February 20, 2012
Dutch Scientists Analyze Lack Of Lunar Volcanoes
A team of Dutch scientists believe that they have discovered why there are no active volcanoes on the Moon, even though recent seismic activity suggests that there is a good amount of magma below the surface.
According to Olivia Solon of Wired.co.uk, Mirjam van Kan Parker and Wim van Westrenen from VU University Amsterdam and their colleagues produced microscopic copies of moon rock collected during the Apollo missions, then melted them at extremely high pressures and temperatures in order to mimic conditions on the lunar surface.The researchers then used powerful X-rays, generated at the European Synchrotron Radiation Facility (ESRF) and discovered that the reason that hot, molten rock contained below the Moon's surface doesn't rise to the surface is because it is most likely too dense to do so.
Their findings were published Sunday in the journal Nature Geosciences.
In order to determine the density of lunar magma, the VU University Amsterdam researchers and their colleagues created synthetic moon rock, using the composition of the Apollo samples as their guide, in their Amsterdam-based laboratory, the ESRF said in a press release.
The pressure near the Moon's core is in excess of 45,000 bar, and temperatures there are approximately 1,500 degrees -- conditions that the researchers were able to recreate by heating samples with an electric current while crushing them in a press, the press release said.
They then measured "the attenuation of a powerful synchrotron X-ray beam" at the ESRF facility in order to determine the density under those high pressure, high temperature conditions.
"Most lunar magmas were found to be less dense than their solid surroundings, just as they are on Earth," Solon said in a February 19 report. "However, some samples from the Apollo 14 mission, which comprised of titanium-rich glass, were found to produce a magma as dense as the rocks found in the deepest part of the lunar mantle today. This magma wouldn't move towards the surface."
"This titanium-rich magma could have only been formed by melting titanium-rich solid rocks," she added. "Previous experiments have shown that these sorts of rocks were formed shortly after the formation of the Moon at shallow levels. It is thought that vertical movements must have occurred early in the history of the Moon, which caused these titanium-rich rocks to descend into the Moon's core-mantle boundary."
The researchers believe that it could still be possible for volcanoes to eventually emerge on the Moon.
"Today, the Moon is still cooling down, as are the melts in its interior," van Westrenen told Wired.co.uk. "In the distant future, the cooler and therefore solidifying melt will change in composition, likely making it less dense than its surroundings. This lighter magma could make its way again up to the surface forming an active volcano on the Moon -- what a sight that would be! -- but for the time being, this is just a hypothesis to stimulate more experiments."
Image 1: Apollo 17 at the edge of the Shorty Crater which forty years ago was suspected to be an extinct lunar volcano. The moon rock collected there included titanium-rich glasses of the type studied in the experiments at the ESRF. Credit: NASA
Image 2: Image of an artificial moon rock sample, measuring about half a millimeter across, made with an electron microprobe at ambient temperature after the experiment with X-rays. The fragmentation of the sample occurred when it was extracted from the small diamond cylinder in which it had been melted under high pressure and temperature. Credit: Nature
Image 3: An exploded view drawing of the high-pressure cell assembly for the synchrotron X-ray experiments. The artificial moon rock samples (orange) were placed inside the ring-shaped, natural diamond sample holder (grey) which in turn was surrounded by a large, disk-shaped container (red). Credit: Nature
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