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As we could not get any radio signals from asteroid ʻOumuamua, couldn't we have sent a powerful radio signal to it and then check if we can get any radio signal in response?

This way we can at least check if it is just a rock or any alien spaceship. If it were an alien spacecraft, then they should definitely give a radio signal in response I believe.

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  • $\begingroup$ what do you mean by "fast"? All radio signals travel the same speed $\endgroup$ – Rory Alsop Sep 28 '20 at 12:29
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    $\begingroup$ If I were an alien and could decode signals from Earth in 2017, I'd keep radio silence and try to look like an asteroid. $\endgroup$ – Mike G Sep 28 '20 at 12:43
  • $\begingroup$ @Mahen are you sure that radar signals have been intentionally sent to it? Can you add a link or reference for that? The distance was always quite far and the size relatively small, it's hard to imagine that there could have been a detectable reflection. $\endgroup$ – uhoh Sep 28 '20 at 15:49
  • $\begingroup$ @uhoh scientists have given its location and speed, and I believe Radar system is the only possible way to find such details for a very far and fast moving object. That way I presume along with Mick's info that Radar system was used. I am not very sure if there is any other way to locate such a far object. $\endgroup$ – Mahen Sep 28 '20 at 18:17
  • $\begingroup$ @Mick are you sure that radar signals have been intentionally sent to it? Can you add a link or reference for that? The distance was always quite far and the size relatively small, it's hard to imagine that there could have been a detectable reflection. $\endgroup$ – uhoh Sep 29 '20 at 0:43
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Answer posted under the wire during closure. Others may be able to write an additional and/or different answer as soon as two more reopen votes are cast.

Would it have been possible to send a radio signal towards ʻOumuamua?

Yes. It is certainly true that at any time, a large radio telescope or even a small transmitter can always sent a signal toward something. New Horizons can receive our signals now even though it's in the Kuiper belt because it knows when and where to listen and at what frequency.

As we could not get any radio signals from asteroid ʻOumuamua, couldn't we have sent a powerful radio signal to it and then check if we can get any radio signal in response?

The asteroid was quite close to us in the 2nd half of 2017, but now it's much farther than New Horizons. However if it had advanced technology it would know we were very active in the electromagnetic radio spectrum and it might be listening. If so, we certainly could have sent it a signal that it could receive.

Checking for a response is also hard because we'd need to know what frequency and when. We'd have to allocate resources, etc.

For the frequency, see also


Below: Plots of the distance of ʻOumuamua (bumpy, blue) and the New Horizons spacecraft (straight, green) from Earth as a function of years since 2017-01-01.

distance from earth after 2017-01-01 for New Horizions (straight green) and ʻOumuamua (bumpy blue)

JPL Horizons

JPL Horizons

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    $\begingroup$ It takes some time for closures to propagate through the system. There may even be a grace period to allow in-progress answers to be posted. $\endgroup$ – Mick Sep 29 '20 at 4:59
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    $\begingroup$ @uhoh Thanks for the answer. I do agree with "Checking for a response is also hard because we'd need to know what frequency and when". $\endgroup$ – Mahen Sep 29 '20 at 5:37
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    $\begingroup$ @Mahen However if you were to post a follow-up question here about all the kinds of measurements that contributed to our understanding of ʻOumuamua's distance and speed (visible, infrared, radar, etc.) that would be an excellent question in either site, and maybe best here in Astronomy since all of those are astronomical observations. You can ask how quickly each one gets weaker as it moves farther away, which is a really interesting question I think. $\endgroup$ – uhoh Sep 29 '20 at 6:30
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    $\begingroup$ @uhoh Sure uhoh. Thanks for the interesting links. $\endgroup$ – Mahen Sep 29 '20 at 6:49
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    $\begingroup$ @uhoh Mick is correct. There is a grace period for four hours after the question is closed where it still accepts answers that were started prior to closure: meta.stackexchange.com/a/316139/228367 $\endgroup$ – called2voyage Sep 29 '20 at 12:44

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