Radio Signals
- MeerKAT’s 64-antenna array in South Africa detected hydroxyl absorption lines at 1665 and 1667 MHz—the same “water-hole” frequencies long proposed for interstellar communication.
- Harvard astrophysicist Avi Loeb says 3I/ATLAS’s signal appeared just five days before its perihelion, when solar radiation should have maximized OH emission, not absorption.
- Next checkpoint: December 19 — Earth’s closest approach, when researchers will test whether the object repeats its signal or stays silent.
By Samuel Lopez
CAPE TOWN (USA HERALD) — A radio telescope on South Africa’s Karoo plain has detected what may be the first microwave whisper from an interstellar object. The MeerKAT Observatory recorded narrow-band hydroxyl (OH) absorption lines at 1665.4018 and 1667.3590 megahertz—frequencies that scientists since the 1970s have nicknamed the “water hole,” a naturally quiet slice of the spectrum between hydrogen and hydroxyl emissions where intelligent civilizations might choose to broadcast.
The detection occurred on October 24, five days before 3I/ATLAS reached its closest pass to the Sun. According to the South African Radio Astronomy Observatory, the signal showed OH absorption rather than emission—possibly because the object’s near-solar geometry favored shadowed absorption.
“Five weeks ago, I encouraged radio observatories like MeerKAT to search for radio emission from 3I/ATLAS,”Prof. Avi Loeb wrote in a Medium post. “In response, I was assured that 3I/ATLAS will be monitored.”
Loeb has noted in the past, that the arrival direction of 3I/ATLAS matches the 1977 Wow! Signal within 9 degrees at 1.4204556 GHz — another coincidence inside the hydrogen-OH band long theorized as an interstellar “greeting channel.”
So far, no other radio detections have been confirmed beyond the OH absorption lines, but the team plans continuous monitoring to see if the molecule’s production fluctuates or if the signal shows any non-thermal modulation that might hint at engineering.
Why OH Is Elegant for Interstellar Communication
