Locating Distant Planets

I was listening to Radio 4 earlier this evening and they were talking
about NASA and their Kepler mission and locating planets around distant
stars using the transit method where the light diminishes due to the
passage of a planet in front of the star.

I didn't hear all the program but it set me thinking, doesn't this
depend on us, Earth, and the distant planet being in the same plane so
that we see the transit? If the distant planet were orbiting so that
from Earth we never saw it transit the star we wouldn't know it existed,
would we?

Am I missing something here?

Isn't it statistically more likely that any such planet would orbit in a
way that we wouldn't see it rather than be aligned correctly so that we
can?
--

Regards

Nick

"Nick Mason" wrote in message
...
I was listening to Radio 4 earlier this evening and they were talking
about NASA and their Kepler mission and locating planets around distant
stars using the transit method where the light diminishes due to the
passage of a planet in front of the star.

I didn't hear all the program but it set me thinking, doesn't this
depend on us, Earth, and the distant planet being in the same plane so
that we see the transit? If the distant planet were orbiting so that
from Earth we never saw it transit the star we wouldn't know it existed,
would we?

Am I missing something here?

Isn't it statistically more likely that any such planet would orbit in a
way that we wouldn't see it rather than be aligned correctly so that we
can?
--

True, but because you can monitor so many stars simultaneously in a wide
field, you should find a few, even if you miss most of them. AFAIK the earth
based surveys have only found one planet using the transit method so far
(TrES-1) but there are also surveys checking stars with known planets,
looking for transits. See www.transitsearch.com for info on a Pro-Am survey.

Robin
--
----------------------------------------------------------------------------
-
Robin Leadbeater
54.75N 3.24W
http://www.leadbeaterhome.fsnet.co.uk/astro.htm
----------------------------------------------------------------------------
-

"Nick Mason" wrote in message
...
I was listening to Radio 4 earlier this evening and they were talking
about NASA and their Kepler mission and locating planets around distant
stars using the transit method where the light diminishes due to the
passage of a planet in front of the star.

I didn't hear all the program but it set me thinking, doesn't this
depend on us, Earth, and the distant planet being in the same plane so
that we see the transit? If the distant planet were orbiting so that
from Earth we never saw it transit the star we wouldn't know it existed,
would we?

Am I missing something here?

Isn't it statistically more likely that any such planet would orbit in a
way that we wouldn't see it rather than be aligned correctly so that we
can?

Yes, such transits would be statistically rare. The astronomers wanting to
do this experiment are after information on the general statistics of
planets, rather than completeness of discovery. Think of it this way:

Question to be answered: What percentage of stars of spectral class G0V-G5V
have planets of "Jupiter class"? (Similar analysis for other spectral
types...)

Assumption: The inclinations of such systems to the line of sight to Earth
are random.

(Simplified) Analysis: The chance of any one star of these classes with a
planet, producing a transit we can observe, is 1% (say), because the range
of inclinations is very restricted. Let's monitor 100,000 such stars as a
statistical sample. If we see 1,000 stars with transits, the implication is
that nearly all such stars have J-type planets. If we see 100, only 10%
have such planets. Etc.

If such planets are relatively common, then they would get statistics on how
many stars had 2, 3 or 4 such planets (each one would produce a different
transit on a given star).

By observing in a rich star field, many stars can be monitored
simultaneously.

There is also the possibility with very precise measurements (needs large
telescope) that terrestrial planets could be detected, but the amount by
which the light would drop is very small.

--
Mike Dworetsky

(Remove "pants" spamblock to send e-mail)

In article , platinum198
@pants.btinternet.com says...


"Nick Mason" wrote in message
...
I was listening to Radio 4 earlier this evening and they were talking
about NASA and their Kepler mission and locating planets around distant
stars using the transit method where the light diminishes due to the
passage of a planet in front of the star.

I didn't hear all the program but it set me thinking, doesn't this
depend on us, Earth, and the distant planet being in the same plane so
that we see the transit? If the distant planet were orbiting so that
from Earth we never saw it transit the star we wouldn't know it existed,
would we?

Am I missing something here?

Isn't it statistically more likely that any such planet would orbit in a
way that we wouldn't see it rather than be aligned correctly so that we
can?

Yes, such transits would be statistically rare. The astronomers wanting to
do this experiment are after information on the general statistics of
planets, rather than completeness of discovery. Think of it this way:

Question to be answered: What percentage of stars of spectral class G0V-G5V
have planets of "Jupiter class"? (Similar analysis for other spectral
types...)

Assumption: The inclinations of such systems to the line of sight to Earth
are random.

(Simplified) Analysis: The chance of any one star of these classes with a
planet, producing a transit we can observe, is 1% (say), because the range
of inclinations is very restricted. Let's monitor 100,000 such stars as a
statistical sample. If we see 1,000 stars with transits, the implication is
that nearly all such stars have J-type planets. If we see 100, only 10%
have such planets. Etc.

If such planets are relatively common, then they would get statistics on how
many stars had 2, 3 or 4 such planets (each one would produce a different
transit on a given star).

By observing in a rich star field, many stars can be monitored
simultaneously.

There is also the possibility with very precise measurements (needs large
telescope) that terrestrial planets could be detected, but the amount by
which the light would drop is very small.


Thanks for the replies, you reassure me that I'm not missing something
obvious when thinking about the statistics. That's what happens when you
miss part of a program, mind you I'm not sure they explained the
statistics in the part I did miss.

Interesting stuff.
--

Regards

Nick

In article , china-
says...
On Thu, 13 Jan 2005 09:53:33 +0000, Mike Dworetsky wrote:


Assumption: The inclinations of such systems to the line of sight to Earth
are random.

Is that so? I could be wrong, but does the plane of rotation of the solar
system not lie in the same plane as the galaxy? When solar systems form
does the rotation of the galaxy impart radial velocity into the disk that
eventually forms the star and its attendant planets?

If that were the case, then planetary systems would all tend to rotate in
the same or similar planes.

Just conjecture, perhaps someone who knows what they are talking about
could chip in.




This was one of the possible explanations that it occurred to me I might
be missing.
--

Regards

Nick

John Stolz wrote:
On Thu, 13 Jan 2005 09:53:33 +0000, Mike Dworetsky wrote:



Assumption: The inclinations of such systems to the line of sight to Earth
are random.


Is that so? I could be wrong, but does the plane of rotation of the solar
system not lie in the same plane as the galaxy? When solar systems form
does the rotation of the galaxy impart radial velocity into the disk that
eventually forms the star and its attendant planets?

If that were the case, then planetary systems would all tend to rotate in
the same or similar planes.

Just conjecture, perhaps someone who knows what they are talking about
could chip in.




I don't pretend to know anything about anything...

Our solar system is tilted quite off the galactic plane. Think of how
you view the Milky Way at night. It is sort up and down, not left to
right. This would indicate that we are tilted sideways...

--
-Sayf

On Thu, 13 Jan 2005 09:53:33 +0000, Mike Dworetsky wrote:


Assumption: The inclinations of such systems to the line of sight to Earth
are random.

Is that so? I could be wrong, but does the plane of rotation of the solar
system not lie in the same plane as the galaxy? When solar systems form
does the rotation of the galaxy impart radial velocity into the disk that
eventually forms the star and its attendant planets?

If that were the case, then planetary systems would all tend to rotate in
the same or similar planes.

Just conjecture, perhaps someone who knows what they are talking about
could chip in.

Our solar system is tilted quite off the galactic plane. Think of how
you view the Milky Way at night. It is sort up and down, not left to
right. This would indicate that we are tilted sideways...


I wish I _could_ see the MW...

Tony P
www.pyroport.com/astro

Tony Pottrell wrote:
Our solar system is tilted quite off the galactic plane. Think of how
you view the Milky Way at night. It is sort up and down, not left to
right. This would indicate that we are tilted sideways...



I wish I _could_ see the MW...

Tony P
www.pyroport.com/astro



I must admit I'm just going by my copy of Starry Night Pro. So if it's
wrong, then so am I! :-)

--
-Sayf

"Sayf Connary" wrote in message
...
Tony Pottrell wrote:
Our solar system is tilted quite off the galactic plane. Think of how
you view the Milky Way at night. It is sort up and down, not left to
right. This would indicate that we are tilted sideways...



I wish I _could_ see the MW...

Tony P
www.pyroport.com/astro



I must admit I'm just going by my copy of Starry Night Pro. So if it's
wrong, then so am I! :-)

Well?

Roger