ASU researchers reveal origin, evolution of Mercury


April 30, 2009

Up until last year globes of Mercury were blank on one side. The Mariner 10 spacecraft explored the small planet in three flybys (1974-1975), but since no more than half was ever seen it remained the least understood of the four terrestrial planets - Mercury, Venus, Earth and Mars.

On Oct. 6, 2008, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft, better known as MESSENGER, made its second close-approach flyby of Mercury. More than 30 years later MESSENGER has revealed Mercury in almost its entirety for the first time. Using high-resolution and multispectral images, researchers have not only constructed a nearly complete globe, they have also started the difficult process of determining the composition of the planet's crust and chronicling its origin and evolution. Download Full Image

Mercury's interior is thought to generally resemble that of the Earth and Mars - however, Mercury's core is anomalously large leading to it sometimes being called the iron planet. With its ancient craters and smooth plains both covered in a fine-grained gray soil (or regolith), the surface of Mercury superficially resembles the surface of the Moon. Unlike Earth's crust, which is constantly changing and evolving due to processes such as plate tectonics, the crust is relatively static on the Moon and Mercury. The bulk of Mercury's crust formed long ago and preserves a record of early events that shaped it and the subsequent forces that modified it.

"Mercury's surface tells us something fundamental about how the planet formed and evolved," said Brett Denevi, a postdoctoral research associate in the School of Earth and Space Exploration at Arizona State University. "Some of the little evidence that we had prior to MESSENGER seemed to indicate that the composition of Mercury's crust was similar to that of the Moon, leading to the presumption that it had formed in the same manner, with any volcanism that may have occurred being only a secondary component," she said.

While the highlands on the Moon are thought to have formed as the result of a global magma ocean, where less dense minerals floated to the surface to form the crust, evidence now points to a mercurian crust that formed in a manner more similar to the crust of Mars than to that of the Moon.

Denevi's research, which appears in the May 1 issue of Science, confirms that volcanism on Mercury was widespread, visible across nearly the entire planet, and that much of the crust may have formed in repeated volcanic eruptions.

Denevi, the lead author on the paper, processed and analyzed the images and spectra. To help determine how much of Mercury's surface was comprised of smooth plains she constructed maps by observing overlapping and abutting relations of different landforms. Denevi also compared spectra of Earth and lunar rocks and soils to constrain the maximum amounts of iron- and titanium-bearing minerals that could be on the surface.

Through mapping of the major geologic terrain types, Denevi and her colleagues distinguished three major terrain types on Mercury: smooth plains, intermediate terrain and low-reflectance material (LRM). "Of the three, smooth plains are a key terrain type," she said. "The smooth plains cover approximately 40 percent of the surface, and the majority is probably of volcanic origin." The extent of smooth plains is greater than on the Moon, where volcanic plains cover less than 20 percent of the surface.

MESSENGER's cameras - one high-resolution narrow-angle camera (NAC) and one multispectral wide-angle camera (WAC) - made this detailed exploration of Mercury's surface possible. Mark Robinson, another member of the research team and professor in the School of Earth and Space Exploration in ASU's College of Liberal Arts and Science, is involved with MESSENGER's imaging experiment and is principal investigator for three cameras onboard the Lunar Reconnaissance Orbiter (LRO) spacecraft slated to launch in June.

"MESSENGER provides us with three close encounters of Mercury; the final flyby will happen this fall. What we are seeing now is just a preview of the kinds of data we will acquire in 2011 when MESSENGER finally settles into its mapping orbit about Mercury," said Robinson. "MESSENGER results so far tell us that Mercury had a very complex volcanic and tectonic history early on, but at some point volcanism shut off and still later tectonic deformation probably ceased. Though Mercury has some superficial similarities with the Moon we now know it evolved in a different manner, perhaps more similar to Mars."

The wide-angle camera takes 11 images in a row of the same spot, each using a different filter that allows only certain wavelengths of light to pass through. These filters include wavelengths of light that are visible to the human eye but also longer wavelengths that humans can't see.

"Minerals reflect sunlight in unique ways at different wavelengths," explained Denevi. "Some reflect a lot of light in the visible but less in the near-infrared, so looking at the light that is reflected from Mercury's surface in different colors can help constrain what minerals are present on the surface."

There are areas on Mercury's surface that reflect comparatively little light at any of the wavelengths observed, and those areas are designated as low-reflectance material. Some of the dark units seen on the crust are consistent with high concentrations of iron- and titanium-bearing oxide minerals being excavated from below the surface. Oxide minerals that contain iron and titanium have extremely low reflectance and match what is seen on Mercury. However, this is not a unique solution, so researchers will use information from other instruments on Mercury, such as the Gamma-Ray and Neutron Spectrometer, to determine if the elements are iron and titanium. However, the team will have to wait until MESSENGER is in its mapping orbit about Mercury to fully settle these important composition questions.

"These materials are thought to originate at depth because we see them mainly in the ejecta of impact craters," Denevi explained. "Impact craters provide a great way to probe to the subsurface because impacts dig up material that we normally wouldn't be able to see and expose it on the surface."

"Before we can begin to understand the new planets being discovered around other stars we need to understand Earth and how it became the way it is today," said Denevi. To understand Earth, humans need to know how Mercury, Venus and Mars formed. The four planets are very different, and because Mercury is an extreme case, it is the key to that understanding.

Nikki Cassis

marketing and communications director, School of Earth and Space Exploration

DOE funds bio-inspired solar fuel center at ASU


April 30, 2009

ASU will be home to a new Energy Frontier Research Center (EFRC) announced by the White House in conjunction with a speech delivered by President Barack Obama.
 
The ASU center, one of 46 new EFRCs, will pursue advanced scientific research on solar energy conversion based on the principles of photosynthesis, the process by which plants convert sunlight to energy. All 46 centers are being established by the U.S. Department of Energy (DOE) as part of an overall effort to tackle the “grand challenges” and accelerate scientific advances needed to build a 21st century energy economy. DOE officials plan to fund ASU’s EFRC for bio-inspired solar fuel production at a level of $14 million over a five-year period.
 
“As global energy demand grows over this century, there is an urgent need to reduce our dependence on fossil fuels and imported oil and curtail greenhouse gas emissions,” says U.S. Secretary of Energy Steven Chu. “Meeting this challenge will require significant scientific advances. These centers will mobilize the enormous talents and skills of our nation’s scientific work force in pursuit of the breakthroughs that are essential to make alternative and renewable energy truly viable as large-scale replacements for fossil fuels.”
 
“The fundamental nature of the work that will be carried out at ASU’s new center speaks to the breadth and depth of research at our university,” adds R.F. “Rick” Shangraw Jr., ASU's vice president of research and economic affairs. “Understanding and using the scientific principles underlying the photosynthesis process will allow us to devise new and environmentally responsible ways of tapping future energy sources. This project will rely on the talents of many people across a range of scientific disciplines, making it perfect for our interdisciplinary approach to research.”
 
Essentially all of the energy we use today – from oil, coal and natural gas – originally was solar energy that was captured by plants through photosynthesis. The traditional way of unlocking energy from these compounds has been to burn them, which also releases greenhouses gases.
 
Over a period of more than 15 years, ASU has assembled a first-class team of scientists who have been studying various pieces of the photosynthetic apparatus, understanding its chemistry and biochemistry, and learning how to design and build solar energy harvesting components based on this fundamental science.
 
“This grant will allow us to put together a complete system that starts with the absorption of sunlight and ends with the creation of a clean fuel, such as hydrogen," says Devens Gust, an ASU professor of chemistry and biochemistry in the College of Liberal Arts and Sciences who is director of the new center.  “It also will provide resources to educate students at all levels about renewable energy, and it could lead to whole new industries. I am especially pleased that this center is being established in Arizona, which has a tremendous potential for solar energy utilization.”
 
The goal of ASU’s new center is to design and construct a synthetic system that uses sunlight to convert water cheaply and efficiently into hydrogen fuel and oxygen. Society requires a renewable source of fuel that is widely distributed, abundant, inexpensive and environmentally clean.
 
The use of solar energy to produce a clean fuel such as hydrogen is essentially the only process that can satisfy these criteria at a scale large enough to meet the world’s energy demands. Plants and similar organisms use photosynthesis to oxidize water, producing oxygen and fuel compounds such as carbohydrate and hydrogen. The system to be developed in the ASU center will be designed using principles borrowed from natural processes.
 
Making a fuel requires not only energy, but also a source of electrons, and the most promising source of electrons on a large scale is water. For more than 2.5 billion years, photosynthetic organisms have been harvesting sunlight and using it to remove electrons from water and produce biological fuels. This process involves solar energy harvesting units that use light to produce electrochemical energy, as well as biochemical catalysts that use this energy to remove electrons from water molecules and employ them to make fuels such as carbohydrates and oils.
 
Following the natural design principles of photosynthesis, scientists in the new ASU center will investigate how to make artificial analogs of these catalysts and light harvesting units, and how to put them together to build a complete system that uses sunlight to oxidize water (producing oxygen gas) and make hydrogen or other fuels.
 
“This project demonstrates the best of chemistry and biochemistry research,” says William Petuskey, chair of ASU’s chemistry and biochemistry department. “It combines the creativity of making new molecules that have not existed before with the purpose of designing in functionality that converts solar light to other useful forms of energy. This effort is the culmination of groundbreaking research that will lead to establishing bioenergy as a major field of research and economic development.”
 
ASU principal investigators on the project in addition to Gust include professors James Allen, Petra Fromme, Giovanna Ghirlanda, Anne Jones, Yan Liu, Ana Moore, Thomas Moore, Kevin Redding, Dong-Kyun Seo and Hao Yan, as well as Clark Miller from the Consortium for Science, Policy & Outcomes (CSPO).
 
The 46 EFRCs, each funded at $2 to $5 million per year for an initial five-year period, were selected from a pool of some 260 applications. Researchers at the newly formed EFRCs will take advantage of new capabilities in nanotechnology, high-intensity light sources, neutron-scattering sources, supercomputing and other advanced instrumentation in an effort to lay the scientific groundwork for fundamental advances in solar energy, biofuels, transportation, energy efficiency, electricity transmission and storage, clean coal and carbon capture and sequestration, and nuclear energy. For more information on the EFRC program, visit the Web site www.sc.doe.gov/bes/EFRC.html. /> 
ASU’s center is one of 16 EFRCs funded by the American Recovery and Reinvestment Act. The criterion for providing an EFRC with Recovery Act funding was job creation. The EFRCs chosen for funding under the Recovery Act provide the most employment for postdoctoral associates, graduate students, undergraduates and technical staff, in keeping with the Recovery Act’s objective to preserve and create jobs and promote economic recovery.
 
“The ASU center will not only investigate new scientific realms, but also study how best to incorporate new discoveries about energy into useful technology and the fabric of everyday life,” Gust says.
 
The EFRC award is an example of the economic benefit a research university can bring to its state. Each year, Arizona universities contribute nearly $1 billion into the Arizona economy from their research, most of which is funded by the U.S. government and entities from outside the state. Research money brought in by universities is restricted money that can be used only for the research activity it supports. It cannot be used to compensate for cuts in other parts of the university’s budget.
 
 
Source:
Devens Gust, (480) 965-4547
 
Media contacts:
Skip Derra, (480) 965-4823;
skip.derra">mailto:skip.derra@asu.edu">skip.derra@asu.edu
Jenny Green, (480) 965-1430; jenny.green">mailto:jenny.green@asu.edu">jenny.green@asu.edu Download Full Image

Director, Media Relations and Strategic Communications

480-965-4823