Orientation Of Solar Systems

1saxman

Are the orientations of solar systems in this galaxy random? The question is related to discovering planets by the occlusion method. Looking at any star, the plane of that solar system must at 180 degrees to the observer in order to detect planets occluding that sun. Depending on the distance, there is a very slight angle possible, but basically we must see the solar system edgewise in order to detect planets crossing their solar disc. My point is, this circumstance must be very rare, yet we have discovered thousands of planets by this method, so that would indicate that there must be many times more planets 'in our neighborhood' that are not discoverable by this method.

Catastrophe

The devil is in the detail
Not entirely sure what you mean. Orientation of our Solar System, assuming you mean plane of orbits of planets, asteroids, et cetera, = ecliptic, presumably derives from plane of protoplanetary disk. Therefore, it appears that you are asking whether planes of all protoplanetary disks in the galaxy are coincident?

Cat

1saxman

I think the ecliptic of each solar system in the galaxy to be at random. The incidence of being able to detect a planet in any system by the occlusion method depends on the ecliptic of that system being edgewise to the observer, which must be a rare occurrence. Hence, the estimation of planets in the galaxy or region going by this method is exceptionally low. IOW, if the ecliptic of a system is tilted relative to your line of sight to the star, no planets of that system will cross that line of sight so you will not detect any dimming.

Catastrophe

The devil is in the detail
You might find this interesting:

Will Earth survive when the sun becomes a red giant? - Phys.org
https://phys.org › Astronomy & Space › Astronomy

“Misalignments between the orbital planes of planets and the equatorial planes of their host stars have been observed in our solar system, in transiting exoplanets, and for the orbital planes of debris discs. We present a mechanism that causes such a spin-orbit misalignment for a protoplanetary disc due to its movement through an ambient medium. Our physical explanation of the mechanism is based on the theoretical solutions to the Stark problem. We test this idea by performing self-consistent hydrodynamical simulations and simplified gravitational N-body simulations.
Intuitively, one might expect that the spin axis of a star should be aligned with the orbital axis of its protoplanetary disc and the planets that form there. However, the solar system is known to exhibit a misalignment of roughly 7° between the equatorial plane of the sun and the orbital planes of its planets (Beck & Giles 2005). Such spin-orbit misalignments have also been observed for transiting exoplanets (Hébrard et al. 2008; Johnson et al. 2009; Gillon 2009; Narita et al. 2009; Pont et al. 2009; Winn et al. 2009) and for debris discs (Watson et al. 2011; Greaves et al. 2014).”

The average distance between stars (iirc) is about 5 LY, however, in galactic centres it is close to 1 LY. (There are 63240 AU in a light year.) If you take 1 - 4 light years between solar systems - this is my estimate, but very high, since I am taking it to the extremes of Oort Clouds (as far as we know what they may be). From 30 AU to Neptune, representing lowest value, it is conjectural (afaik) as to whether there might be overlapping between protoplanetary discs. There is also the possibility of movement, mentioned in the above (top) reference. For these reasons, I don't know whether or not there might be 'sharing' of protoplanetary nebulae, suggesting common planes. I will keep researching this aspect. The question reduces to how protoplanetary disc concentrations form and whether there is interaction between them before and during formation.

Cat

1saxman

My question relates only to the plane of ecliptic in solar systems and how it affects the occlusion of those stars by their planets when viewed from Earth or near space. Imagine that all of them were at 90 degrees from the line of sight from Earth - then no planets could be discovered by the occlusion method. OTOH, if they were all parallel to the line of sight, we would be able to detect dimming from all of them with planets depending on the distance limit of our equipment. Naturally, both instances are impossible for all the solar systems but some of each extreme will exist. The great majority will simply be at random angles - some planes will be close enough to edge-wise to get the dimming effect but most won't. When astronomers make predictions on numbers of undiscovered planets based on the ones they have found by the occlusion method, it doesn't include many planets that we can't find because of the orientation of the planes of ecliptic in many solar systems. If we could develop another way of discovering planets, I think we will find that most stars have them.

Catastrophe

The devil is in the detail
All disk galaxies rotate once every billion years | Astronomy.com
https://astronomy.com › news › 2018/03 › all-galaxies-rot...

This suggests the opposite to me - that they are all approximately in the same plane (or parallel). This would be directly comparable to all planets in the same plane condensing from one protoplanetary plane. This would follow from rotation of the galaxy.

"We know that (our) Galaxy is rotating round its centre, and that our Sun takes about 225 million years to complete one circuit. . . . . . . . . . "
Phillips Atlas of the Universe Sir Patrick Moore Bounty Books 2007.

Cat

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1saxman

Can't rule that out but I would be surprised if more than 40% are parallel to the galactic plane of ecliptic. Whatever, maybe we'll find out some day.

Lariliss

Recent findings show irregular structure in the Milky Way (Spiral Arm ‘Break’). But this is exclusion rather than majority for the near Earth findings.

https://phys.org/news/2021-08-astronomers-milky-spiral-arms.html?utm_source=nwletter&utm_medium=email&utm_campaign=weekly-nwletter

A circle has a pitch angle of 0 degrees, and as the spiral becomes more open, the pitch angle increases. "Most models of the Milky Way suggest that the Sagittarius Arm forms a spiral that has a pitch angle of about 12 degrees, but the structure we examined really stands out at an angle of nearly 60 degrees.

Catastrophe

The devil is in the detail
"Young stars and nebulae are thought to align closely with the shape of the arms they reside in." but spiral arms are not fully understood.

Cat

DamienWindler

Knowing that the north star doesn't move, my guess is that we are either spinning like a frisbee with matching planes to the Milky Way, or tilted 90 degrees to the Milky Ways plane.

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Helio

Are the orientations of solar systems in this galaxy random?
Yes.

The question is related to discovering planets by the occlusion method. Looking at any star, the plane of that solar system must at 180 degrees to the observer in order to detect planets occluding that sun.
I assume you mean the transit method.

The observing angle (i. e. inclination) can be confusing. A satellite orbiting our equator has a 0 deg. orbital inclination. But, for whatever reason, the orbital plane of an exoplanet around its sun is 0 deg. when that plane is perpendicular to us, or "face on". If it is an edge-on orbital plane then the orbital plane is at 90 deg.

So, the Kepler mission, using the transit mission, knew that only a minority of those suns will have a planet blocking its light as it passed in front of the stellar disk. But observing about 150,000 stars didn't require a large percentage of adequate orbital inclinations to get great results.

I recall reading the number for the percentage of stars that would be observable by Kepler, though I think it was close to 20%, maybe.

But the percentage isn't just the angle. A really large star with a close orbiting planet will have a much larger percentage of useable (transiting event) inclination than a small star (e.g. red dwarf) that has a small planet with a planet that is far away from it.

My point is, this circumstance must be very rare, yet we have discovered thousands of planets by this method, so that would indicate that there must be many times more planets 'in our neighborhood' that are not discoverable by this method.
Rod can probably tell us what percent are found using the transit method. My guess is that it is over half.

But, given almost 5k exoplanets are confirmed, it isn't too hard to extrapolate on the number of planets there are out there. I think it is still roughly that the number of planets is as many as stars. This is a little surprising as most stars orbit other stars, which plays havoc on would-be exoplanets.

1saxman

Yes.

I assume you mean the transit method.

The observing angle (i. e. inclination) can be confusing. A satellite orbiting our equator has a 0 deg. orbital inclination. But, for whatever reason, the orbital plane of an exoplanet around its sun is 0 deg. when that plane is perpendicular to us, or "face on". If it is an edge-on orbital plane then the orbital plane is at 90 deg.

So, the Kepler mission, using the transit mission, knew that only a minority of those suns will have a planet blocking its light as it passed in front of the stellar disk. But observing about 150,000 stars didn't require a large percentage of adequate orbital inclinations to get great results.

I recall reading the number for the percentage of stars that would be observable by Kepler, though I think it was close to 20%, maybe.

But the percentage isn't just the angle. A really large star with a close orbiting planet will have a much larger percentage of useable (transiting event) inclination than a small star (e.g. red dwarf) that has a small planet with a planet that is far away from it.

Rod can probably tell us what percent are found using the transit method. My guess is that it is over half.

But, given almost 5k exoplanets are confirmed, it isn't too hard to extrapolate on the number of planets there are out there. I think it is still roughly that the number of planets is as many as stars. This is a little surprising as most stars orbit other stars, which plays havoc on would-be exoplanets.
At last! You understand the question! I got canned on another forum for daring to ask it. Thanks very much for the info that the Kepler team knew this and took it into account. I agree on the probable number of planets. The term 'transit' refers to an exoplanet occluding its sun which results in a dimming that we can detect, which requires the subject planets orbit to be very close to parallel to the line of sight from our sun to the subject sun. So 'occlusion' or 'transiting' become the same thing. We either have to detect them by this method or by direct observation, which is limited by distance, so I would guess that the planets found by the 'transit' method would have to be more than 95%.

Helio

... so I would guess that the planets found by the 'transit' method would have to be more than 95%.
No. There’s six methods, IIRC, used for discovery. Another great way is to look for radial Doppler motions of a star due to an orbiting planet(s).

If you go to this exoplanet catalog you can sort by method.

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Pogo

Pogo

Many of the discoveries were by this Doppler method. As a planet orbits a star, the star also describes a small ellipse, both the planet are actually orbiting a barycenter. If the inclination of this orbital plane is such (less than maybe 60 degrees or so), the line-of-sight component of the star’s motion will be enough to see the periodic red and blue shift as it moves toward us and recedes, and we can calculate the motion of the planet. What we can’t tell is what that inclination of that system is to our line-of-sight. It could be edge on to us or up to 60 degrees or so, or anywhere in between. Many of the early exoplanet discoveries were of this method, and many since then. Probably more than the transit method.

Catastrophe

Catastrophe

The devil is in the detail
angular momentum - Are the orientations of spin-axes and binary/planetary orbits random or is there any relationship with the Galactic plane? - Physics Stack Exchange

"In general the planes of solar systems are not aligned with the plane of the Galaxy, but are oriented in all different directions. The size of a solar system is so much smaller than the size of the Galaxy, that the Galaxy's structure has no impact on the orientation of a solar system. What determines their orientations is the direction of the angular momentum that the system had when it formed, and that's pretty much random. For instance, our own solar system is tipped by about 63 degrees with respect to the plane of the galaxy."

Cat

brandonderek

Are the orientations of solar systems in this galaxy random? The question is related to discovering planets by the occlusion method. Looking at any star, the plane of that solar system must at 180 degrees to the observer in order to detect planets occluding that sun. Depending on the distance, there is a very slight angle possible, but basically we must see the solar system edgewise in order to detect planets crossing their solar disc. My point is, this circumstance must be very rare, yet we have discovered thousands of planets by this method, so that would indicate that there must be many times more planets 'in our neighborhood' that are not discoverable by this method.
Thanks for the suggestion

Catastrophe

The devil is in the detail
"What determines their orientations is the direction of the angular momentum that the system had when it formed, and that's pretty much random. For instance, our own solar system is tipped by about 63 degrees with respect to the plane of the galaxy."

Significant?

Cat

Helio

Helio

"What determines their orientations is the direction of the angular momentum that the system had when it formed, and that's pretty much random. For instance, our own solar system is tipped by about 63 degrees with respect to the plane of the galaxy."

Significant?
That's an interesting question. It seems that inclinations of star systems are random. [Here ]

Catastrophe

Helio

BTW, it's a little confusing that exoplanets treat inclination angles differently. A 63 deg. inclination would mean it is 27 deg. inclined from our viewpoint. 0 degrees would be a face-on view of its orbital plane; 90 degrees would be an edge-on view, and ideal for discovering exoplanets by transits.

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Catastrophe

Catastrophe

The devil is in the detail
Well, Helio, it is an important one for us, so I guess that it is a good starting place - after all, we are (like everything else) at the centre of the observed Universe.

Cat

IG2007 and Helio