Book Reviewed: Alien Earths: The New Science of Planet Hunting in the Cosmos by Dr. Lisa Kaltenegger

An exploration of life in the cosmos The book briefly discusses the methods astronomers use to detect exoplanets and describes briefly extrasolar planets that may support life. Her narratives are not so engaging with personal anecdotes, such as drinking coffee in a European city than discussing alien life. Her drifting into personal stories is not appealing. With respect to finding alien life, certain things have to be imperative for planet formation and evolution, such as low-mass exoplanets of less than ten-Earth masses, smaller than 2.5 Earth radii that are likely to be rocky. Large mass planets are generally gas giants like Jupiter and Saturn that are unlikely to have life. But rocky planets do not guarantee life, they need to have bio-signatures in their atmosphere that support life, like carbon, water and oxygen, the other essential elements, and molecules necessary for life to form, and its gradual evolution. Planets in the habitable zones around solar-like stars are helpful to investigate, and they must have Earth-like periods like Kepler-725 c that has a period of 207.5 days around its star that must have a stable orbit (Kepler-725 c doesn’t). Surface planetary habitability requires an orbit at the right distance from the host star for liquid surface water to be present, geophysical, and geodynamic aspects, atmospheric density, radiation type and intensity, and the host star's plasma environment. The magnetosphere, like we have here on Earth, will help an extrasolar planet for sustained life evolution over hundreds of millions of years. Some of the promising alien planets also have shortcomings in terms of finding life: for example. 1. The planet Proxima Centauri b is at a distance: 4.2 light-years (closest exoplanet to Earth), Star: Proxima Centauri (a red dwarf), Size: 1.1 times Earth's mass, Orbit: Habitable zone (may allow liquid water), Promise: Rocky planet, potentially Earth-like surface temperatures, and challenges: Its star emits strong solar flares, possibly harmful to the planetary atmosphere 2. TRAPPIST-1 System, distance: 39 light-years, Star: TRAPPIST-1 (ultra-cool red dwarf), number of planets: seven Earth-sized planets, at least three in the habitable zone (TRAPPIST-1e, -f, -g), promise: High potential for rocky surfaces and stable orbits likely have water, and challenges: close orbits may cause tidal locking (same side always faces star); stellar activity may strip atmospheres 3. Planet Kepler-442b, Distance: 1,200 light-years, Star: K-type (orange dwarf), Size: 1.3 times Earth's size, Orbit: In the habitable zone, Promise: High habitability score; stable sunlight from its star, and Challenges: Far away; no atmosphere confirmed yet (1,200 light years from Earth) Our technology allows detection of alien planets only in Milky Way galaxy, but the estimated number of galaxies in the observable universe is about 2 trillion, according to data from the Hubble Space Telescope and later studies. Readers interested in the search for extraterrestrial life, I recommend articles from well-known science magazines like Scientific American, Discover, National Geographic, Journal Nature, NASA Exoplanet Archives, and other science focused magazines some of which are available at your local public libraries.