Mercury's surface dominated by volcanic activity

July 2, 2008

Volcanism has played a more extensive role in shaping the surface of Mercury than scientists had thought. This result comes from multispectral imaging data gathered in January 2008 by MESSENGER, the latest spacecraft to visit the sun's innermost planet.

MESSENGER data has also identified and mapped surface rock units that correspond to lava flows, volcanos, and other geological features. At the same time, the spacecraft's suite of instruments has confirmed an apparent planet-wide iron deficiency in Mercury's surface rocks. Download Full Image

MESSENGER (short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is the first spacecraft to visit Mercury since NASA's Mariner 10 made three flyby passes in 1974 and 1975. MESSENGER, which is operated for NASA by the Applied Physics Laboratory of Johns Hopkins University in Baltimore, will make two more Mercury flybys (Oct. 6, 2008 and Sept. 29, 2009) before going into orbit around the planet, March 18, 2011.

Mercury and MESSENGER form the subject of 11 papers in a special section devoted to the January flyby in the July 4, 2008, issue of the scientific journal Science.

Mark S. Robinson of Arizona State University is the lead author for a paper in the issue which spotlights data on composition variations in Mercury's surface rocks using their multispectral colors. Robinson, a professor of geology in ASU's School of Earth and Space Exploration, part of the College of Liberal Arts and Sciences, is a co-investigator on the MESSENGER geology science team. Besides Robinson, the multispectral paper has 12 additional co-authors from other institutions.

"We have now imaged half of the part of Mercury that was never seen by Mariner 10," says Robinson. "The picture is still incomplete, but we'll get the other half on October 6." Back in 1974-1975, the orbital trajectory that let Mariner to make three passes at Mercury limited it to photographing less than half the planet's surface. This left the rest of Mercury unknown until MESSENGER's arrival in January let scientists begin to fill in the gaps.

Lava plains

MESSENGER's big-picture finding, says Robinson, is the widespread role played by volcanism. While impact craters are common, and at first glance Mercury still resembles the moon, much of the planet has been resurfaced through volcanic activity.

"For example, according to our color data the Caloris impact basin is completely filled with smooth plains material that appears volcanic in origin," Robinson explains. "In shape and form these deposits are very similar to the mare basalt flows on the moon. But unlike the moon, Mercury's smooth plains are low in iron, and thus represent a relatively unusual rock type."

The Caloris plains, he adds, cover at least a million square kilometers (390,000 square miles), or big enough to engulf Arizona, Nevada, and California put together. The plains' size implies the existence of large sources of magma in Mercury's upper mantle.

Multispectral imaging also shows that besides lava flows, Caloris has "red spots," which also appear volcanic. "Red spots have diffuse boundaries and sometimes lie centered on rimless depressions," Robinson says. "Right now they look to be caused by explosive, pyroclastic eruptions."

In addition, Robinson notes, three major rock units stand out in MESSENGER's multispectral imaging.

"We mapped the new hemisphere using moderate resolution images of 5 kilometers [3 miles] per pixel," he says. "As on the Mariner hemisphere, we saw three major units defined by their colors. These units are relatively high-reflectance smooth plains, average cratered terrain, and low-reflectance material."

Where's the iron?

The low-reflectance material is particularly enigmatic, says Robinson. "It's an important and widespread rock that occurs deep in the crust as well as at the surface, yet it has very little ferrous iron in its silicate minerals."

That, he says, makes it unusual. "You expect to find low-reflectance volcanic rocks having a high abundance of iron-bearing silicate minerals, but that's not the case here." One possible solution, he says, is that iron is actually present but invisible to MESSENGER's spectrometers because it's hidden within the chemical structure of minerals such as ilmenite.

Solving the paradox should help scientists unravel Mercury's history. "If you want to understand how a planet has evolved," Robinson explains, "you need to know about the minerals in its crust and mantle. Unfortunately, we are not going to be able to drill into Mercury for a long time to come. All we can do is study its volcanic rocks in detail. They give a glimpse into the planet's mantle."

"Right now," says Robinson, "it looks as if Mercury formed with a deficiency in ferrous iron. But we'll know more about its bulk composition, and thus its history, once MESSENGER gets into orbit in 2011. That's when the surface rocks can be studied much more closely, using the full set of instruments."

Besides Robinson, the other authors are Scott L. Murchie, David T. Blewett Deborah L. Domingue, S. Edward Hawkins III, Ralph L. McNutt Jr., Louise M. Prockter (Johns Hopkins University Applied Physics Laboratory), James W. Head (Brown University), Gregory M. Holsclaw, William E. McClintock (Laboratory for Atmospheric and Space Physics, University of Colorado), Sean C. Solomon (Carnegie Institution of Washington), Timothy J. McCoy (National Museum of Natural History, Smithsonian Institution), Thomas R. Watters (National Air and Space Museum, Smithsonian Institution).

Robert Burnham

Science writer, School of Earth and Space Exploration


Garcia tapped as Spencer Postdoctoral Fellow

July 3, 2008

Assistant professor David Garcia has been selected as a 2008-2009 National Academy of Education/Spencer Postdoctoral Fellow to research the convergence of school choice and school accountability with the diversification of the Latino population in the United States.

Garcia, of the Division of Educational Leadership & Policy Studies in ASU’s Mary Lou Fulton College of Education, is one of 20 fellows selected this year from a pool of more than 150 applicants. He will receive a $55,000 award to support salary replacement and research expenses for the two-year fellowship. Download Full Image

In Arizona, school choice offers students the opportunity to attend public, charter or private schools. Garcia says there is a preponderance of evidence that school choice also leads to self-segregation, but these studies used only African-American and white students in the framework.

“There has been no consistent stream of research on Latinos and school choice,” he says. “The research does reveal that students who leave traditional public schools tend to attend charter schools with others of the same race. Latinos, however, do not.”
Garcia says Latino parents have strong opinions that could shape school policy, but previous school choice studies don’t reveal their viewpoint on the issues.

“Dr. Garcia’s study to examine the diversification of the Hispanic community and the union of accountability and school choice policies has the potential to provide critically important information for Arizona and the nation,” says Stafford Hood, associate dean for research with the Fulton College. “The steady and rapid increase of the Hispanic population in major urban areas in the Midwest, South and East Coast – where they had not typically been present in large numbers – increases the potential of Dr. Garcia’s research to inform state and federal policy-makers. His work has consistently been of high quality, and many of us eagerly await what we might learn from this particular project.”

Garcia intends to investigate further the trends associated with school choice, taking into account that Latinos differ from other minority groups in that they have assimilated over generations and are more likely to live in mixed-race neighborhoods. At the same time, a new influx of immigrants is changing community dynamics nationwide. This shift is largely unexplored in the area of school choice, Garcia says.

“Accountability and choice have gone hand-in-hand with groups of people dissatisfied with public schools,” he says. “One outlet has been school choice – giving people an opportunity to go elsewhere.”

But in a previous survey of Arizona parents on school choice, Garcia oversampled Latino parents and found that they are more likely to be dissatisfied with the school choices available to them. They also are more likely to support harsher accountability measures.

“Choice is healthy,” he says. “Choice is good for the system. But we need to keep in mind that we need to have accountability in choice as well. Latino parents are less likely to believe they have good choices for their children. They are more willing to take more drastic, heavy-handed actions with regard to improving schools.

“Understanding where these trends may go is important. The argument in my papers is that understanding how they are going to shape the debate on school choice and accountability could foreshadow what’s going to happen nationally. Arizona now looks like what many states will look like in the future.”

Garcia, whose professional experience includes extensive work in education policy development and implementation, previously served as Arizona’s associate superintendent of public instruction before joining the faculty in the Fulton College in 2004.

The fellowship is funded by a grant to the academy from the Spencer Foundation. The Spencer fellowships are the oldest source of support for education research, nationally or internationally, for recent recipients of the doctorate. Garcia also will receive professional development as well as interact and work with the National Academy of Education and the Spencer Foundation.

“I’m looking forward to participating in the next couple years,” Garcia says, adding that the most exciting part will be when he presents his research to NAE.

Verina Palmer Martin, verina.martin">">
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Mary Lou Fulton College of Education

Lisa Robbins

Editor/publisher, Media Relations and Strategic Communications