Jupiter: orbital period

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. 

The density estimates in Table 7.1 show a distinction between the structures of the planets, with Mercury, Venus, Earth and Mars all having mean densities consistent with a rocky internal structure. The Earth-like nature of their composition, orbital periods and distance from the Sun enable these to be classified as the terrestrial planets. Jupiter, Saturn and Uranus have very low densities and are simple gas giants, perhaps with a very small rocky core. Neptune and Pluto clearly contain more dense materials, perhaps a mixture of gas, rock and ice. 

Comets are generally considered to be weakly consolidated, and active comets are commonly observed to split into fragments. This is sometimes due to the tidal forces of a close planetary encounter, such as affected comet Shoemaker-Levy when it passed close to Jupiter in 1992 and broke into 21 pieces. More commonly, a comet spontaneously fragments multiple times over its orbit period, without any obvious cause. Disintegrating comets leave trails of small particles in their wakes. These trails are known as meteor streams, and when the Earth passes through such a meteor stream, as it does several times a year, a meteor shower occurs. Meter-sized rocks are known to occur within cometary meteor streams. 

The main-belt region is not evenly populated with asteroids, and several zones have been found in which virtually no asteroids reside (Fig. 1). The American astronomer Daniel Kirkwood (1814-1895) first noticed these empty regions, or gaps, in 1866. Now called Kirkwood gaps, these asteroid-devoid zones are located near orbits for which the time to complete one circuit around the Sun is a simple fraction (e.g., 1/2, 2/3, 3/4) of Jupiter s orbital period. For example, given that Jupiter orbits the Sun once every 11.86 years, an asteroid belt gap is expected at a distance of 3.3 astronomical units (AU) from the Sun, where any orbiting body would have a period of 5.93 years, one-half that of Jupiter. Such a gap does indeed exist. These Kirkwood gaps are produced by... 

Comets can be classified into two major groups short-term and long-term comets. Short-term comets are those with orbital periods of less than 200 years. They can be further subdivided into two groups the Jupiter family, with periods of less than 20 years, and... 

In 1978, Christy Harrington (1978) discovered Pluto s rather large, but close-by satellite Charon. The radius of Charon is between 600 and 650 km, which is more than half of that of Pluto (Tholen Buie, 1997). In comparison, the lunar radius is 0.27 that of Earth. Charon orbits Pluto at a distance of 16.5 Pluto radii with an orbital period of 6.4 Earth days. It can safely be assumed that the bodies are tidally locked to each other, which means the rotation periods of Pluto and of Charon equal the orbital period of Charon (Dobrovolskis etal, 1997). Charon must be an impressive sight observed from Pluto hovering over the same equatorial area, it would appear nearly 7.5 times the diameter of the Moon as seen from Earth. Even more dramatic would be Pluto observed from the surface of Charon its apparent diameter would be nearly 14 times the lunar diameter. In contrast to this, the diameter of the Sun subtends only 38 and 48 arcsec as seen from the aphelion and perihelion positions of Pluto, respectively. The maximum angular diameter of Jupiter seen from Earth is about 46 arcsec. 

Short period comets their orbital periods about the Sun are less than 200 years. At aphelion (when their distance from the Sun is at maximum) they are at distances of Jupiter and beyond. The aphelion of comet Halley is about the orbit of Neptune. Comets of the Jupiter family have orbital periods of less than 20 years. The existence of such families of comets can be attributed to the gravitational influence of Jupiter. ... 

Comet Tempel 1 was discovered in 1867 by E. Tempel. At the time of discovery, the comet was 0.7 AU from the Earth and 1.6 AU from the Sun. Currently, Tempel 1 has an orbital period of 5.5 years and a perihelion distance of roughly 1.5 AU. With an orbital eccentricity of 0.5, Tempel 1 s orbit lies between the orbits of Mars and Jupiter. These values varied in the past and will change in the future because of close approaches with the planet Jupiter. It therefore belongs to the group of short period comets. 

Between the main concentration in the Main Belt are relatively empty regions known as Kirkwood gaps. These are regions were an object s orbital period is a simple fraction of that of Jupiter (resonance). 

Table 6.1 Some examples of extrasolar planets. For comparison the values of Jupiter is also given. Mast is the mass of the host star (in solar masses), Porb the orbital period, a the semi major axis (in AU), e the eccentricity, Mp the planet s mass and 2 the planet s rotation period...

In Table 6.1 some examples of exoplanets are given. This table was adapted from Menou et al., 2003 [229]. For comparison, the values for Jupiter are listed in the first row. M is the mass of the central star, Pob the orbital period, a the semi major axis, e the eccentricity of the orbit, Mp the mass of the planet and 2 the rotation period. 

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 ... 

Originally it was thought that SP comets were Oort cloud comets that had been captured into short-period orbits following a close encounter with Jupiter. This process can occur and even explain why SP comets usually have prograde orbits with relatively low inchnations. However, Fernandez (1980) pointed out that this source could not produce the number of SP comets that are observed, and suggested that the SP comets were derived from a disk-hke distribution of bodies beyond Neptune. It was shown by numerical simulations that this trans-Neptunian distribution of comets could quantitatively supply the SP flux and explain their inclinations (Duncan et ok, 1988). 

We perturb now the above two-body problem by adding to the model the gravitational attraction from a major planet (for example Jupiter), which we assume that revolves around the Sun in a circular orbit with constant angular velocity n. The study of the periodic orbits will be made in the rotating frame that rotates with constant angular velocity n. The new Hamiltonian has the form... 

The CRE ages of ordinary chondrites that fell in Antarctica and elsewhere range from a few million years up to several tens of millions of years. Simulations of the celestial mechanics of meteoroids indicate that most of the exposure to cosmic rays occurred in the main asteroid belt from which they were ultimately ejected into Earth-crossing orbits when their periods of revolution came into resonance with that of Jupiter (Faure and Mensing 2007). 

In August 2011, the Juno spacecraft was launched from Earth with the mission of orbiting Jupiter in 2016. The closest distance between Jupiter and Earth is 391 million miles, (a) If it takes 5.0 years for Juno to reach Jupiter, what is its average speed in mi/hr over this period (b) Once Juno reaches Jupiter, what is the minimum amount of time it takes for the transmitted signals to travel from the spacecraft to Earth ... 

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