Evidence of a Ninth Planet

[leblon]

Калтеховские астрономы говорят, что в поясе Куипера, по всей вероятности, есть настоящая 9-я планета, в несколько раз тяжелее Земли, с сильно эксцентричной орбитой и периодом обращения около 20,000 лет. Пиарятся, наверное. (шутка)

Comments

[xgrbml.livejournal.com]

Наивный вопрос: а в чем разница между планетой и планетоидом наподобие бедняги Плутона?

[ez98.livejournal.com]

Согласно принятому МАС определению, планета обязана расчистить окрестности своей орбиты от всякой дряни. Говорят, Плутон не осилил.

[xgrbml.livejournal.com]

Я человек наивный, в физике не мастак. Если это не юмор, поясните, пожалуйста.

[lyuden.livejournal.com]

Нет это не шутка. На конгрессе астрономов было принято решение, что планетой можно называть объект который

1. Обращается вокруг солнца

2. Достаточно массивен, чтобы иметь сферическую форму.

3. Расчистить свою орбиту от мусора.

Плутон действительно не преуспел, и даже не является самым крупным объектом на своей орбите (грубо говоря)

[ez98.livejournal.com]

Я писать не большой мастак. Поэтому позвольте я вам скопирую википедию

2006 IAU definition of planet[edit]
Main article: IAU definition of planet
The matter of the lower limit was addressed during the 2006 meeting of the IAU's General Assembly. After much debate and one failed proposal, 232 members of the 10,000 member assembly, who nevertheless constituted a large majority of those remaining at the meeting, voted to pass a resolution. The 2006 resolution defines planets within the Solar System as follows:[2]

A "planet" [1] is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
[1] The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Under this definition, the Solar System is considered to have eight planets. Bodies that fulfill the first two conditions but not the third (such as Ceres, Pluto, and Eris) are classified as dwarf planets, provided they are not also natural satellites of other planets. Originally an IAU committee had proposed a definition that would have included a much larger number of planets as it did not include (c) as a criterion.[56] After much discussion, it was decided via a vote that those bodies should instead be classified as dwarf planets.[57]

This definition is based in theories of planetary formation, in which planetary embryos initially clear their orbital neighborhood of other smaller objects. As described by astronomer Steven Soter:[58]

"The end product of secondary disk accretion is a small number of relatively large bodies (planets) in either non-intersecting or resonant orbits, which prevent collisions between them. Minor planets and comets, including KBOs [Kuiper belt objects], differ from planets in that they can collide with each other and with planets."
Because it is not presently possible to determine directly whether an exoplanet has cleared its orbit, a mathematical criterion has been proposed that approximately determines whether a planet can clear its orbit during the lifetime of its star, based on the mass of the planet, its semimajor axis, and the mass of its star.[59] This formula produces a value π that is greater than one for planets. The eight known planets and all known exoplanets have π values above 100, while Ceres, Pluto, and Eris have values of 0.1 or less. Objects with π values of 1 or more are also expected to be approximately spherical.[60]

Новая планета - планета

[vk-physics.livejournal.com]

Это раньше следовали определениям, а сейчас можно называть планетой даже не открытую (наблюденную в телескоп) фенечку.