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The widely accepted modern variant of the nebular theory is the solar nebular disk model (SNDM) or solar nebular model. [1] It offered explanations for a variety of properties of the Solar System, including the nearly circular and coplanar orbits of the planets, and their motion in the same direction as the Sun's rotation.
In 1960, 1963, and 1978, [13] W. H. McCrea proposed the protoplanet hypothesis, in which the Sun and planets individually coalesced from matter within the same cloud, with the smaller planets later captured by the Sun's larger gravity. [8] It includes fission in a protoplanetary nebula and excludes a solar nebula.
The most significant criticism of the hypothesis was its apparent inability to explain the Sun's relative lack of angular momentum when compared to the planets. [5] However, since the early 1980s studies of young stars have shown them to be surrounded by cool discs of dust and gas, exactly as the nebular hypothesis predicts, which has led to ...
Counter-Earth, a planet situated on the other side of the Sun from that of the Earth. Fifth planet (hypothetical), historical speculation about a planet between the orbits of Mars and Jupiter. Phaeton, a planet situated between the orbits of Mars and Jupiter whose destruction supposedly led to the formation of the asteroid belt. This hypothesis ...
At their distance from the Sun, accretion was too slow to allow planets to form before the solar nebula dispersed, because the initial disc lacked enough mass density to consolidate into a planet. The Kuiper belt lies between 30 and 55 AU from the Sun, while the farther scattered disc extends to over 100 AU, [ 43 ] and the distant Oort cloud ...
Catching a glimpse of the planets will depend on the time of day and their relative distance from the planet at the time. For example, Venus, Saturn and Jupiter are best viewed after sunset at ...
The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young protostar orbited by a protoplanetary disk. Planets grow in this disk by the gradual accumulation of material driven by gravity, a process called accretion.
The innermost planet takes about nine days to orbit the star. The outermost planet takes about 54 days. The planets orbit the star between 6% and 20% of the distance between Earth and the sun.