What Makes Earth Habitable and Why is it Outstanding?

The planet Earth is really special. And the most exceptional feature is that it hosts life because of a one-in-a-million chance. Let’s find out what factors make Earth habitable.

Judging whether a planet is hospitable to life is a complicated subject, but we will cover the ABCs involved.

The Planet Needs to Orbit Comfortably

Firstly, you want to ensure that the light levels shining on the planet are just right. Therefore, consider the “Goldilocks Zone” or the habitable zone for a star.

The Habitable Zone

Liquid water is required for life as we know it. Thus, if water must be in another state, it will probably not host life. For instance, if Earth orbited as close as Mercury to the Sun, the water would vaporize quickly. On the contrary, if Earth were as far as Neptune from the Sun, the oceans would freeze. Neither of these conditions are optimal for life to exist.

Remember that the temperature on Earth is caused by the light from the Sun. Thus, different stars have different distances for their habitable zones. For instance, if the distance of the planet and a red dwarf is as far as Mercury from the Sun, the temperatures of the planet would range from normal to freezing. On the other hand, that same distance from a yellow dwarf like the Sun means that the planet is scorching hot.

However, the “habitable zone” is a bit controversial because it doesn’t account for many factors, including the greenhouse effect. For instance, even if you place Venus 1 AU from the Sun, the temperature would still be inhabitably hot, approximately 359 Celsius (astro.indiana.edu, n.d.)², (NSSDCA, 2020)³. Furthermore, Europa‘s underwater oceans are likely to contain liquid water despite being far from the Sun.

The Spectral Type

Also, the spectral type of the star is essential, and there are three reasons for that.

1. The star’s lifetime
2. The ultraviolet radiation
3. Planets being tidally locked

Based on the three parameters, the most habitable stars are from K3 to F6 type stars. It must also be the only star in the system unless the star is very far away. Otherwise, the climate of the planets surrounding star systems consisting of multiple stars will be unstable.

Then, why are other groups like red dwarfs and A-, B-, and O-type stars excluded? Well, the habitable zones of red dwarfs are so close to the parent star that the planet may be tidally locked. That means one side of the planet is being fried while the other is frozen.

Or rather, if the planet is orbiting a hot star, it will be bombarded by ultraviolet radiation. Although an ozone layer can add protection, the long-term exposure to strong UV light is still harmful. Moreover, the planet on those hotter stars wouldn’t evolve to have life before it dies. That’s because the stars burn their fuel fast.

A Good Neighborhood

There are also other environmental parameters that make Earth habitable. One of them is a good interstellar neighborhood. What’s up there?

Well, we must be grateful that all stars near our Sun are not too hot and massive. If anything under 50 light-years is high-mass, we’ll face a deadly supernova soon. That’s because of the intense gamma-rays and X-rays we’ll face. To learn more about nearby supernovas, please watch this YouTube video. (What If, 2021)⁵.

Let’s go onto the galactic level. Remember that there’s something even more powerful than supernovas — gamma-ray bursts. Suppose a burst is directed to Earth within our galaxy. In that case, it’s devastating as the energy released is enough to destroy our planet and its atmosphere. (What If, 2019).

Aside from the perilous bursts, the galactic center is also a place to avoid. Stars are packed close together due to the gravity of the black hole, and their UV radiation can harm living organisms in the long run.

The Planetary Factors

Now that we’ve found a perfect location to host life, it’s time for the main factors that support life on Earth — the planetary ones.

Everyone knows that a habitable planet needs to have a sufficient atmosphere and liquid water. But, there are lots more to consider.

Protection Layers and an Atmosphere

For life to thrive, we need protection from dangerous things. Luckily, Earth is geared and ready for that.

Thinking of mass extinctions, the first event that pops up in your mind will be asteroid impacts. Fortunately, the atmosphere does that by creating friction and melting any incoming asteroids as long as it’s not wider than 25 meters.

Furthermore, the ozone layer prevents us from getting sunburns by blocking most incoming UV radiation. Most importantly, the atmosphere is what we breathe, and it’s necessary for life as we know it.

But, our atmosphere isn’t good at protecting us from solar wind, so it’s required to have an extra layer. And that shield is a magnetic field caused by the difference of the rotation rate between the inner core and the outer core in the case of Earth.

Because the solar wind is charged, it interacts with magnetic fields. Therefore, our magnetosphere is responsible for redirecting harmful solar particles to the poles and outside our planet. Otherwise, the environment would be life-threatening.

Internal Factors

Still, there are many factors for life on Earth that are caused by the interior. One of them is tectonic activity, which may be circulating the temperature on Earth to make it habitable. (Shannon Hall, 2017).

Rotation and Size

First of all, the rotational period of the planet must be suitable. It can neither be too long nor too short, or the climate would be extreme. What if Earth stopped rotating? Let’s find out the benefits of our current day-night cycle.

Moreover, the axial tilt that causes seasons may be necessary for life. Regular cycles of temperatures help plants to grow. Without that, the animals may either struggle to live in a crowded place or migrate more often than you’ve ever thought.

Additionally, a planet too small or too big is not suitable for life. If the planet is only half as wide as ours, it’ll have a tough time holding its atmosphere. If it’s much larger than our planet, it’ll attract more asteroids and have stronger gravity. It’ll block the magnetic field, and a thicker atmosphere will exist as well. (What If, 2020)⁹.

A Large Satellite

Moreover, the Moon provides us with stability, which is essential for life to form.

It stabilizes our axial tilt, causing seasons to be regular. It also provides us with tidal waves, which are essential to orient marine life. Moreover, the Moon helps slow down our rotation, preventing it from going faster than expected. What if the Moon disappeared? Let’s find out more of the importance here.

Conclusion

So, we’ve explained the basics of what makes a planet habitable. You’ll learn that being hospitable to life is not only about an atmosphere and liquid water. It requires a lot of “rare” circumstances to happen simultaneously. Therefore, it’s better to treasure Earth rather than finding a new interstellar home for now.

References and Credits

1. (2020, November 10). The Habitable Zone | The Search For Life – NASA Exoplanets. Retrieved January 6, 2021, from https://exoplanets.nasa.gov/search-for-life/habitable-zone/
2. (n.d.). Planet Temperature Calculator. Retrieved January 6, 2021, from https://www.astro.indiana.edu/ala/PlanetTemp/index.html
3. (2020, November 25). Venus Fact Sheet – the NSSDCA – Nasa. Retrieved January 6, 2021, from https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html
4. (n.d.). Stars and Habitable Planets – FCAC WWW Members Server. Retrieved January 6, 2021, from http://members.fcac.org/~sol/solcom/habitable.htm
5. What If. (2021, January 1). What If a Supernova Exploded Close to Earth? – YouTube. Retrieved January 6, 2021, from https://www.youtube.com/watch?v=Uyh4JP1ELpY
6. What If. (2019, July 28). What If a Gamma-Ray Burst Hits the Earth? – YouTube. Retrieved January 6, 2021, from https://www.youtube.com/watch?v=jVHnVcZ6YMQ&t=103s
7. NASA Content Administrator. (2017, August 7). Asteroid Fast Facts | NASA. Retrieved January 6, 2021, from https://www.nasa.gov/mission_pages/asteroids/overview/fastfacts.html
8. Shannon Hall. (2017, July 20). Earth’s Tectonic Activity May Be Crucial for Life–and Rare in Our Galaxy – Scientific American. Retrieved January 6, 2021, from https://www.scientificamerican.com/article/earths-tectonic-activity-may-be-crucial-for-life-and-rare-in-our-galaxy/
9. What If. (2020, August 9). What If We Lived on a Super Earth? – YouTube. Retrieved January 6, 2021, from https://www.youtube.com/watch?v=K_2331JPs8g
10. (2019, October 23). What Is a Supernova? | NASA Space Place – NASA Science For Kids. Retrieved January 6, 2021, from https://spaceplace.nasa.gov/supernova/en/
11. Rob Garner. (2019, November 21). Hubble Studies Gamma-Ray Burst With Highest Energy Ever Seen. Retrieved January 6, 2021, from https://www.nasa.gov/feature/goddard/2019/hubble-studies-gamma-ray-burst-with-highest-energy-ever-seen

Image Credits: NASA’s Eyes, Canva, NASA