"Cosmogony is a term which admits some ambiguity or, at least, flexibility. One dictionary definition states 'a theory of the creation of the Universe' while another, more parochially, says 'a theory of the world's origin and growth'. A large collection of definitions fall between these two extremes but the most common feature they possess is the phrase 'origin of the solar system'."
"The purpose of any cosmogonic theory is to seek out ideally simple conditions which could have initiated the world and from which, by the play of recognized forces, that world, in all its complexity, may be resulted."
Heliogony then is "any cosmogonic theory [that seeks out] ideally simple conditions which could have initiated the" Sun or Helios.
"The German philosopher Kant was the first to conceive the idea that the Sun originated as a condensation from a nebula, and the same idea in a more elaborate and refined form was later put forward by Laplace (1796)."
An "initially spherical and contracting nebula would spin faster as it collapsed. At a certain critical stage it would have a lenticular shape with equatorial material in orbit around a central mass. Any further contraction would leave a disk of freely rotating material in the equatorial plane. In fact Laplace postulated that the evolution of the disk would be discontinuous and that the material would be shed in a series of discrete rings. Condensation in the rings would gradually merge with each other so that each ring would be the originator of a single planet."
The apparent "outstanding failure of this early nebula theory was in explaining the distribution of angular momentum in the solar system. The planets, with 0.13 per cent of the mass of the system, account for about 99.5 per cent of its angular momentum and no spontaneous way of so partitioning mass and angular momentum seems possible."
Another interpretation is that the Solar System did not form this way.
The "rotation axis of the Sun [is] 7° from that of the system as a whole. It seems very unlikely on the basis of the solar-nebula model that the rotation axis of the central body could be so different from that of the disk, or that the orbits of planets derived from the disk could, systematically, be so much out of its plane."
Perhaps the system as a whole did not form with the Sun.
"If the pre-existence of the Sun, with more or less its present rotational characteristics, may be assumed and the [captured material is expected to flatten into a disk-like form] then the angular-momentum problem does not arise with the accretion theory."
"In the floccule theory [...] the process of planetary formation is directly linked to the process by which a whole cluster of stars is formed."
"When floccules collide, they combine, and at intervals throughout the cloud large aggregations of floccules will form and produce a star. [...] By the very nature of the process the star being formed will have little angular momentum since any floccule hitting it must have moved on a path intersecting its surface."
A "collapsing planet will first go through the stages of collapsing and spinning faster until eventually material is lost in the equatorial plane. Eventually the protoplanet attains a density at which it is effectively incompressible [...] Thereafter it will disrupt into two [unequal] main parts [...] Much of the angular momentum of the system is now associated with the motion of the two parts around each other while the individual parts themselves have less than critical rotational speed for further disruption."
For "capture-theory models [...] the initial motion of a newly formed protoplanet is away from the Sun. Recent calculations show that a protoplanet would collapse to become a condensed object in 200-300 yr and it must survive only one perihelion passage [...] The collapse of a protoplanet [with a tidal bulge and no longer axisymmetric] will lead to a filament of matter being left behind as the main bulk forms a central body. Within such a filament protosatellite condensations may form; the characteristics of the major satellite families are well explained by this type of mechanism."
"Using ESO’s very successful HARPS spectrograph, a team of astronomers has found that Sun-like stars which host planets have destroyed their lithium much more efficiently than planet-free stars. This finding does not only shed light on the low levels of this chemical element in the Sun, solving a long-standing mystery, but also provides astronomers with a very efficient way to pick out the stars most likely to host planets. It is not clear what causes the lithium to be destroyed. The general idea is that the planets or the presence of the protoplanetary disc disturb the interior of the star, bringing the lithium deeper down into the star than usual, into regions where the temperature is so hot that it is destroyed."
"An orbital pole is either end of an imaginary line running through the center of an orbit perpendicular to the orbital plane, projected onto the celestial sphere. It is similar in concept to a celestial pole but based on the planet's orbit instead of the planet's rotation."
"The north orbital pole of a celestial body is defined by the right-hand rule: If you curve the fingers of your right hand along the direction of orbital motion, with your thumb extended parallel to the orbital axis, the direction your thumb points is defined to be north."
At right is a snapshot of the planetary orbital poles. The field of view is about 30°. The yellow dot in the centre is the Sun's North pole. Off to the side, the orange dot is Jupiter's orbital pole. Clustered around it are the other planets: Mercury in pale blue (closer to the Sun than to Jupiter), "Venus in green, [the] Earth in blue, Mars in red, Saturn in violet, Uranus in grey [partly underneath Earth] and Neptune in lavender. Dwarf planet Pluto is the dotless cross off in Cepheus."
The orbital poles for the planets now in orbit around the Sun suggest that the Earth and Uranus may have a common origin. The other gas giants may have an associated origin not directly related to the origin of the Sun.
- The Sun and the entity early-on named Helios are not the same.
- The Sun may have captured a much smaller star to form a binary using a nearby star.
- Those objects in the plane of the Sun's equator formed with the Sun.
- M.M. Woolfson (1979). "Cosmogony Today". Quarterly Journal of the Royal Astronomical Society. 20 (06): 97–114. Bibcode:1979QJRAS..20...97W. Retrieved 2014-07-31. Unknown parameter
- Georges Lamaitre (1950). "Primeval Atom; an Essay on Cosmogony". London: Van Nostrand. Cite journal requires
- L. Calçada (11 November 2009). "Burning lithium inside a star (artist's impression)". European Southern Observatory. Retrieved 2014-07-31.
- "Orbital pole, In: Wikipedia". San Francisco, California: Wikimedia Foundation, Inc. December 17, 2012. Retrieved 2013-01-20.
- J. Herschel (1918). "The poles of planetary orbits". The Observatory. 41: 255–7. Bibcode:1918Obs....41..255H. Retrieved 2013-07-10. Unknown parameter
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