Identifying the top three astrobiologists was difficult, as many researchers have made significant contributions to the field. Here are my top three big names who have made significant contributions to the field and are widely recognized for their work:

1. Carl Sagan was an astronomer, cosmologist, and astrobiologist known for his popular science writing and work on the search for extraterrestrial life. He was the co-author of the book “Intelligent Life in the Universe,” considered a classic in astrobiology.
2. Lynn Margulis was a microbiologist and evolutionary theorist. She is known for her work on the endosymbiotic theory, which proposes that the eukaryotic cell, the type of cell that makes up most “evolved” life on Earth, evolved through the integration of multiple simpler cells. For example, a tiny energy-harvesting bacteria could have entered another bacteria for protection while giving its host bacteria the ability to harness energy. Over time, this energy-harvesting bacteria became the organalle, mitocondria.
3. Christopher McKay is an astrobiologist who has significantly contributed to our understanding of the potential for life on other planets. He has researched Mars’s habitability and has played a leading role in the search for microbial life on the planet.