The first trace came in on a Tuesday, buried in three weeks of routine calibration data nobody had gotten around to reviewing. It repeated every 47 seconds, almost too regular to be natural — and almost too faint to be anything at all.
Our first instinct was to blame the array. Ground-based radio receivers pick up more of their own electronics than they'd like to admit, and a repeating pulse at low signal strength is exactly the kind of thing a loose connector produces. So the team spent the better part of three weeks doing the unglamorous work of elimination: swapping cables, rebooting receivers, checking the signal against known satellite passes, and comparing notes with a second array a few hundred kilometers away.
The second array caught it too, at the same interval, arriving a few milliseconds apart — consistent with a source outside the atmosphere rather than inside our own equipment.
What it isn't
It isn't a known satellite. It isn't a known pulsar; the timing doesn't match anything catalogued in that direction. It isn't reflected noise from an existing spacecraft, as far as cross-checking with public tracking data can tell us. That leaves the honest, slightly unsatisfying answer: an unidentified repeating source, out past the orbit of the outer planets, doing something regular enough to make a receiver's needle twitch.
A regular pulse doesn't mean an artificial one. It just means we found something that repeats before we found out why. Notes from the observing log, 12 July
What happens next
The working theory, and the least dramatic one, is a natural object we haven't fully characterized yet — a distant rotating body, or an interaction between solar wind and something at the edge of the heliosphere. Two more observation windows are scheduled over the coming month, aimed at narrowing the bearing enough to rule that in or out.
Until then, this stays logged as exactly what it is: a repeating signal, confirmed by two independent receivers, source unknown. We'll post the follow-up the moment there's something to report — not before.