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Goldilocks Zone Planets.

Puppycow said:
That reminds me:

It's actually quite rare to see a transit of Venus, isn't it? And that's a planet in our own solar system orbiting on a similar plane to our own.

https://en.wikipedia.org/wiki/Transit_of_Venus



Given how rare that is, just imagine how rare it would be for a Venus-like exoplanet to transit where it's in our sight line? It means we are really only just scratching the surface. There's a lot more exoplanets out there that we just can't detect because their orbits aren't aligned in the right way.
Click to expand...

Interesting question, do we expect stars' axes of rotation to be essentially random or to have a preferred alignment in relation to their galaxy?
 
sphenisc said:
Interesting question, do we expect stars' axes of rotation to be essentially random or to have a preferred alignment in relation to their galaxy?
Click to expand...

I believe someone more knowledgeable than me said it's basically random. In fact, the plane of our own solar system is not aligned with the plane of the galaxy (the Milky Way).

There's a pretty cool VSauce video about it, with some nice cinematic bits:

https://www.youtube.com/watch?v=IJhgZBn-LHg

(full screen is best)
 
Puppycow said:
That reminds me:

It's actually quite rare to see a transit of Venus, isn't it? And that's a planet in our own solar system orbiting on a similar plane to our own.

https://en.wikipedia.org/wiki/Transit_of_Venus



Given how rare that is, just imagine how rare it would be for a Venus-like exoplanet to transit where it's in our sight line? It means we are really only just scratching the surface. There's a lot more exoplanets out there that we just can't detect because their orbits aren't aligned in the right way.
Click to expand...

Actually we would see transits of Venus more often if we were further away from the Sun. I suggest anyone who wants to understand to draw a diagram.

But yes, we will miss the majority of planets this way.
 
Speedskater said:
How much does Earth cause the Sun to wobble?
How about the other planets and the Sun?
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https://en.wikipedia.org/wiki/Barycenter

The earth causes the sun to wobble 449 km in either direction, whereas Jupiter makes it wobble 742,000 km in either direction.

Or to state it another way, that's the distance between the barycenter of the two bodies and the center of the Sun.
 
Pixel42 said:
When I first got interested in astronomy as a child, 60 years ago, the books said it was believed many other stars had planets but we would never know as they are impossible to detect. I never imagined I would live long enough for that to no longer be the case. Gob smacking indeed.
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I remember that. Hell even forty years ago it was doubtful that extra-solar planets could be detected.
I remember older books, especially certain sci-fi that dated badly, still relying on the Catastrophic Hypothesis of planetary formation.
 
Puppycow said:
I believe someone more knowledgeable than me said it's basically random. In fact, the plane of our own solar system is not aligned with the plane of the galaxy (the Milky Way).
Click to expand...

My understanding is that it starts random, but the distribution is not perfectly even, so over time a preferred plane will start to emerge.
 
Puppycow said:
That reminds me:

It's actually quite rare to see a transit of Venus, isn't it? And that's a planet in our own solar system orbiting on a similar plane to our own.

https://en.wikipedia.org/wiki/Transit_of_Venus

Given how rare that is, just imagine how rare it would be for a Venus-like exoplanet to transit where it's in our sight line? It means we are really only just scratching the surface. There's a lot more exoplanets out there that we just can't detect because their orbits aren't aligned in the right way.
Click to expand...

It will never happen again in my lifetime. (I didn't know about the 2004 transit when that happened.). I couldn't believe how more people weren't ecstatic about it. I literally chased a hole in the clouds ~20 miles to see it. It was cloudy here but it looked like it might not be off to the south. I drove until I could see a break in the clouds which nicely turned out to be a park. I sat on the picnic table with my wielder's glass watching it. There were people in the park who not only didn't notice, they weren't curious enough about what I was doing to ask me.

It was big compared to Mercury which I have yet to be able to see the little pinpoint when it transits. It was so different from seeing planets through a telescope which I have seen many times. And the Moon we see all the time. This was a planet, right there, not a distant light in the sky.

Those pics in the Wiki page don't do it justice.
 
sphenisc said:
Interesting question, do we expect stars' axes of rotation to be essentially random or to have a preferred alignment in relation to their galaxy?
Click to expand...
Planets align mostly on a plane (called a system) because they are formed from the spinning disc of dust that the star forms from. But solar systems themselves, while aligned for the most part on the galactic plane, are not spinning on the same plane. Think of it as swirling masses of dust on the galactic plane that settle into solar systems as the stars form, but the gas clouds spinning around newly formed stars are not aligned with the galactic center.

Here's a good explanation: Ask an Astronomer - Are the planes of solar systems aligned with the plane of the Galaxy?
They're 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.

Our own solar system is tipped by about 63 degrees with respect to the plane of the galaxy.
Click to expand...
 
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catsmate said:
Pixel42 said:
When I first got interested in astronomy as a child, 60 years ago, the books said it was believed many other stars had planets but we would never know as they are impossible to detect. I never imagined I would live long enough for that to no longer be the case. Gob smacking indeed.
Click to expand...


I remember that. Hell even forty years ago it was doubtful that extra-solar planets could be detected.
I remember older books, especially certain sci-fi that dated badly, still relying on the Catastrophic Hypothesis of planetary formation.
Click to expand...


Then you probably also remember the hypothesis back then that solar systems have small rocky planets close to the sun and gas giants in orbits further away, a generalization based on one actual case. :)
 
dann said:
Then you probably also remember the hypothesis back then that solar systems have small rocky planets close to the sun and gas giants in orbits further away, a generalization based on one actual case. :)
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To be fair, at the time it did seem to make sense - the heavier elements would tend to gather further down the gravity well.
 
arthwollipot said:
To be fair, at the time it did seem to make sense - the heavier elements would tend to gather further down the gravity well.
Click to expand...


It made sense to me at the time. However,
The Sun contains about 92% hydrogen and 8% helium, with just a tiny bit of the other common elements we find on Earth. Compare that to Earth, where the most common elements are oxygen, magnesium, silicon, and iron. On Earth, hydrogen barely makes the top 10 list of common elements, and helium is extremely rare.
The Sun (NASA)
Click to expand...
 
arthwollipot said:
To be fair, at the time it did seem to make sense - the heavier elements would tend to gather further down the gravity well.
Click to expand...
Actually the mechanism is related more to temperature than gravity. Hot planets don't hold on to gases so well and gases are much more mobile.

Don't think that idea is refuted. Do we know ages on the exoplanets that appear to be major exceptions?

ETA: BTW remember that are current methods for detecting exoplanets favor finding exceptions. We're best right now at detecting large planets near their suns.
 
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Gas giants form in the outer solar system. They do have a habit of moving into the inner solar system. Ours was lucky in that they moved out again. This allowed the Earth to form.

If Jupiter had not moved into the inner solar system Earth would have been a lot bigger. This would have made getting into space a lot harder. Like would have been a lot different.
 
Yes, I think the early ideas about how and where planets form were mostly correct, it's just that they didn't realise how unstable the system is once formed. That the gas giants could migrate inwards and outwards never occurred to anyone until they found the first hot Jupiters in other systems.

On the plus side, it does provide a possible explanation for the Late Heavy Bombardment.
 
Puppycow said:
I believe someone more knowledgeable than me said it's basically random. In fact, the plane of our own solar system is not aligned with the plane of the galaxy (the Milky Way).

There's a pretty cool VSauce video about it, with some nice cinematic bits:

https://www.youtube.com/watch?v=IJhgZBn-LHg

(full screen is best)
Click to expand...

We don't have to detect more than a fraction to get a good estimate of how many there are. Once we have mapped a good fraction, we can get a statistical idea of how many there must be, even if we cannot currently detect them.

Ideally we may find some common denominator for stars possessing planet systems, and get an even better estimate.

Hans
 
MRC_Hans said:
We don't have to detect more than a fraction to get a good estimate of how many there are. Once we have mapped a good fraction, we can get a statistical idea of how many there must be, even if we cannot currently detect them.

Ideally we may find some common denominator for stars possessing planet systems, and get an even better estimate.

Hans
Click to expand...


Yes. That is what I was alluding to in the OP.

I read a statement by a philosopher/mathematician* once:

"Not only do I believe there is other life out there in the universe - I think somewhere out there is a cricket team that can beat the English."

No this sounds quite silly but is rather profound. He was suggesting there is such an abundance of other life, that other similar civilisations to ours existed, and had invented the unlikely game of cricket.


* I think it was a philosopher/mathematician but am not sure and have not been able to track it down.
 
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