3 ms·

The actual paper is here, in PDF form: https://iopscience.iop.org/article/10.3847/1538-3881/ada3c7/pdf https://iopscience.iop.org/article/10.3847/1538-3881/ada

The actual paper is here, in PDF form: https://iopscience.iop.org/article/10.3847/1538-3881/ada3c7/pdf https://iopscience.iop.org/article/10.3847/1538-3881/ada3c7/... The authors write that Earth could detect an Earthlike planet from 12000 light-years away via Earth's strong radio emissions -- specifically, the intermittent, celestially targeted radar beams (for example, those originally from Arecibo’s planetary radar). But we'd need to be laser-focused on the planet, and we'd need to catch them when they're emitting. Earth has only been emitting powerful radio waves for ~50 years, so our detection radius is ~50 LY. Besides radio, most other means have a very low range.

vintagedave 2y ago
I've read of occasional strange radio signals we detect that are intermittent or not repeated. Is it possible that, to an external observer, our 'strong radio emissions' that are 'intermittent, celestially targeted' could appear similar? With the natural question, could we have already observed something like what we're producing? I understand without a reproducible signal, no-one knows, but do any of those once-off signals work as a potential similar match?
- ben_w 2y ago
  Several of them could have been, but without any repetitions, and given the lack of obvious signal in we actually recorded, and given the known natural processes that can cause transient radio bursts, the best bet is they're probably not aliens.
  - roughly 2y ago
    > the lack of obvious signal in we actually recorded This is something I’m curious about - I’m led to understand that modern digital signaling is almost impossible to tell from noise, unless you know what you’re looking for (encryption and compression both conspire against obvious structure), is that not the case? Would it be obvious from a signal construction level that we were looking at, well, signal, and not noise?
    - ben_w 2y ago
      If it's encrypted or perfectly compressed, sure; but we wouldn't broadcast that at high power to a distant solar system, or expect to notice it. We won't see accidental emissions, because they will be lower power: To a first approximation, we talk to each other we use the lowest power to guarantee a certain signal to noise ratio, partly to save money and partly to not interfere with other transmissions on the same frequency. We expect to recognise high power emissions sent deliberately by the equivalent of Aracibo, because they won't be compressed or encrypted, precisely because doing either would make it nigh impossible for the aliens at the other end to decode.
    - palmotea 2y ago
      >> the lack of obvious signal in we actually recorded > This is something I’m curious about - I’m led to understand that modern digital signaling is almost impossible to tell from noise, unless you know what you’re looking for (encryption and compression both conspire against obvious structure), is that not the case? Would it be obvious from a signal construction level that we were looking at, well, signal, and not noise? Wouldn't that just be a barrier to decoding the message but not detecting that it was a signal? I'm not an electrical engineer, but wouldn't any digital signal rise up from the noise floor with some detectable artificial structure (like regularly timed but varied pulses; e.g. 1001 1011 1110 0001, each pair of 1s is separated by an integer multiple of the pulse time).
willis936 2y ago
We could detect the active biosphere of Earth from much further away with faster surveys. If we ever discovered an exoplanet like that you can be certain the phone would be ringing off the hook. Sure, that says nothing of technological advancement, but biosphere signatures are roughly a prerequisite for technological advancement.
- TeMPOraL 2y ago
  To expand on it, I believe we could detect signs of possible biosphere by finding oxygen in the spectral lines of the planet's image. The idea being, free oxygen is highly reactive, and thus can exist in the atmosphere only for brief periods before oxidizing the first thing it bumps into. So, should we find a planet with lots of free oxygen in the air, we either got improbably lucky to catch it before it's gone, or... there is some process on the planet that's actively replenishing it. On Earth, that process is the biosphere.
- Buttons840 2y ago
  Can we detect the biosphere of any planet, or only those that pass in front of a star? I'm wondering if we could detect radio transmissions from a planet which we otherwise couldn't detect?

vintagedave 2y ago

I've read of occasional strange radio signals we detect that are intermittent or not repeated. Is it possible that, to an external observer, our 'strong radio emissions' that are 'intermittent, celestially targeted' could appear similar? With the natural question, could we have already observed something like what we're producing? I understand without a reproducible signal, no-one knows, but do any of those once-off signals work as a potential similar match?

ben_w 2y ago
Several of them could have been, but without any repetitions, and given the lack of obvious signal in we actually recorded, and given the known natural processes that can cause transient radio bursts, the best bet is they're probably not aliens.
- roughly 2y ago
  > the lack of obvious signal in we actually recorded This is something I’m curious about - I’m led to understand that modern digital signaling is almost impossible to tell from noise, unless you know what you’re looking for (encryption and compression both conspire against obvious structure), is that not the case? Would it be obvious from a signal construction level that we were looking at, well, signal, and not noise?
  - ben_w 2y ago
    If it's encrypted or perfectly compressed, sure; but we wouldn't broadcast that at high power to a distant solar system, or expect to notice it. We won't see accidental emissions, because they will be lower power: To a first approximation, we talk to each other we use the lowest power to guarantee a certain signal to noise ratio, partly to save money and partly to not interfere with other transmissions on the same frequency. We expect to recognise high power emissions sent deliberately by the equivalent of Aracibo, because they won't be compressed or encrypted, precisely because doing either would make it nigh impossible for the aliens at the other end to decode.
  - palmotea 2y ago
    >> the lack of obvious signal in we actually recorded > This is something I’m curious about - I’m led to understand that modern digital signaling is almost impossible to tell from noise, unless you know what you’re looking for (encryption and compression both conspire against obvious structure), is that not the case? Would it be obvious from a signal construction level that we were looking at, well, signal, and not noise? Wouldn't that just be a barrier to decoding the message but not detecting that it was a signal? I'm not an electrical engineer, but wouldn't any digital signal rise up from the noise floor with some detectable artificial structure (like regularly timed but varied pulses; e.g. 1001 1011 1110 0001, each pair of 1s is separated by an integer multiple of the pulse time).

willis936 2y ago

We could detect the active biosphere of Earth from much further away with faster surveys. If we ever discovered an exoplanet like that you can be certain the phone would be ringing off the hook. Sure, that says nothing of technological advancement, but biosphere signatures are roughly a prerequisite for technological advancement.

TeMPOraL 2y ago
To expand on it, I believe we could detect signs of possible biosphere by finding oxygen in the spectral lines of the planet's image. The idea being, free oxygen is highly reactive, and thus can exist in the atmosphere only for brief periods before oxidizing the first thing it bumps into. So, should we find a planet with lots of free oxygen in the air, we either got improbably lucky to catch it before it's gone, or... there is some process on the planet that's actively replenishing it. On Earth, that process is the biosphere.
Buttons840 2y ago
Can we detect the biosphere of any planet, or only those that pass in front of a star? I'm wondering if we could detect radio transmissions from a planet which we otherwise couldn't detect?