Book Reviewed: Astrobiology - Understanding Life in the Universe by Charles S. Cockell

Looking for life elsewhere in the universe

Does anyone think that planet Earth is unique in Milky Way galaxy? Or do we believe that human beings are peculiar in this universe? If there are planets elsewhere in the universe, are they habitable, and do they sustain millions of years of species evolution?

The author considers several aspects of astrobiology: planetary science, life’s Structure, building the biomolecules, especially, the CHNOPS (Carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur), energy for life, limits of the bio-space, and the ancient history of early earth. One of the fundamental questions in search for extra-terrestrial life is do they have similar geological conditions as we have? The bio-space gives us a basis for a first-order assessment of the habitability. If we find a planetary environment that has physical and chemical conditions suitable for life, we are motivated to explore it and see if it has liquid water, energy supplies and basic elements that build life. Other forms of planetary life could exist that uses other elements and biomolecules and perhaps different biochemistry!

Many environments on the Earth are of interest in astrobiology, extreme temperatures, extreme pH, high salt, toxic-chemical environments and deep oceans. Currently, we have more than 4,000 extrasolar planets discovered. The distribution of extrasolar planets is diverse, different sizes, different physical and chemical characteristics. TRAPPIST-1 star system looks like our solar system and hosts seven planets that are potentially Earth-like. It is about 40 light years from us. Another exoplanet is K2-18b that is 124 light years from us contains water vapor in its atmosphere and exists in the habitable part of its star system. In our solar system, Jovian moons like Europa, Ganymede, and Callisto are known to have oceans beneath the surface. It is also reported that the moons of Saturn such as Enceladus, Titan and possibly Dione are also known to have liquid water oceans. Enceladus is among NASA’s top targets in the search for life beyond Earth because it appears to have three of life’s most important ingredients: the right chemical ingredients (such as carbon or hydrogen), available energy and liquid water. Current evidence suggests that there is microbial life below the surface of Mars in deeply buried oceans.

The author systematically explores various pathways that led to the complex biosphere on Earth. This work is a tour de force that offers a unique perspective on the question that puzzled human beings for centuries. Are we alone? Based on our current understanding, we are still not sure, but there are helpful biosignatures elsewhere, and the list of habitable planets are growing.