What I am asking is how do we differentiate a planet from other celestial bodies?
2006-09-20 05:26:23 · 7 answers · asked by naturalbornthriller69 2 in Science & Mathematics ➔ Astronomy & Space
It has already happened. The International Astronomical Union held a meeting in Prague on 24th August at which it passed three new definitions, of a planet, a dwarf planet and a Small Solar System Body. The IAU definitions are:
PLANET: a celestial body having all the following attributes as a "planet". It:
(1) is in orbit around a star or stellar remnants;
(2) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape;
(3) is above the minimum mass/size for a planet in our solar system*;
(4) if in our solar sytem it has cleared the neighbourhood around its orbit; and
(5) is below the limiting mass for thermonuclear fusion of deuterium.
(*What this mass/size is has not been specifically defined. However, it must be somewhere between the mass required in (2) above, and the mass of the planet Mercury.)
Our solar system is considered to have eight planets under this definition: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Three bodies in orbit around our Sun and which only fulfil conditions (1) and (2), but not (4), and are not natural satellites, are now classified as dwarf planets: Ceres, Pluto and Eris. To date, there have been more than two hundred planets discovered orbiting other stars.
The IAU further defines any celestial object having any of the following attributes as not being a planet:
(1) it is below the minimum mass/size for a planet in our solar system;
(2) it is above the limiting mass for thermonuclear fusion of deuterium; or
(3) it is a free-floating object in a young star cluster.
MY COMMENT: the point about fusing deuterium is to distinguish planets from brown dwarf stars, which can be as small about ten Jupiter masses.
DWARF PLANET: a dwarf planet as an object 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
c) Has not "cleared the neighbourhood" around its orbit
d) Is not a satellite of a planet, or other nonstellar body
SMALL SOLAR AYSTEM BODY: A small solar system body (SSSB) is a term defined in 2006 by the International Astronomical Union to describe solar system objects which are not planets or dwarf planets:
"All other objects orbiting the Sun shall be referred to collectively as "Small Solar System Bodies" ... These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies."
Therefore it refers to these objects that can be further classified based on their orbit or composition:
all known minor planets that are not dwarf planets, i.e.:
i) the classical asteroids (except the largest one, 1 Ceres);
ii) the Centaurs and Neptune Trojans;
iii) the smaller Trans-Neptunian Objects (except dwarf planets such as Pluto and Eris);
iv) all comets;
It is not yet clear whether there will be a lower bound on the group of small solar system bodies, or if it will encompass all material down to the level of meteoroids.
Some of the larger "small solar system bodies" may be reclassified in future as dwarf planets, pending further examination to determine whether or not they are in hydrostatic equilibrium.
MY COMMENT: All rather legalistically phrased and a little dry to read, but that is because these were formal motions put to a General Assembly for approval.
2006-09-20 06:01:43 · answer #1 · answered by Anonymous · 11⤊ 1⤋
(1) A "planet" 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 neighborhood around its orbit.
(2) A "dwarf planet" 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, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.
(3) All other objects orbiting the Sun shall be referred to collectively as "small solar system bodies".
http://www.iau.org/fileadmin/content/pdfs/Resolution_GA26-5-6.pdf
pluto is not a planet, but pluto orbits the sun, is round, does not have an isolated orbit (a bunch of other similar bodies have similar orbits.), and is not a satellite so it is a dwarf planet. this does not change anything about the solar system or pluto. it just corrects the mistake of classifying pluto as a planet initially.
this same thing has happened before. beginning in 1800, astronomers found a few bodies orbiting between the orbits of mars and jupiter, and they finally stopped calling them planets after the fourth discovery. 150 years from now, no one will think of "134340 pluto" as a planet. very few will even know we classified it as a planet. "1 ceres" and "136199 eris" are other dwarf planets.
i have been waiting for this since i was about twelve. i feel somewhat satisfied. i knew that pluto didn't fit the pattern set by the major bodies in the solar system so it was an anomaly. it just felt illogical and "out of place". this was the right thing to do, believe me. i don't understand why so many are having such a problem with this.
i don't know how long this will drag on tho. many planetary scientists are not satisfied that the definition is rigorous enough.
2006-09-20 06:07:26 · answer #2 · answered by warm soapy water 5 · 1⤊ 1⤋
Well, now that is the crux of the whole problem,, until recently there was no need for a clear definition of what a "planet" is.
Now with so many new discoveries of wild varied celestial bodies we need to categorize them,, back to Pluto. Just one of many objects of similar size and shape in both the kuiper belt and the asteroid belt between mars and Jupiter. Also, large moons such as Titan and Europa are just as interesting as far distant Pluto.
Personally, I don't care about the downgrading from "planet" status,, but I do not think they should change the name or scratch it from the list of interesting things to study.
2006-09-20 05:39:12 · answer #3 · answered by landerscott 4 · 0⤊ 0⤋
whilst Pluto replaced into first got here upon it replaced into concept by some to be better than the Earth. considering then extra constructive measurements have shown it to be lots, lots smaller. these days extra gadgets relating to a similar length have been discovered. They have been quite too small to be called planets yet considering they have been around a similar length as Pluto, the two they had to be called planets or Pluto had to be demoted to be consistent. on the instant assembly of the international Astronomical Union the non-unanimous vote replaced into that it replaced into no longer to be called a planet. Scientists reclassify issues continuously as extra constructive suggestions is obtainable in. generally they reclassify micro organism, plant life or in specific situations animals or rocks. This very just about in no way makes the information despite if it extremely is extra probably to be considerable to us simply by fact those issues are right here in the international. Pluto is an extremely good way away and as these days as 1929 no person even knew it replaced into there. So despite in case you call it Pluto, a dwarf planet, a comet, a rocky iceball or "Nellie" is neither right here no longer there. the only people who've a impressive to have an opinion in this are those with distinctive know-how of the image voltaic equipment and astronomical class schemes. What all people else thinks actual would not count selection.
2016-10-17 08:16:44 · answer #4 · answered by Anonymous · 0⤊ 0⤋
A planet has to be nearly spherical and cleared all the junk along its orbit. Since Pluto intersects Neptunes orbit, it isn't a planet. Although, come to think about it, should Neptune be a planet then?
2006-09-20 05:35:06 · answer #5 · answered by Anonymous · 1⤊ 0⤋
a planet is anything of significant size or mass. Pluto is now considered a dwarf planet.
2006-09-20 05:32:00 · answer #6 · answered by Sniper 4 · 1⤊ 1⤋
something with substantial size and mass that orbits a sun and has enough gravity to become roundand have a round orbit plutos orbit is oliptical and thus it is not a planet
2006-09-20 05:35:09 · answer #7 · answered by arianna3at 3 · 2⤊ 1⤋