The Goldilocks zone is a region on the globe where temperatures are just right for liquid water to exist.

The “Goldilocks and the Three Bears” fairy tale inspired the Goldilocks zone. Goldilocks is a picky little girl who insists on her porridge being just right—not too hot or too cold. It’s the same with life—at least, the kind of water-based life we’re used to seeing on Earth.

A planet must be “just right,” or capable of supporting life, in order to maintain life. It cannot be so cold that all water freezes, nor can it be so hot that all water boils away.Only planets in the “Goldilocks zone”—or more technically, the “habitable zone”—are regarded as being capable of supporting life.


It will be too hot for liquid water to exist if a planet’s orbit brings it too close to its parent star, and it will be too cold if it is too far out. On the other hand, the actual distances involved in defining the habitable zone differ between stars.

Our own sun is a G-type yellow dwarf, and its habitable zone is well-defined because the Earth orbits the star at a distance of 93 million miles (150 million kilometers).

The habitable zone is substantially closer to the star for M-type red dwarfs, which are smaller and cooler than the sun. According to NASA, the Goldilocks zone is further out for a larger, hotter A-type star like Sirius.

According to, this is because air pressure and composition must also be considered. As a result, the moon, which has no atmosphere, is unable to sustain life on its own.

It’s also vital not to oversimplify the term “habitable.” Even if all of the conditions on a planet are ideal for liquid water to exist, it doesn’t mean it’s populated. We don’t know what additional minor ingredients are required in addition to water and an atmosphere because scientists haven’t figured out the actual origins of life on Earth.

Our solar system is the most researched of all the planets. By predicting the surface temperature of a planet based on the amount of solar heating it receives, theoreticians have determined where its “Goldilocks” zone should be.

So far, the findings corroborate what we’ve observed. The Earth, a liquid planet rich with life, is comfortably located within the habitable zone. Mars, which formerly had an abundance of water but is now a desolate desert, is on the verge of becoming a desert. According to NASA, Venus is a scorching hot planet due to its close proximity to the sun and its super-thick atmosphere.

In the Goldilocks Zone, EXOPLANETS

The discovery of new exoplanets orbiting faraway stars is now virtually routine. But it’s always thrilling when one is discovered in the Goldilocks zone of its parent star.

In the case of Proxima B, which orbits the sun’s nearest galactic neighbor, the red dwarf Proxima Centauri, just over 4 light-years distant, this happened in 2016. Its habitable zone is so small and dark that it is only a few light years away, yet Proxima B—which orbits the star once every 11 days—is comfortably within it, according to the European Southern Observatory (ESO).

Water may exist on all seven planets, but only in a liquid state on the three closest to the habitable zone. On planets closer to the star, it would take the form of atmospheric water vapour, whereas on the farthest worlds, it would take the form of ice. Trappist-1 is one of the proposed objectives for the James Webb Space Telescope, and astronomers are eager to learn more about it.


There’s no reason planets should preferentially form in the habitable zone when a solar system starts, and the TRAPPIST-1 system is unusual in having as many as three planets there.

Is there, however, a theoretical limit to the number of planets that can be crammed into the Goldilocks zone? Sean Raymond, an astrophysicist, answered this question on his site,

It turns out that there is a theoretical limit beyond which the system becomes unstable due to the near proximity of the planets. Raymond created “The Ultimate Engineered Solar System,” which consists of 412 planets in the habitable zone, grouped around eight concentric orbits that rotate in prograde and retrograde directions alternately.

The Theory of Solar System Building:

Sean Raymond, the creator of the “Ultimate Engineered Solar System,” talks about his work in this video.

Raymond writes about the interface of science and fiction at (Image credit: Sean Raymond

How did you come up with such an unusual planet arrangement?

My day job is to figure out how planetary systems arise, how the solar system differs from previously identified exoplanet systems, and which orbital configurations are stable and which aren’t. I wanted to see what kind of orbital architecture would maximize the number of planets in the habitable zone while being stable and not worrying about how the system evolved. Fortunately, I was able to draw inspiration from a number of recent scientific studies. I also used computer simulations to test the most bizarre systems to ensure that everything worked properly.

Why is it referred to as the “ultimate” or “designed” solar system?

How would we know if such a system existed if we couldn’t see it from Earth?

“The signals we measure to infer the presence of exoplanets—typically, the radial velocity or transit signals—could wind up being so confusing that they could be misinterpreted as noise in the case of the ultimate designed system,” says the author.

Check out Laura La Bella’s book “The Goldilocks Zone: Conditions Necessary for Extraterrestrial Life (Search for Other Earths)” for more information on the Goldilocks zone, as well as the ESA’s video on the habitable zone.

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