Biased data on exoplanets?

The extrasolar planets found thus far are much closer to their star
than are the gas giants in our Solar system.

But isn't this simply because our sample of observed exoplanets is
biased because of the methods used to detect them? The further from
their star, the longer their periodicity and the longer time the star
has to be observed before its movements revleal its planet?

I don't know how many orbits (or how large fraction of an orbit) that
a planet has to complete before its presence can be concluded from the
movements of its star. But conisdering that our Jupiter takes more
than 4000 days to complete one orbit, I wouldn't be surpiced if it
will take decades of observations before exoplanets with Jupiter-like
orbits can be identified.

So, if I'm not completely wrong, shouldn't one expect the average
observed "semi-major axis" to grow as our sample of exoplanets grows?
But then, why are people so quick to conclude that our solar system is
so much different than the ones we've found so far? Isn't it obvious
that the extreme exoplanet systems are the easiest to detect and that
they do not constitute a representative sample?

Btw, the distribution of exoplanet-star distances seems to follow a
nice quadratic function. If ranked after semi-major axis, simply DIST
= 0,000025 * RANK^2 describes the distance (where distance Sun-Jupiter
= 1) quite well. Certainly this is due to the method of observation!
And btw again, where can I find data on when the exoplanets were
discovered? I bet they tend to have larger and larger semi -major
axis...

http://exoplanets.org/almanacframe.html

Regards!

Wasn't it bjorn2004 who wrote:
The extrasolar planets found thus far are much closer to their star
than are the gas giants in our Solar system.

But isn't this simply because our sample of observed exoplanets is
biased because of the methods used to detect them? The further from
their star, the longer their periodicity and the longer time the star
has to be observed before its movements revleal its planet?

Yes.


I don't know how many orbits (or how large fraction of an orbit) that
a planet has to complete before its presence can be concluded from the
movements of its star. But conisdering that our Jupiter takes more
than 4000 days to complete one orbit, I wouldn't be surpiced if it
will take decades of observations before exoplanets with Jupiter-like
orbits can be identified.

So, if I'm not completely wrong, shouldn't one expect the average
observed "semi-major axis" to grow as our sample of exoplanets grows?
But then, why are people so quick to conclude that our solar system is
so much different than the ones we've found so far? Isn't it obvious
that the extreme exoplanet systems are the easiest to detect and that
they do not constitute a representative sample?

You'd expect the average orbital distance to grow if exactly the same
observation technique continued to be used in the same way. However, new
teams keep starting up with more sensitive equipment which detect more
planets but only those that complete at least one orbit since the
observation started.

I suppose there might also be a bit of a tendency for the hotshot
scientists who started the original exoplanet observations ten years ago
to get a bit bored with keeping those series of observations running on
outdated equipment in the hope of adding a few long-period planets to
their bag, when they could update to the latest kit and start again
bagging lots of short-period planets.


Btw, the distribution of exoplanet-star distances seems to follow a
nice quadratic function. If ranked after semi-major axis, simply DIST
= 0,000025 * RANK^2 describes the distance (where distance Sun-Jupiter
= 1) quite well. Certainly this is due to the method of observation!
And btw again, where can I find data on when the exoplanets were
discovered? I bet they tend to have larger and larger semi -major
axis...

If you look at the pages that link from the catalogue at
http://www.obspm.fr/encycl/cat1.html you'll find a list of references.
You probably want to look for the oldest paper in the list of
references.

Note that the planet with the shortest semi-major axis was discovered
quire recently using a technique that has only started to be successful
fairly recently (the decrease of light from the star was observed as the
planet transited across it - later confirmed by the traditional
technique of radial velocity measurements).

Also, one of the longer semi-major axes belongs to a planet that was
only observed for a very short period of time. This planet
(OGLE-235/MOA-53) was observed by gravitational microlensing. A minimum
value for the semi-major axis was determined by observing the distance
of the planet's microlensing effect from that of its star. (The sma
could be much longer than that, but we have no way of knowing how far
the planet was positioned nearer to or farther from us than the star.)
Other candidate planets have been detected by this technique, but since
microlensing events do not repeat they can only be considered confirmed
if they happen to be detected by two teams working independently.

Similarly the dubious "Epsilon Eridani c", with a possible period of 280
years, was not detected by radial velocity measurements.

--
Mike Williams
Gentleman of Leisure

Wasn't it bjorn2004 who wrote:
The extrasolar planets found thus far are much closer to their star
than are the gas giants in our Solar system.

But isn't this simply because our sample of observed exoplanets is
biased because of the methods used to detect them? The further from
their star, the longer their periodicity and the longer time the star
has to be observed before its movements revleal its planet?

Yes.


I don't know how many orbits (or how large fraction of an orbit) that
a planet has to complete before its presence can be concluded from the
movements of its star. But conisdering that our Jupiter takes more
than 4000 days to complete one orbit, I wouldn't be surpiced if it
will take decades of observations before exoplanets with Jupiter-like
orbits can be identified.

So, if I'm not completely wrong, shouldn't one expect the average
observed "semi-major axis" to grow as our sample of exoplanets grows?
But then, why are people so quick to conclude that our solar system is
so much different than the ones we've found so far? Isn't it obvious
that the extreme exoplanet systems are the easiest to detect and that
they do not constitute a representative sample?

You'd expect the average orbital distance to grow if exactly the same
observation technique continued to be used in the same way. However, new
teams keep starting up with more sensitive equipment which detect more
planets but only those that complete at least one orbit since the
observation started.

I suppose there might also be a bit of a tendency for the hotshot
scientists who started the original exoplanet observations ten years ago
to get a bit bored with keeping those series of observations running on
outdated equipment in the hope of adding a few long-period planets to
their bag, when they could update to the latest kit and start again
bagging lots of short-period planets.


Btw, the distribution of exoplanet-star distances seems to follow a
nice quadratic function. If ranked after semi-major axis, simply DIST
= 0,000025 * RANK^2 describes the distance (where distance Sun-Jupiter
= 1) quite well. Certainly this is due to the method of observation!
And btw again, where can I find data on when the exoplanets were
discovered? I bet they tend to have larger and larger semi -major
axis...

If you look at the pages that link from the catalogue at
http://www.obspm.fr/encycl/cat1.html you'll find a list of references.
You probably want to look for the oldest paper in the list of
references.

Note that the planet with the shortest semi-major axis was discovered
quire recently using a technique that has only started to be successful
fairly recently (the decrease of light from the star was observed as the
planet transited across it - later confirmed by the traditional
technique of radial velocity measurements).

Also, one of the longer semi-major axes belongs to a planet that was
only observed for a very short period of time. This planet
(OGLE-235/MOA-53) was observed by gravitational microlensing. A minimum
value for the semi-major axis was determined by observing the distance
of the planet's microlensing effect from that of its star. (The sma
could be much longer than that, but we have no way of knowing how far
the planet was positioned nearer to or farther from us than the star.)
Other candidate planets have been detected by this technique, but since
microlensing events do not repeat they can only be considered confirmed
if they happen to be detected by two teams working independently.

Similarly the dubious "Epsilon Eridani c", with a possible period of 280
years, was not detected by radial velocity measurements.

--
Mike Williams
Gentleman of Leisure

Mike Williams wrote in message ...
Wasn't it bjorn2004 who wrote:
The extrasolar planets found thus far are much closer to their star
than are the gas giants in our Solar system.

You'd expect the average orbital distance to grow if exactly the same
observation technique continued to be used in the same way. However, new
teams keep starting up with more sensitive equipment which detect more
planets but only those that complete at least one orbit since the
observation started.

Good answer! I suppose I've got more to learn about exoplanet
research. Exoplanet hunting with gravitational lensing, wow...

But wouldn't more precise observations make it possible for us to
observe smaller planets further away from their stars, than
previously, and so imply that an ever higher fraction of Jupiter-like
planets will be found?

And what about the DIST = (RANK/200)^2 formula [where RANK is the
ranking of each exoplanets on the "close to its star"-scale, and DIST
is the semi-major axis]? Is that just a coincidence or my
misinterpretation, or are there reasons to believe that exoplanets
generally are much closer to their stars than what "our" gas giants
are? I would guess that the methods of observations would help explain
this. For instance, that there's a strong connection between distance,
periodicity and easiness of observation, and hence a severe bias in
the early sample which we have today.

I'll certainly look at your links and try to compile data on discovery
dates in order to see what actual developments there have been over
time.

Best regards!

Mike Williams wrote in message ...
Wasn't it bjorn2004 who wrote:
The extrasolar planets found thus far are much closer to their star
than are the gas giants in our Solar system.

You'd expect the average orbital distance to grow if exactly the same
observation technique continued to be used in the same way. However, new
teams keep starting up with more sensitive equipment which detect more
planets but only those that complete at least one orbit since the
observation started.

Good answer! I suppose I've got more to learn about exoplanet
research. Exoplanet hunting with gravitational lensing, wow...

But wouldn't more precise observations make it possible for us to
observe smaller planets further away from their stars, than
previously, and so imply that an ever higher fraction of Jupiter-like
planets will be found?

And what about the DIST = (RANK/200)^2 formula [where RANK is the
ranking of each exoplanets on the "close to its star"-scale, and DIST
is the semi-major axis]? Is that just a coincidence or my
misinterpretation, or are there reasons to believe that exoplanets
generally are much closer to their stars than what "our" gas giants
are? I would guess that the methods of observations would help explain
this. For instance, that there's a strong connection between distance,
periodicity and easiness of observation, and hence a severe bias in
the early sample which we have today.

I'll certainly look at your links and try to compile data on discovery
dates in order to see what actual developments there have been over
time.

Best regards!

"bjorn2004" wrote in message
om...
The extrasolar planets found thus far are much closer to their star
than are the gas giants in our Solar system.

But isn't this simply because our sample of observed exoplanets is
biased because of the methods used to detect them? The further from
their star, the longer their periodicity and the longer time the star
has to be observed before its movements revleal its planet?

Yes, but mass is also a factor. It is only those planets with mass somewhat
greater than that of Saturn that can be detected by current instruments.

Earth mass planets are a long ways from being detectable by current
instruments. They are just not sensitive enough to detect Earth mass
planets.



I don't know how many orbits (or how large fraction of an orbit) that
a planet has to complete before its presence can be concluded from the
movements of its star. But conisdering that our Jupiter takes more
than 4000 days to complete one orbit, I wouldn't be surpiced if it
will take decades of observations before exoplanets with Jupiter-like
orbits can be identified.

So, if I'm not completely wrong, shouldn't one expect the average
observed "semi-major axis" to grow as our sample of exoplanets grows?
But then, why are people so quick to conclude that our solar system is
so much different than the ones we've found so far? Isn't it obvious
that the extreme exoplanet systems are the easiest to detect and that
they do not constitute a representative sample?

The problem is that current theories of planet formation have the gas giants
(high mass planets and the only ones we can now detect) forming well away
from the parent star. Somehow, so the thinking goes, the close-in giant
planets drifted in from the farther distances of their solar system ... as
they drifted inward toward the parent star they swallowed up the smaller
planets in their path or expelled the smaller planets (which would include
Earth like candidates) from their Solar Systems. Thus these systems with gas
giants orbiting close to their star probably (so current theories indicate)
have no (NO!) small planets orbiting close to the star (as we have in our
Solar System)! Rats!

The Earth sized planets may in fact be orbiting the gas giants! Who really
knows :-)

The other side of the coin is that there are alot of stars out there! :-)
Really, only a small percentage of stars have been found to have gas giant
planets orbiting close to their star! Not only that, but currently we can
only detect the gas giants! So, personally, I'm not worried ... there may
turn out to be far more Earth size planets than gas giants orbiting
relatively close to their parent stars :-)



Btw, the distribution of exoplanet-star distances seems to follow a
nice quadratic function. If ranked after semi-major axis, simply DIST
= 0,000025 * RANK^2 describes the distance (where distance Sun-Jupiter
= 1) quite well. Certainly this is due to the method of observation!
And btw again, where can I find data on when the exoplanets were
discovered? I bet they tend to have larger and larger semi -major
axis...

http://exoplanets.org/almanacframe.html

Regards!

"bjorn2004" wrote in message
om...
The extrasolar planets found thus far are much closer to their star
than are the gas giants in our Solar system.

But isn't this simply because our sample of observed exoplanets is
biased because of the methods used to detect them? The further from
their star, the longer their periodicity and the longer time the star
has to be observed before its movements revleal its planet?

Yes, but mass is also a factor. It is only those planets with mass somewhat
greater than that of Saturn that can be detected by current instruments.

Earth mass planets are a long ways from being detectable by current
instruments. They are just not sensitive enough to detect Earth mass
planets.



I don't know how many orbits (or how large fraction of an orbit) that
a planet has to complete before its presence can be concluded from the
movements of its star. But conisdering that our Jupiter takes more
than 4000 days to complete one orbit, I wouldn't be surpiced if it
will take decades of observations before exoplanets with Jupiter-like
orbits can be identified.

So, if I'm not completely wrong, shouldn't one expect the average
observed "semi-major axis" to grow as our sample of exoplanets grows?
But then, why are people so quick to conclude that our solar system is
so much different than the ones we've found so far? Isn't it obvious
that the extreme exoplanet systems are the easiest to detect and that
they do not constitute a representative sample?

The problem is that current theories of planet formation have the gas giants
(high mass planets and the only ones we can now detect) forming well away
from the parent star. Somehow, so the thinking goes, the close-in giant
planets drifted in from the farther distances of their solar system ... as
they drifted inward toward the parent star they swallowed up the smaller
planets in their path or expelled the smaller planets (which would include
Earth like candidates) from their Solar Systems. Thus these systems with gas
giants orbiting close to their star probably (so current theories indicate)
have no (NO!) small planets orbiting close to the star (as we have in our
Solar System)! Rats!

The Earth sized planets may in fact be orbiting the gas giants! Who really
knows :-)

The other side of the coin is that there are alot of stars out there! :-)
Really, only a small percentage of stars have been found to have gas giant
planets orbiting close to their star! Not only that, but currently we can
only detect the gas giants! So, personally, I'm not worried ... there may
turn out to be far more Earth size planets than gas giants orbiting
relatively close to their parent stars :-)



Btw, the distribution of exoplanet-star distances seems to follow a
nice quadratic function. If ranked after semi-major axis, simply DIST
= 0,000025 * RANK^2 describes the distance (where distance Sun-Jupiter
= 1) quite well. Certainly this is due to the method of observation!
And btw again, where can I find data on when the exoplanets were
discovered? I bet they tend to have larger and larger semi -major
axis...

http://exoplanets.org/almanacframe.html

Regards!

"Alfred A. Aburto Jr." wrote in
news
The problem is that current theories of planet formation have the gas
giants (high mass planets and the only ones we can now detect) forming
well away from the parent star. Somehow, so the thinking goes, the
close-in giant planets drifted in from the farther distances of their
solar system ... as they drifted inward toward the parent star they
swallowed up the smaller planets in their path or expelled the smaller
planets (which would include Earth like candidates) from their Solar
Systems. Thus these systems with gas giants orbiting close to their
star probably (so current theories indicate) have no (NO!) small
planets orbiting close to the star (as we have in our Solar System)!
Rats!

OK, clue me in. Isn't it possible for life as we know it to develop on a
body that is orbiting a planet?

--
Ed

http://www.geeks.org/~ed/Usenet_Servers.html
strip to reply

"Alfred A. Aburto Jr." wrote in
news
The problem is that current theories of planet formation have the gas
giants (high mass planets and the only ones we can now detect) forming
well away from the parent star. Somehow, so the thinking goes, the
close-in giant planets drifted in from the farther distances of their
solar system ... as they drifted inward toward the parent star they
swallowed up the smaller planets in their path or expelled the smaller
planets (which would include Earth like candidates) from their Solar
Systems. Thus these systems with gas giants orbiting close to their
star probably (so current theories indicate) have no (NO!) small
planets orbiting close to the star (as we have in our Solar System)!
Rats!

OK, clue me in. Isn't it possible for life as we know it to develop on a
body that is orbiting a planet?

--
Ed

http://www.geeks.org/~ed/Usenet_Servers.html
strip to reply

"Ed" wrote in message
.246...
"Alfred A. Aburto Jr." wrote in
news
The problem is that current theories of planet formation have the gas
giants (high mass planets and the only ones we can now detect) forming
well away from the parent star. Somehow, so the thinking goes, the
close-in giant planets drifted in from the farther distances of their
solar system ... as they drifted inward toward the parent star they
swallowed up the smaller planets in their path or expelled the smaller
planets (which would include Earth like candidates) from their Solar
Systems. Thus these systems with gas giants orbiting close to their
star probably (so current theories indicate) have no (NO!) small
planets orbiting close to the star (as we have in our Solar System)!
Rats!

OK, clue me in. Isn't it possible for life as we know it to develop on a
body that is orbiting a planet?

Yes, of course ...


--
Ed

http://www.geeks.org/~ed/Usenet_Servers.html
strip to reply