Listening in from a distance

Readers probably have already seen the various reports that some scientists decided to turn a radio receiver towards that elongated asteroid now heading out of the solar system, just in case it was a spaceship or something artificial.

I meant to post this part of that story, because it says a lot about the sensitivity of radio telescopes:

Breakthrough Listen announced Monday that the program will start checking ‘Oumuamua this week for signs of radio signals using the Green Bank Telescope in West Virginia. The interstellar asteroid is now about twice the distance between the Earth and the sun from our planet, moving at a brisk clip of 38.3 kilometers per second. At this close distance, Green Bank can detect the faintest frequencies. It would take the telescope less than a minute to pick up something as faint as the radio waves from a cellphone. If ‘Oumuamua is sending signals, we’ll hear them.

And here's a report on the first results:

The first batch of four observations ran from 8.45pm UK time on Wednesday until 2.45am on Thursday morning and spanned a frequency range from 1 to 12 GHz. While the search for alien signals has so far found nothing in the 1.7 to 2.6GHz range, the rest of the data is still being processed.

Andrew Siemion, director of Berkeley Seti Research Center, told the Guardian that a review of all four bands observed Wednesday night had come up blank. “We don’t see anything continuously emitting from ‘Oumuamua,” he said. “We’re now digging into some of the intermittent candidates, and trying some new machine learning-based techniques we have been working on. We expect our next observation window to be scheduled for Friday or Saturday, when we should get a view of additional phases of ‘Oumuamua as it rotates.”