Carl Sagan is one of the most well-known scientists of the 20th Century, both as the author of the critically acclaimed book, Cosmos and the face of the immensely popular early-80s TV series of the same name. But in addition to his well-documented interests in planets and galaxies, Sagan also had a secret fascination with a plant that grows right here on Earth – cannabis.

According to Leafly, Sagan was a lifelong marijuana user and privately espoused a belief that cannabis was a positive force for not only himself, but humanity as a whole. In public, Sagan kept his cannabis usage and support to himself, for fear that the stigma of cannabis use could destroy his career. In 1969, Sagan wrote an anonymous essay for the book Marihuana Reconsidered, using the pen name “Mr. X.”

“The illegality of cannabis is outrageous, an impediment to full utilization of a drug which helps produce the serenity and insight, sensitivity and fellowship so desperately needed in this increasingly mad and dangerous world,” Sagan wrote.

Sagan also spent time researching the history of cannabis use, detailing how Pygmy hunters cultivated cannabis as their only agricultural crop, and smoked it ritually before fishing.

“It would be wryly interesting if in human history the cultivation of marijuana led generally to the invention of agriculture, and thereby to civilization,” Sagan proposed.

A recent exhibit of Sagan's personal correspondences at the Library of Congress has revealed the extent of Sagan's efforts to advocate for cannabis reform. In his personal effects, there were four full boxes of letters in which Sagan expressed his concerns over the harmful effects of drug prohibition.

The scientist also argued for medical marijuana, even discussing the “irrational official government position” that terminal patients should not be prohibited from cannabis use due to the risk of addiction during a recorded interview.

“There’s no evidence whatsoever that it’s an addictive drug, but even if it were – these people are dying,” Sagan argued. “What are we saving them from?”

Sagan himself used medical marijuana during the final days of his life while fighting cancer and said that cannabis helped him “refocus on the beauty of life in the midst of such torture,” according to Sagan’s wife, Ann Druyan. Druyan continued to advocate for cannabis reform after Sagan's death, serving as president of NORML from 2006 to 2010. “For me [cannabis] is a sacrament, something that should be used wisely in the context of a loving family existence,” she said.