Paperback cover of 1951 edition of "Life on Other Worlds"

This is the colorful cover of the 1951 Mentor paperback edition of astronomer H. Spencer Jones' "Life on Other Worlds," which was originally published in 1940.

In a nice example of Otto Family Synergy, it pairs nicely as a then-and-now companion with an online "Astrobiology and the Search for Extraterrestrial Life" course that my wife recently completed and documented on the Our School at Home blog.¹

Spencer Jones was England's Astronomer Royal from 1933 to 1955.² The book includes chapters about the necessary conditions for the existence of life, the evolution of Earth's atmosphere, Venus, Mars, the origin of our solar system and much more. Generally, Spencer Jones thought the existence of life on other planets was likely, as evidenced by these excerpts from the book:

• "Though conditions are heavily weighted against suitability for the existence of life, it is concluded that there must nevertheless be many other worlds where the appropriate conditions are to be found and where therefore we may suppose that life in some form or other does actually exist."
• "Yet though these restrictions severely winnow down the possible abodes of life in the universe, we cannot resist the conclusion that life, though rare, is scattered throughout the universe. It may be compared to a rare plant, whose distribution is widespread, but of which never more than a single specimen is found at a time."

Spencer Jones also makes the following statement, though, regarding Mars:

"The evidence that there is vegetation on Mars is almost conclusive, and affords very strong presumptive evidence that life will appear when conditions are suitable for it."

The notion that there might be plant life on Mars persisted in the scientific community until at least the late 1950s. And the overall debate about any kind of life on Mars remains alive and well today.

Footnotes
1. Of the online course, Joan writes:

"The interesting thing is, there are about 139,000 people taking this class with me. The discussion forums and Facebook group are actually too much to keep up with most of the time, and my fellow students range from gifted 12-year-olds to 70-year-old Ph.D.s and everyone in between, which makes it a MUCH more diverse experience than traditional college was for me."

2. While Spencer Jones was optimistic about the idea of life on other worlds, he had his doubts about the practicality of space travel and might or might not have uttered the quote "Space flight is bunk" in the late 1950s. (It's debated.)