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NASA’s James Webb Space Telescope has taken very blurry "photos" of exoplanets around distant stars, such as the exoplanet HIP 65426 b, in different bands of infrared light:

Infrared pictures of HIP 65426b

My question is, is it possible for the next generations of space telescopes to generate detailed, high-resolution images of such planets? Is there enough "data" or "DPI", so to speak, in the light coming from these planets to achieve this? I know there is cosmic dust and all sorts of other interference that affects the light on its way to Earth, but I'm wondering just how much that is. I'm talking about images with the same spatial resolution of this one of Mars:

Optical image of Mars

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    $\begingroup$ If that Mars image is the same one that headlines Wikipedia's Mars article, it was taken by the India's Mars Obiter Mission, presumably from Mars orbit. $\endgroup$
    – notovny
    Feb 13, 2023 at 13:43
  • $\begingroup$ The "data" light carries doesn't decrease with distance. The concept of DPI doesn't really apply either. If photons were particles, they would spread out and get less dense, but photons also behave like waves, and in that sense, the energy is spread out over a continuous area. $\endgroup$ Feb 13, 2023 at 17:42
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    $\begingroup$ @notovny Checking I think it is the one in Wikipedia's mars article and it was taken from 76000km away from Mars. Not sure you want to call that Mars orbit (though of course orbit has nothing to do with distance in essence), but it's a hell of a lot closer than taking it from Earth. $\endgroup$
    – DRF
    Feb 13, 2023 at 19:55
  • $\begingroup$ Since some such photos have been taken, the Question clearly needs editing. $\endgroup$ Feb 13, 2023 at 21:33
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    $\begingroup$ Noting James K's answer, but I'd suggest that the question needs to clarify "high resolution". For example, until relatively recently the best Earth-based telescope could show ice caps on Mars but not much more: would conclusively knowing the presence of ice caps on an extrasolar planet be adequate? $\endgroup$ Feb 14, 2023 at 9:33

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No, not with the current or any projected "next-generation" of telescopes.

The problem isn't dust, it is distance. To put it in context, you can consider a scale model of the universe. There is no limit to the "dpi" in the light (light doesn't have an intrinsic resolution), it is just that these objects are very small, very dim and very very very far away.

Capturing that image of Mars is like taking a photograph of a grain of sand at 20 metres. That is an impressive feat. But to take a similar photograph of an exoplanet you would be like taking a photograph of a grain of sand on the other side of the world!

This would require one of three things: An enormous telescope with a mirror that is kilometers across. Or travel to the gravitational focus of the sun (which is about 100 times further than Pluto). Or optical interferometry: combining the light from two telescopes. This would require the telescopes to be linked and to maintain sub-nanometer positioning over several kilometres.

Of these, optical interferometry would seem most plausible. But while we have managed 100m baseline interferometry with ground-based telescopes (which have the advantage of not floating in space!) the amount of light they can capture means that they are limited to observations of a few bright stars.

One could conceive of an array of moon-based telescopes eventually achieving the kind of resolution required to directly image an exoplanet, but this isn't "next-generation", but closer to science fiction.

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    $\begingroup$ Not to mention exposure time. A planet rotates, so if you want a crisp image of the surface, you likely can't keep gathering light for a month. $\endgroup$
    – Arthur
    Feb 13, 2023 at 12:26
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    $\begingroup$ There is a fundamental diffraction limit . $\endgroup$ Feb 13, 2023 at 13:31
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    $\begingroup$ @user253751 That isn't a limit, just make your telescope bigger. There is no limit to the "dpi" in a light signal, if you have enough time and a big enough telescope. $\endgroup$
    – James K
    Feb 13, 2023 at 17:05
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    $\begingroup$ @JamesK well yes. I think it is probably clear to the asker that a bigger telescope collects more data and if you make a universe-sized telescope you can see everything. The question is about Earth-orbiting telescopes. One can reasonably assume (for a silly upper bound) that a telescope more massive than the Earth cannot be said to orbit the Earth. $\endgroup$ Feb 13, 2023 at 17:07
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    $\begingroup$ I think you need about 1000 more 'very's in that second paragraph... $\endgroup$
    – Jon Custer
    Feb 13, 2023 at 20:34
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There is a fundamental limit to resolution called the "diffraction limit" that depends on three things:

  1. The angular size of the feature you're trying to resolve,
  2. The wavelength of light you're using for observation, and
  3. The diameter of your telescope.

#1 is out of our control: exoplanets are very far away, so their angular sizes are very small. Proxima Centauri b is about 4.2 light years away: about 700,000 times as far away as Mars when it's at its closest approach to Earth, and 100,000 times as far away as Mars at its furthest. So any given feature on Proxima Centauri b appears hundreds of thousands of times smaller than a similar feature on Mars. Distant exoplanets are even further away and even smaller, of course.

#2 is partially within our control — we can choose to observe in UV or X-rays. But most planets aren't very well illuminated in those wavelengths, and anyway, you wanted a similar picture to the Mars one, which is true color, so visible wavelengths it is.

So that leaves #3 — you need to make the telescope really really big. Not because you need the surface area to collect enough light (although that doesn't hurt), but because you need the diameter to collect light from points far enough apart. And you need to be able to point your really big telescope precisely at a very small piece of sky.

Nothing that exists comes close to that, and there are no concrete plans for anything that comes close to that. It's possible to imagine a sci-fi-ish solution (a swarm of high-orbit satellite telescopes with atomic clocks and digital holographic sensors, each keeping tabs on its neighbors with laser rangefinders, orienting by the stars, and sending a huge volume of data down to Earth to be processed using aperture synthesis techniques). All of that is an evolution of things that we know are possible, but given the level of refinement required, and the cost involved, I wouldn't recommend holding your breath.

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The only real problem is lack of angular resolution at optical and near infrared wavelengths. Lack of photons is not an issue.

Suppose there were something the size of Jupiter orbiting Alpha Cen A. At a distance of 1.33 pc, a Jupiter-sized object would subtend an angle of 0.0007 arcseconds.

The best optical/near infrared telescopes in existence are the HST and JWST respectively, but in terms of angular resolution they can just about be beaten by adaptive optics systems on the VLT. Even these deliver an angular resolution of around 0.05 arcseconds, with image pixels that are 0.025 arcseconds in size. The angular resolution is determined by the wavelength of observation divided by the telescope diameter.

i.e. Even the biggest exoplanet would not be resolved at all. There would be a blurry image of a point source around 0.05 arcseconds across. One would need a space telescope or an interferometer (see below) that had at least 100 times larger diameter - i.e. in the 1 km+ class.

In terms of number of photons - already not a problem. We can just scale how bright our Jupiter appears to work this out. Viewed from a distance of 5 au ($2.43\times 10^{-5}$ pc), Jupiter is around magnitude -2.5. This corresponds to an absolute magnitude (seen at 10 pc) of 25.6. Seen at the distance of Alpha Cen this would be magnitude 21.2. The brightness limit of telescopes like the VLT, JWST or HST is a lot fainter than this - probably about 5-6 magnitudes fainter in reasonably long exposures.

A more interesting thing is to consider observations at far infrared and microwave wavelengths. This can be achieved with very long baseline interferometry (see for example the Event Horizon Telescope. With baselines the size of the Earth, these telescopes can achieve angular resolutions of 0.00002 arcseconds, which is sufficient to resolve a giant exoplanet within 10 pc or so from the Earth.

The question then is why hasn't this been done? That is a good question (I'm going to ask it), but I suspect that this is down to a lack of sensitivity, because although the event horizon telescope has the resolution of a telescope the size of the Earth, it does not have the collecting area of one - and giant exoplanets may be quite faint at microwave wavlengths.

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No, not with present telescopes. A very tiny blurred image is all that can be achieved with present telescopes

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    $\begingroup$ I think the question wasn't asking about whether it's possible with current technology, but rather if it is even possible in theory. As in: Are there even enough photons that arrive in our solar system to create a clear picture? $\endgroup$
    – Philipp
    Feb 13, 2023 at 14:09
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In principle yes, although only sophisticated machinery is able to receive and evaluate it.

As always, the basic conundrum is magnification vs. light. Large magnification works best for bright objects.

The theoretical limit for magnification grows with the aperture size which has obvious technical limits on Earth and in space. We can cheat our way out of them by using telescope arrays forming interferometers, whose aperture is the baseline distance. But these are much harder to build for optical wavelengths than for longer-wave radio frequencies. It is a developing field.

Notably, Antoine Émile Henry Labeyrie has suggested a "Hypertelescope" which would exactly do what you asked, namely produce direct optical images of exoplanets at relatively high resolutions.

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Prior to the New Horizons probe flying past Pluto, in our own solar system, the best picture would could get of Pluto was a blurred circular shape.

enter image description here

If we can't get a high quality photo showing the detail of Pluto from Earth based telescopes and cameras we are not going to be able to get one of an exoplanet in another planetary system.

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  • $\begingroup$ Hubble was definitely used to obtain better imagery than that prior to New Horizons. Admittedly there were ten years of improvements in image processing and possibly as many as four servicing missions between the 1993 Hubble image and these composites assembled in '02-'03. $\endgroup$
    – notovny
    Feb 16, 2023 at 14:57
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Considering your question was more on the lines of is there enough data--It sounds like most people are considering relatively instanenous observations (Over a few horus, let's say), but if you just consider it a data collection problem it's just collecting and correlating photons, and a nearly infinit number of photons from any source we can see in the sky will eventually hit the planet.

Seems to me like it is a really difficult data wrangling problem, but if you pointed even just the existing telescopes at a single target for a couple years, correlated them all and could figure out the rotation and changes in lighting you could probably get a pretty good picture, maybe as good as the one from mars, you might even be able to get a globe of the planet if it rotated.

This is amazingly impractical (Let's just say imppossible) considering the requirements to record the exact timing, direction and frequency of each photon (Not to mention compensating for gravity bending, but I'd say the data is there.

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