Bruce Hapke and Space Weathering

It is a tantalizing truth that objects in space do not look the same in the laboratory.  That when we compare the appearance of an asteroid in space - say using reflection spectroscopy - with meteorites that are supposed to come from those asteroids, we see more differences than similarities.  Did our meteorites not come from the most "obvious" sources, or does exposure to space conditions for billions of years change the appearance of the surface?  Space and planetary science consists in large part of remote sensing, using instruments on the ground or mounted on spacecraft to determine the nature of planetary surfaces, so the details of "space weathering" of planetary surfaces is of crucial importance.  Invariably, when this topic comes up at conferences one soon hears mention of the "Hapke model". Bruce Hapke, Professor of Geology and Planetary Science at the University of Pittsburgh, has provided the most successful and widely used description of the processes experienced by grains on the surface of an airless body.  Bruce was in Fayetteville recently to present the fall 2003 Barringer Lecture and for this public talk he drew on his long experience of lunar studies to discuss the Moon.  He described his feelings about this beautiful object and he described the history of its study, and possible future trends.  He also gave a group talk on space weathering to the cosmochemistry group.  He described how a combination of micrometeorite and radiation bombardment produces microscopic scale production of metal and glass, which have a profound effect on the optical properties of a planetary surface. Bruce is about to start a collaboration with the space center using the Andromeda chamber to explore space weathering on other objects.  A major challenge now is to consider how this process occurs on asteroids.  Just as samples of the lunar surface returned by the Apollo program were important in understanding space weathering on the Moon, so the samples returned from near-Earth asteroids by the Hera mission will bring great strides in resolving the long-standing quandary of the asteroid-meteorite mismatch.

Derek Sears, Center Director

Starting this Fall are Julie Chittenden, Cosmochemistry, University of Arkansas and Chris Adcock, Geology, Oklahoma State University.  Julie, originally a native of Arkansas, was educated at Arkansas State University where she gained a bachelors degree in chemistry. Since then she spent time in Arizona and returns home to Arkansas to pursue her doctorate in the space center.  She is working with Dr. Derek Sears on brine on Mars.  Chris Adcock is based at the OSU campus studying for a master’s degree with Dr. Richard Marston; his thesis will focus on geomorphological effects of wind on Mars.  We are very pleased to welcome these students to the space center; they will find their graduate experience demanding, challenging, and occasionally frustrating but, in the long run, we hope, greatly rewarding!

The space center has three of these highly prestigious fellowships available to students entering for Fall 2004.  Students would be based in one of the participating departments: Biological Sciences, Chemistry & Biochemistry, Geology, Mechanical Engineering, Physics. Stipends range up to $30,000 depending on eligibility and qualifications.  Awards are for four years; tuition paid.

Undergraduate students with degrees in science or engineering who have strong interests/experience in the space and planetary sciences are encouraged to apply.

The center offers state-of-the-art research, and a unique multi-disciplinary education experience that will make graduates highly competitive for positions in the field in both industry and academe.

For further details about our programs and application procedures please visit our web site at: www.uark.edu/csaps

Spectral Classification and Characterization of HERA Targets

The HERA spacecraft will visit a number of near-Earth asteroids (NEAs) in order to determine their bulk properties (size, mass , mass distribution, density, spin state, etc.) as well as gathering surface samples for return to the Earth.  Derek Sears, center director, University of Arkansas is the principal investigator on this mission.  In order to maximize the information return from this mission, it is vital for mission planners to know before launch the taxonomic classes of potential targets in order to be sure they sample a variety of NEA types during the mission.  These taxonomic classes are currently unknown for nearly all of the most favorable potential targets (small delta-V).  Sears together with center astronomer, Claud Lacy of the university of Arkansas plans to use the infrared spectrometers of the Infrared Telescope Facility (IRTF) operated by NASA on Mauna Kea to measure the 1-20 micron spectra of potential targets in order to determine their taxonomic classes.  The targets selected will include the same ones for which Dr. Al Grauer of the University of Arkansas, Little Rock, plans to measure light curves.  Dr. Grauer, an affiliate of the center, has an ongoing program to obtain light curves and other physical properties of near-earth asteroids with Steve Larson of the University of Arizona’s Lunar and Planetary Lab.  Spectra of brighter asteroids of known taxonomic classes will also be obtained and used as standards.  By analyzing the light curves and spectra of potential target NEAs, the sizes, shapes, spin state, and surface properties can be reliably estimated before mission launch, which will happen later in this decade.  Armed with this information, mission planners will be able to optimize the launch trajectory and mission timeline, hopefully leading to a successful Arkansas space mission.  In the event that the mission is not selected these measurements will still yield crucial scientific information on the nature of our nearest space neighbors with all this implies for impact mitigation.

"Isn’t that pretty?" 81-year-old Camilla Belle Dillon of Fayetteville summed up the view of Mars from atop the University of Arkansas’ Kimpel hall on an evening in late August.  Astronomer Dr. Claud Lacy and his graduate student Sammy Grimes assembled a 10 inch, $3000 dollar Meade telescope that night for the public to come view the Mars opposition – an event that supposedly takes place once every 300 years.  On August 27, 2003, Mars was currently 35 million miles away from earth, but usually it is 55 million miles away, according to Grimes.  Nearly 250 people stood in line to catch a glimpse of the Red Planet that evening, and due to a misprint in the local paper, about 60 people had come the night before.

"The weather has gone well for us," said Lacy of both nights.  "That was a lucky accident."  The southern ice cap of Mars was clearly visible through the telescope, regardless of light pollution from Fayetteville.  "With something that bright, it doesn’t matter," said Lacy.

Jennifer Lewter, University of Arkansas

Seminars take place via video conference (UArk: Chemistry Bldg., Rm. 226, OSU: Life Sciences East, Rm 216)
Alternative venues have asterisks beside them 

Wed., Sep 24, 3:30 pm
Dr. Derek Sears, University of Arkansas
"Water on Mars"