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138 The only way we can text the visitation hypothesis is by surveying the Sun’s entire family. The field to be searched is vast: Our solar system extends far beyond the known planets. Astronomers already have found that the asteroid population reaches well above and below the disk contain- ing the eight planets known before 1930 (Pluto’s orbit is more inclined). We may, perhaps unintentionally, create tools for this search as a spin-off from more conventional solar system exploration. Rees foresaw that huge numbers of miniaturized robotic probes will, 25 years from now, be dis- persed throughout the solar system, sending back images of planets, moons, comets, and asteroids. This would be consistent with Dyson’s principle for the planning of space operations: Every mission searching for evidence of life should have other exciting scientific objectives, so that the mission is worth flying whether or not it finds evidence of life.*° We cannot prove or disprove direct contact solely by theoretical argu- ments; we can only test it by observation. Cocconi and Morrison’s rule applies. The probability of success is difficult to estimate; but if we never search, the chance of success is zero. The Limits of Observation We already have tested our ability to detect small artifacts on the surface of other planets, from spacecraft in orbit around them. This experience suggests that an initial detection of alien technology in our own solar system may be ambiguous. Space scientist Michael Malin and his colleagues, analyzing imagery from orbiters observing Mars, found what they believed to be evidence of human technology on the Martian surface—the wreckage of the Polar Lander, its parachutes, and the scorch marks of its retro-rockets. Later observations failed to find the white dot assumed to be the lander; it may have been an artifact of the camera, a “noisy pixel.”*! Once again, we were operating at the limits of our technologies. Once again, we may have seen what we hoped to see. The most probable scenario, at least during the foreseeable future, might be called Discovery Without Contact... we obtain unequivocal proof that intelligent ET’s exist (or have existed), but in a manner that excludes If there have been alien visitors to our solar system, we cannot assume that they are recent. A probe sent our way a million years ago might still be circling lifeless about the Sun. Finding such evidence in our own Direct Contact Astroarchaeology communication. —Arthur C. Clarke, 1993°?