Thin, dark, like a junkie needle threaded through space, the ship is barely visible in its approach. Too thin in cross-section to make out any markings, any indication of weapons or crew. Unnoticed until it is barely an AU distant from the planet, sending out pulses of thrust to slow it down.
Panic is immediate.
Talk of launching crude armadas of re-purposed ballistic nuclear warheads, revelation of hidden laser defence satellites, preparations for rapid evacuations to the Moon, to Mars; chatter over radio bands broadcasting signals of welcome, laser pulse transmitters blinking binary messages of peace, any scheme that seems able to carry a signal tried in desparation.
All met with silence.