What makes the Earth habitable? There are many factors, but most are related to a single aspect of our world: it orbits the sun only at the right distance. Each star is surrounded by a region called the habitable zone. This region is around a star where water could potentially exist in liquid form on the planet’s surface. Water is used to determine the habitable zone because it is the main ingredient that life uses on Earth. One of NASA’s motto is “Follow the water.” However, it should be noted that not every world in the inhabited area has a guarantee that liquid water flows on its surface. In our solar system, the habitable zone extends from just beyond the orbit of Venus to Mars, but none of these worlds are currently home to oceans, lakes or rivers. Instead, the habitable zone is simply a way to determine the potential habitability of a world. Not every planet in the habitable zone will be habitable. The habitable zone determines the potential of the world to become habitable.
Different inhabited areas
Depict planets orbiting a red dwarf star. NASA
The habitable zone varies from star to star. The more massive and hot a star is, the farther from the star is the habitable zone. For the smallest stars, the habitable zone is much closer to the star. High-mass stars burn and emit huge amounts of deadly radiation, making it even more difficult for the planet in the habitable zone to form an atmosphere. In addition, high-mass stars are reluctant to stay very long. If our sun were a high-mass star, it might have become a supernova before life even began. The red dwarf stars have shown a lot of promise, simply because more Earth-sized and super-Earth-sized planets have been discovered around them than any other class of stars. But they also have their problems. First, although smaller and colder than most stars, red dwarfs are extremely active, erupting solar flares and solar storms at much higher speeds than most stars.
Solar storms would pose a significant risk to habitability, as the planet must orbit very close to a red dwarf to be in the habitable zone. Second, the close proximity needed to be in the habitat of a red dwarf also means that all the planets in that region will be tidal locked, which means that one side of the planet is always facing the star. In contrast, the other side is always turned away. Half of the planet will live an eternal day, while the other half will live an endless night. Unfortunately, this drastically affects the surface temperature, usually causing the day to be too hot and the night to be too cold. Interestingly, the region separating night from day can potentially serve as an oasis for the development of life, a region that will experience an eternal sunset (or sunrise). In addition, some models predict that, depending on the planet’s atmosphere, heat from the day side may circulate to the night side, maintaining temperatures and allowing liquid water to form on the surface. For now, the sun-like stars seem to be the most promising for life. The sun is active, but solar storms are generally not extreme enough to threaten life on Earth. The temperature of the sun is neither too hot nor too cold, which allows us to orbit at such a distance that our planet is not blocked by the tide. In addition, the sun burns its hydrogen constantly, which allows it to exist long enough for life to develop and flourish long before it dies.
Habitability outside the habitable zone
Europe is a potentially habitable moon orbiting Jupiter. NASA
A planet may orbit in the habitable zone and still never become habitable, but is it possible for a planet outside the habitable zone to become habitable? In recent years, scientists have had to rethink living conditions. It is known that only in our solar system a handful of moons orbiting gas giants have habitable conditions such as liquid water. These moons exist far beyond the habitable zone, but conditions allow the formation of liquid water. For example, Jupiter’s moon Europa and Saturn’s moon Enceladus have underground oceans of liquid water. A world can become habitable outside the habitable zone. This realization allows scientists to expand their search for habitable worlds around other stars.
Aiden Rempel June 16, 2022 at Science
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