Motivation:
The main motivation of my research is to “figure out how planets work”. As a geologist I have numerous questions about our own planet, the Earth. However, I choose a slightly different approach than most geologists to find answers to my questions. I strongly believe that detailed investigations of the geology of planetary bodies in our Solar System will not only expand our knowledge of these bodies, but ultimately will enable us to better understand geologic processes on Earth. Not all planets work the same way as the Earth, and for this reason it is beneficial to abandon our terracentric point of view, learn about other planets, and then come back to Earth to apply this knowledge. A strong component of comparative geology, and linking the results to Earth, is essential to successfully address questions such as: Why does Earth have plate tectonics, and other planets do not? How important is impact cratering in the inner Solar System and what are the implications for life on Earth? Only by looking at all the solid bodies in our Solar System and understanding as much as we can, will we have a chance to unravel the history and evolution of planet Earth.
I find it particularly interesting and exciting to study the influence of basic characteristics (size, density, gravity, distance from the sun, bulk composition, and atmospheric properties) on the evolution of a planet. This leads to kinds of questions like why is volcanism on Mars so different from volcanism on the Moon and tectonism on Venus so different from Mercury?
Planetary science is a very exiting field and offers ample opportunities for students to actively pursue research projects. On the basis of my experience with undergraduate research, the students' "fresh approach" can yield the most stunning results and I am looking forward to engage students at Central Connecticut State University to work with the latest data of various space missions.
Moon:
With my colleagues at the German Aerospace Center (DLR) and Brown University, I am working on a detailed stratigraphy of lunar mare basalts. I am particularly interested in the thermal evolution of the Moon and its consequences for volcanism. When did volcanism start and when did it end? Was volcanism continuously active or were there periods with more activity that alternated with more quiet periods? What is the influence of impact cratering on volcanism? Did the mineralogy of the erupted lavas change with time? In order to address these questions, I have dated large areas of the lunar nearside with remote sensing techniques. On the basis of the most extensive crater counting yet done, I found that lunar mare volcanism lasted from ~3.9 to ~1.2 b.y. ago, with most of the basalts erupting between ~3.3 and ~3.7 b.y. ago. Because most basalts occur within large lunar impact structures, scientists have argued for a close link between basin formation and volcanism; the impact event fracturing the crust to allow extrusion of basalts. However, my results indicate that these two processes are not necessarily linked with each other, as volcanism continued to be active for several hundreds of millions of years after the basin forming event.
The combination of my age data with multispectral and gamma-ray data allowed the detailed investigation of the mineralogical evolution of mare basalts with time. From the Apollo and Luna samples, an early reading of the data suggested that Ti-poor basalts were generally younger than Ti-rich basalts, and models were proposed in which lunar mare volcanism began with high-TiO2 content but decreased with time. However, I found no distinct correlation between the deposit age and the composition of lunar mare basalts. Instead, FeO and TiO2 concentrations appear to vary independently with time, and generally eruptions of TiO2-rich and TiO2-poor basalts must have occurred contemporaneously, as is the case for basalts with varying FeO contents. Currently I am investigating this relationship using new high-resolution mineralogical data, provided by the most recent missions, such as Lunar Prospector and Clementine. In this context, the lunar Smart-1 mission will hopefully prove very helpful, as this mission will return data at very high spectral resolution.
Another critical issue for our understanding the history and evolution of the Moon is the flux of lunar basaltic volcanism; that is, what volumes of basalt were erupted within a certain period of time and how the flux varied with time. Accurate lava flow thicknesses estimates are necessary to place constraints on volcanic flux estimates. I refined the technique of using the shape of crater size-frequency distribution curves to estimate the thicknesses of individual mare flow units. This technique expands considerably the ability to assess lava flow unit thicknesses and volumes on the Moon and the other planets. My measurements indicate that lunar lava flow units are on average 30–60 m thick. These thicknesses are commonly greater than those typical of terrestrial basaltic lava flows and more comparable to those of terrestrial flood basalts; a correlation consistent with evidence for high effusion rates and volumes for basalt eruptions in the lunar environment.
Finally, do mare basalts on the farside differ in their composition and ages from the basalts on the nearside, and if so, what does this tell us about the crustal structures and evolutions of the two hemispheres? In order to answer these questions, I have planned new crater counts for the basalt deposits on the lunar farside. In addition, I am currently working on a detailed investigation of the structure and evolution of the largest and oldest impact basin in the Solar System, the South Pole-Aitken basin, which has been given high priority for a future sample return mission.
As a co-investigator, I submitted a
proposal to NASA to fly two camera systems on the Lunar Reconnaissance
Orbiter, which is scheduled for launch in 2008. This proposal has been
accepted for funding and I am currently working on the preparation of
this mission. Besides other things, the Lunar Reconnaissance Orbiter
will provide new global high-resolution data suitable for future crater
counts in areas currently poorly imaged, will allow a detailed
characterization of future landing sites, and will provide information
on lunar resources and the illumination conditions close to the lunar
poles.
Mars:
My interests in the planet Mars are wide-ranging, including hydrology, tectonism, volcanism, and the evolution of impact basins. For these studies I am using high-resolution Martian topographic data, obtained by the Mars Orbiter Laser Altimeter (MOLA) as well as images from the MOC camera of the Mars Global Surveyor spacecraft. Images from the High Resolution Stereo Camera (HRSC) and thermal-infrared images of the THEMIS instrument on Mars Odyssey are newly available data sets, which proved to be very valuable for my research.
So far my research focused on investigating the existence of a potential north polar ocean, the formation process of giant polygons in Utopia Planitia, the history and hydrologic evolution of the Argyre basin, and the geology of Syrtis Major. The formation of giant polygons and my work on the north polar ocean and the Argyre basin directly relate to NASA’s Mars exploration philosophy of “follow the water”. There is ample evidence that Mars once had copious amounts of water and one of the major scientific questions regards the fate of the water.
Together with my colleagues, I tested several lines of evidence for a putative north polar ocean. These tests included the evaluation of the topographic position of potential shoreline features, the comparison of the surface roughness below and above the shoreline, the distribution of morphologic features, interpreted to be related to a water-rich substrate, and the estimation of water volumes contained in the polar ocean. On the basis of this study, we concluded that the geologic evidence is consistent with the putative northpolar ocean. The results of our investigation have been published in Science.
The formation process of large-scale Martian polygons remained an enigma since they were first discovered in Mariner and Viking data. Using new topography and imaging data, I tested several models of the polygon formation process. As none of these models were fully consistent with the data, I proposed a new model, by which giant polygons form via isostatic rebound and fracturing of the surface after the removal of an ice sheet or ocean several kilometers thick.
It has been proposed that during the Noachian, the Argyre basin was part of the longest drainage system on Mars. In this model, melt water from the South Pole supposedly filled the basin to its rim before it spilled over and formed large channels that ultimately delivered water to the northern lowlands. On the basis of my investigation I concluded that this hypothesis is inconsistent with the current data. However, the data are consistent with a partial fill of the basin with melt water that originated from a retreat of the south polar cap during the middle history of Mars, the Hesperian.
I am also very interested in Syrtis Major, one of the most prominent Hesperian volcanic complexes on Mars, located at the western rim of the Isidis basin. One major motivation for this research was to investigate the modification of the Isidis basin rim by lava flows from Syrtis Major. Crater counts reveal that Syrtis Major is older than previously thought and new topography data indicate that the Syrtis Major lavas are extremely flat and only 0.5-1 km thick. High-resolution MOC images show that Syrtis Major experienced significant amounts of eolian modification and high-resolution thermal-infrared THEMIS images allowed the detailed study of the two calderas of Syrtis Major.
Currently I am investigating the geology of the Isidis basin. On the basis of Viking, THEMIS and MOC data, numerous curvilinear ridges that consist of individual cone-like features with central caldera-like depressions were identified on floor of the Isidis basin. These ridges are highly unusual in their morphology and there are several hypotheses for their formation process. Thus, my research explores the formation of these ridges with new high-resolution topography and imaging data.
Most
recently I was working with new HRSC data of one of the large Tharsis
volcanoes, Ascraeus Mons. By mapping and measuring the dimensions of
individual young lava flows on the flanks of Ascraeus Mons, I was able
to derive their rheological properties. A comparison with terrestrial
lava flows indicated that the Martian flows are likely basaltic in
composition, were erupted within months and have viscosities similar to
lava flows in Hawaii.
Ganymede:
Ganymede,
one of the four Galilean satellites, shows evidence for extensive
tectonism. Together with my co-workers, I used mathematical techniques,
including Fourier analyses, to investigate the tectonic history of
Ganymede’s grooved terrain. On the basis of this study we identified
two wavelengths of surface modification. Our results support the
hypothesis that longer topographic wavelengths in Ganymede’s groove
lanes formed by means of extensional necking of the lithosphere, while
multiple shorter wavelengths formed by normal faulting of the brittle
lithosphere. In addition, my geologic and tectonic mapping of
high-resolution Galileo images allowed me to study the stratigraphy of
Nippur Sulcus in unprecedented detail.
Mission planning:
Besides working on specific geologic problems, I enjoy planning future missions. In the past, I was involved in defining the imaging strategy for the HRSC camera on the European Mars Express mission, and the target selection for the SIR spectrometer on the lunar Smart-1 mission. In addition, I will be involved in the development of an imaging plan for the two cameras of the Lunar Reconnaissance Orbiter. I enjoy this type of work because it adds a different layer of complexity to my professional development. It requires a solid understanding of the planets’ geology and “thinking ahead” about how to acquire the kind of data that would be best suited to answer specific scientific questions. It also requires an understanding of the capabilities and limitations of any specific instrument. Not only is mission planning very different from “using” data, it also provides great experiences in working with engineers and people from different disciplines.
