That is silly, if their systems are passive it will look like a rock.

https://archive.fo/thGkC :

Astronomers to Check Mysterious Interstellar Object for Signs of Technology - The Atlantic

'For Milner, it’s worth examining every interstellar object for signs of artificial technology. '

'Eastern Time, the Green Bank Telescope will aim at the first known interstellar object in our solar system. '

'When they speak of ‘Oumuamua, astronomers recall the tale in Arthur C. Clarke’s 1973 novel Rendezvous with Rama. '

'In our solar system, there are far more comets than asteroids lurking near the boundary before interstellar space. '

'When our solar system was young, the biggest planets wreaked havoc as they swirled into shape and settled into their orbits. '

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