View Full Version : Pluto - lonely planet

2005-Apr-02, 05:53 AM
OK, this is just an outlet for random thoughts about Pluto, so I've posted it here. Actually, I also hope to start a discussion about Pluto.

Pluto- named after the Roman God of the dark world of the Dead. The outermost planet (scientists are now disputing it's status) , possibly the smallest, lying after four huge planets. With a frigid, frozen atmosphere, it circles aroung a medium sized star which is not even the brightest in it's sky. Unusual even in the narrowest sense of the word, it has a moon which is large compared to itself, travelling slowly in an elongated orbit titled at 17 degrees to the mean plane of orbit of the other planets. It must be lonely, but lovely, out there.

If you have survived this, here's a question: Why is Pluto's plane of orbit tilted w.r.t. the other planets' plane ?

2005-Apr-02, 09:54 AM
W.R.T. ?
Probebly but not only, becouse some thing in the past has disterbed the Ninth planet. A colission or close pass could have coused this odd orbital path. Its highly probeble that Pluto may have been a moon of Jupiter or Satern. Run the clock back a few billion years and have a look. Ask a passing Vogon or Docter Who.

2005-Apr-03, 11:46 PM
I think it's becaue that Pluto really isn't a planet, it's more like a very large Kuiper object. If you look at the other known Kuiper objects (Quoar or something like that Sedna) it seems to be normal that they have very eccentric orbits.

2005-Apr-04, 02:59 AM
It was odd we didn't seen any small objects hitting pluto during its eccentric revolution around the Sun.

2005-Apr-04, 11:23 AM

We dident see; Becouse its a long way out there.
Definning a clear image of Pluto is still beond us.
Pluto is as small as our moon ( nearly ) and at that distance, we would not see it unless it was a huge object. Or made an equallybig impact.
I have it as, on record That Pluto is observed every night by a large imaging telesope some ware. should anything come near to it we would know.
From Pluto our sun SOL is not the brightest star. Serius out shines it.

2005-Apr-05, 09:13 PM
Actually, the reasons for the eccentricity and tilt of Pluto's orbit are pretty well understood.

It's in a 3:2 resonance with Neptune. This means that in the time Neptune goes around the sun 3 times, Pluto goes around the sun twice. That's a stable configuration, even though Pluto's orbit is so eccentric that it actually crosses Neptune's. You see, when Pluto is at the point in it's orbit where it meets Neptune's orbit, Neptune is 90 degrees ahead of it. A full orbit later, when Pluto is back at that spot, Neptune has gone through 1.5 orbits, and is 90 degrees behind Pluto. They can never collide in this arrangement.

But because of this arrangement, Neptune's gravitational influence on Pluto is always in the same direction, and it builds up. The result is that Pluto's eccentricity and inclination get "pumped up". That's why it's orbit is tilted and elongated.

Pluto isn't the only object with an orbit like that. There are over a hundred "plutinos" - KBOs that are in the same 3:2 resonance with Neptune. They all have tilted, elongated orbits, just like Pluto.

And there's a family of asteroids called "Hildas" that are in a 1:2 relationship with Jupiter, also in eccentric, tilted orbits, every one. The only difference is that they are inside Jupiter's orbit, where Pluto is outside Neptune's, but the principle is the same.

2005-Apr-05, 10:46 PM
The exploration of stable orbits wrt the 'giants' of the solar system is fascinating!

In addition to TheThorn's excellent post, consider:
- the Trojans: a large number of asteroids which are 'in' orbits around the stable Lagrange points wrt Jupiter and the Sun
- ditto, for several of Saturn's moons (but not, apparently, any moons of any other planet)
- ditto, for at least one object in Neptune's orbit
- several small asteroids in 'odd' orbits that are quasi-stable wrt the Earth's (and Jupiter's, etc)
- the 'Titus-Bode law': an interesting relationship between the semi-major axes of the major planets - a result of 'orbital migration' in the early days of our solar system?

2005-Apr-06, 03:47 PM
No way does Sirius outshine the Sun even from as far away as Pluto.

2005-Apr-06, 07:38 PM
No way does Sirius outshine the Sun even from as far away as Pluto.

I must agree. Sol shines at roughly magnitude -26, and Sirius at -1.8, a difference of 24.2 magnitudes. Each magnitude of difference is (roughly) a multiplier of 2.512. This is the fifth root of 100, the basis for the visual magnitude system. 2.512 exp24.2 yields 4,791,540,558. Thus the Sun's apparent brightness is 4.79 billion times that of Sirius. To find the distance at which they would appear the same (expressed in multiples of the Earth-sun distance, or 1 AU), take the square root, yielding 69,221+ AU. If the sun is any closer than that, it outshines Sirius. Pluto cycles between 39 and 50 AU, for comparison. Best regards-- Steve

[Edits req'd due to faulty memory-- now ok, meds in place. S]

2005-Apr-07, 11:24 AM
I read it somewhere- that the sun isn't the brightest star from Pluto's surface. From an (otherwise) trustworthy book. That's why I believed it.

2005-Apr-07, 11:49 AM
Great topic - learning plenty here. Does Uranus not approach almost as close to Pluto as Neptune in some orbits?
Also nice to know how magnitudes are calculated - thanks.

2005-Apr-07, 12:00 PM
I think Neptune's orbit is twice as far from the sun as Uranus's is. Will have to look it up.... Wait a sec... well almost, Uranus is about 20 AU and Neptune is about 30 AU.

2005-Apr-07, 12:35 PM
Let's hope that NASA or ESA or some agency sends a probe there one day for a look as I for one can't wait to see how it looks with its 'moon' Charon. Lets not forget Charon in all of this as correct me, but isn't it about half the size of Pluto? I bet they are quite a sight!

2005-Apr-07, 10:25 PM
I see where you are coming from Rahul, however this has caused me to read some more about it :

http://physics.fortlewis.edu/Astronomy/ast...TML/AT31308.HTM (http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/AT313/HTML/AT31308.HTM)

has a decent picture demonstrating the constant pulling Neptune exerts on Pluto and also asserts:

Because of the orbital resonance and Pluto's tilted orbit plane, the distance between the two planets at closest approach is actually about 17 A.U. (compare with Pluto's closest approach to Uranus of just 11 A.U.)

The second graph on the next one shows Pluto's distance from various bodies however I do not necessarily agree with the author's claims as to the effects this could have: