PLANETARY MUSINGS

Entries in "Venus"

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).

Venus 2 Flyby a Success

MESSENGER's second flyby of Venus yesterday was a success! The spacecraft whizzed by the cloud tops at more than 30,000 miles per hour and changed its velocity by more than 15,000 miles per hour all to alter its orbit in preparation for its date with Mercury. Congratulations to the whole team of MESSENGER that designed, built and operates the mission!

The first data should start coming down on June 7-8 and then we can start learning what these new data tell us about our sister planet as well as fine-tune anything we need to in time for the first flyby of Mercury in 33 years next January.

More details are in the public press release from APL and at the MESSENGER website and NASA's MESSENGER webpage.

Venus Flyby 2

Late in the afternoon on Tuesday, June 5, 2007 the MESSENGER spacecraft is going to slingshot around Venus for the second time on it way to Mercury. The spacecraft will use Venus' gravity to assist in its journey to the solar system's inner most planet. During the first flyby of Venus last October the planet was on the far side of Sun from Earth (solar conjunction) and communication with the spacecraft was difficult at best, so no scientific data were taken, and MESSENGER flew by in a safe configuration with a closest approach of nearly 3000 km. On Tuesday the spacecraft will flyby as close as about 340 km and will be taking data this time with most of its instruments. The instruments onboard MESSENGER are optimized for surveying Mercury, however several are capable of taking important observations of Venus, particularly its atmosphere. It is also a great "dress rehearsal" for our first flyby of Mercury on January 14, 2008. There should be some exciting data from our sister planet coming down from MESSENGER in the next several weeks after the flyby. Several of these data will be compared with coordinated observations by ESA's Venus Express. We will be looking forward to some interesting new results in the coming months...

The shape of a plume

Farnetani, CG and H Samuel, Beyond the thermal plume paradigm, GRL, 32, L07311, doi:10.1029/2005GL022360, (2005).

The issue of mantle plumes (i.e., whether they exist) is a long-running problem that just keeps going back and forth on the teeter-totter. I've always thought that with as complex a planet as we have here that they yes or no approach was a bit limiting given that the fluid physics of thermal plumes is well-established... but I digress.

Farnetani and Samuel tackle the formation of plumes from a more general framework than is usually taken. The canonical view of plumes is that a mushroom-like head and thin conduit tail plume structure is created at a deep thermal boundary layer and traverses the mantle to the surface with modest entrainment of surrounding mantle. The head impacts the surface, creates a large igneous province and the conduit creates a following chain of volcanic centers as a plate moves over it. That's the broad framework, first-order and all. The Earth is more complex and this paper shows what happens if chemical buoyancy effects, mantle wind (caused by imposed plate motion at the surface), phase transitions, and heterogeneities are considered (if memory serves, many of these effects have been considered before, though maybe not all at once with the spatial resolution of this study). And in this more "relaxed" study of the relevant parameters, the authors have discovered that the plume head-tail structure is but one possible structure of a plume as it reaches the upper mantle. A plume head isn't even necessary, and a concentrically zoned plume tail isn't even necessary either. Basically, models of the Earth can be messy - consistent with the geochemical and seismological view.

Mantle plumes are just plain hard to avoid - there is heat coming out of the core, the boundary layer down at the core-mantle boundary is going to get unstable in some places every once in a while, and there are going to be plumes. The real questions are: what do they look like, how do they sample the mantle, and what happens when (if?) they reach the surface? These questions are still open. But this paper shows us that not every plume looks alike.

But... this view of plumes that a plume head is possible not necessary is interesting when extended to other planets. Now the "mantle wind" may not be as extensive on a planet without plate tectonics, but what is the driver behind the headless-plume? On Venus there are all the coronae and volcanic rises, many of which seem consistent with a thermal plume or diapir source (e.g., recent conceptual framework of Johnson and Richards, 2003). If even some of those, e.g. coroane, require head-like features, what does that mean for the mantle? Maybe it is just a question of scale... but the questions about mantles and their plumes seem to abound.