Uranus's axis

In article ,
Russell Wallace wrote:

On Sun, 7 Sep 2003 08:46:53 -0700, "Chosp" wrote:

Your question was, in fact, answered.
You used the word pull in the present tense.
Nothing has to continually pull it in a direction
perpendicular to its orbit around the sun.
How it originally got that way is not known
for certain. There simply isn't enough information
to completely rule out any one of a number of
hypotheses.

I suspect "how it originally got that way" was the intent of his
question. That's something I'm curious about as well, though I don't
have a clue about the answer - in particular, if an impact tipped the
axis over (which is the one candidate explanation I know of), how
would that have made its moons follow suit? Are there any hypotheses
which would account for that?

Well, at least that can easily be explained: the moons of Uranus were
formed after the rotational axis of Uranus had been tipped.

--
----------------------------------------------------------------
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/

I suspect that even more people are disappointed when science CAN
explain something...

:-)


On Mon, 8 Sep 2003 06:28:10 +0000 (UTC), (Paul
Schlyter) wrote:

In article ,
Greg Neill wrote:

"Bill" wrote in message
ink.net...
I apologize for using the word astrology instead of astronomy,
however I was surprised that no one knew the answer and could
only reply to my misuse of words. I was disappointed. Thanks anyway.

??? You received several answers. How is it you missed them?

In one way he was right though: currently, science has no answer to
why Uranus' rotation axis has such a large inclination. And some
people who don't understand the scientific process but instead view
science as a kind of religion get disappointed when learning about
something science cannot explain.

In message , Paul Schlyter
writes
In article ,
Russell Wallace wrote:

I suspect "how it originally got that way" was the intent of his
question. That's something I'm curious about as well, though I don't
have a clue about the answer - in particular, if an impact tipped the
axis over (which is the one candidate explanation I know of), how
would that have made its moons follow suit? Are there any hypotheses
which would account for that?

Well, at least that can easily be explained: the moons of Uranus were
formed after the rotational axis of Uranus had been tipped.

Not necessarily. The original moons would probably have been ejected or
destroyed during the impact, but if not, tidal forces would bring them
into line with the equator.
--
"Forty millions of miles it was from us, more than forty millions of miles of
void"

(Paul Schlyter) wrote in message ...
In article ,
Russell Wallace wrote:
I suspect "how it originally got that way" was the intent of his
question. That's something I'm curious about as well, though I don't
have a clue about the answer - in particular, if an impact tipped the
axis over (which is the one candidate explanation I know of), how
would that have made its moons follow suit? Are there any hypotheses
which would account for that?

Well, at least that can easily be explained: the moons of Uranus were
formed after the rotational axis of Uranus had been tipped.

What if the last collision or a couple of the collisions, that formed
Uranus, were at one of the poles ?

Would that not make the resulting planet rotate at an angle to the
ecliptic ?

It would also tear material out of the planet, for formation of the
moons. Any earlier moons could be chewed up by colliding with the
disc.

The original planetisimals of course rotated like Jupiter, but there
was 50 of them.

Some must have collided so they counteracted rotation, and others to
support it.

Regards

Carsten Nielsen
Denmark

On Mon, 8 Sep 2003 18:37:54 +0100, Jonathan Silverlight
wrote:

Not necessarily. The original moons would probably have been ejected or
destroyed during the impact

How do you reckon? Wouldn't the impactor miss most or all of them?

but if not, tidal forces would bring them
into line with the equator.

They would? Okay, fair enough. (Why doesn't this happen with e.g.
Earth's moon, various bits of debris orbiting the Sun in inclined
orbits, or globular clusters orbiting our galaxy in such orbits? Is it
a case of they will eventually but the forces involved are relatively
weaker so not enough time has elapsed yet?)

--
"Sore wa himitsu desu."
To reply by email, remove
the small snack from address.
http://www.esatclear.ie/~rwallace

"Russell Wallace" wrote in message
...
On Mon, 8 Sep 2003 18:37:54 +0100, Jonathan Silverlight
wrote:

Not necessarily. The original moons would probably have been ejected or
destroyed during the impact

How do you reckon? Wouldn't the impactor miss most or all of them?

but if not, tidal forces would bring them
into line with the equator.

They would? Okay, fair enough. (Why doesn't this happen with e.g.
Earth's moon, various bits of debris orbiting the Sun in inclined
orbits, or globular clusters orbiting our galaxy in such orbits? Is it
a case of they will eventually but the forces involved are relatively
weaker so not enough time has elapsed yet?)

Earth's moon is rather large as far as moons go. There's
a *lot* of angular momentum to deal with. The relaxation
time would be very long indeed.

On Tue, 9 Sep 2003 09:43:34 -0400, "Greg Neill"
wrote:

Earth's moon is rather large as far as moons go. There's
a *lot* of angular momentum to deal with. The relaxation
time would be very long indeed.

So if our moon were the size of e.g. Phobos or Deimos, it would be
orbiting over Earth's equator by now? How does that work? I would have
though the gravitational force per kilogram on a moon didn't vary with
the moon's mass?

--
"Sore wa himitsu desu."
To reply by email, remove
the small snack from address.
http://www.esatclear.ie/~rwallace

"Russell Wallace" wrote in message
...
On Tue, 9 Sep 2003 09:43:34 -0400, "Greg Neill"
wrote:

Earth's moon is rather large as far as moons go. There's
a *lot* of angular momentum to deal with. The relaxation
time would be very long indeed.

So if our moon were the size of e.g. Phobos or Deimos, it would be
orbiting over Earth's equator by now? How does that work? I would have
though the gravitational force per kilogram on a moon didn't vary with
the moon's mass?

It's a matter of torque and energy dissipation. In other
words, inertia. Phobos and Deimos are mere specks of
dirt compared with the Moon. So I'd say, yes, if they
were in orbit about the Earth at a comparably close
distance, then they would be tidally locked and orbiting
very nearly in the plane of the equator by now. The
Sun's influence would cause purturbations, of course,
since the equator is tilted w.r.t. the ecliptic.

In article ,
Greg Neill wrote:

"Russell Wallace" wrote in message
...
On Tue, 9 Sep 2003 09:43:34 -0400, "Greg Neill"
wrote:

Earth's moon is rather large as far as moons go. There's
a *lot* of angular momentum to deal with. The relaxation
time would be very long indeed.

So if our moon were the size of e.g. Phobos or Deimos, it would be
orbiting over Earth's equator by now? How does that work? I would have
though the gravitational force per kilogram on a moon didn't vary with
the moon's mass?

It's a matter of torque and energy dissipation. In other
words, inertia. Phobos and Deimos are mere specks of
dirt compared with the Moon. So I'd say, yes, if they
were in orbit about the Earth at a comparably close
distance, then they would be tidally locked and orbiting
very nearly in the plane of the equator by now.

Yes they would, but the reason would be the proximity to the
Earth, not their small sizes.

Phobos and Deimos may be tiny specks compared to the Moon,
but they're huge giants compared to the artificial satellites
we've launched. And our artificial satellites don't move
towards an equatorial orbit much faster because of their
very low mass....

The
Sun's influence would cause purturbations, of course,
since the equator is tilted w.r.t. the ecliptic.

--
----------------------------------------------------------------
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 Schlyter" wrote in message
...
In article ,
Greg Neill wrote:


It's a matter of torque and energy dissipation. In other
words, inertia. Phobos and Deimos are mere specks of
dirt compared with the Moon. So I'd say, yes, if they
were in orbit about the Earth at a comparably close
distance, then they would be tidally locked and orbiting
very nearly in the plane of the equator by now.

Yes they would, but the reason would be the proximity to the
Earth, not their small sizes.

Phobos and Deimos may be tiny specks compared to the Moon,
but they're huge giants compared to the artificial satellites
we've launched. And our artificial satellites don't move
towards an equatorial orbit much faster because of their
very low mass....

Suppose we could perform two trials. In one we
put, say, Phobos in a given proximate orbit to
the Earth and timed its orbit's relaxation to
an equitorial one, and then did the same with a
small satellite (after removing Phobos, of course).

Would we see the same relaxation time? What
factors might influence the results? Certainly
the smaller satellite would present less volume for
tidal action (inverse cube with distance) and
dissipation of energy in its structure. The
satellite would also be much more rigid. The small
satellite would not raise measurable tides on the
Earth, but then tides due to Phobos would be tiny,
too. The larger size of Phobos would present a
slightly larger "handle" for torques, due to the
tidal bulge of the Earth, to act.

In computing the gravitational parameter mu for
the system, the satellite's mass would be totally
negligible, and Phobos' nearly so. But the
mutual gravitational force would be ever so slightly
larger and the orbital period ever so slightly
shorter.

Have I missed anything?