Space Review: Review: Alien Earth


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Alien Earth: The New Science of Planet Hunting in the Universe
By Lisa Kaltenegger
St. Martin's Press, 2024
Hardcover, 288 pp., illus.
ISBN 978-1-250-28363-4
US$30

In a paper published last week, astronomers reported the first detection of an atmosphere around a rocky “Earth-like” exoplanet. However, the problem with the announcement was that the exoplanet in question, 55 Cancri e, did not look like Earth: it had a diameter twice the size of Earth and a temperature of more than 1,500 degrees Celsius. (“Describing 55 Cancri e as 'rocky', however, may give the wrong impression,” a press release said, adding that its surface is probably molten.) It is thought to be composed of carbon monoxide and/or carbon dioxide. Combine that with the atmosphere, and 55 Cancri E doesn't seem particularly friendly to life.

However, astronomers hardly consider the discovery a shock, instead pointing out how it shows the James Webb Space Telescope, which made the observation, could help find other potentially habitable worlds. “This is truly enabling a new type of science,” Renyu Hu, lead author of the study, said in a statement.

She writes, “It's important to ask the right questions in science because you only have one lifetime to figure things out.” But, she adds, “some answers are written in the night sky.”

Since astronomers found the first exoplanets around a Sun-like star nearly three decades ago, scientists have studied which planets might be habitable. It coincides with the academic and professional career of Lisa Kaltenegger, director of the Carl Sagan Institute for the Search for Life in the Universe at Cornell University. in his new book alien earthShe describes efforts to discover worlds beyond our solar system, including worlds that could support life.

This book is, largely, a comprehensive introduction to exoplanet science and astrobiology. Kaltenegger examines a number of key topics in areas ranging from what is needed to make a world habitable or even habitable, to the diversity of exoplanets discovered to date, many of which scientists have Once thought impossible. For those who have been following the search for exoplanets and habitable worlds, much of this material will be familiar, but it is well presented here. The book includes anecdotes from his own career as well as other aspects of his life.

Kaltenegger is studying how exoplanets form and determining their habitability. It's an effort that goes beyond astronomy, as she makes clear in the book, as exoplanet science evolves into an interdisciplinary field that includes geology and biology. She describes how in the book she set out to conduct laboratory research at Cornell to determine what the spectra of those worlds would be based on their composition and the presence of life. This also includes dealing with clashes in terminology, with simple terms like “metal” and “glass” meaning different things to astronomers versus geologists, he said.

That interdisciplinary work, language difficulties aside, is vital to the future of exploration of worlds beyond Earth where life might exist. She now holds the same office as Carl Sagan at Cornell and leads the institute named after him, which brings together researchers from many fields on major questions in astronomy. She writes, “It's important to ask the right questions in science because you only have one lifetime to figure things out.” But, she adds, “some answers are written in the night sky.”


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