How special is the Solar System?

Andrew Nowicki ) wrote:
: "How special is the Solar System?" by M. E. Beer1.,
: A.R. King1, M. Livio2 and J. E. Pringle2 is posted
: at: http://arxiv.org/pdf/astro-ph/0407476

: MY COMMENT

: The high eccentricity of the extraterrestrial gas giants
: implies that all or nearly all extraterrestrial planets
: have eccentric orbits and that solar system is uncommon.

Could this be due to us having several gas giants and that Jupiter and
Saturn are both large? Or that the measurements from AU are much better
than from LY, and that if we were actually near these extraterrestial
planets would be much more like our own? Further, does our solar system
from a few LY appear to have a 20 year wobble that coincides with
Jupiter and Saturn's synodic period? Since Jupiter's period is 12 years
this 8 year anomaly might make the orbit seem more eccentric.

: In addition to the nearly circular orbits (except for
: Pluto), the solar planets are almost evenly distributed
: as predicted by the Titius-Bode Law. The Titius-Bode Law
: also works for moons orbiting solar planets, but does not
: work well for Neptune and Pluto:
: http://astrosun2.astro.cornell.edu/a.../bodes_law.htm

: Apparently the solar system accretion disk was not
: disturbed by interlopers when planets and moons
: formed 4.5 billion years ago, except for the most
: distant planets: Neptune and Pluto. We still do not
: know if planetary orbits are inherently unstable.

We know that they are stable and have predicted when the perhelion points
move as well. See: http://ssd.jpl.nasa.gov/elem_planets.html

: It seems that planetary systems having many planets
: should be less stable than planetary systems having
: few planets. The absence of massive bodies in the
: middle of the solar system (known as the main
: asteroid belt) may have stabilized the solar system.
: If planetary orbits are inherently unstable than solar
: system is uncommon and SETI is a waste of time. Simple
: forms of life may survive on a somewhat unstable planet,
: but they cannot create a technological civilization.

My guess is that our solar system is typical of others, at least
others that have only one star.

: We need better computer simulations of orbital
: stability -- these simulations are more important
: than all the microwave SETI research.

Right, you cannot infer AU-based data with other data like it at LY-based
data. There is simply too much room for error.

Eric

: PS. I wonder if the Moon (Luna) acts like a vacuum
: cleaner in a sense that it hurls deadly asteroids
: away from the Earth.

: __________________________________________________ ______________


: RELATED ARTICLES


: Computer simulations of orbital stability are difficult.
: For example, the following paper is based on simulations
: made on a supercomputer having 128 processors, and yet it
: neglects possible inclinations as well as planetary systems
: having more than 3 planets:
: Stability of Terrestrial Planets in the Habitable Zone of
: Gl 777 A, HD 72659, Gl 614, 47 Uma and HD 4208
: http://arXiv:astro-ph/0403152


: Excerpt from "The Stability Of The Orbits Of Earth-Mass Planets
: In And Near The Habitable Zones Of Known Exoplanetary Systems"
: by Barrie W Jones, David R Underwood, P Nick Sleep,
: http://www.astrophys-assist.com/educate/cgino617.pdf:
: "We have shown that Earth-mass planets could survive in
: variously restricted regions of the habitable zones (HZs)
: of most of a sample of nine of the 93 main-sequence exoplanetary
: systems confirmed by May 2003. In a preliminary extrapolation
: of our results to the other systems, we estimate that roughly
: a third of the 93 systems might be able to have Earth-mass
: planets in stable, confined orbits somewhere in their HZs."
: This is a poor quality article. It does not explain
: how they calculated the orbital stability.


: Excerpt from "Dynamical Stability and Habitability of a
: Terrestrial Planet in HD74156" by M. Colleen Gino,
: http://www.astrophys-assist.com/educate/cgino617.pdf:
: "The dynamical stability of the system must be taken into
: account as well, particularly in light of the impact that
: large planets can have on the orbit of the terrestrial planet.
: For a terrestrial planet to remain habitable, there is a
: dynamical requirement that other planets in the system don’t
: gravitationally perturb the planet outside of its habitability
: zone. In a recent study involving 85 of the known extrasolar
: planetary systems, Menou and Tabachnik (2003) found that more
: than half of these systems, primarily those with distant
: eccentric giant planets, are not likely to support terrestrial
: planets and are therefore dynamically inhabitable. Marcy and
: Butler (2000) give similar evidence for the likelihood of
: terrestrial planets to be scattered gravitationally from the
: high eccentricity of Jupiter-like planets that exist between
: 2 – 3 AU. Under such circumstances the circular orbits and the
: long term survival of terrestrial planets is not guaranteed."

In article ,
(Eric Chomko) writes:
: The high eccentricity of the extraterrestrial gas giants
: implies that all or nearly all extraterrestrial planets
: have eccentric orbits and that solar system is uncommon.

Could this be due to us having several gas giants and that Jupiter and
Saturn are both large? Or that the measurements from AU are much better
than from LY, and that if we were actually near these extraterrestial
planets would be much more like our own?

I don't see why there should be any doubt about the derived
eccentricities, which are based on the radial velocity curves. The
problem is selection effects. It's much easier to detect systems
with heavy planets close to the star than systems like ours, where
the heavy planets are distant from the star. Observations so far are
incapable, or at best just barely capable, of detecting solar systems
like ours.

Further, does our solar system
from a few LY appear to have a 20 year wobble that coincides with
Jupiter and Saturn's synodic period?

No. With sufficient observations -- which would have to span a few
decades -- both periods would be seen. Try plotting the sum of two
sine waves with different amplitudes and periods.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

Steve Willner ) wrote:
: In article ,
: (Eric Chomko) writes:
: : The high eccentricity of the extraterrestrial gas giants
: : implies that all or nearly all extraterrestrial planets
: : have eccentric orbits and that solar system is uncommon.
:
: Could this be due to us having several gas giants and that Jupiter and
: Saturn are both large? Or that the measurements from AU are much better
: than from LY, and that if we were actually near these extraterrestial
: planets would be much more like our own?

: I don't see why there should be any doubt about the derived
: eccentricities, which are based on the radial velocity curves. The
: problem is selection effects. It's much easier to detect systems
: with heavy planets close to the star than systems like ours, where
: the heavy planets are distant from the star. Observations so far are
: incapable, or at best just barely capable, of detecting solar systems
: like ours.

: Further, does our solar system
: from a few LY appear to have a 20 year wobble that coincides with
: Jupiter and Saturn's synodic period?

: No. With sufficient observations -- which would have to span a few
: decades -- both periods would be seen. Try plotting the sum of two
: sine waves with different amplitudes and periods.

My understanding is that when Jupiter and Saturn are near conjunction,
the barycenter between them and the sun is about 100K miles away from the
solar corona in the direction of the planets. I believe that Asimov
discussed this in his book, "Jupiter".

Also, don't we know about the existence of planets outside the solar
system due to the relationship between the barycenter of the star and its
apparent motion related to it?

Eric

: --
: Steve Willner Phone 617-495-7123
: Cambridge, MA 02138 USA
: (Please email your reply if you want to be sure I see it; include a
: valid Reply-To address to receive an acknowledgement. Commercial
: email may be sent to your ISP.)

In article ,
(Eric Chomko) writes:
My understanding is that when Jupiter and Saturn are near conjunction,
the barycenter between them and the sun is about 100K miles away from the
solar corona in the direction of the planets. I believe that Asimov
discussed this in his book, "Jupiter".

That's about 0.35 of a solar radius, which sounds about right. I
haven't done the calculation.

Also, don't we know about the existence of planets outside the solar
system due to the relationship between the barycenter of the star and its
apparent motion related to it?

Well, sort of. The thing that is actually measured is the radial
velocity of the star. If we imagined that the whole effect above was
due to Jupiter, the Sun would move 2.7 times its radius in about 6
years (half Jupiter's sidereal period). (The barycenter stays
"fixed," while the Sun moves from one side of it to the other.) For
a distant observer located in the orbital plane, the average velocity
seen would be 1.9E9 m/1.8E8 s = 10 m/s. (Of course the radial
velocity won't be constant; it will follow a sine wave in the case of
a single planet.) Measurement errors these days are of order 1 m/s
(Any experts want to correct me on this?), so in the simplest case,
Jupiter's effect on the Sun ought to be detectable by a distant
observer after monitoring for a dozen years.

There are, however, complications. On average, a distant observer
will not be exactly in the orbital plane, and Saturn, with its 29
year period, will make the motion more complex.

You might want to plug in all the numbers and do a little simulation.
Any spreadsheet program should suffice. Calculate the velocity for,
say, every tenth of a year for 100 years, and plot the results. If
you do this, you should check whether Uranus and Neptune will produce
a noticeable effect. (Once you have done one planet, adding in more
columns for more planets should be easy.)

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

Steve Willner ) wrote:
: In article ,
: (Eric Chomko) writes:
: My understanding is that when Jupiter and Saturn are near conjunction,
: the barycenter between them and the sun is about 100K miles away from the
: solar corona in the direction of the planets. I believe that Asimov
: discussed this in his book, "Jupiter".

: That's about 0.35 of a solar radius, which sounds about right. I
: haven't done the calculation.

Does that create a wobble similar to what we see from other stars?

: Also, don't we know about the existence of planets outside the solar
: system due to the relationship between the barycenter of the star and its
: apparent motion related to it?

: Well, sort of. The thing that is actually measured is the radial
: velocity of the star. If we imagined that the whole effect above was
: due to Jupiter, the Sun would move 2.7 times its radius in about 6
: years (half Jupiter's sidereal period). (The barycenter stays
: "fixed," while the Sun moves from one side of it to the other.) For
: a distant observer located in the orbital plane, the average velocity
: seen would be 1.9E9 m/1.8E8 s = 10 m/s. (Of course the radial
: velocity won't be constant; it will follow a sine wave in the case of
: a single planet.) Measurement errors these days are of order 1 m/s
: (Any experts want to correct me on this?), so in the simplest case,
: Jupiter's effect on the Sun ought to be detectable by a distant
: observer after monitoring for a dozen years.

: There are, however, complications. On average, a distant observer
: will not be exactly in the orbital plane, and Saturn, with its 29
: year period, will make the motion more complex.

: You might want to plug in all the numbers and do a little simulation.
: Any spreadsheet program should suffice. Calculate the velocity for,
: say, every tenth of a year for 100 years, and plot the results. If
: you do this, you should check whether Uranus and Neptune will produce
: a noticeable effect. (Once you have done one planet, adding in more
: columns for more planets should be easy.)

Depending on the distance is key. 100s of LY away won't indicate anything
noticable.

I think that only Jupiter and Saturn have any effect. Again, this is based
upon "Jupiter" by Asimov and I read that a looong time ago.

Eric

: --
: Steve Willner Phone 617-495-7123
: Cambridge, MA 02138 USA
: (Please email your reply if you want to be sure I see it; include a
: valid Reply-To address to receive an acknowledgement. Commercial
: email may be sent to your ISP.)

Wasn't it Eric Chomko who wrote:
Steve Willner ) wrote:
: In article ,
: (Eric Chomko) writes:
: My understanding is that when Jupiter and Saturn are near conjunction,
: the barycenter between them and the sun is about 100K miles away from the
: solar corona in the direction of the planets. I believe that Asimov
: discussed this in his book, "Jupiter".

: That's about 0.35 of a solar radius, which sounds about right. I
: haven't done the calculation.

Does that create a wobble similar to what we see from other stars?

Yes. The mechanism is exactly the same.



: Also, don't we know about the existence of planets outside the solar
: system due to the relationship between the barycenter of the star and its
: apparent motion related to it?

: Well, sort of. The thing that is actually measured is the radial
: velocity of the star. If we imagined that the whole effect above was
: due to Jupiter, the Sun would move 2.7 times its radius in about 6
: years (half Jupiter's sidereal period). (The barycenter stays
: "fixed," while the Sun moves from one side of it to the other.) For
: a distant observer located in the orbital plane, the average velocity
: seen would be 1.9E9 m/1.8E8 s = 10 m/s. (Of course the radial
: velocity won't be constant; it will follow a sine wave in the case of
: a single planet.) Measurement errors these days are of order 1 m/s
: (Any experts want to correct me on this?), so in the simplest case,
: Jupiter's effect on the Sun ought to be detectable by a distant
: observer after monitoring for a dozen years.

The smallest radial velocity I've seen for confirmed extrasolar planets
is about 8 metres/sec. It's one of the two "Neptune sized" planets
announced on 31-Aug-2004. The light curve graph showing the amount
of radial velocity is at
http://planetquest.jpl.nasa.gov/images/per2phasebl_CHART-simple_500x375.jpg

Before Tuesday's announcement, the smallest RV was about 20 m/s.



: There are, however, complications. On average, a distant observer
: will not be exactly in the orbital plane, and Saturn, with its 29
: year period, will make the motion more complex.

: You might want to plug in all the numbers and do a little simulation.
: Any spreadsheet program should suffice. Calculate the velocity for,
: say, every tenth of a year for 100 years, and plot the results. If
: you do this, you should check whether Uranus and Neptune will produce
: a noticeable effect. (Once you have done one planet, adding in more
: columns for more planets should be easy.)

Depending on the distance is key. 100s of LY away won't indicate anything
noticable.

For this purpose, the distance doesn't make much of a difference. All you need
is to have an apparent magnitude bright enough to be able to get a good
spectrum, and a planet that causes a wobble in the star that gives a change in
the star's radial velocity of a few tens of metres per second.

For example, HD330075, HD68988 and HD76700 are all over 160 light years away and
we've detected the wobbles caused by their planets.

--
Mike Williams
Gentleman of Leisure

Mike Williams ) wrote:
: Wasn't it Eric Chomko who wrote:
: Steve Willner ) wrote:
: : In article ,
: : (Eric Chomko) writes:
: : My understanding is that when Jupiter and Saturn are near conjunction,
: : the barycenter between them and the sun is about 100K miles away from the
: : solar corona in the direction of the planets. I believe that Asimov
: : discussed this in his book, "Jupiter".
:
: : That's about 0.35 of a solar radius, which sounds about right. I
: : haven't done the calculation.
:
: Does that create a wobble similar to what we see from other stars?

: Yes. The mechanism is exactly the same.


:
: : Also, don't we know about the existence of planets outside the solar
: : system due to the relationship between the barycenter of the star and its
: : apparent motion related to it?
:
: : Well, sort of. The thing that is actually measured is the radial
: : velocity of the star. If we imagined that the whole effect above was
: : due to Jupiter, the Sun would move 2.7 times its radius in about 6
: : years (half Jupiter's sidereal period). (The barycenter stays
: : "fixed," while the Sun moves from one side of it to the other.) For
: : a distant observer located in the orbital plane, the average velocity
: : seen would be 1.9E9 m/1.8E8 s = 10 m/s. (Of course the radial
: : velocity won't be constant; it will follow a sine wave in the case of
: : a single planet.) Measurement errors these days are of order 1 m/s
: : (Any experts want to correct me on this?), so in the simplest case,
: : Jupiter's effect on the Sun ought to be detectable by a distant
: : observer after monitoring for a dozen years.

: The smallest radial velocity I've seen for confirmed extrasolar planets
: is about 8 metres/sec. It's one of the two "Neptune sized" planets
: announced on 31-Aug-2004. The light curve graph showing the amount
: of radial velocity is at
: http://planetquest.jpl.nasa.gov/images/per2phasebl_CHART-simple_500x375.jpg

: Before Tuesday's announcement, the smallest RV was about 20 m/s.


:
: : There are, however, complications. On average, a distant observer
: : will not be exactly in the orbital plane, and Saturn, with its 29
: : year period, will make the motion more complex.
:
: : You might want to plug in all the numbers and do a little simulation.
: : Any spreadsheet program should suffice. Calculate the velocity for,
: : say, every tenth of a year for 100 years, and plot the results. If
: : you do this, you should check whether Uranus and Neptune will produce
: : a noticeable effect. (Once you have done one planet, adding in more
: : columns for more planets should be easy.)
:
: Depending on the distance is key. 100s of LY away won't indicate anything
: noticable.

: For this purpose, the distance doesn't make much of a difference. All you need
: is to have an apparent magnitude bright enough to be able to get a good
: spectrum, and a planet that causes a wobble in the star that gives a change in
: the star's radial velocity of a few tens of metres per second.

Thanks for that info. I have been operating on the way things were done
when this work first began. I was a kid when they found the first two
extrasolar planets. That was when the field was in its infancy. At that
time it was stated than only stars in close proximity to our sun (less
than 15 LY) were candidates for planetary discovery. It is obvious that I
need to dig deeper into this as we have come a long way.

: For example, HD330075, HD68988 and HD76700 are all over 160 light years away and
: we've detected the wobbles caused by their planets.

I vaguely recall a big breakthrough in all this about a decade or so ago
but lack the details. Thanks again.

Eric

: --
: Mike Williams
: Gentleman of Leisure

Wasn't it Eric Chomko who wrote:
Mike Williams ) wrote:
: Wasn't it Eric Chomko who wrote:
:
: Depending on the distance is key. 100s of LY away won't indicate anything
: noticable.

: For this purpose, the distance doesn't make much of a difference. All you need
: is to have an apparent magnitude bright enough to be able to get a good
: spectrum, and a planet that causes a wobble in the star that gives a change in
: the star's radial velocity of a few tens of metres per second.

Thanks for that info. I have been operating on the way things were done
when this work first began. I was a kid when they found the first two
extrasolar planets. That was when the field was in its infancy. At that
time it was stated than only stars in close proximity to our sun (less
than 15 LY) were candidates for planetary discovery. It is obvious that I
need to dig deeper into this as we have come a long way.

: For example, HD330075, HD68988 and HD76700 are all over 160 light years away
and
: we've detected the wobbles caused by their planets.

I vaguely recall a big breakthrough in all this about a decade or so ago
but lack the details. Thanks again.

I've just discovered
http://www.eso.org/outreach/press-re...ages/phot-05d-
03-preview.jpg
which indicates that the furthest exoplanet discovered by the radial
velocity technique is HD47536 with a distance of 396 LY. (The numbers
shown on that image are logarithms of parsecs, e.g. "3.0" indicates a
distance of 1000 parsecs.) Ogle-TR-56b was discovered by observing a
transit, then later confirmed by the radial velocity technique, and that
may well be something like 5000 light years away.


Other methods of detecting exoplanets might be able to find ones that
are further away. There's an unconfirmed planet Q 0957+561 that's so far
away that the galaxy that it was found in hasn't yet been catalogued.

--
Mike Williams
Gentleman of Leisure