Number of low eccentricity distant planets

Hot jupiters are easier to detect than the more distant planets like
Solar System giants. However, some planets on long period orbits have
been found.

Planets on circular orbits, like in Solar System, should be no harder
to find than planets on eccentric orbits. Yet most planetary systems
have eccentric orbits.

How rare are systems with low eccentricity orbits like Solar System -
excluding the hot jupiters?

On 23 Feb, 20:49, Crown-Horned Snorkack
wrote:
Hot jupiters are easier to detect than the more distant planets like
Solar System giants. However, some planets on long period orbits have
been found.

Planets on circular orbits, like in Solar System, should be no harder
to find than planets on eccentric orbits. Yet most planetary systems
have eccentric orbits.

How rare are systems with low eccentricity orbits like Solar System -
excluding the hot jupiters?

I believe that the problem of how many planets with an orbit with a
given eccentricity
is not a real problem, if planetery system orbits are only designed to
describe certain
periodical phenomena! Clearly Kepler system is no more adequate once
it was discovered
the first dwarf planet, Ceres. Now the list of dwarf planet are more
consistent!
But how long planetary model system can be last based on possible
modification
of eccentricity coefficient?
This is really not the case.
It's more important discover the star that through its expansion
produced our original nebula, but this is really hard
since that star is surely not visible!

Wasn't it Crown-Horned Snorkack who wrote:
Hot jupiters are easier to detect than the more distant planets like
Solar System giants. However, some planets on long period orbits have
been found.

Planets on circular orbits, like in Solar System, should be no harder
to find than planets on eccentric orbits. Yet most planetary systems
have eccentric orbits.

How rare are systems with low eccentricity orbits like Solar System -
excluding the hot jupiters?

This page lists extrasolar planets detected by radial velocity ordered
by eccentricity
http://exoplanet.eu/catalog-RV.php?&mode=5
(You can order by any column by clicking on the column name).

Decide what value you consider to be "low eccentricity" and count off
the proportion. As a guide, the eccentricity of the Earth is 0.0167.
About 16% of those extrasolar planets have orbits that are less
eccentric than that of the Earth. I ignored exoplanets for which the
eccentricity has not been calculated.

This page allows you to display a histogram of exoplanet eccentricities.
http://exoplanet.eu/catalog-RV.php?mdAff=stats#tc
Choose "Planet Ecc" as the "Ref" field.

You can also use that page to produce a correlation diagram. If you plot
Planet Mass (log) vs Planet Eccentricity (linear) you'll see that
there's a slight tendency for low mass planets to have more circular
orbits.

--
Mike Williams
Gentleman of Leisure

On 23 veebr, 22:43, Mike Williams wrote:
Wasn't it Crown-Horned Snorkack who wrote:

Hot jupiters are easier to detect than the more distant planets like
Solar System giants. However, some planets on long period orbits have
been found.

Planets on circular orbits, like in Solar System, should be no harder
to find than planets on eccentric orbits. Yet most planetary systems
have eccentric orbits.

How rare are systems with low eccentricity orbits like Solar System -
excluding the hot jupiters?

This page lists extrasolar planets detected by radial velocity ordered
by eccentricity
http://exoplanet.eu/catalog-RV.php?&mode=5
(You can order by any column by clicking on the column name).

Decide what value you consider to be "low eccentricity" and count off
the proportion. As a guide, the eccentricity of the Earth is 0.0167.
About 16% of those extrasolar planets have orbits that are less
eccentric than that of the Earth. I ignored exoplanets for which the
eccentricity has not been calculated.

This page allows you to display a histogram of exoplanet eccentricities.
http://exoplanet.eu/catalog-RV.php?mdAff=stats#tc
Choose "Planet Ecc" as the "Ref" field.

Very nice.

Looking by the order of orbital period:

there are 22 planets with orbital periods from 95 days (HIP 14810 c)
to 228 days (HD8574 b) inclusive (that is, between the orbital periods
of Mercury and Venus). Those 22 include 1 with eccentricity - and 2
with eccentricity 0. Out of the remaining 19, just 7 have eccentricity
under 0,2 (the eccentricity of Mercury)

You can also use that page to produce a correlation diagram. If you plot
Planet Mass (log) vs Planet Eccentricity (linear) you'll see that
there's a slight tendency for low mass planets to have more circular
orbits.

Crown-Horned Snorkack wrote:

Hot jupiters are easier to detect than the more distant planets like
Solar System giants. However, some planets on long period orbits have
been found.

Planets on circular orbits, like in Solar System, should be no harder
to find than planets on eccentric orbits. Yet most planetary systems
have eccentric orbits.

How rare are systems with low eccentricity orbits like Solar System -
excluding the hot jupiters?

We don't know yet. We're still collecting data.

--
Erik Max Francis && && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM, Y!M erikmaxfrancis
Stretch a bow to the very full, / And you will wish you had stopped
in time. -- Laotse, ca. 6th C. BC

Mike Williams wrote:

Decide what value you consider to be "low eccentricity" and count off
the proportion. As a guide, the eccentricity of the Earth is 0.0167.
About 16% of those extrasolar planets have orbits that are less
eccentric than that of the Earth. I ignored exoplanets for which the
eccentricity has not been calculated.

Note that there are very strong selection effects here which are sure to
affect the distribution of known eccentricities. The real answer is
that we don't yet know.

--
Erik Max Francis && && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM, Y!M erikmaxfrancis
Stretch a bow to the very full, / And you will wish you had stopped
in time. -- Laotse, ca. 6th C. BC

Erik Max Francis wrote:
Crown-Horned Snorkack wrote:

Hot jupiters are easier to detect than the more distant planets like
Solar System giants. However, some planets on long period orbits have
been found.

Planets on circular orbits, like in Solar System, should be no harder
to find than planets on eccentric orbits. Yet most planetary systems
have eccentric orbits.

How rare are systems with low eccentricity orbits like Solar System -
excluding the hot jupiters?

We don't know yet. We're still collecting data.



Sadly, my math seems to be rusting away, and I don't know If it was ever
good enough to figure this. My intuition, though, makes me think that a
planet with a highly eccentric orbit would be easier to detect (using
stellar doppler shift) than one with a circular orbit of similar period.
Am I full of crap?

-- Gene the lurker

Wasn't it Gene Hatch who wrote:

Sadly, my math seems to be rusting away, and I don't know If it was
ever good enough to figure this. My intuition, though, makes me think
that a planet with a highly eccentric orbit would be easier to detect
(using stellar doppler shift) than one with a circular orbit of similar
period. Am I full of crap?

My intuition suggests that the two opposing factors probably come close
to cancelling out. Perhaps the orientation of the ellipse with respect
to the line of sight from the Earth may be significant.

A planet with a very highly eccentric orbit reaches points that are
nearly twice as far from the primary as a planet of the same period in a
circular orbit, this causing nearly twice the displacement in the star's
position. However, it's not the position of the star that is observed by
monitoring the Doppler shift, but the rate of change of position. The
large shift in the stars position occurs when the planet is far from the
star and therefore moving more slowly.

--
Mike Williams
Gentleman of Leisure

:: Gene Hatch
:: Sadly, my math seems to be rusting away, and I don't know If it was
:: ever good enough to figure this. My intuition, though, makes me
:: think that a planet with a highly eccentric orbit would be easier to
:: detect (using stellar doppler shift) than one with a circular orbit
:: of similar period. Am I full of crap?

: Mike Williams
: A planet with a very highly eccentric orbit reaches points that are
: nearly twice as far from the primary as a planet of the same period in a
: circular orbit, this causing nearly twice the displacement in the star's
: position. However, it's not the position of the star that is observed by
: monitoring the Doppler shift, but the rate of change of position. The
: large shift in the stars position occurs when the planet is far from the
: star and therefore moving more slowly.

The two detection scenarios being compared are both with doppeler shift;
whether an eccentric orbit would help or hinder detection by
displacement is another issue.

Comparing to an orbit with similar period, there's a high-speed period
of a planet's orbit that will (via momentum conservation) impart a larger
velocity to the star, and so should be easier to observe via doppler.
These periods of higher velocity would be briefer, and would require the
major axis of the orbit to be perpendicular to the sightline to the star,
so all is not a bed of roses. But if the problem is whether the dopper
gets above a detectable threshold, and a circular orbit of similar period
is below threshold, it can only help.

Or so it would seem to me.


Wayne Throop http://sheol.org/throopw

"Mike Williams" wrote in message
...
| Wasn't it Gene Hatch who wrote:
|
| Sadly, my math seems to be rusting away, and I don't know If it was
| ever good enough to figure this. My intuition, though, makes me think
| that a planet with a highly eccentric orbit would be easier to detect
| (using stellar doppler shift) than one with a circular orbit of similar
| period. Am I full of crap?
|
| My intuition suggests that the two opposing factors probably come close
| to cancelling out. Perhaps the orientation of the ellipse with respect
| to the line of sight from the Earth may be significant.
|
| A planet with a very highly eccentric orbit reaches points that are
| nearly twice as far from the primary as a planet of the same period in a
| circular orbit, this causing nearly twice the displacement in the star's
| position.

Egads! "Twice" is proportional to "very highly", with eccentricity in
the range 0-1.

| However, it's not the position of the star that is observed by
| monitoring the Doppler shift, but the rate of change of position.

Yeah...


| The
| large shift in the stars position occurs when the planet is far from the
| star and therefore moving more slowly.

However, it's not the position of the star that is observed by
monitoring the Doppler shift, but the rate of change of position.

What is it you are trying to say?

Aside from some vague reference to orbital inclination cancelling out
your intuition, are you asking a question, stating an opinion, giving
us the benefit of your wisdom, mumbling under your breath, what?