Our Solar System

Planet formation followed the planetesimal and protoplanet formation in the final stage of the disk evolution (Chapter 10). Gas giants, Jupiter and Saturn, captured disk gas due to their large gravities, and other planets, including Earth, may also have some evidence of disk-gas capture. In the second part of this section, we will seek constraints on the timing of dust and gas dispersal in the proto-solar disk from planets (Section 9.3.2). 

Bulk isotopic compositions of chondrites. Isotopic compositions of bulk chondrites are essentially uniform within variations of 0.1-0.01% except for light elements such as H, C, N, and O and for presolar grains (see e.g. Lodders 2003 Palme Jones 2003). Presolar grains have isotopic compositions significantly different from those of Solar System materials, suggesting that they were dust particles formed in circumstellar environments and incorporated into the proto-solar molecular cloud (Chapter 2 and see e.g. Nittler 2003 Zinner 2005). Presolar grains are thus considered to be the first dust components that formed in the proto-solar disk. The rarity of presolar grains in chondrites (several ppb for silicon nitride to 200 ppm 

The lines of evidence from CAIs and AOAs suggest that disk gas was present in the earliest epoch of solid formation in the Solar System. However, it is not clear what stage of the proto-solar disk evolution corresponds to the earliest solid formation in the Solar System. This makes it difficult to compare the evolution of the proto-solar disk with that of protoplanetary disks (see Section 9.4). 

Chondrules. Chondrules are major constituents of chondrites, which are millimeter- to submillimeter-sized spherules consisting of silicate phenocrysts (relatively large crystals), glassy mesostasis, and a small fraction of opaque phases (Lauretta et al. 2006 and references therein Chapter 8). Their textural, mineralog-ical, and chemical features suggest that chondrules formed from dust aggregates that were melted by localized transient high-temperature events and were cooled relatively rapidly. 

Although chondrules have diverse chemical compositions, their sizes are narrowly sorted (Grossman et al. 1988 Brearley Jones 1996). Such a narrow size distribution may be explained by aerodynamic sorting provided by turbulence in the proto-solar disk, i.e. in the presence of disk gas. A correlation was found between the volume of the chondrule and the volume of the accretionary fine-grained dust rim on chondrules in the Allende meteorite (Paque Cuzzi 1997). These results could also be explained in terms of aerodynamic sorting in the gaseous disk. 

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It is estimated that the earth s age is in the neighborhood of 4 to 7 billion years. These estimates are basically derived from carbon-14, potassium-40, uranium-235, and uranium-238 dating of earth rocks and meteorites. The meteorites give important data as to the age of our solar system. Geologic time is felt to be represented by the presence of rock intervals in the geologic column (layers of rock formations in vertical depth) or by the absence of equivalent rocks in correlative columns in adjacent locations [25,26]. The two basic factors that are used to determine geologic time are ... 

Our solar system consists of the Sun, the planets and their moon satellites, asteroids (small planets), comets, and meteorites. The planets are generally divided into two categories Earth-like (terrestrial) planets—Mercury, Venus, Earth, and Mars and Giant planets—Jupiter, Saturn, Uranus, and Neptune. Little is known about Pluto, the most remote planet from Earth. 

In order to understand the Earth s character as a planet, it also is helpful to have an understanding of how the elements in our solar system were formed. Chapter 2 starts with the Big Bang theory and continues with how very small grains eventually came together and accreted to form the beginnings of what would eventually become the Earth and other planets, about 4.5 X 10 years ago (4.5 Gyr). The initial processes of the Earth s evolution involved heat... 

How can scientists collect experimental evidence about possible life on another planet Sending astronauts to see for themselves is impractical at our current level of technology. Nevertheless, it is possible to search for life on other worlds without sending humans into space. In the late 1970s, NASA s Viking spacecraft lander collected a sample of dirt from Mars, the planet in our solar system most like Earth. The sample showed no signs of life. Nevertheless, speculation continues about Martian life. 

Our planet Earth contains significant amounts of elements all the way up to Z = 92. This indicates that our solar system resulted from the gravitational collapse of a cloud of matter that included debris from second-generation stellar supemovae. Thus, our sun most likely is a third-generation star. The composition of a third-generation star includes high-Z nuclides, but the nuclear reactions are the same as those in a second-generation star. 

Two types of theory have been put forward to explain the formation and development of our solar system catastrophe and evolution. The former assumes a collision or coming together of two stars. As early as 1745, the French scientist Count Buf-fon postulated that the Earth had been torn out of the sun by a passing comet. He estimated the age of the Earth to be 70,000 years, while theology proclaimed that the Earth was less than 6,000 years old. 

According to present-day concepts, our solar system was formed from a huge gas-dust cloud several light years across in a side arm of the Milky Way. The particle density of this interstellar material was very low, perhaps 108-1010 particles or molecules per cubic metre, i.e., it formed a vacuum so extreme that it can still not be achieved in the laboratory. The material consisted mainly of hydrogen and helium with traces of other elements. The temperature of the system has been estimated as 15 K. 

The two rare earth elements niobium (Nb) and tantalum (Ta) were the main subject of study in the investigation referred to. Both elements have very similar properties and almost always occur together in our solar system. However, the silicate crust of the Earth contains around 30% less niobium (compared to its sister tantalum). Where are the missing 30% of niobium They must be in the Earth s FeNi core. It is known that the metallic core can only take up niobium under huge pressures, and the conditions necessary for this may have been present on Earth. Analyses of meteorites from the asteroid belt and from Mars show that these do not have a niobium deficit. 

Long-period comets their extended ellipsoidal orbits reach far outside our solar system (up to half the distance to the next fixed star). This group includes the comet Kohoutek, discovered in the 1970s, which requires about 75,000 years for a single orbit. 

Although the terms exobiology and astrobiology really mean the same thing, astro-biology , introduced by NASA in 1995, has become the one of choice. This branch of science reaches from cosmochemistry via biogenesis to all the other themes involving research on traces of life (of whatever sort) on planets and on moons, both within and outside our solar system. 

Of the three extraterrestrial targets in our solar system, the Saturnian moon Titan is the least likely to provide signs of life. To quote Christopher McKay from the NASA Ames Research Center, Titan is an interesting world. For example, its organic haze layer could be an example of the prebiotic chemistry which led to life on Earth . Direct links to extraterrestrial life have not, however, yet been found, as water (one of the main preconditions for life) has not been detected on Titan, apart from traces of water vapour in the higher layers of the Titanian atmosphere (Brack, 2002). 

The discovery of planets outside our solar system, using the transit method. For the first time, the search will be directed particularly towards planets which are only slightly larger than the Earth. The first, Corot-Exo-lb, was discovered in April 2007. 

It is assumed that the greatest part of our solar system, and indeed of the Milky Way, is hostile to life. The term habitable zone (Franck et al., 2002) takes into account... 

When, many, many million years in the future, our sun expands in its Anal phase to become a red giant, the habitable zone of our solar system will shift by 1-2 AU, to the region where Triton, Pluto/Charon and the Kuiper Belt are found. This zone is referred to as the delayed gratification habitable zone . All the heavenly bodies in this zone contain water and organic material, so that chemical and molecular... 

In which development phase of the universe could there have been the greatest chance of panspermia processes taking place A research group from the Potsdam Institute for Climate Research has tried to provide answers to this difficult question on the basis of research results from astronomy and astrophysics. Using mathematical models, they concluded that the maximum number of habitable planets in our galaxy must have been present at the time when our solar system and the young Earth were evolving (von Bloh et al., 2003). 

The radiation balance problem is not specific to our solar system and can be applied to all stellar planetary systems, although the number of planets outside our solar system - so-called extrasolar planets - is unknown. As noted earlier, the highest... 

Planets orbiting their own local star outside our solar system... 

Concepts Titan - the test case Physical and chemical properties of the only other body in our solar system with a significant atmosphere... 

Use this as a unit factor to determine the distance in miles between Alpha Centauri and our solar system. 

The careful study of at least five different carbonaceous chondrites establishes the fact that these meteorites contain carbon compounds of extraterrestrial origin and of great significance in chemical evolution. Their presence confirms that the chemical reaction paths producing biologically important monomer molecules occur in the far reaches of our solar system. 

Our chemical experiences suggest that differential equations seem to be something stable, and by that we mean that, if there is a small change in one of the conditions, either initial concentrations or rate constants, we expect small changes in the outcomes as well. The classical example for a stable system is our solar system of planets orbiting the sun. Their trajectories are defined by their masses and initial location and velocity, all of which are the initial parameters of a relatively simple system of differential equations. As we all know, the system is very stable and we can predict the trajectories with an incredible precision, e.g. the eclipses and even the returns of comets. For a long time, humanity believed that the whole universe behaves in a similarly predictable way, of course much more complex but still essentially predictable. Descartes was the first to formally propose such a point of view. 

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