Stefan of Backreaction posted a blog entry called,”Mercury looks like the Moon, nearly… that brought me up to speed on what the planet actually looks like.
His article provides for the links here in this entry, as well sets the stage for the culminating vision I have of our solar system. Looking at the solar system in the processes I outline are important point of seeing the gravitational aspects of the universe as we have come to know it.
I had never considered what the actual surface of Mercury would look like, other then what I had thought it to be, when told as a child. A molten surface.
Using the laser altimeter, MESSENGER will verify the presence of a liquid outer core in Mercury by measuring the planet’s libration. Libration is the slow 88-day wobble of the planet around its rotational axis.
Seeing Mercury the way it is below provides for some thought about Mercury facing toward the Sun. It’s surface looking at the picture below, I was wondering if facing directly in opposition to the Sun would showing brighter spots as we look to the right of this image.
This also raised an interesting question on my mind about how the uniformity of the surface could retain it’s moon like look while undergoing the passage of “increased heat” as it faced the sun at anyone time through it’s rotation.
Question 4 : What is the structure of Mercury’s core?
More recently, Earth-based radar observations of Mercury have also determined that at least a portion of the large metal core is still liquid to this day! Having at least a partially molten core means that a very small but detectable variation in the spin-rate of Mercury has a larger amplitude because of decoupling between the solid mantle and liquid core. Knowing that the core has not completely solidified, even as Mercury has cooled over billions of years since its formation, places important constraints on the thermal history, evolution, and core composition of the planet.
<a href="http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=121" target=_Blank title="MESSENGER Reveals Mercury’s Geological History-
A NASA Discovery mission to conduct the first orbital study of the innermost planet”>
This MESSENGER image was taken from a distance of about 18,000 kilometers (11,000 miles) from the surface of Mercury, at 20:03 UTC, about 58 minutes after the closest approach point of the flyby. The region shown is about 500 kilometers (300 miles) across, and craters as small as 1 kilometer (0.6 mile) can be seen in this image.
The Gravity Field
Clementine color ratio composite image of Aristarchus Crater on the Moon. This 42 km diameter crater is located on the corner of the Aristarchus plateau, at 24 N, 47 W. Ejecta from the plateau is visible as the blue material at the upper left (northwest), while material excavated from the Oceanus Procellarum area is the reddish color to the lower right (southeast). The colors in this image can be used to ascertain compositional properties of the materials making up the deep strata of these two regions. (Clementine, USGS slide 11)
This is always of interest to be because it is an accumulation of the synthesis of views we gain as we come to understand not only the views of on the Window of the universe, as we look at the Sun under information obtain in the neutrino laboratory’s and information modelling of how we can now look at the sun with this new view.
But the truth is, the Earth’s topography is highly variable with mountains, valleys, plains, and deep ocean trenches. As a consequence of this variable topography, the density of Earth’s surface varies. These fluctuations in density cause slight variations in the gravity field, which, remarkably, GRACE can detect from space.
Well, by adding the label of Grace and Grace satellite systems, it is important to me that not only is gravity considered in context of the exploration of space in terms of Lagrangian, but of viewing how we map the earth and the views we obtain of that new gravity model of earth. This application then becomes of interest as we understand how we see the gravity model of Mercury and how the geological structure of Mercury will be reflected in that gravity model.
The Culminating Vision
Fig. 1. Story line showing the principle of least action sandwiched between relativity and quantum mechanics See A call to action