Did you know that in the 19th century it was widely believed that the other planets in our solar system were likely inhabited? At the same time, the quality of telescopes was rapidly increasing, making it possible for astronomers to see and sketch the incredible details of the geography of Mars. As we’ll see the initial excitement fades as science begins to cast doubt on the possibility of life on our planetary neighbor.
As astronomers charted the features of the red planet, many believed they were seeing oceans that confirmed ideas about the likelihood of life on Mars. Later, observations of canals and apparent straight lines on the surface of Mars seemed to offer evidence of intelligent life and civilizations on the planet.
We know now that there is no intelligent life on Mars. Understanding the history of the arguments around that possibility offers insight into how evidence and authority work in scientific reasoning and argumentation.
Mars Presumed Inhabited
An 1831 astronomy textbook, The Young Astronomer, explained, “To the people who live on Mars, this earth probably appears larger than Mars does to us” (27). This was not simply a colorful turn of phrase. In the 1830s many astronomers believed Mars, the other planets, and even the sun, were inhabited.
Our image of Mars developed along with advancements in the quality of our instruments to study it. As that picture came into focus, similarities between Mars and Earth, and in particular the belief that dark portions of the planet were oceans, lead many to speculate about the possibility of life on the planet.
For example, in Celestial scenery or, The wonders of the planetary system displayed (1838) astronomer Thomas Dick suggested that “There is land and water analogues to those on our globe” and further that, “from the size of the dark spots, about one third or one fourth of the surface of that planet is covered with water.” Based on this evidence he suggests, “respecting the physical and moral state of the beings that inhabit it, we might be apt to conclude that they are in a condition not altogether very different from that of inhabitants of our globe” (p.139). Much of this work was grounded in the notion of teleology, that everything in nature serves a purpose in a divine design. If the planets were places like earth, this line of reasoning suggested that a creator would have put life there like he did here.
The Plurality of Inhabited Worlds
By the 1860’s the idea of life on other worlds had become particularly popular in the works of French author and astronomer Camille Flammarion. His book La pluralité des mondes habités (The Plurality of Inhabited Worlds, 1862) brought considerable attention to the idea.
His ideas about life on Mars also made their way into his popular astronomy books. English translations of books, like The wonders of the heavens (1871) and Astronomy for amateurs (1904) helped to disseminate his ideas. Throughout these works Flammarion devotes considerable discussion to the amount of water and ice on Mars. Between these books, how early maps of Mars were drawn and various interpretations of the light coming off the planet many scientists and astronomer’s believed that Mars had oceans or seas.
Read More – Seeing and Interpreting Martian Oceans and Canals
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