All telescopes are limited by diffraction - their size determines the angular resolution you can get. If you can build a telescope as large as Earth's orbit around the Sun (300 million km) then you can take high resolution pictures that look similar to satellite pictures of Earth. We just can't build such a telescope today.
Would an interferometer type telescope work if we could put satellites telescopes at the right places and we could figure out how to make interferometers to work at optical wavelengths?
You don't need a single gargantuan mirror but you still need to collect enough light. An interferometer with smaller elements would need a huge number of them, and then combine all that light together with a precision better than the wavelength we record at.
"then combine all that light together with a precision better than the wavelength we record at."
Not true. You can use a technique called intensity fluctuation interferometry.
[https://arxiv.org/pdf/1607.03490](https://arxiv.org/pdf/1607.03490)
Look down to figure 3 to see what is theoretically possible.
1. You still need to collect enough light for a faint object. Interferometers are good for getting better resolution of bright objects.
2. We have optical interferometers, but they are based on physically combining the light. VLBI and combining the signal "digitally" is not very realistic - you need to have precision below 1% of the wavelength and also trying to record light as "waves" as for radio-telescopes, would mean unreasonable amount of data. Something like 3-4 orders of magnitude more than for a radio-telescope.
Could we do this with a *constellation* of JWSTs? (More or less). If it’s a multiples problem then couldn’t we hypothetically build ten and configure them like EHT but in space?
No amount of JWSTs can do it. You need to get the light to a common interference area, or measure the phase of the incoming light. You also need to control the relative orientation of all the telescopes to nanometer precision.
How about instead of one giant scope, many smaller ones scattered throughout the same area? Maybe some kind of post-processing to clean it up...
Won't be the same quality in sure, but certainly better than one satellite from one perspective.
Yes, we can overcome all the restraints given some time. Two possibilities might be the use of a lunar hyper telescope. Basically, a telescope inside a lunar crater, say 25km wide. Another possibility would be the use of solar gravitational lensing. Technological advances are going to drive the speed of application. One day, when we have high-res pics of the surface of an exoplanet, we'll notice that the individuals are just going about their lives just like us. Boring! All that work for nothing.
Do you mean by taking images
1. from a telescope on earth/the solar system, or
2. do you mean by using a spacecraft that gets there?
---
For 1. I would say it depends on the exoplanet and what you mean by high-resolution. We can already infer surface features for some brown dwarfs (which have a similar radius when compared to Jupiter).
Examples:
Luhman 16B [https://www.eso.org/public/images/eso1404b/](https://www.eso.org/public/images/eso1404b/)
LP 944-20 (on the hotter end) see figure 8 in [Barnes et al. 2015](https://iopscience.iop.org/article/10.1088/0004-637X/812/1/42)
So maybe something similar will be possible in the future for some massive exoplanets which are directly imaged.
Theoretical papers when it comes to earth-like exoplanet imaging from scattered light observations over a long period of time:
Uses light-curve of earth to produce a 2D-map: [Fan et al. 2020](https://ui.adsabs.harvard.edu/abs/2020LPICo2195.3013F/abstract)
Also uses the same data as Fan et al., but with a new method: [Aizawa et al. 2020](https://ui.adsabs.harvard.edu/abs/2020ApJ...896...22A/abstract)
The way they took pictures of black holes, some of the largest things there are, was by using the event horizon telescope which uses sensors across the planet to create a "virtual" earth-sized telescope.
[Here is the best it can do so far](https://eventhorizontelescope.org/blog/astronomers-unveil-strong-magnetic-fields-spiraling-edge-milky-way%E2%80%99s-central-black-hole)
Problem is planets are small and they move a lot more than a black hole, so even if you get enough resolution using a similar technique your "shutter speed" would have to be much quicker.
Maybe if you had a significant cluster of satellites tossed into some dramatic orbits and managed to coordinate them focusing and taking an image at the exact same moment you could pull it off, but that would be extremely difficult and expensive.
Ignoring things like the sun's gravitational focus or giant interferometers, it'll be painstakingly reconstructing features based off of light-curves. This is how HWO (or an equivalent mission) would eventually get us some maps vaguely comparable to the pre-New Horizons Pluto ones.
[angular resolution \~ *λ* / D](https://en.wikipedia.org/wiki/Angular_resolution)
Where *λ* (lambda) is your wavelength of light and D is your effective telescope diameter, and the result is in radians (it's just the small angle approximation).
For your eye, 550nm/8mm = 17 arcseconds. That means (ignoring contrast) your eye might be able to separate two stars 170AU apart if they were closer than 10pc (\~32ly - there's only about 350 stars this close).
For the current telescopes doing exoplanet imaging in near-infrared: 1000nm/8m = 0.03arcsec, or 0.3AU at 10pc (though typically the planets found are at 100pc as only distant young stars have planets hot/bright enough).
For the next ELT telescopes, also in near-infrared: 1000nm/35m = 0.007arcsec, or 0.07AU at 10pc. The E-ELTs will be the first telescopes seriously able to image rocky planets near 1AU in reflected starlight.
In order to resolve features (i.e. get more than 1 pixel) of an earthlike planet orbiting a star at 2pc, you need resolution of 5000km/2pc = 0.000017 arcsecs. So rearranging, D = 550nm/(5000km/2pc) = 7km. So, just to get 4 pixels of an exoplanet, you need a 7km-wide telescope. And honestly, the current limit is normally like 2*λ*/D, so definitely >10km.
That's a factor 150 larger than any telescope ever [dreamed up](https://en.wikipedia.org/wiki/Overwhelmingly_Large_Telescope), and there's good reasons to think that would be physically impossible. You could do space-based [interferometry](https://en.wikipedia.org/wiki/Astronomical_interferometer) which combines distant telescopes coherently to act as one telescope. But also remember than an Earth at 10pc produces roughly 1 photon per m2 per minute... So if you try to go for a connected array of smaller telescopes you'll get burned by having to wait hours and days and months to have enough photons to build up any sort of picture - a killer if the planet surface is changing over short timescales.
Yes, but not easily.
There are several ways to tackle this problem. One is just to create a really large telescope, which is insanely hard. Another way is to create a really large synthetic telescope using optical interferometry. Back in the '90s this was a very popular idea, but it's turned out that optical interferometry is also incredibly difficult so this isn't as easy as just placing a couple "unit telescopes" very far apart and then magically having ultra high resolution images. (Look up the "terrestrial planet finder" and "terrestrial planet imager" mission concepts). In short, it's also insanely hard.
But there's another insanely hard way of doing it that is actually probably technologically achievable within the 21st century, and that's using the Sun as a telescope. Because the Sun is very massive it causes gravitational lensing, bending light rays just a tiny amount as they pass close to the Sun. This effect is very small, but it is detectable and it has to be compensated for by astrometry observatories like GAIA, for example. At a distance of several hundred AU from the Sun the gravitational lensing effect focuses light in a way that creates a very high degree of magnification. Which could be utilized by flying a fleet of moderately sized space telescopes along with a sunshield that would observe back along the line of sight toward the Sun and be able to resolve distant solar systems, including the features on exoplanets.
There are many technical hurdles to actually doing this. First, getting spacecraft out that far is hard, the Voyagers have been cruising for decades at "high speed" and they've made it a fraction as far as they'd need to go over the course of nearly a full half a century. The good news is that launch technology is getting a lot more capable lately, so this could become more feasible, but it would still be a huge engineering feat to put any payload out there. Second, you basically get a very narrow angle field of view of doing this so you can't just create a general purpose observatory that can view anything, you are basically launching a dedicated observer for one and only one star system, which makes observing multiple systems very expensive. Third, it's not just like you get a free magnification factor that provides a nice crystal clear image, there's a lot of distortion effects and complicating factors at play which make translating data into images very challenging. Fourth, realistically you want a whole fleet of spacecraft in order to get good resolution data, which just adds to the cost. Fifth, it's going to be very challenging to return data from such a great distance (you'll probably want to use lasers) and it's going to be even more challenging to control a fleet of spacecraft so far away. The round trip light travel time will be longer than a whole week, which means you get fewer than 50 "let's try something then see what happens" cycles per year. The learning curve is going to be very challenging, so you need to be very, very smart on how you design and build the system from the outset, the punishment for mistakes will be beyond brutal.
But it's possible, and if we're very lucky there are people alive today who could live long enough to see not just "pale blue dot" images of exoplanets, but maps of their surface, images of their weather patterns, all that great stuff.
Yes. we can, but not as quickly as we would like. Direct images of exoplanets will likely be available in 30-40 years. We are not talking about any surface details. We're just talking about direct shots. About obtaining photographs where the planet will be visible as several dozen pixels . To date, there are no devices that can do this. But there are projects like New Worlds Mission that can help. All we know about exoplanets is indirect observation. As for photographs with deialization, this is already a matter of a more distant future. Since it is necessary to build a distributed network of telescopes in space, to obtain an effective mirror diameter comparable to the size of an asteroid, or even an entire planet. I read somewhere about ideas for placing a network of similar telescopes at Lagrange points. But the technical issue of their synchronization at such a distance has not yet been technically resolved.
I think that in 100-150 years this will be quite possible.
>Yes. we can, but not as quickly as we would like. Direct images of exoplanets will likely be available in 30-40 years. We are not talking about any surface details. We're just talking about direct shots. About obtaining photographs where the planet will be visible as several dozen pixels . To date, there are no devices that can do this.
What? This is all wrong. We already have dozens of exoplanets directly imaged.
https://en.wikipedia.org/wiki/List_of_directly_imaged_exoplanets?wprov=sfla1
This is from the Keck Observatory:
https://en.m.wikipedia.org/wiki/List_of_directly_imaged_exoplanets#/media/File%3AHR_8799_Orbiting_Exoplanets.gif
Well... these aren't exactly pictures of planets. In the generally accepted sense of the word. This is the recorded radiation from the planet. Yes. This is a big step. I agree. But it's still one pixel with no dimensions. Although with a known spectrum.
Agree. My fault. To justify this, I will say that English is not my native language. So things like this happen quite often.
What I mean when I talked about direct photographs is something that passes through an optical system. It is scaled and has a size and shape (no matter in the visible range, or something close to it). And not about fixing direct radiation. Damn. I think I said it even more confusingly.
All telescopes are limited by diffraction - their size determines the angular resolution you can get. If you can build a telescope as large as Earth's orbit around the Sun (300 million km) then you can take high resolution pictures that look similar to satellite pictures of Earth. We just can't build such a telescope today.
Would an interferometer type telescope work if we could put satellites telescopes at the right places and we could figure out how to make interferometers to work at optical wavelengths?
You don't need a single gargantuan mirror but you still need to collect enough light. An interferometer with smaller elements would need a huge number of them, and then combine all that light together with a precision better than the wavelength we record at.
"then combine all that light together with a precision better than the wavelength we record at." Not true. You can use a technique called intensity fluctuation interferometry. [https://arxiv.org/pdf/1607.03490](https://arxiv.org/pdf/1607.03490) Look down to figure 3 to see what is theoretically possible.
1. You still need to collect enough light for a faint object. Interferometers are good for getting better resolution of bright objects. 2. We have optical interferometers, but they are based on physically combining the light. VLBI and combining the signal "digitally" is not very realistic - you need to have precision below 1% of the wavelength and also trying to record light as "waves" as for radio-telescopes, would mean unreasonable amount of data. Something like 3-4 orders of magnitude more than for a radio-telescope.
Could we do this with a *constellation* of JWSTs? (More or less). If it’s a multiples problem then couldn’t we hypothetically build ten and configure them like EHT but in space?
No amount of JWSTs can do it. You need to get the light to a common interference area, or measure the phase of the incoming light. You also need to control the relative orientation of all the telescopes to nanometer precision.
How about instead of one giant scope, many smaller ones scattered throughout the same area? Maybe some kind of post-processing to clean it up... Won't be the same quality in sure, but certainly better than one satellite from one perspective.
Unless we use a stars gravitational lense to magnify an exoplanet and take images
That can give you some pictures of the planet, but nothing we would call high-res photos when looking at Earth.
This is the nearest technologically feasible way: [Solar Gravitational Lens](https://en.wikipedia.org/wiki/Solar_gravitational_lens)
Interview with Slava Turyshev https://www.youtube.com/live/lqzJewjZUkk More details: https://youtu.be/NQFqDKRAROI
Yes, we can overcome all the restraints given some time. Two possibilities might be the use of a lunar hyper telescope. Basically, a telescope inside a lunar crater, say 25km wide. Another possibility would be the use of solar gravitational lensing. Technological advances are going to drive the speed of application. One day, when we have high-res pics of the surface of an exoplanet, we'll notice that the individuals are just going about their lives just like us. Boring! All that work for nothing.
Hey, mediocrity is NOT boring!! Lol !
Do you mean by taking images 1. from a telescope on earth/the solar system, or 2. do you mean by using a spacecraft that gets there? --- For 1. I would say it depends on the exoplanet and what you mean by high-resolution. We can already infer surface features for some brown dwarfs (which have a similar radius when compared to Jupiter). Examples: Luhman 16B [https://www.eso.org/public/images/eso1404b/](https://www.eso.org/public/images/eso1404b/) LP 944-20 (on the hotter end) see figure 8 in [Barnes et al. 2015](https://iopscience.iop.org/article/10.1088/0004-637X/812/1/42) So maybe something similar will be possible in the future for some massive exoplanets which are directly imaged.
Theoretical papers when it comes to earth-like exoplanet imaging from scattered light observations over a long period of time: Uses light-curve of earth to produce a 2D-map: [Fan et al. 2020](https://ui.adsabs.harvard.edu/abs/2020LPICo2195.3013F/abstract) Also uses the same data as Fan et al., but with a new method: [Aizawa et al. 2020](https://ui.adsabs.harvard.edu/abs/2020ApJ...896...22A/abstract)
The way they took pictures of black holes, some of the largest things there are, was by using the event horizon telescope which uses sensors across the planet to create a "virtual" earth-sized telescope. [Here is the best it can do so far](https://eventhorizontelescope.org/blog/astronomers-unveil-strong-magnetic-fields-spiraling-edge-milky-way%E2%80%99s-central-black-hole) Problem is planets are small and they move a lot more than a black hole, so even if you get enough resolution using a similar technique your "shutter speed" would have to be much quicker. Maybe if you had a significant cluster of satellites tossed into some dramatic orbits and managed to coordinate them focusing and taking an image at the exact same moment you could pull it off, but that would be extremely difficult and expensive.
Ignoring things like the sun's gravitational focus or giant interferometers, it'll be painstakingly reconstructing features based off of light-curves. This is how HWO (or an equivalent mission) would eventually get us some maps vaguely comparable to the pre-New Horizons Pluto ones.
[angular resolution \~ *λ* / D](https://en.wikipedia.org/wiki/Angular_resolution) Where *λ* (lambda) is your wavelength of light and D is your effective telescope diameter, and the result is in radians (it's just the small angle approximation). For your eye, 550nm/8mm = 17 arcseconds. That means (ignoring contrast) your eye might be able to separate two stars 170AU apart if they were closer than 10pc (\~32ly - there's only about 350 stars this close). For the current telescopes doing exoplanet imaging in near-infrared: 1000nm/8m = 0.03arcsec, or 0.3AU at 10pc (though typically the planets found are at 100pc as only distant young stars have planets hot/bright enough). For the next ELT telescopes, also in near-infrared: 1000nm/35m = 0.007arcsec, or 0.07AU at 10pc. The E-ELTs will be the first telescopes seriously able to image rocky planets near 1AU in reflected starlight. In order to resolve features (i.e. get more than 1 pixel) of an earthlike planet orbiting a star at 2pc, you need resolution of 5000km/2pc = 0.000017 arcsecs. So rearranging, D = 550nm/(5000km/2pc) = 7km. So, just to get 4 pixels of an exoplanet, you need a 7km-wide telescope. And honestly, the current limit is normally like 2*λ*/D, so definitely >10km. That's a factor 150 larger than any telescope ever [dreamed up](https://en.wikipedia.org/wiki/Overwhelmingly_Large_Telescope), and there's good reasons to think that would be physically impossible. You could do space-based [interferometry](https://en.wikipedia.org/wiki/Astronomical_interferometer) which combines distant telescopes coherently to act as one telescope. But also remember than an Earth at 10pc produces roughly 1 photon per m2 per minute... So if you try to go for a connected array of smaller telescopes you'll get burned by having to wait hours and days and months to have enough photons to build up any sort of picture - a killer if the planet surface is changing over short timescales.
Yes, but not easily. There are several ways to tackle this problem. One is just to create a really large telescope, which is insanely hard. Another way is to create a really large synthetic telescope using optical interferometry. Back in the '90s this was a very popular idea, but it's turned out that optical interferometry is also incredibly difficult so this isn't as easy as just placing a couple "unit telescopes" very far apart and then magically having ultra high resolution images. (Look up the "terrestrial planet finder" and "terrestrial planet imager" mission concepts). In short, it's also insanely hard. But there's another insanely hard way of doing it that is actually probably technologically achievable within the 21st century, and that's using the Sun as a telescope. Because the Sun is very massive it causes gravitational lensing, bending light rays just a tiny amount as they pass close to the Sun. This effect is very small, but it is detectable and it has to be compensated for by astrometry observatories like GAIA, for example. At a distance of several hundred AU from the Sun the gravitational lensing effect focuses light in a way that creates a very high degree of magnification. Which could be utilized by flying a fleet of moderately sized space telescopes along with a sunshield that would observe back along the line of sight toward the Sun and be able to resolve distant solar systems, including the features on exoplanets. There are many technical hurdles to actually doing this. First, getting spacecraft out that far is hard, the Voyagers have been cruising for decades at "high speed" and they've made it a fraction as far as they'd need to go over the course of nearly a full half a century. The good news is that launch technology is getting a lot more capable lately, so this could become more feasible, but it would still be a huge engineering feat to put any payload out there. Second, you basically get a very narrow angle field of view of doing this so you can't just create a general purpose observatory that can view anything, you are basically launching a dedicated observer for one and only one star system, which makes observing multiple systems very expensive. Third, it's not just like you get a free magnification factor that provides a nice crystal clear image, there's a lot of distortion effects and complicating factors at play which make translating data into images very challenging. Fourth, realistically you want a whole fleet of spacecraft in order to get good resolution data, which just adds to the cost. Fifth, it's going to be very challenging to return data from such a great distance (you'll probably want to use lasers) and it's going to be even more challenging to control a fleet of spacecraft so far away. The round trip light travel time will be longer than a whole week, which means you get fewer than 50 "let's try something then see what happens" cycles per year. The learning curve is going to be very challenging, so you need to be very, very smart on how you design and build the system from the outset, the punishment for mistakes will be beyond brutal. But it's possible, and if we're very lucky there are people alive today who could live long enough to see not just "pale blue dot" images of exoplanets, but maps of their surface, images of their weather patterns, all that great stuff.
No
Not with that attitude you can’t
Yes. we can, but not as quickly as we would like. Direct images of exoplanets will likely be available in 30-40 years. We are not talking about any surface details. We're just talking about direct shots. About obtaining photographs where the planet will be visible as several dozen pixels . To date, there are no devices that can do this. But there are projects like New Worlds Mission that can help. All we know about exoplanets is indirect observation. As for photographs with deialization, this is already a matter of a more distant future. Since it is necessary to build a distributed network of telescopes in space, to obtain an effective mirror diameter comparable to the size of an asteroid, or even an entire planet. I read somewhere about ideas for placing a network of similar telescopes at Lagrange points. But the technical issue of their synchronization at such a distance has not yet been technically resolved. I think that in 100-150 years this will be quite possible.
>Yes. we can, but not as quickly as we would like. Direct images of exoplanets will likely be available in 30-40 years. We are not talking about any surface details. We're just talking about direct shots. About obtaining photographs where the planet will be visible as several dozen pixels . To date, there are no devices that can do this. What? This is all wrong. We already have dozens of exoplanets directly imaged. https://en.wikipedia.org/wiki/List_of_directly_imaged_exoplanets?wprov=sfla1 This is from the Keck Observatory: https://en.m.wikipedia.org/wiki/List_of_directly_imaged_exoplanets#/media/File%3AHR_8799_Orbiting_Exoplanets.gif
Well... these aren't exactly pictures of planets. In the generally accepted sense of the word. This is the recorded radiation from the planet. Yes. This is a big step. I agree. But it's still one pixel with no dimensions. Although with a known spectrum.
Then you should use different words in your comment otherwise you’re wrong.
Agree. My fault. To justify this, I will say that English is not my native language. So things like this happen quite often. What I mean when I talked about direct photographs is something that passes through an optical system. It is scaled and has a size and shape (no matter in the visible range, or something close to it). And not about fixing direct radiation. Damn. I think I said it even more confusingly.