Freethought & Rationalism Archive

Vinnie · 10-27-2002, 11:00 AM

Quote:

Since there is no official and discrete definition for the word "planet" it doesn't really matter what you call it.

It should matter a little at least for teachers.

Vinnie

Vinnie · 10-27-2002, 11:04 AM

""""Yes, it should be called a planet because it has a moon."""

As Ida was already mentioned it will suffice to note the "double planet" argument. Charon is very large compared to Pluto when we note the size of other moons with their respective planets. Then again, how do we define "moon" or natural satellite?

ohwilleke · 10-28-2002, 09:58 AM

I'm in favor of the Pluto standard. If it's smaller than Pluto and doesn't revolve around a planet its a space rock, if it is equal to or larger than Pluto and revolves around the Sun, it's a planet.

Arrowman · 10-28-2002, 08:13 PM

According to my vintage 1844 navigation text

Quote:

There are eleven planets in the solar system...

and of course the list doesn't include Pluto. I'll dig up the list later. Meantime - any of our resident astronomers care to guess the names of the eleven?

[ October 28, 2002: Message edited by: Arrowman ]</p>

Defiant Heretic · 10-28-2002, 09:11 PM

Was Titan one of them?

Aquila ka Hecate · 10-28-2002, 09:19 PM

Quote:

There are eleven planets in the solar system...

Quote:

and of course the list doesn't include Pluto

Hi Arrowman,
The last also wouldn't include Neptune, in 1844!

I think that four or so of the largest asteroids were classified as planets at that time.

My guess would be Ceres,Pallas, Vesta and Juno-
along with Mercury,Venus,Mars,Jupiter,Saturn and Uranus.
Oh yes, and Us of course!

Autonemesis · 10-28-2002, 09:26 PM

Eleven planets in 1844:

Mercury
Venus
Earth
Mars
Pallas
Vesta
Juno
Ceres
Jupiter
Saturn
Uranus

B. H. Manners · 10-28-2002, 10:02 PM

Why not define a planet as a body that circles a star but not a non-solar object too, has enough mass where its own gravity makes it spherical, and it can harbor at least a weak atmosphere. As far as I am aware this definition covers all the planets as we know them today.

Autonemesis · 10-28-2002, 11:14 PM

Quote:

<a href="http://www.astro.rug.nl/~mwester/aos/aosKBO.html" target="_blank">What are the properties of Kuiper Belt Objects?</a>
There are three types of KBO's: Plutino's, Classical and Scattered KBO's.

Plutino's
A surprising result of the new observational work is that many of the distant objects are in or near the 3:2 resonance with Neptune. This means that they complete 2 orbits around the sun in the time it takes Neptune to complete 3 orbits.The same resonance is also occupied by Pluto.
... In fact, it is well known that Pluto's orbit crosses inside that of Neptune, but close encounters are always avoided. This property is also shared by a number of the known Plutinos (e.g. 1993 SB, 1994 TB, 1995 QY9), further enhancing the dynamical similarity with Pluto. Approximately 35% of the known trans-Neptunian objects are Plutinos. (emphasis added)

If you search on Google for Plutino and "Scattered Kuiper Belt" you will find many other references to objects very similar to Pluto, but smaller. While there is a well-defined belt of objects, the Kuiper belt has more diffuse components too. Pluto is really the largest known Kuiper belt object. If instead it was discovered in 1995, there would not even be any question. If it weren't for Percival Lowell's eccentricities (I wish I could be a rich, looney astronomer

), it might not even have been discovered at all (until much more recently). Some other objects like Pluto could have been found if it weren't for Lowell's purpose to find Planet X. The search was stopped when it was thought they had succeeded.

It's clear that tradition is the only reason that makes any sense to continue to regard Pluto as a planet. It does have special status as the first to be discovered in its class, though it took a long time before anyone realized it was "just" an outstanding example of a class.

The eight known "real" planets clearly stand out from ordinary solar system rubble in that each one dominates the dynamical environment near itself and often quite far from itself, and also of a class or classes of other much less massive solar system objects in related orbits.

Here's another interesting question: when is an asteroid (or a KBO) too small to be called an asteroid (or a KBO)? Half a mile? 500 yards? 200 feet? 30 feet? 5 feet? No? 2 inches? Absolutely not? Hmmm...

[ October 29, 2002: Message edited by: Kind Bud ]</p>

Shadowy Man · 10-29-2002, 06:00 AM

And here is some info for those who think having a "moon" helps make it a "planet".

From <a href="http://xxx.lanl.gov/abs/astro-ph/0210593" target="_blank">astro-ph/0210593</a>:

Quote:

Detection of Two Binary Trans-Neptunian Objects, 1997 CQ29 and 2000 CF105, with the Hubble Space Telescope, Noll, et al.

Images of the trans-Neptunian objects 1997 CQ29 and 2000 CF105 obtained with the Hubble Space Telescope's WFPC2 camera show them to be binary. The two components of 1997 CQ29 were separated in our images by 0.20 arcsec in November 2001 and by 0.33 arcsec in June/July 2002. The corresponding minimum physical distances are 6100 km and 10,200 km. The companion to 2000 CF105 was 0.78 arcsec from the primary, at least 23,400 km. Six other objects in the trans-Neptunian region, including Pluto and its moon Charon, are known to be binaries; 1997 CQ29 and 2000 CF105 are the seventh and eighth known pair. Binarity appears to be a not-uncommon characteristic in this region of the solar system, with detectable companions present in 4% of the objects we have examined.

[ October 29, 2002: Message edited by: Shadowy Man ]</p>

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10-27-2002, 11:04 AM	#22
Vinnie Veteran Member Join Date: Apr 2001 Location: Waterbury, Ct, Usa Posts: 6,523	""""Yes, it should be called a planet because it has a moon.""" As Ida was already mentioned it will suffice to note the "double planet" argument. Charon is very large compared to Pluto when we note the size of other moons with their respective planets. Then again, how do we define "moon" or natural satellite?

10-28-2002, 09:58 AM	#23
ohwilleke Veteran Member Join Date: Jun 2000 Location: Denver, Colorado, USA Posts: 4,834	I'm in favor of the Pluto standard. If it's smaller than Pluto and doesn't revolve around a planet its a space rock, if it is equal to or larger than Pluto and revolves around the Sun, it's a planet.

10-28-2002, 09:11 PM	#25
Defiant Heretic Veteran Member Join Date: Jul 2002 Posts: 1,288	Was Titan one of them?

10-28-2002, 09:26 PM	#27
Autonemesis Contributor Join Date: Feb 2002 Location: I've left FRDB for good, due to new WI&P policy Posts: 12,048	Eleven planets in 1844: Mercury Venus Earth Mars Pallas Vesta Juno Ceres Jupiter Saturn Uranus

10-28-2002, 10:02 PM	#28
B. H. Manners Veteran Member Join Date: Jan 2002 Location: Texas Posts: 1,213	Why not define a planet as a body that circles a star but not a non-solar object too, has enough mass where its own gravity makes it spherical, and it can harbor at least a weak atmosphere. As far as I am aware this definition covers all the planets as we know them today.

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