We have just released a short AAS Research Note on a search for technosignatures from asteroid (514017) 2015 BZ509 (aka BZ509). While we didn't find any candidate signals, we'll be searching a selection of intriguing asteroids as part of the ongoing Breakthrough Listen program.
BZ509 dances around the Sun in a remarkable retrograde (backward) orbit, stabilized by perfectly-timed close encounters with Jupiter's regular orbit (a 'resonance'). A leading explanation for BZ509's unusual orbit is that it came from outside the Solar system and got trapped by the Sun's gravitational pull.
If this theory is correct, then like 'Oumuamua, BZ509 is an interstellar visitor to our neighbourhood. Recently, Amir Siraj & Avi Loeb sifted through the trajectories of known asteroids, and found eight asteroids that they believe could be of interstellar origin.
The potential interstellar origin of objects such as BZ509 makes them interesting targets for SETI searches: several authors have postulated that a sufficiently advanced extraterrestrial civilization could send probes or beacons to other star systems. Indeed, we took a close look at 'Oumuamua with the Green Bank Telesope, but didn't find anything unusual.
As detailed in our recently published Research Note, we searched BZ509 for narrowband transmissions, but didn't identify any signals above our sensitivity limit of 4.8 W (a radiated power level between that of a cell phone, and the telemetry link of a NASA space probe like New Horizons). But with a new bounty of interstellar asteroids, it's just the beginning for targeted SETI searches of these kinds of objects.
Image Credit: Large Binocular Telescope Observatory