Soon 12 planets in the solar system !

Hi,

Soon there will be probably 12 planets in the solar system !
ercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto,
Charon and 2003 UB313
See the latest IAU news at :
http://www.iau2006.org/mirror/www.ia...1_release.html

It is amazing that knowing that the definition states that "A planet is a
celestial body that (a) has sufficient mass for its self-gravity to overcome
rigid body forces so that it assumes a hydrostatic equilibrium (nearly
round) shape, and (b) is in orbit around a star, and is neither a star nor a
satellite of a planet." that IAU committee has considered Charon as a true
planet... Isn't it the satellite of a planet itself orbiting the Sun ?
And the Moon is this case ? In-betwene lines, IAU's definition means that a
body has to show a mass over about 5x10^20 kg, and show a diameter 800 km
or so. The Moon is round, and close to 3400 km in diameter... !

I wonder what does Michael Brown (who is not member of IAU) think of this
idea paradox (I image his answer, it is not more a question for astronomers
but only administrative).

Anyway, in all cases that will be always the status quo for amateurs... ;-)

Have a clear and dark sky (as far as possible;..)

Thierry
http://www.astrosurf.org/lombry

is neither a star nor a
satellite of a planet."

That takes Pluto's 3 moons and our moon out of the planet class.


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Thierry wrote in message ...
Hi,

Thierry wrote:
Hi,

Soon there will be probably 12 planets in the solar system !
ercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto,
Charon and 2003 UB313
See the latest IAU news at :
http://www.iau2006.org/mirror/www.ia...1_release.html

It is amazing that knowing that the definition states that "A planet is a
celestial body that (a) has sufficient mass for its self-gravity to overcome
rigid body forces so that it assumes a hydrostatic equilibrium (nearly
round) shape, and (b) is in orbit around a star, and is neither a star nor a
satellite of a planet." that IAU committee has considered Charon as a true
planet... Isn't it the satellite of a planet itself orbiting the Sun ?
And the Moon is this case ? In-betwene lines, IAU's definition means that a
body has to show a mass over about 5x10^20 kg, and show a diameter 800 km
or so. The Moon is round, and close to 3400 km in diameter... !

I wonder what does Michael Brown (who is not member of IAU) think of this
idea paradox (I image his answer, it is not more a question for astronomers
but only administrative).

Anyway, in all cases that will be always the status quo for amateurs... ;-)

Have a clear and dark sky (as far as possible;..)

Thierry
http://www.astrosurf.org/lombry

Lets hope nostalgia over Pluto and it's discoverer does not have any
effect on a decision.

Starlord wrote:
is neither a star nor a
satellite of a planet."

That takes Pluto's 3 moons and our moon out of the planet class.



Nope. They have covered this. Charon is a planet (part of a double
planetary system) The other moons stay planetary satellites.

Quote from IAU draft resolution
http://www.iau2006.org/mirror/www.ia...esolution.html

"2 For two or more objects comprising a multiple object system, the
primary object is designated a planet if it independently satisfies the
conditions above. A secondary object satisfying these conditions is
also designated a planet if the system barycentre resides outside the
primary. Secondary objects not satisfying these criteria are
"satellites". Under this definition, Pluto's companion Charon is a
planet, making Pluto-Charon a double planet."

Looks like the IAU are going to have to rename the Minor Planets Centre
though!

Robin

"robin_astro" wrote in message
ps.com...

Starlord wrote:
is neither a star nor a
satellite of a planet."

That takes Pluto's 3 moons and our moon out of the planet class.



Nope. They have covered this. Charon is a planet (part of a double
planetary system) The other moons stay planetary satellites.

Quote from IAU draft resolution
http://www.iau2006.org/mirror/www.ia...esolution.html

"2 For two or more objects comprising a multiple object system, the
primary object is designated a planet if it independently satisfies the
conditions above. A secondary object satisfying these conditions is
also designated a planet if the system barycentre resides outside the
primary.

I am agree with any definition, but between us, is it logical ?
I suspect they made the comparison with stellar binary systems to arrive to
this conclusion.
They simply apply to planets what exists for stars... so that all celestial
objects are included in the definition
But up to now, the common sense - which of course is not a scientific
concept, tells that any object orbiting a planet is a satellite.
With their new definition, that means that is not only the gravitational
mass and radius that are taken into account but also the distance to the
host object. For me it is no more logical. Soon Jupiter-like exoplanets will
lost their psosible satellites because they are so-called outside the
barycenter !...

Thierry

Secondary objects not satisfying these criteria are
"satellites". Under this definition, Pluto's companion Charon is a
planet, making Pluto-Charon a double planet."

Looks like the IAU are going to have to rename the Minor Planets Centre
though!

Robin

Rich,

Say you discovered Pluto and what would you think after 76 years that
it was going to be demoted?

I don't think you would like it either.

Personally, I thought just saying Pluto is the lower limit might have
been fine.
To demote it to me at least is like saying that Websters dictionary ...

Waits a full 76 years until it includes a new word and it's definition
which would make
Astronomers look pretty ridiculous.

Thierry wrote:
"robin_astro" wrote in message
ps.com...

Starlord wrote:
is neither a star nor a
satellite of a planet."

That takes Pluto's 3 moons and our moon out of the planet class.



Nope. They have covered this. Charon is a planet (part of a double
planetary system) The other moons stay planetary satellites.

Quote from IAU draft resolution
http://www.iau2006.org/mirror/www.ia...esolution.html

"2 For two or more objects comprising a multiple object system, the
primary object is designated a planet if it independently satisfies the
conditions above. A secondary object satisfying these conditions is
also designated a planet if the system barycentre resides outside the
primary.

I am agree with any definition, but between us, is it logical ?
I suspect they made the comparison with stellar binary systems to arrive to
this conclusion.
They simply apply to planets what exists for stars... so that all celestial
objects are included in the definition
But up to now, the common sense - which of course is not a scientific
concept, tells that any object orbiting a planet is a satellite.
With their new definition, that means that is not only the gravitational
mass and radius that are taken into account but also the distance to the
host object. For me it is no more logical. Soon Jupiter-like exoplanets will
lost their psosible satellites because they are so-called outside the
barycenter !...

Thierry

Secondary objects not satisfying these criteria are
"satellites". Under this definition, Pluto's companion Charon is a
planet, making Pluto-Charon a double planet."

Looks like the IAU are going to have to rename the Minor Planets Centre
though!

Robin


It might make sense to refer to Pluto/Charon as a binary planet, but
Charon can't be considered one on its own. Triton is far larger, but
won't be counted because it orbits a larger planet (Neptune).

Stan Jensen wrote:
And no mention of Quaoar or Senda. And I think there's one other one
out there, starts with a "V"?

It's Sedna, and there are hundreds of other distant objects out there
larger than Ceres. Most don't have names.

What I found interesting about the draft resolution is that they
included Ceres in the list of regular (not plutons) planets, I guess
because it is big enough to be perfectly round.

Clif Ashcraft

The solar system had 12 planets already some 160 years ago.....

After the discovery of (4) Vesta in 1807, no more asteroids were discovered
for 38 years, until (5) Astraea was discovered in 1845.

Then Neptune was discovered in 1846.

Then (6) Hebe was discovered in 1847 .... and since then, new asteroids
were discovered almost each and every year.


But from 1807 to 1844 only 4 asteroids were known. They were counted
among the planets -- thus the solar system had 11 known planets during
this time period. In 1845, the 12th planet, Astraea, was discovered,
and in 1846, the 13th planet, Neptune, was discovered.

In the years following 1846, many more small planets were discovered.
The word "planet" was redefined so it included only the major planets,
reducing the number of known planets in the solar system to 8.


Now, when the word "planet" is about to be redefined again, the solar
system may get 12 known planets for the second time....

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