Goldilocks Zone Planets.

[Thor 2]

When I read about the method used to detect the Goldilocks Zone Planets I am filled with awe.

Given the method can only detect a minute number of the possible planets and the large number that have been found is staggering - 16 of these in the so called Goldilocks zone.

 

[shemp]

If there's 16 planets in the Goldilocks Zone there must be many more in the Three Bears Zone.

 

[arthwollipot]

Turns out looking for big things very far away is pretty hard. I'm gobsmacked that we've been finding any planets around other stars at all, let alone rocky goldilocks-zone ones.

 

[Bikewer]

A recent Science Friday segment had an interview with an astronomer who talked about developing techniques to analyze the atmospheres of some extra-solar planets.
Very tricky.... Evidently trying to run a very focused spectrographic analysis on the rim (from our POV) on the planet at exactly the right point in it’s orbit.

 

[Thor 2]

Turns out looking for big things very far away is pretty hard. I'm gobsmacked that we've been finding any planets around other stars at all, let alone rocky goldilocks-zone ones.

I have looked into this and it leaves me gobsmacked.

The planets themselves cannot be seen but are only detected if they move in front of the star they are orbiting. When you think of the probability of that, when you consider the other possible orbits where they could not be detected, you can see the possibility of so many more planets being in existence.

 

[Puppycow]

I have looked into this and it leaves me gobsmacked.

The planets themselves cannot be seen but are only detected if they move in front of the star they are orbiting. When you think of the probability of that, when you consider the other possible orbits where they could not be detected, you can see the possibility of so many more planets being in existence.

That's one way to detect them (called the transit method), but not the only way. The transit method only works if the planet passes directly in front of the sun. If it orbits at another angle, it won't work.

Another way is to look for a slight wobble in the position of the star. Sometimes they see the wobble due to a slight red shift or blue shift depending on whether the orbiting planet is on the near side or the far side.

 

[Thor 2]

That's one way to detect them (called the transit method), but not the only way. The transit method only works if the planet passes directly in front of the sun. If it orbits at another angle, it won't work.

Another way is to look for a slight wobble in the position of the star. Sometimes they see the wobble due to a slight red shift or blue shift depending on whether the orbiting planet is on the near side or the far side.

Yes I have read about that too but I would imagine it would only apply to larger planets.

Our Goldilocks planet Earth for example is 100th the diameter and therefore 1/10,000 the volume of the Sun. Our mass would be so small that any wobble of the Sun would be minute.

 

[RecoveringYuppy]

Our Goldilocks planet Earth for example is 100th the diameter and therefore 1/10,000 the volume of the Sun. Our mass would be so small that any wobble of the Sun would be minute.

You either meant to say 1,000,000 instead of 10,000, or "area" instead of "volume". Probably the former based on the argument you are making.

Note that the "wobble" method also depends on orbit orientation to some degree. A planetary system that is at right angles to us won't be producing a wobble we can detect via red/blue shift.

 

[Thor 2]

You either meant to say 1,000,000 instead of 10,000, or "area" instead of "volume". Probably the former based on the argument you are making.

Note that the "wobble" method also depends on orbit orientation to some degree. A planetary system that is at right angles to us won't be producing a wobble we can detect via red/blue shift.

You're right of course. My mistake.

 

[Puppycow]

Yes I have read about that too but I would imagine it would only apply to larger planets.

Our Goldilocks planet Earth for example is 100th the diameter and therefore 1/10,000 the volume of the Sun. Our mass would be so small that any wobble of the Sun would be minute.

You either meant to say 1,000,000 instead of 10,000, or "area" instead of "volume". Probably the former based on the argument you are making.

Note that the "wobble" method also depends on orbit orientation to some degree. A planetary system that is at right angles to us won't be producing a wobble we can detect via red/blue shift.

Yeah, obviously the wobble method works better the more massive the planet and the closer its orbit is. I doubt we could find an exoplanet the size of earth in the same orbit as we have around the sun using the wobble method.

By the way, volume is less relevant here than mass.

Here is a little comparison I found with a Google search:

https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html

While the volume of the sun is 1,304,000 earths, the mass of the sun is only 333,000 earth masses. So the earth is actually almost 4 times denser on average than the sun.

 

[Thor 2]

Yeah, obviously the wobble method works better the more massive the planet and the closer its orbit is. I doubt we could find an exoplanet the size of earth in the same orbit as we have around the sun using the wobble method.

By the way, volume is less relevant here than mass.

Here is a little comparison I found with a Google search:

https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html

While the volume of the sun is 1,304,000 earths, the mass of the sun is only 333,000 earth masses. So the earth is actually almost 4 times denser on average than the sun.

Thanks for that and you are right of course. I did not know the mass of the Sun.

 

[Roboramma]

Yeah, obviously the wobble method works better the more massive the planet and the closer its orbit is. I doubt we could find an exoplanet the size of earth in the same orbit as we have around the sun using the wobble method.

By the way, volume is less relevant here than mass.

Here is a little comparison I found with a Google search:

https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html

While the volume of the sun is 1,304,000 earths, the mass of the sun is only 333,000 earth masses. So the earth is actually almost 4 times denser on average than the sun.

RY mentioned not only the issue of mass and radius of the orbit, but also the orientation of the orbit.

The point is that while the transit method only works for planets whose orbit puts it in a direct line of sight between us and its star, the wobble method also requires an orbit which is oriented close to that same axis. It needn't be as precisely oriented, but the further it is from that axis the less we'll be able to detect that wobble, with the limiting case being perpendicular to that axis and completely undetectable to us (with this method).

Not suggesting you don't understand this, just that your reply seemed to have missed that detail, so I thought it worth emphasizing.

Aside from the methods already mentioned (which I understand are responsible for almost all detections so far), there is also direct imaging, but it's much more difficult.

New telescopes coming online in the next decade or so should detect orders of magnitude more planets than we already have, and with much more precise data. Exciting times!

 

[RecoveringYuppy]

Thanks, Roborama, I was about to write that myself.

 

[Puppycow]

Would we have any method to detect exoplanets that orbit perpendicular to our line of sight?

I thought maybe the wobble method could work in that case too. If you can see the actual movement of the star.

 

[Roboramma]

Would we have any method to detect exoplanets that orbit perpendicular to our line of sight?

My understanding of direct imaging is that you basically block the light of the star and then try to actually see the light reflected from the planet. Incredibly difficult, but it has been done. Unless I'm misunderstanding the technique, I think it should work for any alignment of orbit.

 

[catsmate]

Turns out looking for big things very far away is pretty hard. I'm gobsmacked that we've been finding any planets around other stars at all, let alone rocky goldilocks-zone ones.

I remember Gamma Cephei Ab back in '88. Heady days.

 

[RecoveringYuppy]

Would we have any method to detect exoplanets that orbit perpendicular to our line of sight?

I thought maybe the wobble method could work in that case too. If you can see the actual movement of the star.

That's theoretically possible with the wobble method but beyond our current capabilities. It requires measuring the position of the start to a greater degree than currently possible.

"wobble method" is a bit ambiguous term. Detecting the wobble via redshift is the method that requires the planetary plane be aligned with the sun. That's called the radial-velocity method. And we've found a lot that way. Direct measurement of the wobble from any angle is called the "Astrometric" method. No successful detections for that method that I know of.


https://www.planetary.org/articles/wobbly-stars-the-astrometry-method

 

[Pixel42]

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.

 

[Skeptic Ginger]

I saw the transit of Venus a few years ago. It was stunning. Compared to the transit of Mercury which looks like a pinpoint, I doubt we could see the dimming at all with a Mercury sized planet. But one the size of Venus should be observable. [/fun note]

 

[Puppycow]

I saw the transit of Venus a few years ago. It was stunning. Compared to the transit of Mercury which looks like a pinpoint, I doubt we could see the dimming at all with a Mercury sized planet. But one the size of Venus should be observable. [/fun note]

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

Transits of Venus are among the rarest of predictable astronomical phenomena.[1] They occur in a pattern that generally repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years. The periodicity is a reflection of the fact that the orbital periods of Earth and Venus are close to 8:13 and 243:395 commensurabilities.[2][3]

The last transit of Venus was on 5 and 6 June 2012, and was the last Venus transit of the 21st century; the prior transit took place on 8 June 2004. The previous pair of transits were in December 1874 and December 1882. The next transits of Venus will take place on 10–11 December 2117 and 8 December 2125.[4][5][6]

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.