Last week, a team of astrophysicists from the University of Cambridge announced that they had discovered the “strongest indication” ever of extraterrestrial life. The source did not come from Mars or Venus or any nearby moon. It came from K2-18b, a massive planet some 120 light-years from Earth.

If this finding checks out, it is, without question, one of the most important discoveries in the history of science. But many scientists think that ... well, it might not check out at all.

Today’s guest is Sara Seager, a celebrated astrophysicist at MIT. Seager is a pioneer in the study of exoplanets and their atmospheres. She has done as much as practically anybody to develop the science of interpreting light from faraway stars to make inferences about planets. In today’s show, Seager and I slowly worked our way up to last week’s announcement by building a foundation of the basic science at play. What are exoplanets? How do we know that they’re there? How do we have any idea about the chemicals present on that planet if we can’t send probes to test their air? What does the K2-18b finding really tell us? And what larger philosophical questions about life and aliens are raised by this new science of exoplanet atmospheres?

If you have questions, observations, or ideas for future episodes, email us at PlainEnglish@Spotify.com.

Host: Derek Thompson

Guest: Sara Seager

Producer: Devon Baroldi

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