Goldilocks Zone and the Three Planets

Goldilocks Zone and the Three Planets

Have you ever heard of the story of Goldilocks and the Three Bears? In the story, Goldilocks sneaks into a bear family’s house and comes across three bowls of porridge. She finds that the first one is too hot, the second one too cold, and the third one is just right. Interestingly, there is also a principle called the “Goldilocks zone” in astrobiology. The Goldilocks zone (or habitable zone) is a space shaped like a doughnut around a star, where the temperature is “just right” for water to remain liquid, signaling the potential for life. In our solar system, the Goldilocks zone is a doughnut-shaped area between Venus and Mars’s orbit, with our earth in the middle. The only habitable planet orbiting the Sun is Earth, but there could be thousands of other exoplanets in the universe that have the conditions for liquid water. We can’t be sure yet, but some might even have life.

One example of an exoplanet that suits the Goldilocks principle is Proxima Centauri B. Proxima Centauri is a red dwarf star that is the closest star to our sun by a distance of 4.2 light-years. Although Proxima Centauri B lies in the habitable zone and could have an atmosphere and liquid water, there are obstacles that make it harder for people to settle there. For one, Proxima Centauri B suffers from overwhelming stellar wind pressures from its star. Also, as the planet might be tidally locked to its star, meaning that the same side faces the star at all times, one side might be boiling and the other extremely cold. As of now, we are unsure of whether the planet is rocky, icy, or gaseous. However, because the planet is very close to Earth, it might be the first exoplanet for humans to visit, so we should keep it in mind.

Another example of an exoplanet in the Goldilocks zone is Trappist-1e. Located about 40 light-years from Earth, its star Trappist-1 is a red dwarf star that weighs 0.09 times the Sun’s mass. All of Trappist-1’s seven planets have rocky surfaces like Earth and almost all have water in vapor, liquid, or solid form, which make humans look for opportunities to settle there. Out of these seven planets, Trappist-1e has the best chance of being habitable. Trappist-1e has an ocean and land, and if it has an atmosphere similar to that of Earth, people might be able to live there without gas masks or space suits. One interesting fact is that because Trappist-1 and its planets were formed 3 billion years earlier than our solar system, they might even support life that is more evolved than humans!

The last planet we’ll talk about was recently discovered in January 2020. Orbiting around the star TOI 700, TOI 700 d is the first earth-sized exoplanet discovered in the Goldilocks zone. TOI 700’s other two planets are so close to the star that all their water will boil away, while TOI 700 d luckily sits in the habitable zone with liquid water. Out of all the exoplanets in their star’s habitable zones, there aren’t many with the same size as Earth, which makes TOI 700 d one of the best options for settling. However, the distance of 101 light-years hinders us from visiting in the near future.

All three of these exoplanets have a possibility for harboring life. Even though the possibility that any of them are habitable for humans is very slim, we will continue our discovery of exoplanets. Only about 30 years have passed since we first discovered planets outside our solar system. This is only a start, and we can hope that astronomers will find a new exoplanet with the same conditions as Earth. Who knows? Maybe someday in the far future we will settle on a Goldilocks planet outside our solar system.

By Evan Jee, age 12, grade 6, South Korea. Evan writes: “I am interested in this topic of studying space and planets in school classes. And I usually read science novels or watch movies to understand the detailed aspects. As an international school student, I sometimes have time to discuss with foreign friends as well.”

References and Recommended Resources:

  1. NASA May Have Found the Goldilocks Planet of Goldilocks Planets: TOI 700d 
  2. Earth, our Goldilocks Planet; Datasets from ‘Science on a Sphere’
  3. Goldilocks Meets Desidero by Carl Spetzler, 2011

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