minerals inside of the volcano makes a stronger argument for granite. Mars hasn't been known to contain much of either anorthosite or granite, so either way, the findings suggest the Red Planet is more geologically interesting than before.

"We talk about water on Mars all the time, but the history of volcanism on Mars is another thing that we'd like to try to understand," Wray said. "What kinds of rocks have been forming over the planet's history? We thought that it was a pretty easy answer, but we're now joining the emerging chorus saying things may be a little bit more diverse on Mars, as they are on Earth."

This research is supported by the NASA Mars Data Analysis Program under award NNX13AH80G. Any conclusions or opinions are those of the authors and do not necessarily represent the official views of the sponsoring agencies.

Author: Brett Israel | Source: Georgia Institute of Technology [November 18, 2013]

Sostanze chimiche che sottendono la vita, su Marte.

Martian clay contains chemical implicated in the origin of life

Researchers from the University of Hawaii at Manoa NASA Astrobiology Institute (UHNAI) have discovered high concentrations of boron in a Martian meteorite. When present in its oxidized form (borate), boron may have played a key role in the formation of RNA, one of the building blocks for life.

Electron microscope image showing the 700-million-year-old Martian clay veins containing boron (100 µm = one tenth of a millimeter) [Credit: Institute for Astronomy at the University of Hawaii at Manoa]

The Antarctic Search for Meteorites team found the Martian meteorite used in this study in Antarctica during its 2009-2010 field season. The minerals it contains, as well as its chemical composition, clearly show that it is of Martian origin.

Using the ion microprobe in the W. M. Keck Cosmochemistry Laboratory at UH, the team was able to analyze veins of Martian clay in the meteorite. After ruling out contamination from Earth, they determined boron abundances in these clays are over ten times higher than in any previously measured meteorite.

"Borates may have been important for the origin of life on Earth because they can stabilize ribose, a crucial component of RNA. In early life RNA is thought to have been the informational precursor to DNA," said James Stephenson, a UHNAI postdoctoral fellow.

RNA may have been the first molecule to store information and pass it on to the next generation, a mechanism crucial for evolution. Although life has now evolved a sophisticated mechanism to synthesize RNA, the first RNA molecules must have been made without such help. One of the most difficult steps in making RNA nonbiologically is the formation of the RNA sugar component, ribose. Previous laboratory tests have shown that without borate the chemicals available on the early Earth fail to build ribose. However, in the presence of borate, ribose is spontaneously produced and stabilized.

This work was born from the uniquely interdisciplinary environment of UHNAI. The lead authors on the paper, Stephenson, an evolutionary biologist, and Lydia Hallis, a cosmochemist who is also a UHNAI postdoctoral fellow, first came up with the idea over an after-work beer. "Given that boron has been implicated in the emergence of life, I had assumed that it was well characterized in meteorites," said Stephenson. "Discussing this with Dr. Hallis, I found out that it was barely studied. I was shocked and excited. She then informed me that both the samples and the specialized machinery needed to analyze them were available at UH."

On our planet, borate-enriched salt, sediment and clay deposits are relatively common, but such deposits had never previously been found on an extraterrestrial body. This new research suggests that when life was getting started on Earth, borate could also have been concentrated in deposits on Mars.

The significance goes beyond an interest in the red planet, as Hallis explains: "Earth and Mars used to have much more in common than they do today. Over time, Mars has lost a lot of its atmosphere and surface water, but ancient meteorites preserve delicate clays from wetter periods in Mars' history. The Martian clay we studied is thought to be up to 700 million years old. The recycling of the Earth's crust via plate tectonics has left no evidence of clays this old on our planet; hence Martian clays could provide essential information regarding environmental conditions on the early Earth."

The presence of ancient borate-enriched clays on Mars implies that these clays may also have been present on the early Earth. Borate-enriched clays such as the ones studied here may have represented chemical havens in which one of life's key molecular building blocks could form.

UHNAI is a research center that links the biological, chemical, geological, and astronomical sciences to better understand the origin, history, distribution, and role of water as it relates to life in the universe.

The work was published on June 6 in PLOS ONE.

Source: Institute for Astronomy at the University of Hawaii at Manoa [June 10, 2013]