Robotic missions on interstellar trajectories
Since the 1970s, the United States has launched several unmanned spacecraft that are now on escape trajectories from the Solar System. Pioneer 10 and 11, the Voyager 1 and 2 probes, and the New Horizons spacecraft are gradually leaving the Sun's sphere of influence and could eventually enter another star system. Although these probes will no longer be operational after decades of travel, they demonstrate that a space‑faring civilization can build interstellar vehicles.
The question of foreign probes
A recent paper examines whether an extraterrestrial civilization might have sent its own probes into our planetary system. Astronomer T. Joseph W. Lazio points out that no comprehensive search for such objects has been conducted to date, meaning that potential alien artifacts could remain undetected.
Current technological gaps
Lazio notes that existing telescopes and radar installations lack the sensitivity required to detect small, possibly dormant objects in the outer Solar System. He calls for enhanced infrared and radio‑wave detectors and new data‑analysis techniques capable of picking up faint signals.
Future prospects
The study concludes that a systematic search program will only become feasible once measurement precision improves dramatically. Only then can scientists assess whether humanity is truly alone in interstellar space or already hosts foreign visitors in its cosmic backyard.