PLEASE NOTE:
*
CCNet SPECIAL: RENEWED CALLS FOR RECLASSIFICATION OF PLUTO'S
STATUS
--------------------------------------------------------------------
17/2001 - 31 January 2001
"Kevin Zahnle, also a space scientist at NASA Ames, said
Pluto is a
true-blue American planet, discovered by an American for
America."
--Leonard David, Space.com, 30 January 2001
"Such romanticism has no place in science, a system which
must never
cease trying to determine the objective truth, a truth free from
human prejudice and emotion. Neither does nationalism."
--Joshua Kitchener, 30 January 2001
"I confess I am disappointed in the learned community that
joins
with astrologers in holding onto an outdated classification
scheme."
--Wendell Mendell, JSC/NASA, 30 January 2001
"My personal view is that Pluto should probably have dual
citizenship, in that its planetary status ought to be maintained
partly for historical reasons and partly for its physical
characteristics. But it seems clear that it is also 'object one'
in what we
now recognize as a large class of Kuiper Belt objects."
--Dale Cruikshank, President of the IAU's commission for the
physical study of the planets and satellites in the
solar system, 30 January 2001
"On the whole, I do not agree with the dual status because
it
complicates matters too much in the public perception. I
certainly think
that Pluto could be included in a list of Kuiper Belt objects,
with
which it seems to be a part. Pluto can retain its status as a
major planet
and as a Kuiper Belt object. But how can it possibly be both a
major planet
and a minor planet?"
--David H. Levy, 30 January 2001
"Had other TNOs been discovered in 1935 and not in 1992, it
is quite
possible that we would not be having this debate now."
--Mark Kidger, 30 January 2001
(1) RENEWED CALLS TO RECLASSIFY PLUTO'S STATUS IN THE SOLAR
SYSTEM
Benny J Peiser <b.j.peiser@livjm.ac.uk>
(2) DUAL CITIZENSHIP SEEN FOR PLUTO
Space.com, 30 January 2001
(3) KUIPER BELT OBJECTS AND THE FORMATION OF THE SOLAR SYSTEM
Andrew Yee <ayee@nova.astro.utoronto.ca>
(4) NO TO DUAL CITIZENSHIP, BUT PLUTO COULD BE INCLUDED AS KBO
David H. Levy <david@jarnac.org>
(5) WHY PLUTO'S STATUS HAS ALWAYS BEEN IN DOUBT
Mark Kidger <mrk@ll.iac.es>
(6) PLANETS AND PLANETARY SCIENCE
Wendell Mendell <wendell.w.mendell1@jsc.nasa.gov>
(7) PLUTO ROMANTICISM HAS NO PLACE IN SCIENCE
Joshua Kitchener <staff@meteors.com>
(8) THOUGHTS ON THE ONGOING PLUTO QUESTION
Greg Bryant <jbryant@mail.usyd.edu.au>
(9) WHY NEPTUNE AND PLUTO CAN'T COLLIDE
Duncan Steel <D.I.Steel@salford.ac.uk>
(10) LARGE KUIPER BELT OBJECTS COULD BE CALLED PLUTINOS
Giesinger Norbert <norbert.giesinger@siemens.at>
=============
(1) RENEWED CALLS TO RECLASSIFY PLUTO'S STATUS IN THE SOLAR
SYSTEM
From Benny J Peiser <b.j.peiser@livjm.ac.uk>
To the astonishment of many, the proposal to assign Pluto dual
classification as both a major and a minor planet is back with a
vengeance.
This surprise is even greater given that the public call for a
change is
coming from planetary scientists in U.S. who, in the past couple
of years,
strongly objected to the very idea. Many readers will recall how
a campaign
organised by the Division for Planetary Sciences, the main body
of planetary
astronomers in the U.S., forced the IAU to abandon the compromise
idea of
dual citizenship for Pluto.
Why, then, this sudden change? What has triggered this remarkable
U-turn?
Has it to do with some startling new discoveries of very large
Kuiper Belt
Objects in recent years, such as recently discovered 2000 WR106?
After all,
with an impressive size of 900km, this trans-Neptunian object has
a diameter
almost identical to that of Ceres, thus raising the chances that
sooner or
later KBO's even bigger than Pluto may be discovered.
Or is the conspicuous transformation of the hard-line opposition
perhaps the
direct result of Neil de Grasse Tyson's gutsy action to
down-grade Pluto? At
the heart of this sudden change of mind, lies the fear, among
some in the
astronomical community, that the bold move by America's most
eminent
Planetarium to classify Pluto exclusively as a Kuiper Belt Object
might soon
be copied and supported by other institutions of science and
astronomy
education. In short, this rear-guard action now appears almost
like a damage
limitation exercise.
Whatever the reasons may be, the fact remains that some of the
most
outspoken critics of the initial idea for Pluto's "dual
citizenship,"
invented by Mike A'Hearn and advocated by Brian Marden and
others, appear to
have softened their hard-line opposition. Crucially, Dale
Cruikshank, the
president of the IAU's commission for the physical study of the
planets and
satellites in the solar system has voiced his view loud and
clearly that
Pluto's current status ought to be changed. In an interview with
Space.com
(see below) he states:
"Pluto should probably have dual citizenship, in that its
planetary
status ought to be maintained partly for historical reasons and
partly
for its physical characteristics. But it seems clear that it is
also
'object one' in what we now recognize as a large class of Kuiper
Belt
objects."
Equally important is David Levy's latest statement on the Pluto
controversy
in today's CCNet. In his letter, David underlines that he still
objects to
the original "dual citizenship" concept. However, he
seems perfectly happy
with the idea to classify Pluto also as a Kuiper Belt Object.
Since David's main concern has always been that Pluto should not
loose his
status as a major planet (at least not for the time being), I
feel that his
latest comments and those by Dale Cruikshank, should help and
encourage the
astronomical community to come up with a new compromise solution
for Pluto
that is acceptable to the vast majority of astronomers around the
globe.
While these are positive and welcome developoments, we should not
ignore the
darker and unpleasent aspects of this bitter conflict that still
linger on.
It fills me with consternation to read some of the extreme
comments quoted
in yesterday's Space.com article. It would appear that this
scientific
discussion is regarded by some researchers, particularly in the
U.S., almost
like a combat in which opponents are either accused of treachery
or lack of
patriotism. How else should one explain the charge by Jeff Moore
(NASA Ames)
who likened the demoting of Pluto by the Hayden Planetarium to
"subterfuge,
if not sabotage." Neither can I come to terms with Kevin
Zahnle's bizarre
statement that "Pluto is a true-blue American planet,
discovered by an
American for America." Joshua Kitchener is quite right when
he notes in his
letter that "such romanticism has no place in science, a
system which must
never cease trying to determine the objective truth, a truth free
from human
prejudice and emotion."
Benny J Peiser
=============
(2) DUAL CITIZENSHIP SEEN FOR PLUTO
From Space.com, 30 January 2001
http://www.space.com/scienceastronomy/solarsystem/plutos_citizenship_010130.html
By Leonard David
Senior Space Writer
MOUNTAIN VIEW, Calif. -- Not describing Pluto as a planet is
being viewed
like the solar system snub of the century. The ninth wonder of
the worlds,
distant Pluto, has lost favor as a planet worth counting on.
That's the belief of Neil de Grasse Tyson, director of the Hayden
Planetarium in New York City.
Tyson supports the planetarium's exhibit that ranks Pluto as
belonging to
the Kuiper Belt of icy objects past Pluto and has given a
thumbs-down vote
on exalting the way-out world as the solar system's ninth planet.
But space scientists here at the NASA Ames Research Center are
defending the
planetary status of Pluto, with some caveats, however.
Planet-like attributes
"It's mostly a specious discussion," said Dale
Cruikshank, a NASA research
scientist in the astrophysics branch and specializing in small
bodies and
the Kuiper Belt.
Cruikshank is also president of the International Astronomical
Union's (IAU)
commission for the physical study of the planets and satellites
in the solar
system. The commission's official position is that Pluto is one
of the nine
planets in the solar system, a status that the faraway object has
held since
it was discovered in 1930, he said.
The late astronomer, Clyde Tombaugh, first spotted Pluto, the
only planet
ever to be discovered by an American, and the only planet found
that added
to the growth of our solar system in the 20th century.
"Pluto has many attributes which suggest it should be called
a planet. It
has its own moon, for example. It has an atmosphere. It has a
surface that
interacts and changes with the atmosphere. Like Neptune's moon,
Triton,
Pluto probably has a haze in the atmosphere. For all we know it
has clouds,"
Cruikshank said.
Object of affection
"My personal view is that Pluto should probably have dual
citizenship, in
that its planetary status ought to be maintained partly for
historical
reasons and partly for its physical characteristics,"
Cruikshank told
SPACE.com. "But it seems clear that it is also 'object one'
in what we now
recognize as a large class of Kuiper Belt objects.
If Pluto does get that designation, either for common use or
eventually by
some official body such as the IAU, then it should also retain
its status as
a planet, Cruikshank said.
"This whole business of trying to somehow devalue Pluto as
an interesting
object...I'm not sure what purpose that serves," said Jeff
Moore, a NASA
Ames research scientist who studies the satellites of the outer
planets, as
well as Pluto.
Moore likened the demoting of Pluto by the Hayden Planetarium as
"subterfuge, if not sabotage."
"First of all, it's rather amazing that Tyson, an
astrophysicist, would even
venture into such waters. I feel, as a planetary geologist,
equally
qualified to demote the Magellanic Clouds to glorified star
clusters as
opposed to small galaxies. So in that spirit, I think he's full
of baloney,"
Moore said.
Traditionally and culturally, Pluto has been treated as the ninth
planet,
Moore said. "People will want to stick with their cultural
traditions," he
said.
Changing face of the solar system
Kevin Zahnle, also a space scientist at NASA Ames, said Pluto is
a true-blue
American planet, discovered by an American for America. As far as
debating
the issue, "any person, who knows the names of the planets
are in a position
to have an opinion on this matter," he said.
Planets of the solar system.
Zahnle said that no other object yet discovered in the Kuiper
Belt is as
large as Pluto. "But as soon as they discover another one
that's the same
size, at that point the planet Pluto is going to loose its
support," he
said.
Cruikshank said giving Pluto dual citizenship, adoring it as both
planet and
Kuiper Belt object is a compromise, in a sense.
"I think it correctly recognizes the changing face of the
solar system,"
Cruikshank said.
Kuiper Belt objects are more numerous than the Asteroid Belt,
with first
detection of a Kuiper Belt object made less than 10 years ago.
For Cruikshank, Pluto is a place calling out for further
exploration.
"Whether Pluto is the last outpost of the planets or the
first outpost to a
whole new system of objects, it is a meritous place to go."
Copyright 2001, Space.com
==============
(3) KUIPER BELT OBJECTS AND THE FORMATION OF THE SOLAR SYSTEM
From Andrew Yee <ayee@nova.astro.utoronto.ca>
Harvard-Smithsonian Center for Astrophysics
Cambridge, Massachusetts
Science contacts:
Scott J. Kenyon, skenyon@cfa.harvard.edu
Rogier A. Windhorst, Rogier.Windhorst@asu.edu
For Release: 9:00 am EST, January 29, 2001
Release No.: 01-02
The Cosmos and the Solar System
Cambridge, MA -- It may be hard to imagine that the dark night
sky is a
profound astronomical observation. Yet the darkness of the night
sky, also
known as Olbers Paradox, is one of astronomy's great puzzles.
Four hundred
years ago, Johannes Kepler concluded that an infinite universe
uniformly
filled with stars and galaxies produces an infinitely bright
night sky. The
finite size of the Milky Way galaxy solves the paradox for stars.
The finite
age of an infinite, expanding universe eliminates the paradox for
galaxies.
Now, two astronomers have shown that the dark night sky also
tells us about
the structure and formation of our solar system. In a recent
paper published
in the Astrophysical Journal Letters (547,L69)
[ http://www.journals.uchicago.edu/ApJ/journal/issues/ApJL/v547n1/005778/brief/005778.abstract.html
],
Scott J. Kenyon (Smithsonian Astrophysical
Observatory) and Rogier A. Windhorst (Arizona State University)
have used
the dark night sky to set new limits on the amount of material in
the outer
reaches of the solar system. Their results tell us about the
formation of
planets like Pluto in the outer solar system.
In 1992, Jane Luu (Leiden Observatory) and Dave Jewitt
(University of
Hawaii) discovered the first solar system objects outside the
orbits of
Neptune. Using ground-based telescopes, Luu, Jewitt, and others
have now
discovered over one hundred Kuiper Belt objects, KBOs for short,
in orbit
around our Sun. The largest KBO has a diameter of nearly 2,000
kilometers;
the smallest
KBO is only about 100 km across.
Kenyon and Windhorst used the dark night sky to estimate the
number of KBOs
smaller than 100 km across. Each of these small KBOs is too faint
for
observations even with the largest telescopes on earth. All
together, these
KBOs produce enough diffuse light for astronomers to observe with
instruments like the Hubble Space Telescope. The amount of
diffuse light is
related to the number of small KBOs; more KBOs reflect more light
from the
Sun. Small dust particles in the inner solar system produce a
similar
effect, the Zodiacal light, a cone-shaped glow near the Sun which
can be
observed with the naked eye shortly after sunset or shortly
before sunrise.
The relative numbers of small and large KBOs is an important
prediction of
theories for planet formation in the outer solar system. Most
theories of
planetary formation begin with a thin circumstellar disk of gas
and dust
rotating around a newly-formed star. Planets like the Earth,
Mars, and
Jupiter grow from mergers of much smaller bodies, known as
planetesimals,
embedded in the disk. The planetesimals, ranging in size from
rougly one
meter to one kilometer across, collide almost continuously,
careening off
each other like pinballs in an arcade game. Eventually, enough of
these
small bodies stick together to make rocky planets like the Earth
and Mars or
icy bodies like Pluto. The slow growth process is similar to the
proverbial
snowball growing larger and larger as it rolls down a snowy
slope.
As the larger objects grow even larger, they stir up and
accelerate smaller
bodies in the nebula. The grinding, shattering effect of constant
high-speed
collisions produces untold millions of micrometer-sized to
meter-sized
particles that reflect light from the Sun. In the outer solar
system, this
process should produce large KBOs which can be detected by
telescopes on
earth. The high speed collisions make small collision fragments
which
produce the diffuse light that Kenyon and Windhorst used to
estimate the
numbers of small KBOs.
Kenyon and Windhorst's result shows that the night sky is too
dark for some
models of planet formation. Surprisingly, the dark night sky is
connected to
the formation of the planet Neptune. If Neptune forms before the
large KBOs,
there are too few large KBOs and too many small KBOs. If Neptune
forms at
about the same time as the large KBOs, the brightness of the
night sky is
just right. In these models, most of small KBOs are the fragments
of
collisions between much larger objects.
Kenyon and Windhorst plan to refine their analysis with images
from Hubble
Space Telescope in the next year or two.
============================
* LETTERS TO THE MODERATOR *
============================
(4) NO TO DUAL CITIZENSHIP, BUT PLUTO COULD BE INCLUDED AS KBO
From David H. Levy <david@jarnac.org>
Dear Benny,
Yes, I was a bit sharp in yesterday's message; I am sorry. I am
so sad that
this issue has come up again-- every time I think it is over, it
just keeps
right on coming back! Also on a personal note, Wendee and I just
said
goodbye to our own Pluto, our beagle Odie, who had been ill for
some
time.
It seems this Pluto status debate comes up every two years.
Perhaps it is
because Pluto has a second moon-- probably far bigger than it
is-- with a
two year orbit that incites this debate whenever it comes to
peripluto.
Actually, the Tombaugh family recalls that this debate first
opened in the
1950s when Kuiper suggested that Pluto had been a moon of
Neptune. A
reporter stated then that Pluto was not a planet.
On the whole, I do not agree with the dual status because it
complicates
matters too much in the public perception. I certainly think that
Pluto
could be included in a list of Kuiper Belt objects, with which it
seems to
be a part. Pluto can retain its status as a major planet and as a
Kuiper
Belt object. But how can it possibly be both a major planet and a
minor
planet?
David H. Levy
==============
(5) WHY PLUTO'S STATUS HAS ALWAYS BEEN IN DOUBT
From Mark Kidger <mrk@ll.iac.es>
Dear Benny:
I must react to one detail in David Levy's comments which is, I
think,
misleading. Pluto's status has been questioned for many years.
Although the
debate has heated up in the last few years, that is entirely for
other
reasons.
Had other TNOs been discovered in 1935 and not in 1992, it is
quite possible
that we would not be having this debate now. There is though the
historical
"accident" that Pluto's albedo is so much larger than
the rest of the TNOs
that only Pluto of the TNOs was detectable to Tombaugh. Tombaugh
himself
continued his search until 1943 because of the grave doubts that
the object
was the one that he was searching for. In fact, initially it was
seriously
considered that Pluto might simply be a distant satellite of
another, much
larger planet. For this reason, as David knows, he made an urgent
seach of
the circum-Pluto region as soon as it was realised that there was
something
wrong with the object and that it was not the one that the Lowell
Observatory staff had expected to find.
As we know, Clyde Tombaugh found no other objects because the
albedos of the
other TNOs are probably around 4-5% rather than the 60%-ish of
Pluto. Give
Pluto a lower albedo and Tombaugh would have had a tough time
finding it.
Ceres was relatively rapidly downgraded because even though it
outsizes all
the other asteroids in about the same proportion that Pluto
currently
outsizes the other TNOs (an interesting parallel), the other
major asteroids
have similar or larger albedos and are not so different in
brightness, thus
a few of them could be easily detected (although for many years
there were
just 4 known).
However, going back to the '60s and '70s, there are some
interesting
questions being raised even then, before the mass of Pluto was so
massively
downgraded on the discovery of Charon.
In his late '60s book, now published as "The History of
Astronomy", Patrick
Moore made the interesting comment that "Pluto may just be
the largest
member of an outer asteroid belt". I don't know if that was
an original
idea, or he was quoting someone else. If it was a prediction, it
was a
brilliant one, because the concept of the Kuiper Belt was barely
known at
the time - in fact, it wasn't until the 1990s when people like
David Jewitt
made the community take it seriously by the force of an arduous
search that
had already lasted several years.
A few years later I remember very well one question from my first
year
undergraduate astronomy course (London University's equivalent of
"Astronomy
101"). It was "Recent discoveries show that Pluto does
not merit being
considered a major planet, discuss" - this was the late
'70s. I dissented
strongly from this view and, coincidence or not, my grade was not
quite what
I had hoped for...
The question is that the doubts about Pluto have not arisen in
the last few
years, they date back to the moment of discovery. Over the last
few years,
as new information has come to light, the arguments have simply
hard a more
solid footing. When Pluto was still regarded as being several
thousand
kilometers across and, although the smallest planet, not that
much less
massive than Mercury and certainly more massive than the entire
asteroid
belt, it seemed churlish to consider it not to be a proper
planet. Today
though, we know that we were wrong and even the doubters were
still
overrating Pluto's size and mass. Now, we know that Pluto is down
in mass by
such a huge amount over Mercury that it's hard to pass over.
There are even
half a dozen planetary satellites that are more massive.
I've always had a strong affection for Pluto. If it is finally
officially
downgraded it will be a sad moment for all Pluto lovers. The
problem is that
sometimes one has to face the facts and admit that one has been
living a
lie. Perhaps it's best to find a solution that preserves the
dignity, both
of Pluto and of Clyde Tombaugh. There's no hurry, but it is
becoming sadly
inevitable.
Mark Kidger
==========
(6) PLANETS AND PLANETARY SCIENCE
From Wendell Mendell <wendell.w.mendell1@jsc.nasa.gov>
Dear Benny,
I am a planetary scientist who is new to the CCNet. I have been
teaching for
several years that Pluto is not truly a planet. I agree totally
with your
original comments. I particularly would like to comment on the
problem of
defining a planet.
First, I will digress briefly to suggest a litmus test for those
whose
opinions might be 'political'. As a gedanken experiment, imagine
that the
Bill & Melissa Gates Foundation establishes a 10^9 dollar
grant to build and
fly a nuclear electric spacecraft to rendezvous with 3 Kuiper
Belt objects
but not with any planet. Which scientists would alter the status
of Pluto?
Planets, as we all know, were first defined as those points of
light that
are not fixed in sky. There were 5 of them. Earth was not
one.
By the end of the 17th Century, we had Copernicus' suggestion,
Brahe's
observations, Kepler's Laws, Newton's Law of Gravitation, and
successful
computational predictions using all of the above. Planets were
objects
orbiting the Sun; Earth was one. Other objects called
satellites orbited
planets. The Moon and the Galilean Satellites were examples.
Uranus was discovered in a sky survey and was labeled a planet.
It went
around the Sun.
You have already covered the discovery of Ceres, et al, in the
early 19th
Century, which were originally labeled planets because they
orbited the Sun.
As it became clear that a number of objects occupied the same
radial space
in the ecliptic, they became minor planets. I have on my shelf a
1971 NASA
Special Publication entitled "Physical Studies of Minor
Planets". Even when
I was a student, there was a strong feeling that the minor
planets were
pieces of a major planet that occupied its rightful position in
the
Titius-Bode sequence. The term has vanished as we have
realized that some
of these objects are whizzing around the inner solar
system. We never hear
of Near Earth Minor Planets.
In the 19th Century a prize was established for the discovery of
a
hypothetical planet responsible for the disturbance of Uranus.
After the
discovery of Neptune, observations with substantial error bars
were the
basis for postulating another planet responsible for disturbing
both Uranus
and Neptune. At the time of Tombaugh's observation, the discovery
of planets
was still an activity and the road to fame and fortune
(possibly). Solar
system taxonomy consisted only of planets (with satellites),
comets, and the
special case of minor planets. What else was Tombaugh to
call Pluto, except
a planet? If Chiron had been discovered in the 1930's, would it
have been a
planet?
For the next couple of decades real astronomers did stellar
astrophysics.
When I came to work for NASA in 1963, data on lunar surface
conditions
consisted of observations using stellar tools, e.g., UBV color
differences.
All that changed with Project Apollo. Great numbers of scientists
signed up
to study lunar samples, which became the new road to fame and
fortune. NASA
had no idea how to deal with scientists, so they put each
investigator under
contract. I was the Contracting Officer's Technical
Representative to three
contracts, including one with John Adams who later went on to
fame in
planetary reflectance spectroscopy.
Contracts must result in final reports. However, these strange
scientists
wanted to give their results at a scientific conference. In
addition, there
was the problem that the first announcement of any measurement on
a lunar
rock was going to be historic. If two different people were
under contract
to make the same kind of measurement, who would get precedence?
The NASA solution was to swear everyone to secrecy until a
"Principal
Investigators Meeting" in 1970 where everyone would give
results
simultaneously. That oral presentation and accompanying paper
would satisfy
the contract reporting requirement. Subsequent meetings were held
annually
and began to be called the Lunar Science Conference. NASA figured
out
something called a grant that would not have all the red tape of
a contract.
Something strange began to happen at the LSC events over the next
5 years.
Famous chemists, famous astronomers, famous geologists, and
famous others
argued vehemently over such things as the origin of the Moon.
None of them
could comprehend the jargon or methodologies of the others. Out
of this
Babel came the new discipline of Planetary Science. Today,
planetary
scientists are reasonably comfortable integrating astronomical
observations
with petrologic observations with photogeologic analyses.
Planetary scientists view planets in terms of their physical
processes and
evolution, not in terms of their orbital context. Thus, the Moon
is widely
recognized as a planet. It is one end member in a sequence that
goes through
Mars to Venus and Earth. (Mercury may have a pathological
history.) The
Earth-Moon is really a double planet system. That point of view
raises the
issue of the identities of the Galilean satellites. Two of them
are bigger
than Mercury. What about Triton and Titan? These are all bodies
that undergo
indigenous evolution in terms of a suite of planetary processes.
Pluto is
inert except for the volatilization and condensation of its
atmosphere.
We understand much better the structure and evolution of the
solar system
than we did before 1960. Pluto fits quite well into the
context of
processes in the Kuiper belt. Even its size is no longer a
defining
characteristic. (Remember the famous plot of Pluto's reported
size versus
time, indicating by extrapolation that it would soon vanish?)
I confess I am disappointed in the learned community that joins
with
astrologers in holding onto an outdated classification scheme.
Wendell Mendell, Ph.D.
================
(7) PLUTO ROMANTICISM HAS NO PLACE IN SCIENCE
From Joshua Kitchener <staff@meteors.com>
Dear Benny,
In my rather humble opinion what we have before us in this
historic Pluto
debate is a group of romantics (note the entomology), versus a
group of
objective scientists.
Several articles about Hayden Planetarium's couragous decision to
deplanetize Pluto included quotes like this:
'When I was a kid, we were taught that there are
nine planets. Mary's
Violet Eyes....'
And so forth. Sheer nonsense if you ask me.
It's not too hard to imagine the same type of people back in
Galileo's age,
saying, "I've been taught that the Earth is the center of
the universe since
I was a child. Why change it? I like things the way they
are."
Such romanticism has no place in science, a system which must
never cease
trying to determine the objective truth, a truth free from human
prejudice
and emotion. Neither does nationalism.
Today there is little justification for teaching the Solar System
simply as
"The Sun and The Nine Planets". The last few years have
brought great new
insights into the structure of our planet's neighborhood; we
should
compliment these discoveries with textbooks which illustrate the
Solar
System as it truly seems to be: a dynamic, complex system which
includes
many different types of objects.
Schoolchildren can handle a model of our glorious Solar System
which more
accurately reflects reality: rocky planets, asteroids, gaseous
planets,
cometary objects, and some objects which seem to fall in-between.
The Roman Catholic Chuch was the Plutocracy of Galileo's age. We
should
honor the lessons of the past and not be swayed by convention or
emotion.
Rather, we must always strive for the truth. Always.
Quite sincerely,
Joshua Kitchener
Publisher, NearEarth.net Magazine
staff@dot-comet.com
http://NearEarth.net
================
(8) THOUGHTS ON THE ONGOING PLUTO QUESTION
From Greg Bryant <jbryant@mail.usyd.edu.au>
Dear Benny,
I was surprised to see the Pluto issue raised again. It's
certainly an issue
with emotion on both sides of the debate, not just the pro-planet
side.
Indeed, to give Pluto dual status would fan the fire as the
"pro minor
planet" people would probably never refer to Pluto again as
a major planet.
Give it a label such as (10000) and it would have been forever
separated
from the rest of the major planets.
With the explosion in extrasolar planet discoveries in the last
five years,
not only has our "Sol-based" view of planetary systems
been completely
shaken (who could have imagined a Jupiter-sized world orbiting 51
Pegasi in
just 4 days) but it provides an opportunity to look again at
Pluto.
One of the early complaints about Pluto was that its orbit was
too
elliptical compared to the other major planets. Yet, a look at
some of the
orbital eccentricities of extrasolar worlds would suggest that
nice circular
orbits are far from common. One can only wonder what the
Universe will
surprise us with when we are able to measure orbital inclinations
of
extrasolar worlds.
Another view put forward about Pluto not being a major planet was
that it
shared a resonance relationship with Neptune. A few weeks ago, it
was
announced that two planets had been discovered with a 2 to 1
resonance
around the red dwarf Gliese 876. Resonance is no barrier to
planetary
status.
Some say that Pluto, being an icy world, doesn't fit into the
other classes
of major planets - gas giant and rocky terrestial. Why stop
at two classes?
Can we not consider icy accretion?
As we try to find an acceptable definition of a planet, let's
pose a
question for what awaits us in the next few decades. Space-borne
observatories will be built that have the power to image
individual planets
around other stars. A planetary system is found containing a few
rocky
planets within 3 AU of the star, one or more gas giants beyond
that,...and
then a 5 - 10,000km icy world at 30 or 40 AU. Would we deny
planetary status
to that body?
Regards,
Greg Bryant
===============
(9) WHY NEPTUNE AND PLUTO CAN'T COLLIDE
From Duncan Steel <D.I.Steel@salford.ac.uk>
Hi Benny.
Gerrit Verschuur asked: "(11) CAN 'REAL PLANETS'
COLLIDE?"
Neptune and Pluto cannot collide. Although THE ORBIT of Pluto
crosses THE
ORBIT of Neptune, they are locked into a 3:2 mean motion
resonance (i.e.
Pluto's orbital period is precisely 1.5
times that of Neptune) and the two objects never have a
separation of less
than 18 AU. (When they have the same solar longitude Pluto is at
aphelion.)
I believe that this behaviour has been shown
to be stable over a timescale of the same order as the age of the
solar
system. Otherwise, of course, Pluto would have been dismissed
from its orbit
long ago. That is, one might imagine that once upon a time there
were many
Plutos, and the one we see left in place has survived only
because of its
ability to avoid Neptune. I did look into this some years ago
using
statistical techniques and showed that the timescale for Pluto
orbital
disruption would be only 10^4-10^5 years if it were not for this
resonant
stability:
D.I. Olsson-Steel, 'Results of close encounters between Pluto and
Neptune,'
Astronomy & Astrophysics, 195, 327-330 (1988).
...but I believe that more detailed long-term numerical
integrations have
been done since.
Cheers,
Duncan
=========
(10) LARGE KUIPER BELT OBJECTS COULD BE CALLED PLUTINOS
From Giesinger Norbert <norbert.giesinger@siemens.at>
Dear Dr. Peiser,
Concerning Your comments yesterday on naming Pluto a planet or
not, I agree
with You that a dogmatic view should be avoided.
Some years ago,I sent some remarks to Sky&Telescope with a
quantitative
view.
In short summary, the points I made are:
a) An object circling a central star may be called a planet, when
it is a
self-rounded object. The diameter can be estimated, it is
somwehere between
500 and 1000 km diameter (depending on density), thus Ceres is
near the
limit and Pluto beyond it.
b) Ceres is now not named "planet". Comparing the
masses of Pluto and Ceres,
we find that the mass of Pluto is not only a multiple of the mass
of Ceres,
but also - and this is more important - Pluto's mass is higher
than the
estimated mass of all asteroids (in the belt) combined.
Now, more and more and bigger objects in the (so called) Kuiper
belt are
found. There is reasonable speculation that objects comparable to
Pluto will
be found. When this will be the case in the future and there will
be a list
of Pluto, "Pluto 2", "Pluto 3" etc., a new
designation for the Plutos should
be used (Plutino, Planetino ...).
Until then, no change in the naming is really required. An
additional
argument (not a strong but a viable one) is, that the estimated
combined
mass of all Kuiper-belt objects found until now is probably below
the mass
of Pluto.
Greetings from Vienna!
Sincerely Yours
Norbert Giesinger
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