The 10:th planet

Recently, A 10:th planet was discovered in the Solar system: Sedna.

But I also learned that it would probably not be classified as a
planet, and also that Pluto should lose it's planetary status.

The question is then, how should "planet" be defined? If Pluto and
Sedna wouldn't qualify as planets, wouldn't it be equally wrong to
lump together the small inner planets (Mercury, Venus, Earth, Mars)
and the giant gaseous outer planets (Jupiter, Saturn, Uranus, Neptune)
as one group of celestial objects, planets?

Another question: When Pluto was discovered in 1930, wasn't its
existence and position predicted to explain the disturbances of
Neptune's orbit, just as Neptune's existence and position was
predicted in 1846, to explain the disturbances of Uranus' orbit?

But, as I understand it today, it was a coincidence that Pluto was
discovered near the predicted position, for Pluto is too small to
cause the disturbances of Neptune's orbit (as is Sedna). We also see
that over the decades, the estimates of Pluto's size decreased. 30-40
years ago, Pluto was believed to be about the same size, or even
somewhat bigger, than Mars, but nowadays, it is believed to be even
smaller than Mercury! (Sedna is even smaller.) Was it the erroneus
belief that Pluto caused of the disturbances in Neptune's orbit, that
led to these overestimations of Pluto's size in the past?

But what is then the cause of the disturbances in Neptune's orbit?
About 1986, I heard that a 10:th planet was discovered, a very big,
but cold, object, that was detected by some space telescope. This
object was big enough to cause the disturbances of Neptune's orbit.
But what happened to this big, cold object? I never heard about it
after that. Were the telescope data discovered to be misinterpreted,
or what?

All information about these issues would be appreciated.


Regards,

Erland Gadde

"Erland Gadde" wrote in message
om...
Recently, A 10:th planet was discovered in the Solar system: Sedna.

Sedna has not been given planet status.


But I also learned that it would probably not be classified as a
planet, and also that Pluto should lose it's planetary status.

The question is then, how should "planet" be defined? If Pluto and
Sedna wouldn't qualify as planets, wouldn't it be equally wrong to
lump together the small inner planets (Mercury, Venus, Earth, Mars)
and the giant gaseous outer planets (Jupiter, Saturn, Uranus, Neptune)
as one group of celestial objects, planets?

This issue will never be settled to everyone's satisfaction.
Philosophical inertia leaves Pluto as a planet, so far.


Another question: When Pluto was discovered in 1930, wasn't its
existence and position predicted to explain the disturbances of
Neptune's orbit, just as Neptune's existence and position was
predicted in 1846, to explain the disturbances of Uranus' orbit?

But, as I understand it today, it was a coincidence that Pluto was
discovered near the predicted position, for Pluto is too small to
cause the disturbances of Neptune's orbit (as is Sedna). We also see
that over the decades, the estimates of Pluto's size decreased. 30-40
years ago, Pluto was believed to be about the same size, or even
somewhat bigger, than Mars, but nowadays, it is believed to be even
smaller than Mercury! (Sedna is even smaller.) Was it the erroneus
belief that Pluto caused of the disturbances in Neptune's orbit, that
led to these overestimations of Pluto's size in the past?

It had more to do with the poor knowledge of the albedo of
Pluto. The size estimate of a reflecting object depends
strongly on its albedo.


But what is then the cause of the disturbances in Neptune's orbit?

Mass estimates for the outer planets were slightly off, and
corrected by the information gathered by Voyager probes. When
the new masses were inserted into the gravitational models,
the "disturbances" vanished.

About 1986, I heard that a 10:th planet was discovered, a very big,
but cold, object, that was detected by some space telescope. This
object was big enough to cause the disturbances of Neptune's orbit.
But what happened to this big, cold object? I never heard about it
after that. Were the telescope data discovered to be misinterpreted,
or what?

It was a wisp of interstellar cirrus imaged in the infra red.
It was never a solid body. The lousy bit of sensationalitic
reporting that appeared in the popular press provided a shopping
list of things it could have been. This list included a giant
planet at great distance, amongst other things. The woo-woos
latched onto this speculation and pretended it was fact. They've
been doing so ever since, despite repeated corrections and
information to the contrary in the literature; they simply choose
to ignore all publications on the topic that appeared after the
original speculative one.


All information about these issues would be appreciated.


Regards,

Erland Gadde

"Erland Gadde" wrote in message
om...

But, as I understand it today, it was a coincidence that Pluto was
discovered near the predicted position, for Pluto is too small to
cause the disturbances of Neptune's orbit (as is Sedna).

Correct... Pluto was discovered photographically... not via mathematical
prediction.

On Mon, 17 May 2004 19:15:22 GMT, in sci.astro you wrote:

"Erland Gadde" wrote in message
. com...

But, as I understand it today, it was a coincidence that Pluto was
discovered near the predicted position, for Pluto is too small to
cause the disturbances of Neptune's orbit (as is Sedna).

Correct... Pluto was discovered photographically... not via mathematical
prediction.


But were not the places they were looking for Pluto determined
mathematically? This was how Neptune was discovered. They pointed
their telscopes at certain locations which were determined
mathematically. Later when they realized that Neptune was not massive
enough to account for all the deviation in Uranus's position they went
back and looked for another planet.

Until the discovery of Chiron, the mass of Pluto was unknown.

As for Pluto loosing its classification as a planet, this will
probably never happen. What will most likely happen is that Pluto
will be placed at the bottom end of the scale for determining if an
object is a planet or just a very large rock/iceball.

IIRC the "disturbances of Neptune's orbit" were eventually proven to be
observational errors.
--
Curtis Croulet
Temecula, California
33° 27' 59" N, 117° 05' 53" W

In article ,
Paul Curran wrote:

On Mon, 17 May 2004 19:15:22 GMT, in sci.astro you wrote:

"Erland Gadde" wrote in message
.com...

But, as I understand it today, it was a coincidence that Pluto was
discovered near the predicted position, for Pluto is too small to
cause the disturbances of Neptune's orbit (as is Sedna).

Correct... Pluto was discovered photographically... not via mathematical
prediction.

But were not the places they were looking for Pluto determined
mathematically? This was how Neptune was discovered. They pointed
their telscopes at certain locations which were determined
mathematically.

In the case of Neptune, the telescope was pointed at the predicted
position, and within a degree from that position Neptune was
discovered, visually, the first night.

The discovery of Pluto was much more tedious: several predictions
were issued, and several searches was made, but no "Planet X" was
found. Lowell himself ran a few of these searches, but he died
without finding anything. The search for "Planet X" was down a
number of years until a new assistant, Clyde Tombaugh, was hired to
resume the search. Tombaugh used a new method, the blink microscope,
to compare a pair of plates. He searched a quite large area of the
sky systematically before he encountered Pluto, tens of degrees
away from any predicted position.

It was immediately obvious that Pluto was much fainter than expected.
So Tombaugh continued the search, and examined all of the sky within
a few tens of degrees from the ecliptic -- twice! Tombaugh did not
find any other planet.


Later when they realized that Neptune was not massive enough to
account for all the deviation in Uranus's position they went
back and looked for another planet.

Until the discovery of Chiron, the mass of Pluto was unknown.
^^^^^^
Charon, not Chiron.....

As for Pluto loosing its classification as a planet, this will
probably never happen. What will most likely happen is that Pluto
will be placed at the bottom end of the scale for determining if an
object is a planet or just a very large rock/iceball.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

"Paul Curran" wrote in message
...
On Mon, 17 May 2004 19:15:22 GMT, in sci.astro you wrote:

"Erland Gadde" wrote in message
. com...

But, as I understand it today, it was a coincidence that Pluto was
discovered near the predicted position, for Pluto is too small to
cause the disturbances of Neptune's orbit (as is Sedna).

Correct... Pluto was discovered photographically... not via mathematical
prediction.


But were not the places they were looking for Pluto determined
mathematically? This was how Neptune was discovered. They pointed
their telscopes at certain locations which were determined
mathematically. Later when they realized that Neptune was not massive
enough to account for all the deviation in Uranus's position they went
back and looked for another planet.

Except they were incorrect... Neptune's mass was enough... they just had not
calculated the masses of Netpune and Uranus correctly, and, in fact, could
not until the Voyager probes passed by them.

Except they were incorrect... Neptune's mass was enough... they just had not
calculated the masses of Netpune and Uranus correctly, and, in fact, could
not until the Voyager probes passed by them.

Yes, we know that now. But at the time they did not. And it was
because of these excesses that they bothered to searxh as hard as they
did for a tenth planet.

I KNOW that Neptune's mass was enough. But my point is that they did
not know that it was and continued to look for another planet to
account for their observed excesses.That's why Tombaugh kept looking
so far off the ecliptic.

Erland Gadde writes:

Another question: When Pluto was discovered in 1930, wasn't its
existence and position predicted to explain the disturbances of
Neptune's orbit, just as Neptune's existence and position was
predicted in 1846, to explain the disturbances of Uranus' orbit?

No. Rather, the predictions were based on unexplained residuals
in the orbit of Uranus. The discovery of Neptune removed some,
but not all, of the unexplained residuals in the orbit of Uranus.
The remainder was attributed to a ninth planet. At the time, the
orbit of Neptune wasn't known very well; the observational arc was
much shorter than the orbital period, thus it was easier to satisfy
the observations of Neptune without invoking a ninth planet.

But, as I understand it today, it was a coincidence that Pluto was
discovered near the predicted position, for Pluto is too small to
cause the disturbances of Neptune's orbit (as is Sedna). We also see
that over the decades, the estimates of Pluto's size decreased. 30-40
years ago, Pluto was believed to be about the same size, or even
somewhat bigger, than Mars, but nowadays, it is believed to be even
smaller than Mercury! (Sedna is even smaller.) Was it the erroneus
belief that Pluto caused of the disturbances in Neptune's orbit, that
led to these overestimations of Pluto's size in the past?

No. It was the presumed disturbances in the orbit of Uranus that let
to the overestimations.

But what is then the cause of the disturbances in Neptune's orbit?

There aren't any. Nor are there any remaining unexplained residuals
in the orbit of Uranus. Improved reference star catalogs and improved
masses for the perturbing planets have eliminated the residuals that
were used to predict Pluto's position.

About 1986, I heard that a 10:th planet was discovered, a very big,
but cold, object, that was detected by some space telescope. This
object was big enough to cause the disturbances of Neptune's orbit.
But what happened to this big, cold object? I never heard about it
after that. Were the telescope data discovered to be misinterpreted,
or what?

http://spider.ipac.caltech.edu/staff...lanet_yet.html