How accurately could late 50s - early 60s humans have mapped the solar system? What if early SETI investigations had focused on our own solar system, rather than distant stars?
Given the technology that existed around the 1950s, how much surveillance would humanity be able to do? This is in the era between Sputnik and Apollo 1, so various governments and scientific organizations would have had different equipment and personnel to devote to the task. So this change of focus would have impacted the way various governments, scientific organizations and civilian groups approached the search for intelligent life in space, and altered the focus of technological development.
What were the near-space observation capabilities of radio telescopes and related devices at that time? For example if Cornell University's Project Ozma or Ohio State University's Big Ear were used to look more closely at our own solar system, rather than distant stars, what would they have been able to detect or confirm?
If answers can address what kinds of information mid-20th-century technology could have detected, what level of detail, how often various regions could be scanned etc - that would be wonderful. I would also love recommendations about other scientific developments from that era which might be relevant to this topic.
(Note: I'm doing this research for an alternate-history science fiction writing project. I've edited the question to only ask about real, historical science, since the goal is a narrative that accurately represents the past as much as possible.)
I recall hearing Professor Lovelock about 10 years ago, describing a discussion with his students in the 1960s - what observation would indicate life on another planet? They concluded that spectroscopic analysis would show that the chemistry of the planet was inconsistent with the planet's age. A slower than expected rate of entropy would indicate the presence of life, because the chemistry of Earth life uses photosynthesis to build giant molecules which store energy by absorbing solar radiation
Spectroscopic analysis was used to examine of the atmosphere of Mars in the 19th century, many decades earlier than the context of your question. Before the space race began, scientists had already seen enough to rule out the possibility of life on other planets in the solar system
Lovelock's discussions about extra-terrestrial life led to his Gaia hypothesis, a set of models which demonstrate that Earth's current atmosphere and ocean chemistry emerged from billions of years of life on Earth