What Is the Habitable Planet ?

                                    What Is the Habitable Planet?


What Is the Habitable Planet ? | Explained in 2.2 Minutes

A planet’s habitability, or ability to harbor life, results from a complex network of interactions between the planet itself, the system it’s a part of, and the star it orbits. The standard definition for a habitable planet is one that can sustain life for a significant period of time. As far as researchers know, this requires a planet to have liquid water. To detect this water from space, it must be on the planet’s surface. The region around a star where liquid surface water can exist on a planet’s surface is called the “habitable zone.” However, this definition is confined to our understanding of current and past life on Earth and the environments present on other planets. As researchers learn more and discover new environments in which life can sustain itself, the requirements for life on other planets may be redefined.

Different types of planets may drive processes that help or hinder habitability in different ways. For example, planets orbiting low-mass stars in the habitable zone may be tidally locked, with only one hemisphere facing the star at all times. Some planets may be limited to only periodic or local habitable regions on the surface if, e.g., they experience periodic global glaciations or are mostly desiccated. In order to understand the full range of planetary environments that could support life and generate detectable biosignatures, we require more detailed and complete models of diverse planetary conditions. In particular, understanding the processes that can maintain or lead to the loss of habitability on a planet requires the use of multiple coupled models that can examine these processes in detail, especially at the boundaries where these processes intersect each other.

The availability of liquid water is the most important factor that makes a planet habitable, because water is a very effective polar molecule and hence an excellent solvent and facilitator for the complex chemistry of life. Its presence presupposes a planet with a significant mass that guarantees the presence of a substantial atmosphere, and a reasonable spinning rate to avoid overheating. It also implies that the planet is at moderate distances from its central star, a range that is called the Ecosphere or the Habitable Zone. Since the evolution of life to high intelligence seems to take billions of years, it requires also that the central star must be neither too massive, that will produce a lot of lethal UV radiation and will have too short a life-span to allow life to evolve, nor of very small mass which will be producing too feeble a radiation to sustain life. The detection of free Oxygen in the atmosphere of a planet is very strong evidence for the presence of life because Oxygen is highly reactive and would rapidly disappear by combining with other elements unless it is continuously replenished by life as the by-product of the process of photosynthesis that builds food for life (sugars) from CO2 and H2O.

For additional information:

https://www.planetary.org/articles/what-is-the-habitable-zone

https://www.amnh.org/exhibitions/permanent/planet-earth/why-is-the-earth-habitable

https://exoplanets.nasa.gov/search-for-life/habitable-zone/

https://www.mso.anu.edu.au/~charley/papers/KastingReviewFinal.pdf

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