In which Your Hero fails at orbital mechanics

On Oct 1, 6:11*pm, Brian Davis wrote:
If the jovian is spiraling in, why isn't the terrestrial? That might
be an important constraint.

I was hoping a brown-dwarf encounter could affect one and not the
other. Since it's going to take place in a fictional context, I can
always call in Sufficiently Advanced Aliens if the brown dwarf
wouldn't pan out.

On Oct 1, 9:43*pm, Andrew Plotkin wrote:
The abstract does imply that we don't expect Earthlike planets
to form at all in such systems, so the original question seems
unlikely.)

I'm sorry I was unclear here. The system in question gets perturbed
several billion years after planetary formation.

In sci.space.history message a6b02556-5327-4b49-b104-941be44e6f32@j19g2
000vbn.googlegroups.com, Sat, 1 Oct 2011 19:08:13, Brian Davis
posted:

On Oct 1, 8:58*pm, Orval Fairbairn wrote:

All orbits are conics...

Well... not quite. Orbits are conics if the are generated in a
universe with only two objects, both of which are point-like, under
the influence of only one force, which varies as one over the distance
^ central
squared. Add other objects, non-point-like objects, other forces, or
forces that don't have a 1/r^2 dependance, and orbits are no longer
simply conics.

That is, slightly, too restrictive.

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms and links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.

In rec.arts.sf.science, Damien Valentine wrote:
On Oct 1, 9:43*pm, Andrew Plotkin wrote:
The abstract does imply that we don't expect Earthlike planets
to form at all in such systems, so the original question seems
unlikely.)

I'm sorry I was unclear here. The system in question gets perturbed
several billion years after planetary formation.

Hm. Spirals and slow migration are hard to arrange, then.

I don't know if anybody's done a simulation of a close approach
between a dwarf star and a planetary system. I can imagine a slow
increase in influence leading to chaotic behavior, but not to jovian
planets moving inward in a steady manner.

--Z

--
"And Aholibamah bare Jeush, and Jaalam, and Korah: these were the borogoves..."
*

In article
,
Damien Valentine wrote:

On Oct 1, 9:43*pm, Andrew Plotkin wrote:
The abstract does imply that we don't expect Earthlike planets
to form at all in such systems, so the original question seems
unlikely.)

I'm sorry I was unclear here. The system in question gets perturbed
several billion years after planetary formation.

What perturbs it? The close approach of a rogue star?

On 10/03/2011 12:14 PM, Damien Valentine wrote:
On Oct 1, 4:53 pm, "Jorge R. wrote:
Assuming the Jovian is *slowly* spiraling toward the star...

I'm assuming it takes around a million years, plus or minus an order
of magnitude. Your call whether that counts as "slow".


Close enough. And mind you, I'm not commenting on the plausibility of
your scenario - just describing how the scenario would play out if one
accepts the premise that it's possible.

On Oct 3, 10:08*pm, "Jorge R. Frank" wrote:
On 10/03/2011 12:14 PM, Damien Valentine wrote:

On Oct 1, 4:53 pm, "Jorge R. *wrote:
Assuming the Jovian is *slowly* spiraling toward the star...

I'm assuming it takes around a million years, plus or minus an order
of magnitude. *Your call whether that counts as "slow".

Close enough. And mind you, I'm not commenting on the plausibility of
your scenario - just describing how the scenario would play out if one
accepts the premise that it's possible.

Of course.

"Orval Fairbairn" wrote in message
news
In article
,
Damien Valentine wrote:

All right, this is probably a simple question, but I haven't got the
maths even to know where to start. A planet somewhere between Saturn-
and Jupiter-mass is spiraling inward, on its way to becoming a hot
jovian. There's a roughly Earth-mass planet in its way. Which is
more likely: that the rocky planet impacts the jovian head-on, that
orbital decay makes it fall into its star, or that it's expelled from
the system?

Feel free to forward this to any other Usenet group that might help.

What would cause such a "spiraling?" If one planet is spiraling in, then
how is the disturbance that caused the spiraling limited to that planet?

All orbits are conics -- whether hyperbolas (exo-Solar origin),
parabolas (indefinite origin), ellipses (Solar capture) or cirles
(ellipses with zero eccentricity). Unless the planet is shedding energy
in a retrograde direction, (exercising propulsion), its orbit is never a
spiral.


Larry Niven and Jerry Pournelle wrote a story in which a space hero's coffin
is dropped into the sun, by launching it from the linear accelerator on the
Moon, fired retrograde with precisely enough velocity to counteract the
Earth's orbital speed. Though a reporter describes the path of the coffin as
"a final spiral into the sun" the narrator states that there's no such
thing.

"The Earth went on and the coffin stayed behind, then it started to fall
into the Sun...ninety-three million miles just like a falling safe".
--
Gordon Davie
Edinburgh, Scotland

"Slipped the surly bonds of Earth...to touch the face of God."

In article ,
"GordonD" wrote:

"Orval Fairbairn" wrote in message
news
In article
,
Damien Valentine wrote:

All right, this is probably a simple question, but I haven't got the
maths even to know where to start. A planet somewhere between Saturn-
and Jupiter-mass is spiraling inward, on its way to becoming a hot
jovian. There's a roughly Earth-mass planet in its way. Which is
more likely: that the rocky planet impacts the jovian head-on, that
orbital decay makes it fall into its star, or that it's expelled from
the system?

Feel free to forward this to any other Usenet group that might help.

What would cause such a "spiraling?" If one planet is spiraling in, then
how is the disturbance that caused the spiraling limited to that planet?

All orbits are conics -- whether hyperbolas (exo-Solar origin),
parabolas (indefinite origin), ellipses (Solar capture) or cirles
(ellipses with zero eccentricity). Unless the planet is shedding energy
in a retrograde direction, (exercising propulsion), its orbit is never a
spiral.


Larry Niven and Jerry Pournelle wrote a story in which a space hero's coffin
is dropped into the sun, by launching it from the linear accelerator on the
Moon, fired retrograde with precisely enough velocity to counteract the
Earth's orbital speed. Though a reporter describes the path of the coffin as
"a final spiral into the sun" the narrator states that there's no such
thing.

"The Earth went on and the coffin stayed behind, then it started to fall
into the Sun...ninety-three million miles just like a falling safe".

The delta-V required is on the order of 98000 ft/sec. -- a pretty tall
order!

"Orval Fairbairn" wrote in message
news
In article ,
"GordonD" wrote:

"Orval Fairbairn" wrote in message
news
In article
,
Damien Valentine wrote:

All right, this is probably a simple question, but I haven't got the
maths even to know where to start. A planet somewhere between Saturn-
and Jupiter-mass is spiraling inward, on its way to becoming a hot
jovian. There's a roughly Earth-mass planet in its way. Which is
more likely: that the rocky planet impacts the jovian head-on, that
orbital decay makes it fall into its star, or that it's expelled from
the system?

Feel free to forward this to any other Usenet group that might help.

What would cause such a "spiraling?" If one planet is spiraling in,
then
how is the disturbance that caused the spiraling limited to that
planet?

All orbits are conics -- whether hyperbolas (exo-Solar origin),
parabolas (indefinite origin), ellipses (Solar capture) or cirles
(ellipses with zero eccentricity). Unless the planet is shedding energy
in a retrograde direction, (exercising propulsion), its orbit is never
a
spiral.


Larry Niven and Jerry Pournelle wrote a story in which a space hero's
coffin
is dropped into the sun, by launching it from the linear accelerator on
the
Moon, fired retrograde with precisely enough velocity to counteract the
Earth's orbital speed. Though a reporter describes the path of the coffin
as
"a final spiral into the sun" the narrator states that there's no such
thing.

"The Earth went on and the coffin stayed behind, then it started to fall
into the Sun...ninety-three million miles just like a falling safe".

The delta-V required is on the order of 98000 ft/sec. -- a pretty tall
order!


The figure quoted in the story is eighteen miles a second, which is a little
over 95,000 ft/sec so presumable they were rounding off.
--
Gordon Davie
Edinburgh, Scotland

"Slipped the surly bonds of Earth...to touch the face of God."