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JWST reveals its first direct image discovery of an exoplanet

(www.smithsonianmag.com)
342 points divbzero | 2 comments | 27 Jun 25 17:44 UTC | HN request time: 0.43s | source
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GMoromisato ◴[27 Jun 25 23:00 UTC] No.44401068[source]▶
In case anyone is wondering, we are (sadly) very far from getting an image of this planet (or any extra-solar planet) that is more than 1 pixel across.

At 110 light-years distance you would need a telescope ~450 kilometers across to image this planet at 100x100 pixel resolution--about the size of a small icon. That is a physical limit based on the wavelength of light.

The best we could do is build a space-based optical interferometer with two nodes 450 kilometers apart, but synchronized to 1 wavelength. That's a really tough engineering challenge.

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nico ◴[27 Jun 25 23:06 UTC] No.44401110[source]▶
How big would the telescope/mirror/lens need to be to get a picture of something in the Alpha Centauri system, 4.37 light years away?

Also, could the image be created by “scanning” a big area and then composing the image from a bunch of smaller ones?

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joshvm ◴[28 Jun 25 03:57 UTC] No.44402225[source]▶
It's a lot easier to reason about this using angular resolution, because that's normally what the diffraction limit formula is in reference to. If you know the angular diameter of the system (α) and the wavelength (say λ=500 nm for visible), you can use α ≈ λ/d and solve for the aperture of the telescope (d).

That puts a basic limit on the smallest thing you can resolve with a given aperture. You can use the angular diameter of the planet and the resolution you're after. For Alpha Centauri A it's 8.5 milli arc-second, so O(1 μas) for a 100px image? That's just for the star!

The Event Horizon Telescope can achieve around 20-25 μas in microwave; you need a planet-scale interferometer to do that. https://en.wikipedia.org/wiki/Event_Horizon_Telescope It's possible to do radio measurements in sync with good clocks and fast sampling/storage, much harder with visible.

I'm not super up to date on visible approaches, but there is LISA which will be a large scale interferometer in space. The technology for synchronising the satellites is similar to what you'd need for this in the optical.

https://www.edmundoptics.com/knowledge-center/application-no...

https://arxiv.org/abs/astro-ph/0303634

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1. kadoban ◴[28 Jun 25 05:50 UTC] No.44402536[source]▶
Is there another limit in terms of just: how many photons from X object even hit an area of Y telescope apeture size from distance Z in like, say a year? We can't see the thing if no photons from it even intersect our telescope, right? Or maybe that limit is way way less restrictive than the other...
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2. hnaccount_rng ◴[28 Jun 25 06:20 UTC] No.44402644[source]▶
The number of photons themselves is not too restrictive (i think the voyager probe still emits 6ish photons per second directed at the receiving dish). And we easily build sensors that detect every photon (far above 99% levels). The tricky part will be differentiating between “source photons” and “background photons” (for Voyager we exactly know what to look for, here we wouldn’t have any baseline for distinguishing)