Book Reviewed: Goldilocks and the Water Bears: The Search for Life in the Universe, by Louisa Preston

Searching for habitable worlds

Earth has a unique spot in the solar system; it is just at the right distance from the Sun so that water stays in liquid form so that life could be born and evolve. A protective shielding of the atmosphere from harmful ionizing radiation from the parent star would be essential for sustained evolution. The planet must also have a stable atmosphere for life. The habitable worlds could be rocky planets or rocky moons as we have been learning from recent discoveries that Europa and Ganymede, two Jovian moons, and Enceladus, moon of Saturn have oceans of water beneath then surface and likely to have some primitive form of marine species. Plume of ice particles and liquid water are detected from Europa and Enceladus. NASA hopes catch the water from hundreds of miles long geysers and look for marine species.

Author Luisa Preston systematically explores various aspects of habitable worlds including the origin of life; the planets that can support and sustain life; looking for habitable worlds beyond solar system and how we can colonize Mars. Developments in technology, advanced telescopes, and new methods to identify and evaluate the habitable worlds have made significant strides in astrobiology. A number of habitable worlds have been reported since this book has been written.

A brief discussion of the current state of discoveries of exoplanets is as follows: It is progressively becoming evident that we have to treat life as a cosmic phenomenon whose emergence and driving forces should be viewed independently from the natural history of Earth. We are learning that life may be born and thrive in the harshest environments such as severe droughts, in presence of toxic compounds, extreme cold temperatures and even certain amount of ionizing radiation from the harshest environments. It has already been detected and identified as Tardigrades (water bears) on earth. They are microscopic animals that survive exposure to space and survives over sub-zero temperatures, unrelenting solar winds and an oxygen-deprived space vacuum.

Planets come in a huge variety of sizes and orbits. Some are gas giants hugging close to their parent star; others are icy, some rocky. NASA and other agencies are looking for a special kind of planet: one that’s the same size as Earth, orbiting a sun-like star in the habitable zone. As of now, according to NASA, there are 3394 confirmed exoplanets; 1250 are ice giants; 1006 gas giants; 777 super earths: 348 terrestrial and 13 exoplanets are of unknown nature. Among these, the most earth like planets are; Kepler 181f (1.11 times Earth radius); Kepler 442b (1.34 times Earth); Kepler 438b (1.1 times Earth); Kepler 62f (1.41 times Earth); GJ 66.7C c (1.5 times Earth) and Wolf 1061c (1.64 times Earth). In August 2016 a planet orbiting Proxima Centauri known as Proxima b, (1.3 times earth) was discovered. It is a rocky world, residing in the star's habitable zone, just 4.7 million miles from its host star (Earth is 93 million miles from Sun), and completes one orbit every 11.2 Earth-days. The exoplanet is tidally locked, which means it does not spin on its own axis like Earth. Moon is also tidally locked to Earth and shows only one face to Earth.

Mars exploration by three NASA rovers have yielded a wealth of information; Life forms existed on Mars billions of years ago. But when the planet lost its magnetic field, it had nothing to block the solar wind, which slowly bled off the planet's atmosphere. This complicated the evolution of a biosphere. The ionizing radiation broke up organic molecules. If life was on Mars in the past, when the planet was wetter with a thicker atmosphere. Then organisms could have gotten a foothold, life could have then adapted to a higher-radiation environment over time and retreated deeper underground for protection.

Another star that is currently drawing enormous interest in the news is the "Tabby's Star," also known as KIC 8462852 found by the NASA's planet-hunting Kepler space telescope. This shows dramatic dips in brightness, this brightness change has been attributed to orbiting comets around the star or alien mega structure built by an advanced civilization.