Earth-Moon differences

Earth-Moon Differences. Scientists believe that the moon s surface has a large number of craters formed by the impact of meteorites. In contrast, there are relatively few meteorite craters on the Earth, even though, based simply on its size, the Earth is likely to have been hit by as many or even more meteorites than the Moon. This notable difference is attributed to the Earth s atmosphere, which bums up incoming meteorites, particularly small ones (the Moon does not have an atmosphere). Larger meteorites can pass through the Earth s atmosphere, but their impact craters may have been filled in or washed away over millions of years. Only the more recent ones, such as Meteor Crater in northern Arizona, with a diameter of 4,000 feet and a depth of 600 feet, remain easily recognizable. 

The quantity g is called the acceleration due to gravity and is equal to m2G/r2. At sea level and 45° latitude on the Earth (i.e., the condition for standard gravity, gstd) the value of g is 32.174ft/s2 or 9.806m/s2. The value of g is obviously different on the moon (different r and m2) and varies slightly over the surface of the earth as well (since the radius of the earth varies with both elevation and latitude). 

Poitrasson F, Freydier R (2005) Heavy iron isotope composition of granites determined by high resolution MC-ICP-MS. Chem Geol 222 132-147 Poitrasson F, Halhday AN, Lee DC, Levasseur S, Teutsch N (2004) Iron isotope differences between Earth, Moon, Mars and Vesta as possible records of contrasted accretion mechanisms. Earth Planet Sci Lett 223 253-266... 

Co-accretion. This theory proposes that the Earth and Moon simply accreted side by side. The difficulty with this model is that it does not explain the angular momentum of the Earth-Moon system, nor the difference in density, nor the difference in volatile depletion (Taylor, 1992). 

Wolf R. and Anders E. (1980) Moon and Earth compositional differences inferred from siderophiles, volatiles, and alkalis in basalts. Geochim. Cosmochim. Acta 44, 2111-2124. 

Observations of the Moon from Earth, reveal different phases of the Moon with respect to the percentage of lunar surface reflecting sunlight back to Earth. As the Moon orbits Earth, it comes between Earth and the Sun once a month at the time of a new Moon, and orbits Earth in very nearly the same plane that the Earth orbits the Sun. If the Moon s orbital plane had zero tilt off the Earth s orbital plane, a total lunar eclipse would be visible every month. 

From a mathematical point of view, the task of finding (approximate) eigenfunctions of Equation 1.5 for a molecule is no more complicated than solving the Newtonian equations for a mechanical system with a similar number of bodies such as the solar system. An important difference is that the interactions between all particles in a molecule are of comparable magnitude, on the order of electronvolts (leV x NA = 96.4 kJ mol ). In calculations of satellite trajectories or planetary movements, on the other hand, one can start with a small number of bodies (e.g. Sun, Earth, Moon, satellite) and subsequently add the interactions with other, more distant or lighter bodies as weak perturbations. This greatly simplifies the task of calculating a satellites trajectory. 

In reviewing noble gas studies of Mars, we will touch on topics that are covered for the Earth, Moon or more common meteorites in several other chapters. In most cases. Mars provides another place to apply the techniques developed for the Earth and Moon, and gives intriguingly different results. 

During the late 1600s, the Danish astronomer Ole Romer (1644-1710) measured the orbits of several of Jupiter s moons. These moons move much faster than our own—they have orbits of 1-7 days and are eclipsed by Jupiter s shadow at every revolution. Over many months, Romer measured discrepancies of up to 10 minutes in the times of these orbits. He reasoned that the discrepancies occurred because Jupiter was farther from Earth at different times of the year. Thus, light from the Sun, which reflected off Jupiter and ultimately to his telescope, had farther to travel at different times of the year, implying that light travels at a finite speed. Romer s data led to the first estimate of the speed of light, 3.5 X 10 m/s. 

Earth at different times such deviations are called the libration of the Moon. The planes of the lunar equator, of the ecliptics, and of the lunar orbit are always crossed in one straight line. 

This difficulty is not peculiar to electrons the same limitations also hold in the case of the earth and moon. Since, however, the mass of the moon (7.4 X 10 g) is so very much greater than that of the electron (9.1 x 10" g), the product of errors Sv 5q is completely negligible in the case of the moon but disastrous in the case of the electron, the relative importance of the errors for the electron and for the moon differing by no less than fifty-eight powers of ten. Any attempt to calculate the orbit of the electron in hydrogen is therefore doomed to kilure because we cannot get the information needed to do it. 

The history of the formation processes of the two now very close but distinctly different objects (Pluto and Charon) is discussed by Dobrovolskis etal. (1997) and by Stem et al. (1997). A collision scenario, similar to that invoked in the formation of the Earth-Moon system, is presently the preferred theory. Information on Pluto and Charon can also be found in articles by Lunine et al. (1989) and by Buie (1992). 

Tidal Power. Tidal power is caused by the gravitational pull of the sun and especially the moon, as they pull at the earth. Reacting to this pull, the ocean s waters rise, causing a high tide where the moon is closest. The difference between low and high tide can range from a few cm to several meters. Harnessing tidal power for electricity production by the use of dams requires a tidal difference of at least 4.5 m, a requirement met at few locations in the United States. Thus, the principal demonstration sites of tidal power are in Canada, China, and France. 

An element is a substance that cannot be broken down into simpler substances by ordinary means. A few more than 100 elements and many combinations of these elements—compounds or mixtures—account for all the materials of the world. Exploration of the moon has provided direct evidence that the earth s satellite is not composed of any different elements than those on earth. Indirect evidence, in the form of light received from the sun and stars, confirms the fact that the same elements make up the entire universe. Helium, from the Greek Helios, meaning sun, was discovered in the sun by the characteristic light it emits, before it was discovered on earth. 

The elements occur in widely varying quantities on earth. The 10 most abundant elements make up 98% of the mass of the crust of the earth. Many elements occur only in traces, and a few are synthetic. Fortunately for humanity, the elements are not distributed uniformly throughout the earth. The distinct properties of the different elements cause them to be concentrated more or less, making them more available as raw materials. For example, sodium and chlorine form salt, which is concentrated in beds by being dissolved in bodies of water which later dry up. Other natural processes are responsible for the distribution of the elements which now exist on earth. It is interesting to note that the different conditions on the moon—for example, the lack of water and air on the surface—might well cause a different sort of distribution of the elements on the earth s satellite. 

A corroboration of the theory that the moon was formed mostly from material coming from the Earth is due to researchers from the Max Planck Institute for chemistry in Mainz (Mtinker et al., 2003). The chemical analysis of material from the surface of the moon shows great similarity with material from the Earth s crust however, there are certain differences. For example, the concentration of iron on the moon is much lower than that on Earth. 

Now, apart from the planets, many meteorites were formed, moving in quite different orbits and of quite different chemical composition. In particular, the so-called C-l meteorites composed of carbonaceous chondrites have a composition of elements much closer to that of the Sun. It is proposed (see for example Harder and also Robert in Further Reading) that many of these meteorites collided with very early Earth and became incorporated in it, so that eventually some 15% of Earth came from this material (see Section 1.11). Other planets such as Mars and the Moon could have had similar histories, but the remote planets and Venus are very different. 

It is interesting to note that the action of the moon on the oceans is such as to excite vibrations approximating the I2 modes with a phase difference of a quarter cycle between them. This is why the period of the tides is 12 hours although the earth rotates under the moon with a period of 24 hours. 

The O isotopes show signihcant heterogeneity between the different meteorite classes (Fig. 8a Clayton et al. 1976, 1977). Differences are small, but, each chondrite group has a distinct bulk O isotopic composition. O isotopes also indicate the close ties between the Earth and the Moon. O therefore can be used to identify members of a family that formed from a common reservoir, which is the definition of a tracer. Such differences are also formd between chondrules within the same meteorites related to their size (Gooding et al. 1983). This is a survival of the initial isotopic heterogeneity in already high temperature processed materials like chondrules. 

Extraterrestrial materials consist of samples from the Moon, Mars, and a variety of smaller bodies such as asteroids and comets. These planetary samples have been used to deduce the evolution of our solar system. A major difference between extraterrestrial and terrestrial materials is the existence of primordial isotopic heterogeneities in the early solar system. These heterogeneities are not observed on the Earth or on the Moon, because they have become obliterated during high-temperature processes over geologic time. In primitive meteorites, however, components that acquired their isotopic compositions through interaction with constituents of the solar nebula have remained unchanged since that time. 

Would the process function differently if it took place on the moon instead of on Earth ... 

The Apollo astronauts returned 382 kg of lunar sample to Earth, and this collection was supplemented by 326 g of soil samples collected by the Soviet Luna landers. The first lunar meteorite was found in 1982 in Antarctica. Since that time, over 120 lunar meteorites representing about 60 different fall events have been collected. The total mass of these meteorites is -48 kg. About one-third of these meteorites were recovered in Antarctica by American and Japanese teams, and most of the rest were recovered in the deserts of North Africa and Oman. The lunar meteorites have significantly expanded the areas of the Moon from which we have samples. 

A great deal is known about chemical and isotopic fractionations on or within the Earth these are the business of geochemistry. It is important to remember, though, that our planet is a grand experiment carried out under a particular, and possibly unique, set of conditions. Meteorites, and the few samples available from the Moon and Mars, allow us to see how similar grand experiments proceeded under different conditions. Based on measured element and isotopic fractionations in meteorites, a rich variety of fractionation processes is indicated. 

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