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If some stellar civilization sent a space probe (say something similar to our Voyager probes in shape/size/materials and communication capability) and it ended up in a regular orbit around the Earth in something below geosynchronous orbit, would we be able to randomly detect it? This detection could be visually or via detection of RF emissions aimed towards its' origin location.

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Small asteroids are occasionally, but routinely discovered, often just before or just after closest approach. For example a 3.5m asteroid 2021 RS2 was discovered at a MEO distance. It has a comparable size to Voyager but is probably darker.

So a Voyager probe in MEO would probably be picked up by asteroid scanning systems.

Once an orbit was determined, and it was found to be in Earth orbit, interest would pique, and people would become interested, spectra would be taken, and the spectrum of something artificial is very different from that of rock.

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    $\begingroup$ What is an "asteroid scanning system"? What are some examples? Just because one was seen doesn't mean that 1,000 were missed, so "would probably be picked up" is completely unjustified. On the other hand, don't you think 24/7 space situational awareness via radar would be a heck of a lot more likely to see it than an optical telescope poking around the night sky during clear nights? $\endgroup$
    – uhoh
    Commented Feb 3, 2022 at 23:18
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    $\begingroup$ gizmodo.com/… $\endgroup$
    – planetmaker
    Commented Feb 3, 2022 at 23:19
  • $\begingroup$ @planetmaker excellent! I don't know what "a bit of a purple patch" means though: "ATLAS is just one in a suite of asteroid defense systems which are having a bit of a purple patch. As recently reported by Gizmodo, NASA’s upgraded Sentry-II system “eats probabilities for breakfast,” giving NASA more precise odds than its predecessor did." That links to A Novel Approach to Asteroid Impact Monitoring $\endgroup$
    – uhoh
    Commented Feb 3, 2022 at 23:22
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    $\begingroup$ @uhoh "purple patch" just means a streak of luck. It's a colloquial expression, probably something from gambling, nothing specific about astronomy or technology. $\endgroup$
    – uUnwY
    Commented Feb 4, 2022 at 8:59
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    $\begingroup$ @uhoh Good point that we don't know how many the system misses, but detecting a satellite in orbit would be easier because it's there permanently, while an approaching small asteroid is detectable only for a few days perhaps. So if the system scans every day, it has only a few opportunities to see the asteroid, but 365 opportunities a year to see the probe. So even if it only detects 1/1000, we're likely find it after 3 years. $\endgroup$
    – uUnwY
    Commented Feb 4, 2022 at 9:05

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