It doesn’t take a Carl Sagan-style tear-jerker to realize how unique and awesome our planet is (although it never hurts), but as astronomers ramp up the search for exoplanets orbiting other stars it’s becoming clear that places as chill as Earth are even more rare than anyone thought.
To find other exoplanets that might be like Earth, astronomers tune their telescopes to the ‘Goldilocks region’ around a star. This is the habitable zone that is far enough away from the star so the planet’s surface isn’t scorched like Venus, but close enough that it isn’t freezing like Mars. Astronomers have found over 40 exoplanets in Goldilocks regions to date (a small fraction of the thousands of exoplanets that have been discovered), but according to new research coming out of Yale, this doesn’t necessarily tell us anything about their ability to support life.
As detailed in a paper published Friday in Science Advances, there is a second Goldilocks factor that needs to be taken into consideration when attempting to determine a planet’s habitability: its internal temperature during formation.
Prior to the new study, it was thought that planets had the ability to self-regulate their internal temperatures via a process called mantle convection, or the slow movement of Earth’s solid mantle as a result of the heat from the core of the planet. Regardless of the planet’s internal temperature during formation, the shifting of underground rock as it was heated or cooled would regulate the planet’s temperature until it was just right.
According to the new research, however, it is unlikely that Earth-like planets regulate their internal temperature through mantle convection. Rather, an Earth-like planet’s habitability depends on having just the right temperature during its formation.
“If you assemble all kinds of scientific data on how Earth has evolved in the past few billion years and try to make sense out of them, you eventually realize that mantle convection is rather indifferent to the internal temperature,” said Jun Korenaga, the author of the study and a professor of geology and geophysics at Yale. “The lack of the self-regulating mechanism has enormous implications for planetary habitability.”
According to Korenaga, planets like Earth are shaped through multiple giant impacts with space junk, a “highly random” process with diverse and as yet unpredictable results. If mantle convection actually played a role in regulating a planet’s temperature, it would offset the results of these random events and still allow for an Earth-like planetary evolution. But since this is unlikely to be the case according to Korenaga’s research, this means that the planet’s starting temperature plays a significant role in how it will develop.
“What we take for granted on this planet, such as oceans and continents, would not exist if the internal temperature of Earth had not been in a certain range,” said Korenaga. “This means that the beginning of Earth’s history cannot be too hot or too cold.”
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