Pluto now called Plutoid

dari yahoonews

The International Astronomical Union has decided on the term “plutoid” as a name for dwarf planets like Pluto.

Sidestepping concerns of many astronomers worldwide, the IAU’s decision, at a meeting of its Executive Committee in Oslo, comes almost two years after it stripped Pluto of its planethood and introduced the term “dwarf planets” for Pluto and other small round objects that often travel highly elliptical paths around the sun in the far reaches of the solar system.

The name plutoid was proposed by the members of the IAU Committee on Small Body Nomenclature (CSBN), accepted by the Board of Division III and by the IAU Working Group for Planetary System Nomenclature (WGPSN), and approved by the IAU Executive Committee at its recent meeting in Oslo, according to a statement released today.

Here’s the official new definition:

“Plutoids are celestial bodies in orbit around the sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit.”

In short: small round things beyond Neptune that orbit the sun and have lots of rocky neighbors.

The two known and named plutoids are Pluto and Eris, the IAU stated. The organization expects more plutoids will be found.

Controversy continues

Already the IAU recognizes it is adding to an ongoing controversy.

The IAU has been responsible for naming planetary bodies and their satellites since the early 1900s. Its decision in 2006 to demote Pluto was highly controversial, with some astronomers saying simply that they would not heed it and questioning the IAU’s validity as a governing body.

“The IAU is a democratic organization, thus open to comments and criticism of any kind,” IAU General Secretary Karel A. van der Hucht told SPACE.com by email today. “Given the history of the issue, we will probably never reach a complete consensus.”

It remains to be seen whether astronomers will use the new term.

“My guess is that no one is going to much use this term, though perhaps I’m wrong,” said Caltech astronomer Mike Brown, who has led the discovery of several objects in the outer solar system, including Eris. “But I don’t think that this will be because it is controversial, just not particularly necessary.”

Brown was unaware of the new definition until the IAU announced it today.

“Back when the term ‘pluton’ was nixed they said they would come up with another one,” Brown said. “So I guess they finally did.”

More debate coming

The dwarf planet Ceres is not a plutoid as it is located in the asteroid belt between Mars and Jupiter, according to the IAU. Current scientific knowledge lends credence to the belief that Ceres is the only object of its kind, the IAU stated. Therefore, a separate category of Ceres-like dwarf planets will not be proposed at this time, the reasoning goes.

A meeting, planned earlier this year for Aug. 14-16 at Johns Hopkins University Applied Physics Laboratory, aims to bring astronomers of varying viewpoints together to discuss the controversy. “No votes will be taken at this conference to put specific objects in or out of the family of planets,” APL’s Dr. Hal Weaver, a conference organizer, said in a statement in May. “But we will have advocates of the IAU definition and proponents of alternative definitions presenting their cases.”

The term plutoid joins a host of other odd words — plutinos, centaurs, cubewanos and EKOs — that astronomers use to define objects in the outer solar system.

—-

wuih, makin bingung aja deh nih tata surya kita, kasian anak SD, makin susah buat ngapalin planet yang ada ;D

anyway, ternyata sistem tata surya kita terbagi dua jenis planet: planet dan dwarf planet

dari wiki

A planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.

A dwarf planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting the Sun that is massive enough to be rounded by its own gravity but which has not cleared its neighbouring region of planetesimals and is not a satellite. More explicitly, it has to have sufficient mass for its self-gravity to overcome rigid body forces in order to assume a hydrostatic equilibrium and acquire a near-spherical shape.

A table summarizing features of the planets and dwarf planets in the Solar System.

Planets

Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
Astronomical symbol Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
Mean distance
from Sun
km
AU
57,909,175
0.38709893
108,208,930
0.72333199
149,597,870
1
227,936,640
1.52366231
778,412,010
5.20336301
1,426,725,400
9.53707032
2,870,972,200
19.19126393
4,498,252,900
30.06896348
Mean radius km
:E
2,439.64
0.3825
6,051.59
0.9488
6,378.15
1
3,397.00
0.53226
71,492.68
11.209
60,267.14
9.449
25,557.25
4.007
24,766.36
3.883
Surface area km²
:E
75,000,000
0.1471
460,000,000
0.9010
510,000,000
1
140,000,000
0.2745
64,000,000,000
125.5
44,000,000,000
86.27
8,100,000,000
15.88
7,700,000,000
15.10
Volume km3
:E
6.083×1010
0.056
9.28×1011
0.87
1.083×1012
1
1.6318×1011
0.151
1.431×1015
1,321.3
8.27×1014
763.59
6.834×1013
63.086
6.254×1013
57.74
Mass kg
:E
3.302×1023
0.055
4.8690×1024
0.815
5.9742×1024
1
6.4191×1023
0.107
1.8987×1027
318
5.6851×1026
95
8.6849×1025
14
1.0244×1026
17
Density g/cm3 5.43 5.24 5.515 3.940 1.33 0.70 1.30 1.76
Equatorial gravity m/s2 3.70 8.87 9.81 3.71 23.12 8.96 8.69 11.00
Escape velocity km/s 4.25 10.36 11.18 5.02 59.54 35.49 21.29 23.71
Rotation period days 58.646225 -243.0187 0.99726968 1.02595675 0.41354 0.44401 -0.71833 0.67125
Orbital period years 0.2408467 0.61519726 1.0000174 1.8808476 11.862615 29.447498 84.016846 164.79132
Mean orbital speed km/s 47.8725 35.0214 29.7859 24.1309 13.0697 9.6724 6.8352 5.4778
Eccentricity 0.20563069 0.00677323 0.01671022 0.09341233 0.04839266 0.05415060 0.04716771 0.00858587
Inclination deg. 7.00487 3.39471 0.00005 1.85061 1.30530 2.48446 0.76986 1.76917
Axial tilt deg. 0.0 177.3 23.45 25.19 3.12 26.73 97.86 29.58
Mean surface temp. K 440 730 288-293 186-268 152
Mean air temp. K 288 165 135 76 73
Atmospheric composition He  Na+ P+ CO2 N2 N2 O2 CO2 N2 Ar H2 He H2 He H2 He  CH4 H2 He  CH4
Number of known moons 0 0 1 2 63 60 27 13
Rings? No No No No Yes Yes Yes Yes
Planetary discriminant 9.1×104 1.35×106 1.7×106 1.8×105 6.25×105 1.9×105 2.9×104 2.4×104

Dwarf planets

Ceres Pluto Eris
Astronomical symbol Ceres Pluto
Mean distance
from Sun
km
AU
413,715,000
2.766
5,906,376,200
39.48168677
10,210 million
67.6681
Mean radius km
:E
471
0.0738
1,148.07
0.180
1,200
0.19
Volume km3
:E
2,800,000
0.0055
17,000,000
0.0333
18,000,000
0.0353
Surface area km²
:E
?×108
0.00042
7.15×109
0.0066
?×109
0.007
Mass kg
:E
9.5×1020
0.00016
1.3×1022
0.0022
1.7×1022
0.0028
Density g/cm3 2.08 2.0
Equatorial gravity m/s2 0.27 0.60
Escape velocity km/s 0.51 1.2
Rotation period days 0.3781 -6.38718
Orbital period years 4.599 247.92065 557
Mean orbital speed km/s 17.882 4.7490 3.436
Eccentricity 0.080 0.24880766 0.44177
Inclination deg. 10.587 17.14175 44.187
Axial tilt deg. 4 119.61
Mean surface temp. K 167 40 30
Mean air temp. K
Atmospheric composition CH4
Number of known moons 0 3 1
Rings? No No No
Planetary discriminant 0.33 7.7×10−2 0.10

Latest pictures of our solar system that I’ve found:

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