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Comment by carrozo | Hacker News Reader

A question I’ve always had is, assuming we do pick up very strong signatures or signals of life very far out, would it ever make sense (or, is it even possible) to create a ginormous optical telescope in space that could attempt to take pictures at a resolution that would be the next best thing to being there?

How big would it have to be in order to get a Google Earth resolution on a planet many light years away?

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> How big would it have to be in order to get a Google Earth resolution on a planet many light years away?

If you're ok to settle for a lower resolution, then a couple hundred astronomical units. Surprisingly, this may actually be feasible by using the sun as a gravitational lens. It would just take a lot of time to get the light collecting instrument in position at the focal point.

https://news.stanford.edu/press-releases/2022/05/02/gravity-...

Edit: the Stanford press release says that without exploiting gravitational lensing, "we would need a telescope 20 times wider than the Earth".

To use the Sun, the focal point would have to be situated about 542 AUs. Certainly not impossible, and the resolution would be quite good, good enough to see surface details of an exoplanet.

And could you imagine the bokeh on a portrait?!

542 AU is 0.008 LY. Not sure any planets you see there would count as exo.

That's where the focal point is, where we can capture the light, not where the exoplanets are.

That's one approach to use the sun as a gravitational lens for looking at exoplanets. There's another approach that instead of one big telescope sends a series of much smaller telescopes, small enough that light sails would be effective for getting them to where they need to go.

Here's a PBS Space Time episode [1] that talks about this general topic, and then about the series of smaller telescopes approach.

[1] https://www.youtube.com/watch?v=4d0EGIt1SPc

Google Earth resolution? You'd need satellites in low orbit around that planet.

For taking images from earth, the resolution would depend on the size and distance of the planet. Within a couple hundred light-years a $10b starshade spacecraft may be able to get a 30px by 30px optical image.

The physics are pretty limiting.

(this is all from memory, I worked as an engineer at an astrophysics institute for 8 yrs, but left that job almost two years ago, so the raw numbers are a bit rusty)

Consider that only last year they managed to image a star to a resolution greater than a single point, and that a planet is much smaller and much fainter. "Ginormous" doesn't quite convey the size of the aperture you'd need.

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