Re: Number of low eccentricity distant planets

:: 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 ****ft) than one with a circular orbit
:: of similar period.  Am I full of crap? 

: Mike Williams <nospam@[EMAIL PROTECTED]
>
: 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 ****ft, but the rate of change of position. The 
: large ****ft 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 ****ft;
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   throopw@[EMAIL PROTECTED]
   http://sheol.org/throopw