Earth Detecting Earth
6 comments
·February 3, 2025A_D_E_P_T
The actual paper is here, in PDF form: 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.
00N8
It seems like they're calculating the farthest distances where it would be theoretically possible for aliens with Earth level tech to detect us, for various different ways of detection. I'm curious about a related question: At what distance would we likely have been able to detect 'ourselves' with current technology? Ie. if there was another Earth 100 or 1000 light years away, would we have seen it by now? (Assume they are x years ahead so the signals have had time to propagate).
I think it may be a relatively short distance, which could have implications for resolving the Fermi paradox, but I haven't seen any definitive estimates & I'm curious to learn more.
falcor84
My understanding based on their use of "technology similar to ours" is that this is exactly what they're doing:
>If an extraterrestrial civilization existed with technology similar to ours, would they be able to detect Earth and evidence of humanity? If so, what signals would they detect, and from how far away?
00N8
I was thinking we probably can't watch the whole sky in maximum detail all at once, so in practice we'll miss most possible detections.
InDubioProRubio
They could get a 25km high-resolution picture of the planet? https://en.wikipedia.org/wiki/Solar_gravitational_lens
I'm so glad that someone has finally tried to answer this question as it's something I've been wondering for years. It's interesting that atmospheric indicators are only detectable to around 5ly as that is I believe one of the primary methods we are using to look for technosignatures on other planets.