What makes A Planet Habitable


Hey there, fellow Inquirers! In this article, we're trying to answer what does it take for a planet to be habitable. We'll have to take into consideration what makes Earth so special, what planetary characteristics does it have so it can support life and what will our next home in space need to have to satisfy the preconditions necessary for life, and human life in particular. Throughout this Article, we’ll be thinking about features of the only planet for which we’re certain that it supports life and try to make some conclusions about life sustainability on planets in general. The distance from Sun to our planet is roughly 149,597,871 kilometers or 92,955,807 miles. This number is fairly significant, as it is one of the fundamental units for measuring length in astronomy, known as the astronomical unit So, the average distance of the Earth’s orbit from the Sun is one astronomical unit. The first precondition a planet has to satisfy to support life as we know it is to be situated in the, so called ‘Goldilocks zone’ and it usually depends on star’s luminosity. Basically, if the planet was too close to its star, all the water would evaporate. If it was too far, all the water would freeze. The Goldilocks zone is “just the right distance” to have liquid water. Our planet is rushing around Sun at 30 kilometers per second or 108 000 kilometers per hour or 67 000 miles per hour. It takes around 365 days and 6 hours for it to make a circle around the Sun. However, A planet’s rotation around its axis usually has the more immediate effect on the weather. During its rotation around Sun, the Earth rotates around its axis 366,26 times. There are two types of a day. The first one is Earths’ rotation around its axis. That day lasts for 23 hours, 56 minutes and 4 seconds and is measured by looking at the very distant stars. But, since the Earth is orbiting the Sun, it has to rotate just a bit more to face the Sun and it’s called a solar day. The Earth’s axial tilt is yet another very important feature that Earth has. A cataclysmic event happened in the good old days of the early Earth, some 4.5 billion years ago, when a proto-Earth planet named Gaia collided with Theia, a planet roughly the size of Mars, which caused the Earths axial tilt. It marked the start of THAT period, the period of planetary self-discovery, our planet’s adolescence, the process of our planet reaching its maturity. It is believed that these early planets fused together by the force of gravity making the chunk of mass that we today call Earth. The leftover piles of space junk blended together to form the Moon. As mentioned, this collision was the main cause of the Earth’s tilt which causes Earth’s climate to have seasons. Seasons play a huge role in the evolution by natural selection. It is believed that seasons are a good thing and that humanity would suffer without them. Humans would likely never advance beyond living in tiny, scattered settlements, fighting for their lives and dying from insect-borne diseases. The Earth without the tilt would probably have climate belts, the coldest ones being the ones that are the furthest from the equator. Humans would never survive in extreme colds, so they would gather in the tropical belt. It is possible that there would be no ice ages OR there would be one ice age that would last forever. Living creatures would’ve never evolved to adjust to the seasons. They would reproduce throughout the entire year, they would never hibernate, there wouldn’t be migration etc. There’s even a possibility that huge masses of water would gather around the poles and that the sea level would be much lower. One thing is certain, If there were no seasons, it would be much easier to shop for clothing. The Moon was also formed by the Great Collision of 4.5 billion B.C. The Moon is located approximately 384,402 kilometers or 238,856 miles from Earth. If there was no Moon, there would be no Moon landing conspiracy theories. Our planet would be different better. Just kidding nights would be much darker. Tides would still exist, but they would be around one-third or half of the current intensity, because of the Sun. The days would also become shorter. This phenomenon is called tidal friction and it is, believe it or not, caused by the tides. Tides probably had a crucial role in transferring primordial lifeforms from one large body of water to the other, which was a necessary condition for life to evolve in the first place. The Moon also stabilizes Earth’s orbit around the Sun, so it is not as chaotic as it would otherwise be, thus likely having an indirect positive outcome on evolution of life. Considering how much of a positive impact the ancient collision had on Earth and the development of life, we are very lucky that our planet had ‘rocky’ past The Universe is a very hostile place for life and stars can have sudden and violent outbursts of radiation. That’s why planets need to have radiation protection. The Earth has quite an effective radiation protection in the form of its magnetic field. If it didn’t exist, compasses would not function, birds would not migrate because they wouldn’t have evolved magneto receptors. This goes even further. If, against all odds, life and humans somehow evolved in spite of constant bombardment of deadly space radiation, we would not be able to develop most of our modern infrastructure. It simply could not function with constant solar flares and coronal mass ejections that would prevent any attempts of building any type of electrical devices, let alone the whole grid that is the lifeblood of contemporary global economy. Above all, solar winds would easily just blow away the Earth’s atmosphere, so any talks about electrical grid or economy or any social concept or structure for that matter is just redundant. One thing is certain, we would be in quite dissatis factory position if it weren’t for our planet’s magnetic field. It’s probably the case for any type of life form. Let’s say a planet did satisfy all the above conditions. Would such a planet be able to develop life? We’re not quite there yet! The important factor is also a rocky surface. Life can hardly form on a gas giant like Jupiter or Uranus. In addition to that, we need to have an atmosphere that traps heat and provides chemicals essential for the development of life, like oxygen, nitrogen or carbon dioxide. The atmospheric pressure should not be too high or too low, something around Earth’s 101,325 kPa is neat! The temperature should not be lower than -20°C or -4 °F and it shouldn’t be higher than 121 °C or 250 °F. These are not average values but the maximum temperatures that lifeforms can survive. Only the most resistant microorganisms can survive on these temperatures. Most other organisms prefer living in habitats where the average temperature is around 15°C or 59°F. Gravity plays a huge role as well. It can vary, but it shouldn’t vary too much from the Earth’s average of 9.81 meters per second squared, or 1g. Mars, for example, has 3.71 meters per second squared which is still considered fine, but it shouldn’t get much lower than that. If you were to evolve on the Red Planet, you would be much taller than people on Earth. The main reason for that is gravity, but not in a way you think. The human heart wouldn’t have to work as hard to pump the blood into the highest parts of your body, mainly the head, so weaker gravity would allow for taller growth. Also, your bones and muscle mass would be much weaker, but it is believed that genetic mutations would allow us to fight these “problems”. On the other end of the gravitational spectrum, if you were to evolve on a planet that has, let’s say 2g, you would be much stronger and shorter. It would feel like you were forced to carry yourself on the shoulders every single day! There were some experiments on chickens in similar conditions and they have shown that chickens wouldn’t evolve to be much different than they are today. But still, for most of higher lifeforms, living in conditions where gravity is stronger than this is hardly imaginable. We need to emphasize it again: water is crucial! It’s essentially the factor that determines the “Goldilocks zone”. That’s why we need to repeat it: in order to sustain life, planets needs to have liquid water for cells to grow, as well as dissolve and exchange chemicals! And chemicals, mainly in the form of nutrients, have a huge role in emergence and evolution of life. At the end, there are two schools of thought when it comes to evolution of life on other planets in conditions not so similar to those on Earth. The first one, the boring one, is that evolution always finds similar solutions. This argument is backed by the fact that many species interdependently evolved in different areas and environments on our planet. In other words, if the life evolves in oceans, its forms will be similar to fish and dolphins, if it evolves on the land, its forms will be similar to the kinds we can find on Earth’s land. The other school of thought goes in the opposite direction. According to this school, lifeforms can evolve in many ways, depending on the outside factors like the features of the planet or the star that it orbits. It is possible that lifeforms would receive and process information much differently. For example, they wouldn’t have receptors for light or sound waves, but would communicate and perceive the world around them in radically different ways. We’re not sure how much this hypothesis is feasible, but it is much more exciting to think about it. Well, we just provided you with food for thought, and quite tasty one. These are just some of the most important features that a planet should have to support life. There are a lot more of these. The point is: the Universe is hostile. Very hostile. We are very lucky to be born on this planet that has all the necessary features to sustain us. Life is truly a gift. Our planet is a gift. 

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