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A Bright Moon Impact
2 days ago
Together with the metamorphic and igneous rocks of the adjacent Serie dei Laghi (SdL), collectively forming the Massiccio dei Laghi (Boriani et al., 1990), the rocks of the region record Palaeozoic accretion, metamorphic and magmatic processes, the effects of the Hercynian orogeny, post-orogenic magmatic underplating and associated lithospheric stretching and thinning, Mesozoic extension and effects associated with the position of the region in Alpine tectonism (e.g. Handy et al., 1999) (Fig.3).To the extent I have a particular interest in a specific sub-discipline of geology (I don't really), I would probably have to say igneous petrology is it. Petrology is the study of how rocks are formed; igneous petrology deals specifically with rocks that cool and crystallize from a molten state. The above implies, to me at least, that we're dealing with hot-spot volcanism. The ability to look at the compositional variations, along with temperature and pressure as recorded in minerals, from the top of the mantle to the surface of the earth is as exciting as anything I can conceive. And for those of you into structure, there are some diagrams that almost qualify as pornography (see, for example, the bottom of page 8 and top of page 9).
Geology and volcanology have seen some warranted increase in notoriety and recognition since the release of movies like Supervolcano, and since the publication of supervolcano articles in popular scientific magazines like Scientific American and Discover, however overdramatized or inexact the popular renditions might be. The Wikipedia article Supervolcano, for example, says that "Supervolcanoes are relatively new to science; they were previously unknown because they do not fit the stereotypical model of volcanoes." This statement is incorrect: very large-scale explosive caldera-forming eruptions have been known to geologists for quite some time. Hey, I knew about them way back in the dark ages, before I reached the age of thirty!I know that the enormous eruptions at Yellowstone had been well-documented by the early 80's when I started in geology, and I think it's important to keep in mind that only 15 years earlier, plate tectonic theory was only starting to be widely accepted in the US.
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Question 1: Why is Mercury so dense?Note that most of the questions are equivalent to geology. Even though Mercury is quite close compared to the other planets, it's hard to observe because it's so close to the sun from our perspective. And though intuitively it seems that falling deeper into the gravity well should be easy, there are two issues that make it much more difficult than one might think: first, we're traveling pretty rapidly around the sun. If you want to fall inward, you have to slow your orbital velocity dramatically. Second, on the fall inward, a tremendous amount of gravitational potential energy is converted into kinetic energy; the space craft's velocity, despite its initial decrease, is enormously increased during the fall toward the sun. So if you want to get it to orbit Mercury, you have to slow it down once again when it arrives. Simply put, it's not possible to carry enough fuel (with current technology) to pull this off without some ballistic trickery. MESSENGER has performed 5 "gravity assist" maneuvers already. The last one, today, will allow it to be captured on its next approach.
Mercury's density implies that a metal-rich core occupies at least 60% of the planet's mass, a figure twice as great as for Earth! MESSENGER will acquire compositional and mineralogical information to distinguish among the current theories for why Mercury is so dense.
Question 2: What is the geologic history of Mercury?
Before the MESSENGER mission, only 45% of the surface of Mercury had been photographed by a spacecraft! Using its full suite of instruments, MESSENGER will investigate the geologic history of Mercury in great detail, including the portions of the planet never seen by Mariner 10.
Question 3: What is the nature of Mercury's magnetic field?
Mercury has a global internal magnetic field, as does Earth, but Mars and Venus do not. By characterizing Mercury's magnetic field, MESSENGER will help answer the question of why the inner planets differ in their magnetic histories.
Question 4: What is the structure of Mercury's core?
Through a combination of measurements of Mercury's gravity field and observations by the laser altimeter, MESSENGER will determine the size of Mercury's core and verify that Mercury's outer core is molten.
Question 5: What are the unusual materials at Mercury's poles?
At Mercury's poles, some crater interiors have permanently shadowed areas that contain highly reflective material at radar wavelengths. Could this material be ice, even though Mercury is the closest planet to the Sun? MESSENGER will find out.
Question 6: What volatiles are important at Mercury?
MESSENGER will measure the composition of Mercury's thin exosphere, providing insights into the processes that are responsible for its existence.