Planets, giant

Hydrogen is the primary component of Jupiter and the other gas giant planets. At some depth in the... 

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. 

The giant planets possess low surface temperatures and have atmospheres that extend several thousand miles. The markings on Jupiter, the largest planet, consist of cloud formations composed of methane containing a small amount of ammonia. The atmosphere of Jupiter absorbs the extreme red and infrared portions of the spectrum. These absorptions correspond to the absorption spectra of ammonia and methane, suggesting the presence of these gases in Jupiter s... 

In about 4 billion years our sun will also develop into a red giant. The diameter will then reach the orbit of Mars, and the inner planets will cease to exist. 

Binzel et al. (1991) give an account of the origin and the development of the asteroids, while Gehrels (1996) discusses the possibility that they may pose a threat to the Earth. The giant planets, and in particular Jupiter, caused a great proportion of the asteroids to be catapulted out of the solar system these can be found in a region well outside the solar system, which is named the Oort cloud after its discoverer, Jan Hendrik Oort (1900-1992). Hie diameter of the cloud has been estimated as around 100,000 AU (astronomic units one AU equals the distance between the Earth and the sun, i.e., 150 million kilometres), and it contains up to 1012 comets. Their total mass has been estimated to be around 50 times that of the Earth (Unsold and Baschek, 2001). 

The gas giant planets Jupiter, Saturn, Uranus and Neptune. The planet Pluto has a status of its own, and has recently been renamed a dwarf planet. 

One more important property of Jupiter must be mentioned the Earth owes its relatively quiet periods (in geological terms) to the huge gravitational force of the giant planet. Jupiter attracts most of the comets and asteroids orbiting in its vicinity, thus protecting the Earth from impact catastrophes ... 

Although Uranus and Neptune also belong to the group of gas giant planets, they are constructed differently from Jupiter and Saturn ... 

Short-period comets these display a strong tendency for their farthest point from the sun (aphelia) to coincide with a giant planet s orbital radius, so that we can distinguish so-called comet families . The Jupiter family of comets is the largest and numbers around 70 comets. The shortest orbital period known is that of the short-period comet Encke—about 3.3 years. 

On the Chemical Abundances of Stars with Giant Planets... 

In this paper we will review the current situation regarding the study of the chemical abundances of stars with giant planets, and discuss the implications these results have on the theories of planetary formation. 

Soon after the discovery of the first extra-solar planets, it has been noticed that planet-host stars these were particularly metal-rich when compared with single field dwarfs [12], i.e., on average they present a metal-content that is above the one found in stars now known to have any planetary-mass companion. This result, clearly confirmed by an uniform spectroscopic analysis of large samples of stars with and without detected giant planets [22] is obtained by using different... 

On the one side, the traditional core accretion scenario (e.g. [1]) tells us that giant planets are formed as the result of the runaway accretion of gas around a previously formed icy core with about 10-20 times the mass of the Earth. Opposite to this idea, some authors have proposed that giant planets may form by a disk instability process [4]. 

The results presented above, showing that the probability of finding a planet is a strong function of the stellar metallicity, thus favor the core-accretion model as the main mechanisms responsible for the formation of giant planets (although they do not completely exclude the disk instability model - see e.g. [19]). Indeed, it has even be shown that according to the core-accretion model it is possible to predict the observed [Fe/H] distribution of planet-host stars [9]. 

N. Santos On the chemical abundances of stars with giant planets . In This volume. 

Two completely different scenarios attempt to explain the presence of large Li abundances among the RGB stars. One is the result of an external contamination (pollution) produced by the engulfing of near giant planets or brown dwarfs companions. The second one is the result of an internal action known as the Cameron-Fowler 7Be mechanism. Here, we will make a brief discussion of both. 

The formation of the planets around the proto-sun initially started as a simple accretion process, aggregating small particles to form larger particles. This process was common to all planets, even the gas giants Jupiter and Saturn and to a lesser extent Neptune and Uranus. The planetesimals form at different rates and as soon as Jupiter and Saturn had reached a critical mass they were able to trap large amounts of hydrogen and helium from the solar nebula. The centres of Jupiter... 

A new reservoir of comets may have formed at around 5 AU in a local orbit around Jupiter or at least perturbed by its gravitational attraction. A comet close to Jupiter would simply have been captured, delivering its chemical payload to the ever-increasing gas giant. Some comets would merely have been deflected towards the inner terrestrial planets, delivering a similar payload of water and processed molecules. Cometary impacts such as the spectacular collision of the comet Shoemaker-Levy 9 with Jupiter would have been common in the early formation phase of the solar system but with a much greater collision rate. Calculations of the expected collision rate between the Earth and potential small comets deflected from the snow line may have been sufficient to provide the Earth with its entire... 

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