Planetary taxonomy: A diplomatic solution

"Margo Schulter" wrote in message
...
George Dishman wrote:

According to this, no:

http://www.iau2006.org/mirror/www.ia...602/index.html

A planet must be "in orbit around the Sun". Even
if the dwarf were part of a binary with another
main sequence star, it would be a planet, just
as "extra-solar planets" are no longer planets!


Hello, there, and while I'm not sure about the first part of
your statement (may we could clarify this binary star
situation you raise), ..

At some point there needs to be a dividing line drawn
between a binary system and a star with a planetary
system. Based on your other posts, I would say the
latter is easy, it is one in which only one object
reaches the point of fusion. If more than one achieves
that then it is a binary star system, possibly also
including planets and other debris.

If none reaches fusion it could be harder for the
case of systems where no one body dominates. You
get free-floating double planetary systems I suppose.

I think that I can clarify the
second point concerning "extra-solar planets."

Actually IAU Resolution 5A restricts its domain to
classifying objects in our own solar system; the question
of defining planets elsewhere is simply left unaddressed,
and likely reserved for a future meeting (the next one in
Rio, 2009).

Well that may be the idea but the outcome has been
to produce a definition of the word "planet" that
should find its way into most good dictionaries.
The idea that an object identical to Earth but
around another star identical to the Sun might not
be a planet (but we haven't decided yet) is not
one that is going to be treated with any respect.

The actual text says this:

"Contemporary observations are changing our
understanding of planetary systems, and it
is important that our nomenclature for
objects reflect our current understanding.
This applies, in particular, to the
designation 'planets'. The word "planet"
originally described "wanderers" that were
known only as moving lights in the sky.
Recent discoveries lead us to create a new
definition, which we can make using currently
available scientific information."

Note in particular "Recent discoveries lead us to
create a new definition" for the "designation
'planets'." That is not restricted to the solar
system but states it is a definition of the word.
It goes on
"The IAU therefore resolves that planets and
other bodies in our Solar System, except
satellites, be defined into three distinct
categories in the following way:"

so there are only three categories of planets and
all reside in our solar system.

There is a note saying

"An IAU process will be established to assign
borderline objects into either dwarf planet
and other categories."

but I see nothing whatsoever on the page to say
that this definition is not applicable to objects
outside the solar ystem or that it will be further
considered in 2009.

Thus the resolution doesn't directly affect the status of
any extra-solar planet, much less remove its planethood,
which is simply left officially unaddressed.

Sorry, that isn't the case according to the page
I cited. That's why I asked if this was merely
one of the drafts and the final resolution
corrected these problems. Replacing "the Sun" by
"a star" would have resolved that problem (with
perhaps a footnote regarding binary systems etc.).

We can debate whether the IAU was wise to adopt a planetary
taxonomy for objects in our own solar system only, as well as
the wisdom of its specific conclusions. However, I would
emphasize that extra-solar planets are just as much planets
as they were on August 23, the day before the resolution was
adopted.

While your interpretation may seem resonable, it
is not the resolution that was passed.

Hmmm, is that really the version that was adopted?

In my post in this thread I include a proposal giving the
text of the adopted version plus some suggested changes ..

Tough luck, the meetings have finished and the
resolutions passed. I'm sure a lot of other people
have alternative views too, but then the whole
point of the process is to reach a consensus that
is at some level acceptable to the majority and
after that we are all stuck with it. I don't intend
to stop considering extra-solar planets to be planets
but that appears to be the official result.

George

George Dishman replied to Margo Schulter:

"The IAU therefore resolves that planets and
other bodies in our Solar System, except
satellites, be defined into three distinct
categories in the following way:"

so there are only three categories of planets and
all reside in our solar system.

To me, the passage you quoted unambiguously says that the
definition applies only to planets and other bodies in the
Solar System, and says nothing about planets and other
bodies outside the Solar System.

If you interpret the statement to mean that things outside
the Solar System are not "planets" under the definition,
then do you also interpret it to mean that things outside
the Solar System are not "other bodies"?

There is a note saying

"An IAU process will be established to assign
borderline objects into either dwarf planet
and other categories."

but I see nothing whatsoever on the page to say
that this definition is not applicable to objects
outside the solar system or that it will be further
considered in 2009.

The first passage you quoted clearly says that the
definition is applicable to "planets and other bodies in
our Solar System". It says nothing about planets or other
bodies outside the Solar System.

-- Jeff, in Minneapolis

George Dishman wrote:

At some point there needs to be a dividing line drawn
between a binary system and a star with a planetary
system. Based on your other posts, I would say the
latter is easy, it is one in which only one object
reaches the point of fusion. If more than one achieves
that then it is a binary star system, possibly also
including planets and other debris.

Thank you, George, for the clarification, and we're in
agreement here.


If none reaches fusion it could be harder for the
case of systems where no one body dominates. You
get free-floating double planetary systems I suppose.

This raises an interesting situation which I'm not sure
I've seen specifically mentioned in the papers I've read
so far on planetary definition.

However, it might be a nice kind of problem to illustrate
the difference between focusing solely or mostly on the
"characteristics" of an object (here two non-fusors, maybe
on the "superplanet" extreme of the spectrum, say 2-13
Jupiter masses), and also considering "circumstances" (here
that neither body is orbiting a fusor).

If we follow Basri, each would be a "planemo" or "planetary
mass object," but under a circumstantial definition of a
planet as a planemo _orbiting a fusor_, neither would qualify
as a "planet."

A more purely "characteristics-oriented approach" would say
that they're both non-fusors with sufficient mass to result
in near-sphericity or rounding -- and therefore planemos --
and that any planemo should be regarded as a planet, too.

Thus we indeed have a "free-floating binary planemo system";
and also also a "double planetary system," as you have
suggested, if we do not require that a planet orbit a fusor.

Anyway, that's my first take on this.

Most appreciatively,

Margo Schulter

Margo Schulter wrote:
George Dishman wrote:

snip side issue

Anyway, that's my first take on this.

Most appreciatively,

I'm glad you found my comment on that useful and
it is god to know we agree that topic.

Pehaps as a "second take" you could address my
comments on the issue we were actually discussing,
that of whether objects in other star systems can
fall within the new IAU definition of 'planets'.
I repeat that section below for your convenience:


George Dishman wrote:
"Margo Schulter" wrote in message
...
....
I think that I can clarify the
second point concerning "extra-solar planets."

Actually IAU Resolution 5A restricts its domain to
classifying objects in our own solar system; the question
of defining planets elsewhere is simply left unaddressed,
and likely reserved for a future meeting (the next one in
Rio, 2009).

Well that may be the idea but the outcome has been
to produce a definition of the word "planet" that
should find its way into most good dictionaries.
The idea that an object identical to Earth but
around another star identical to the Sun might not
be a planet (but we haven't decided yet) is not
one that is going to be treated with any respect.

The actual text says this:

"Contemporary observations are changing our
understanding of planetary systems, and it
is important that our nomenclature for
objects reflect our current understanding.
This applies, in particular, to the
designation 'planets'. The word "planet"
originally described "wanderers" that were
known only as moving lights in the sky.
Recent discoveries lead us to create a new
definition, which we can make using currently
available scientific information."

Note in particular "Recent discoveries lead us to
create a new definition" for the "designation
'planets'." That is not restricted to the solar
system but states it is a definition of the word.
It goes on

"The IAU therefore resolves that planets and
other bodies in our Solar System, except
satellites, be defined into three distinct
categories in the following way:"

so there are only three categories of [bodies] and
all reside in our solar system.

There is a note saying

"An IAU process will be established to assign
borderline objects into either dwarf planet
and other categories."

but I see nothing whatsoever on the page to say
that this definition is not applicable to objects
outside the solar ystem or that it will be further
considered in 2009.

Thus the resolution doesn't directly affect the status of
any extra-solar planet, much less remove its planethood,
which is simply left officially unaddressed.

Sorry, that isn't the case according to the page
I cited. That's why I asked if this was merely
one of the drafts and the final resolution
corrected these problems. Replacing "the Sun" by
"a star" would have resolved that problem (with
perhaps a footnote regarding binary systems etc.).

We can debate whether the IAU was wise to adopt a planetary
taxonomy for objects in our own solar system only, as well as
the wisdom of its specific conclusions. However, I would
emphasize that extra-solar planets are just as much planets
as they were on August 23, the day before the resolution was
adopted.

While your interpretation may seem resonable, it
is not the resolution that was passed.

best regards
George

George Dishman wrote:

[...]

Pehaps as a "second take" you could address my
comments on the issue we were actually discussing,
that of whether objects in other star systems can
fall within the new IAU definition of 'planets'.
I repeat that section below for your convenience:

Please let me say that I'd be glad to explain my
views on how extrasolar planets have been "left as
an exercise for a future General Assembly of the IAU"
rather than excluded from planethood.



George Dishman wrote:
"Margo Schulter" wrote in message
...

Actually IAU Resolution 5A restricts its domain to
classifying objects in our own solar system; the question
of defining planets elsewhere is simply left unaddressed,
and likely reserved for a future meeting (the next one in
Rio, 2009).

Well that may be the idea but the outcome has been
to produce a definition of the word "planet" that
should find its way into most good dictionaries.
The idea that an object identical to Earth but
around another star identical to the Sun might not
be a planet (but we haven't decided yet) is not
one that is going to be treated with any respect.

What I'd suspect is that everyone would find _that_
case easy to decide, but that this year the IAU didn't
feel quite ready to consider the likely range of cases
that might arise, and issues such as whether or how the
criteria for extrasolar planets should cater to present
technical limitations in obtaining relevant data.

I must add that your point that a definition of "planet"
restricted to only our Solar System isn't necessarily the
ideal choice, even as an interim measure, has been voiced
by many. We can discuss why the IAU may have decided on
this kind of action for the time being -- an interesting
question.


The actual text says this:

"Contemporary observations are changing our
understanding of planetary systems, and it
is important that our nomenclature for
objects reflect our current understanding.
This applies, in particular, to the
designation 'planets'. The word "planet"
originally described "wanderers" that were
known only as moving lights in the sky.
Recent discoveries lead us to create a new
definition, which we can make using currently
available scientific information."

The use of the plural, "planetary systems," indeed
might lead one to anticipate a definition applying
to extrasolar as well as solar planets.

Note in particular "Recent discoveries lead us to
create a new definition" for the "designation
'planets'." That is not restricted to the solar
system but states it is a definition of the word.
It goes on

"The IAU therefore resolves that planets and
other bodies in our Solar System, except
satellites, be defined into three distinct
categories in the following way:"

so there are only three categories of [bodies] and
all reside in our solar system.

Here I'd say, along with other interpreters whom I find
persuasive, that the IAU in this resolution opens with
language that indeed focuses on the wider question of
"planetary systems," but then addresses only our Solar
System for now.

There is a note saying

"An IAU process will be established to assign
borderline objects into either dwarf planet
and other categories."

but I see nothing whatsoever on the page to say
that this definition is not applicable to objects
outside the solar ystem or that it will be further
considered in 2009.

Going on the hypothesis that those who voted for Resolution
5A are rational people -- even if not always people who
share my taste as to certain definitional nuances grin --
I'd conclude that the reservation of questions regarding
extrasolar planetary systems for consideration in 2009, or
at any rate at some future General Assembly, is pretty
clearly understood.

Thus the resolution doesn't directly affect the status of
any extra-solar planet, much less remove its planethood,
which is simply left officially unaddressed.

Sorry, that isn't the case according to the page
I cited. That's why I asked if this was merely
one of the drafts and the final resolution
corrected these problems. Replacing "the Sun" by
"a star" would have resolved that problem (with
perhaps a footnote regarding binary systems etc.).

What I and lots of others get out of the language is that
Resolution 5A (whose text you correctly quote) chooses
to leave objects beyond our Solar System unaddressed for
now. However, whatever our readings, people are now
focusing on the task of drafting definitions that can
apply to extrasolar as well as solar planets.

I agree that to achieve this we'd want to replace "the
Sun" by "a star or infrastar (i.e. a brown dwarf)" for
example -- or "a fusor," to use Basri's term.

We can debate whether the IAU was wise to adopt a planetary
taxonomy for objects in our own solar system only, as well as
the wisdom of its specific conclusions. However, I would
emphasize that extra-solar planets are just as much planets
as they were on August 23, the day before the resolution was
adopted.

While your interpretation may seem resonable, it
is not the resolution that was passed.

I agree that strictly speaking the interpretation is distinct
from the actual text of the resolution that was passed; but I'd
say that it's a pretty widely shared interpretation.

best regards
George

Best,

Margo

Margo Schulter wrote:
George Dishman wrote:
....
Please let me say that I'd be glad to explain my
views on how extrasolar planets have been "left as
an exercise for a future General Assembly of the IAU"
rather than excluded from planethood.

Margo, thanks for responding to this.

George Dishman wrote:
"Margo Schulter" wrote in message
...

Actually IAU Resolution 5A restricts its domain to
classifying objects in our own solar system; the question
of defining planets elsewhere is simply left unaddressed,
and likely reserved for a future meeting (the next one in
Rio, 2009).

Well that may be the idea but the outcome has been
to produce a definition of the word "planet" that
should find its way into most good dictionaries.
The idea that an object identical to Earth but
around another star identical to the Sun might not
be a planet (but we haven't decided yet) is not
one that is going to be treated with any respect.

What I'd suspect is that everyone would find _that_
case easy to decide, but that this year the IAU didn't
feel quite ready to consider the likely range of cases
that might arise, and issues such as whether or how the
criteria for extrasolar planets should cater to present
technical limitations in obtaining relevant data.

Actually, resolution 5B would have gone some way
to resolving that since any object of sufficient mass
could be assumed to be "nearly round", it could have
been described as a "planet" with the differentiation
into "classical" or "dwarf" left undecided. Another
simplification is to use the definition M^2/P as the
determining factor rather than M/m since the latter
requires knowledge of the remnant material in the
orbital zone which would be difficult to determine
for extra-solar objects.

What would then be left to make it scientific would
be a study of the known extra-solar systems to find
an appropriate cutoff level.

I must add that your point that a definition of "planet"
restricted to only our Solar System isn't necessarily the
ideal choice, even as an interim measure, has been voiced
by many. We can discuss why the IAU may have decided on
this kind of action for the time being -- an interesting
question.

I can see good resons why they would want to do
so, for example our discussions on "binary plameno"
systems and the merits of M^2/P versus M/m as a
criterion. What does puzzle me is if what you say is
true then why didn't the resolution say that the term
"planet" may also be used in an extra-solar context
but the details of the criteria would be left for a future
study group or congress. What has been published
is unequivocal and limits "planet" to object orbiting
the Sun.

The actual text says this:

"Contemporary observations are changing our
understanding of planetary systems, and it
is important that our nomenclature for
objects reflect our current understanding.
This applies, in particular, to the
designation 'planets'. The word "planet"
originally described "wanderers" that were
known only as moving lights in the sky.
Recent discoveries lead us to create a new
definition, which we can make using currently
available scientific information."

The use of the plural, "planetary systems," indeed
might lead one to anticipate a definition applying
to extrasolar as well as solar planets.

Or it can equally be read merely to say that studying
numerous systems has allowed them to better
understand our own system and find a universal
criterion which can be applied to differentiating true
planets from other objects.

Note in particular "Recent discoveries lead us to
create a new definition" for the "designation
'planets'." That is not restricted to the solar
system but states it is a definition of the word.
It goes on

"The IAU therefore resolves that planets and
other bodies in our Solar System, except
satellites, be defined into three distinct
categories in the following way:"

so there are only three categories of [bodies] and
all reside in our solar system.

Here I'd say, along with other interpreters whom I find
persuasive, that the IAU in this resolution opens with
language that indeed focuses on the wider question of
"planetary systems," but then addresses only our Solar
System for now.

My Fench is extremely limited but having read
both the English and French versions, I don't
believe there is any significant difference that
could be attributed to translation, but neither
includes any explicit restriction that says the
definition "addresses only our Solar System for
now.".

There is a note saying

"An IAU process will be established to assign
borderline objects into either dwarf planet
and other categories."

but I see nothing whatsoever on the page to say
that this definition is not applicable to objects
outside the solar ystem or that it will be further
considered in 2009.

Going on the hypothesis that those who voted for Resolution
5A are rational people -- even if not always people who
share my taste as to certain definitional nuances grin --
I'd conclude that the reservation of questions regarding
extrasolar planetary systems for consideration in 2009, or
at any rate at some future General Assembly, is pretty
clearly understood.

A commonly used methd of getting contentious
resolutions passed is to promise that 'it is only
temporary', knowing that if resolving differences
is so difficult, it may well be 'temporary' for more
than the lifetime of the members ;-)

I wouldn't be surprised if every single member of
the IAU "understood" that this would be revisited,
but that's not what is in 5A.

Thus the resolution doesn't directly affect the status of
any extra-solar planet, much less remove its planethood,
which is simply left officially unaddressed.

Sorry, that isn't the case according to the page
I cited. That's why I asked if this was merely
one of the drafts and the final resolution
corrected these problems. Replacing "the Sun" by
"a star" would have resolved that problem (with
perhaps a footnote regarding binary systems etc.).

What I and lots of others get out of the language is that
Resolution 5A (whose text you correctly quote) chooses
to leave objects beyond our Solar System unaddressed for
now.

I have often seen people get many things out of
printed text that owe more to their own views than
what is actually written. What I note is that you
are stating only your opinion of the "understanding"
of what was "intended" but have not been able to
identify any clear statement to that effect. I can
as easily say consider the intention is that the IAU
will at some time formally define "planemo" as the
term for what used to be known as an "extra-solar
planet" with an accompanying set of criteria.

However, whatever our readings, people are now
focusing on the task of drafting definitions that can
apply to extrasolar as well as solar planets.

Or "planemos" as we should perhaps now call them
since formally "extra-solar planet" is self-contradictory.
Maybe we also need "dwarfemos" - yuk!

I agree that to achieve this we'd want to replace "the
Sun" by "a star or infrastar (i.e. a brown dwarf)" for
example -- or "a fusor," to use Basri's term.

Replacement being the key to understanding
the present situation. They have neither worded
the resolution in a way that allows the addition
of an additional criterion to extend "planet" to
the extra-solar case nor included a comment on
this saying "extra-solar planet" in an acceptable
term which will be clarified in the future.

Regarding "fusor", I cannot see a need for that
since "brown dwarf" is obviously an abbreviation
of "brown dwarf star" making "fusor" redundant.
Any celestial body that will at some point in its
life have the conditions to allow fusion is a star,
with perhaps those that have yet to reach that
stage being called "proto-stars". Perhaps Basri
just likes the idea of having invented a new term.

We can debate whether the IAU was wise to adopt a planetary
taxonomy for objects in our own solar system only, as well as
the wisdom of its specific conclusions. However, I would
emphasize that extra-solar planets are just as much planets
as they were on August 23, the day before the resolution was
adopted.

While your interpretation may seem resonable, it
is not the resolution that was passed.

I agree that strictly speaking the interpretation is distinct
from the actual text of the resolution that was passed; but I'd
say that it's a pretty widely shared interpretation.

You mean a widely shared misunderstanding ;-)

As you say, it is quite distinct from the actual text
that was voted on and accepted. I don't consider
this nitpicking incidentally because if the IAU were
to publish a "clarification" that your view was what
was intended despite the actual text, then it
becomes hypothetically possible for a further
"clarification" to say that it was really intended that
Pluto remain a planet despite the loss of 5B.
Effectively the whle assembly and voting process
can then be bypassed by a few in the organisation,
a dangerous precedent to set even if only to resolve
a non-contentious issue such as the use of the term
"extra-solar planet".

best regards
George