giant planets


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giant planets

The planets Jupiter, Saturn, Uranus, and Neptune, which have diameters between 3.9 and 11.2 times that of the Earth and masses of between 14 and 318 Earth masses. They orbit the Sun at mean distances ranging from 5.21 AU for Jupiter to 30.06 AU for Neptune in periods from 11.86 to 164.79 years. All have low densities – from 0.7 to 1.8 times that of water – and are probably composed largely of hydrogen in its molecular or metallic state. Their visible surfaces are thought to be clouds of ammonia or methane. They all have planetary ring systems and share at least 150 satellites between them (see Table 2, backmatter).

giant planets

[¦jī·ənt ′plan·əts]
(astronomy)
The planets Jupiter, Saturn, Uranus, and Neptune.
References in periodicals archive ?
None of the giant planets imaged were around sun-like stars.
This is why the research team from the University of California, Riverside, looked up and identified these 121 giant planets.
By providing specific constraints on when precisely giant planets become "bad neighbors," Georgakarakos, Eggl, and Ian Dobbs-Dixon, NYUAD assistant professor of physics, were able to identify prime targets in the ongoing search for a "second Earth." "The general idea is the farther away the giant planet is from the habitable zone, the better.
As Jupiter moved inward, however, gravitational perturbations from the giant planet would have swept the inner planets (and smaller planetesimals and asteroids) into close-knit, overlapping orbits, setting off a series of collisions that smashed all the nascent planets into pieces.
Heller and Barnes show that a moon needs to be roughly the mass of Earth to maintain an atmosphere and a magnetic field that could deflect deadly radiation from the giant planet next door and other sources.
Juno's launch is scheduled for August 5 and will take five years to reach the giant planet.
Previously, the only gas giant planet found to travel around a star in a near circular orbit, at three Earth-Sun distances, was the outer planet of the 47 UrsaMajoris system.
The research completely contradicts the widely held assumption that it takes at least one million years for gas giant planets like Jupiter and Saturn to evolve.
The researchers identified 121 giant planets that have orbits within the habitable zones of their stars.
However, this process acts too slowly to grow giant planets far from their star.
The core of this new work is in the calculation of the size of the magnetospheres of giant planets that are located in the habitable zones of their host stars.
But last October, when astronomer Hal Levison presented what he called a "slightly radical" mechanism for building the solar system's giant planets, he was ready.