There was always the possibility that the planet race or races could not survive on earth, or that their communications did not include the methods that we used. But I found that hard to believe. Such a superior race would certainly be able to master our radio operations, or anything else that we had developed, in a fairly short time. And it should be equally simple to devise some means of survival on earth, just as we were already planning special suits and helmets for existence on the moon. During a talk with a former Intelligence officer, I got a key to the probable explanation. “Why don’t you just reverse it—list what we intend to do when we start exploring space? That’ll give you the approximate picture of what visitors to the earth would be doing.” Naturally, all the details of space plans have not been worked out, but the general plan is clear. After the first successful earth satellites, we will either attempt a space base farther out or else launch a moon rocket. Probably many round trips to the moon will be made before going farther in space. Which planet will be explored first, after the moon? According to Air Force reports, it is almost a certainty that planets outside the solar system are inhabited. But because of the vast distances involved, expeditions to our neighboring planets may be tried before the more formidable journeys. More than one prominent astronomer believes that life, entirely different from our own, may exist on some solar planets. Besides Mars, Jupiter, and Venus, there are five more that, like the earth, revolve around the sun. One of the prominent authorities is Dr. H. Spencer Jones, Astronomer Royal. In his book _Life on Other Worlds_, Dr. Jones points out that everything about us is the result of changing processes, begun millenniums ago and still going on. We cannot define life solely in our own terms; it can exist in unfamiliar forms. “It is conceivable,” Dr. Jones states in his book, “that we could have beings, the cells of whose bodies contained silicon instead of the carbon which is an essential constituent of our cells and of all other living cells on the earth. And that because of this essential difference between the constitution of those cells and the cells of which animal and plant life on the earth are built up, they might be able to exist at temperatures so high that no terrestrial types of life could survive.” According to Dr. Jones, then, life could be possible on worlds hotter and drier than ours; it could also exist on a very much colder one, such as Mars. Even if a survey of the sun’s planets proved fruitless, it would decide the question of their being populated. Also, it would provide valuable experience for the much longer journeys into space. No one expects such a survey until we have a space vehicle able to make the round trip. One-way trips would tell us nothing, even if volunteers offered to make such suicidal journeys.