PLANETARY MUSINGS

Entries in "MESSENGER"

Iron snow on Mercury

One of the active areas of research in our group is developing understanding of mechanisms that can drive convection inside the metallic cores of solid planets and moons. Why? To understand what may be driving magnetic fields. Previously, we had demonstrated that in contrast to the Earth, Ganymede's magnetic field could be the result of solid iron precipitating at the core-mantle boundary and "snowing" inward, driving compositional convection. Based on new experimental results by colleagues Bin Chen and Jie Li at the University of Illinois we have shown that a similar set of results is possible for Mercury. The effect at Mercury is pronounced by non-ideal melting behavior of the Fe-FeS system at modest pressures. Indeed, it turns out that Mercury could also evolve to a state of having to distinct and separated zones of snowing iron in its core. All of these results will be useful in understanding the results that will be gained by the MESSENGER mission to Mercury once it gets into orbit.

Citation:
Chen, Bin, Jie Lie, and Steven A. Hauck, II, Non-ideal liquidus curve in the Fe-FeS system and Mercury's snowing core , Geophys. Res. Lett., 35, L07201, doi: 10.1029/2008GL033311 (2008). Article

Graduate Study in Earth and Planetary Science

The Department of Geological Sciences at Case Western Reserve University is currently accepting applications from students interested in pursuing graduate studies leading to M.S. and Ph.D. degrees in the earth, environmental, and planetary sciences. The Department offers flexible, research-intensive programs for graduate students. Applications are accepted on a continuing basis, though students requesting financial support are strongly encouraged to apply by February 1, 2008. Online applications are available through the School of Graduate Studies.

There are several opportunities for students interested in pursuing research in planetary science, particularly in the areas of planetary geology and geophysics, high-pressure and temperature geochemistry, and meteorites working with a group of faculty that includes myself, Prof. Harvey, and Prof. Van Orman.

At present I am collaborating with students to (1) understand the nature of Mars' crust and lithosphere and tectonic activity and (2) the mechanisms responsible for driving Ganymede's magnetic field. (3) I am also looking for graduate students interested in working with me on analyzing data from the MESSENGER Mission to Mercury to understand both the internal and tectonic evolution of that planet Additional opportunities within these may be available depending upon interest. We are also in the process of focusing new study on large lunar impact basins.

I would welcome the opportunity to discuss opportunities for graduate study in planetary science and/or geophysics with interested students (my contact info is available on my webpage).

Predicted recovery of Mercury's internal structure by MESSENGER

A major focus of research in our group over the last several years and now looking forward with our involvement with the MESSENGER is the planet Mercury. A question of primary interest to the scientific community is the origin of the planet's large bulk density and the nature of its core. Recent work by Jean Luc Margot of Cornell and colleagues recently demonstrated that Mercury likely has a core that is at least partially molten. This is an important advance, and the MESSENGER mission will bring more, particularly through measurement of the planet's low-degree gravity field.

In preparation for MESSENGER's arrival we have calculated a series of models of Mercury's internal structure in order to estimate how well new data will constrain the state of the interior. Working with Sean Solomon (CIW) and Derek Smith (former Case student now pursuing a Ph.D. at Dartmouth) we have calculated that within current estimates of the quality of MESSENGER's forthcoming measurements that it may be possible to determine the size and density of Mercury's core and mantle with considerable confidence, especially for a body for which we have no samples and placed no landers nor seismometers on its surface.

The results of this work were recently published in Geophysical Research Letters.

Hauck, Steven A., II, Sean C. Solomon and Derek A. Smith, Predicted recovery of Mercury's internal structure by MESSENGER, Geophys. Res. Lett., 34, L18201, doi: 10.1029/2007GL030793 (2007). Article

24 million km laser link

D. E. Smith, M. T. Zuber, X. Sun, G. A. Neumann, J. F. Cavanaugh, J. F. McGarry, T. W. Zagwodzki, Two-Way Laser Link over Interplanetary Distance, Science, 311, 53, (2006), Article.

Clearly one of the coolest "simple" experiments I have seen lately.  The MESSENGER spacecraft, which is on its way to Mercury, made a two-way laser link with Earth last May.  Apparently, at approximately 24 million km (a true interplanetary distance) that is a new distance record for detecting a laser.  The link was made both by the Mercury Laser Altimeter (MLA) pointing at telescopes at NASA's Goddard Geophysical and Astronomical Observatory and simultaneous pointing of an Earth-based laser at the same location toward the spacecraft.  The experiment is useful as a calibration of the MLA instrument in space as well as establishing that such an experiment can be accomplished.  Two-way laser communication may become important for future spacecraft which need precise distance and other measurements, like the proposed LISA mission to search for gravity waves.