I know that with our current technology, we can’t image an exoplanet directly or in any kind of detail due to the combination of the vast distances involved and the brightness of the parent star overpowering the light reflected from its planets. That got me thinking: Does SETI face the same issues trying to pick out an artificial signal from the natural background “white noise” produced by stars, planets, and other things in th universe? And if so, how do they overcome it? Because it seems like it would get lost in the shuffle the same way the individual details of an exoplanet get lost to an optical telescope.
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Yes, Here is a link to how they do it
One thing to keep in mind is that basically all of our searches are for intentional signals specifically designed to attract attention. It’s vanishingly unlikely we could detect an Earthlike civilization around the closest star, other than maybe their military radar “blips”.
But if they had an Arecibo-class transmitter blasting an intentionally interstellar signal directly at us in order to try to get our attention… we might notice that.
It might be more accurate to say they face different issues to optical telescopes but still in the family of “stuff you don’t want to be observing making the image messy”.
The good news is that fewer things emit radio waves than emit visible light. It’s not zero but there are fewer radio sources than optical sources in deep space and they are distributed across a wider spectrum so it’s easier to filter out what you’re not looking for. But it’s harder to block radio waves than it is to block visible light and unfortunately there’s a lot of man-made machines that produce radio waves. There’s a big radio telescope in West Virginia that has strict rules about nearby sources of EM interference including banning Wifi in all the homes nearby. Remember that any form of telescope is trying to focus and magnify incredibly faint signals from millions of miles away so even a relatively small source nearby is going to cause interference. https://www.youtube.com/watch?v=eQEGPATQe5s
One of the advantages of radio telescopes over optical telescopes is that radiowaves aren’t distorted by the atmosphere in the way that light is disrupted or blocked by clouds etc. So we tend to launch incredibly accurate optical telescopes into space and don’t need to do that for radio telescopes. But radiowaves being larger than visible light means radio telescopes need to be a LOT bigger and it would be impractical to deploy one as a satellite like Hubble or JWST. They are also very expensive to build and maintain, The Arecibo Telescope from the movie Contact succumbed to disrepair a few years ago.
There is a slightly insane plan to build a radio telescope on the moon. Pick a suitably large crater on the far side of the moon and use the natural bowl shape as the foundations for a giant dish far larger than Arecibo or the current largest one FAST. There would be engineering challenges and we’ve never built anything larger than a single flagpole on the moon so planning to build something several kilometers wide is incredibly optimistic. But being on the far side of the moon would shield it from any radio interference from Earth, you could theoretically build something larger in the low gravity environment of the moon than on Earth.
So maybe not any time soon but in another hundred years there could be a giant radio telescope on the moon.