NASA-Funded Scientists Make Lunar Watershed Discovery

Dwayne Brown

Headquarters, Washington

 

Cathy Weselby

Ames Research Center, Moffett Field, Calif.

 

Maria Martinez

Southwest Research Institute, San Antonio

 

Richard Lewis

Brown University, Providence, R.I.

MOFFETT FIELD, Calif. -- A team of NASA-funded researchers has measured for the first time water from the moon in the form of tiny globules of molten rock, which have turned to glass-like material trapped within crystals. Data from these newly-discovered lunar melt inclusions indicate the water content of lunar magma is 100 times higher than previous studies suggested.

The inclusions were found in lunar sample 74220, the famous high-titanium "orange glass soil" of volcanic origin collected during the Apollo 17 mission in 1972. The scientific team used a state-of-the-art ion microprobe instrument to measure the water content of the inclusions, which were formed during explosive eruptions on the moon approximately 3.7 billion years ago.

The results published in the May 26 issue of Science Express raise questions about aspects of the "giant impact theory" of how the moon was created. That theory predicted very low water content of lunar rock due to catastrophic degassing during the collision of Earth with a Mars-sized body very early in its history.

The study also provides additional scientific justification for returning similar samples from other planetary bodies in the solar system.

"Water plays a critical role in determining the tectonic behavior of planetary surfaces, the melting point of planetary interiors and the location and eruptive style of planetary volcanoes," said Erik Hauri, a geochemist with the Carnegie Institution of Washington and lead author of the study. "I can conceive of no sample type that would be more important to return to Earth than these volcanic glass samples ejected by explosive volcanism, which have been mapped not only on the moon but throughout the inner solar system."

In contrast to most volcanic deposits, the lunar melt inclusions are encased in crystals that prevent the escape of water and other volatiles during eruption.

"These samples provide the best window we have on the amount of water in the interior of the moon where the orange glass came from," said science team member James Van Orman of Case Western Reserve University in Cleveland.

In a 2008 study led by Alberto Saal of Brown University in Providence, R.I., the same team reported the first evidence of water in lunar volcanic glasses. They used magma degassing models to estimate how much water was originally in the magmas before eruption.

Building on that study, a Brown undergraduate student, Thomas Weinreich, searched for and found the melt inclusions. With that data, the team measured the pre-eruption concentration in the magma and estimated the amount of water in the moon's interior.

"The bottom line is that in 2008, we said the primitive water content in the lunar magmas should be similar to lavas coming from the Earth's depleted upper mantle," Saal said. "Now, we have proven that is indeed the case."

The study also puts a new twist on the origin of water-ice detected in craters at the lunar poles by several recent NASA missions. The ice has been attributed to comet and meteor impacts, but the researchers believe it is possible that some of the ice came from water released by the eruption of lunar magmas eons ago.

The paper entitled, "High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions," was written by Hauri, Weinreich, Saal, Van Oman and Malcolm Rutherford of Brown. The research is funded by NASA's Lunar Advanced Science and Exploration Research and Cosmochemistry Programs in Washington, the NASA Lunar Science Institute (NLSI) at the agency's Ames Research Center at Moffett Field, Calif., and the Astrobiology Institute at Ames.

The NLSI is a virtual organization enabling collaborative, interdisciplinary research in support of agency lunar science programs. The researchers are members of NLSI teams from the Southwest Research Institute in San Antonio and Brown. The institute uses technology to bring scientists together around the world, and it is comprised of seven competitively selected U.S. teams and several international partners. NASA's Science Mission and Exploration Systems Mission Directorates in Washington fund the institute.

For more information about the NLSI, visit http://lunarscience.nasa.gov.

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NASA Spacecraft Reveals Dramatic Changes In Mars' Atmosphere

Dwayne Brown

Headquarters, Washington     

 

Guy Webster

Jet Propulsion Laboratory, Pasadena, Calif.

 

Maria Martinez

Southwest Research Institute, San Antonio, Texas

 

WASHINGTON -- NASA's Mars Reconnaissance Orbiter (MRO) has discovered the total amount of atmosphere on Mars changes dramatically as the tilt of the planet's axis varies. This process can affect the stability of liquid water if it exists on the Martian surface and increase the frequency and severity of Martian dust storms.

Researchers using MRO's ground-penetrating radar identified a large, buried deposit of frozen carbon dioxide, or dry ice, at the Red Planet's south pole. The scientists suspect that much of this carbon dioxide enters the planet's atmosphere and swells the atmosphere's mass when Mars' tilt increases. The findings are published in a report in the journal Science.

The newly found deposit has a volume similar to Lake Superior's nearly 3,000 cubic miles. The deposit holds up to 80 percent as much carbon dioxide as today's Martian atmosphere. Collapse pits caused by dry ice sublimation and other clues suggest the deposit is in a dissipating phase, adding gas to the atmosphere each year. Mars' atmosphere is about 95 percent carbon dioxide, in contrast to Earth's much thicker atmosphere, which is less than .04 percent carbon dioxide.

"We already knew there is a small perennial cap of carbon-dioxide ice on top of the water ice there, but this buried deposit has about 30 times more dry ice than previously estimated," said Roger Phillips of Southwest Research Institute in Boulder, Colo. Phillips is deputy team leader for MRO's Shallow Radar instrument and lead author of the report.

"We identified the deposit as dry ice by determining the radar signature fit the radio-wave transmission characteristics of frozen carbon dioxide far better than the characteristics of frozen water," said Roberto Seu of Sapienza University of Rome, team leader for the Shallow Radar and a co-author of the new report.

Additional evidence came from correlating the deposit to visible sublimation features typical of dry ice.

"When you include this buried deposit, Martian carbon dioxide right now is roughly half frozen and half in the atmosphere, but at other times it can be nearly all frozen or nearly all in the atmosphere," Phillips said.

An occasional increase in the atmosphere would strengthen winds, lofting more dust and leading to more frequent and more intense dust storms. Another result is an expanded area on the planet's surface where liquid water could persist without boiling. Modeling based on known variation in the tilt of Mars' axis suggests several-fold changes in the total mass of the planet's atmosphere can happen on time frames of 100,000 years or less.

The changes in atmospheric density caused by the carbon-dioxide increase also would amplify some effects of the changes caused by the tilt. Researchers plugged the mass of the buried carbon-dioxide deposit into climate models for the period when Mars' tilt and orbital properties maximize the amount of summer sunshine hitting the south pole. They found at such times, global, year-round average air pressure is approximately 75 percent greater than the current level.

"A tilted Mars with a thicker carbon-dioxide atmosphere causes a greenhouse effect that tries to warm the Martian surface, while thicker and longer-lived polar ice caps try to cool it," said co-author Robert Haberle, a planetary scientist at NASA's Ames Research Center in Moffett Field, Calif. "Our simulations show the polar caps cool more than the greenhouse warms. Unlike Earth, which has a thick, moist atmosphere that produces a strong greenhouse effect, Mars' atmosphere is too thin and dry to produce as strong a greenhouse effect as Earth's, even when you double its carbon-dioxide content."

The Shallow Radar, one of MRO's six instruments, was provided by the Italian Space Agency and its operations are led by the Department of Information Engineering, Electronics and Telecommunications at Sapienza University of Rome. NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the MRO project for NASA's Science Mission Directorate at the agency's headquarters in Washington. Lockheed Martin Space Systems in Denver built the spacecraft.

For more information about MRO, visit http://www.nasa.gov/mro.

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