The “habitable zones” around stars can change over time along with the star’s luminosity. Therefore, scientists have developed a metric that allows them to take into account the evolution of stars when searching for worlds with biological organisms that are potentially suitable for life.
Habitable zone
The science of exoplanets is gradually moving away from their discovery as a primary task. There is no longer any need to prove that they exist and are widespread throughout the universe. Now we can focus on searching among them for worlds that are potentially suitable for Earth-like life.
This means searching primarily for planets that are located in the so-called “habitable zone.” This term mainly refers to the range of orbits in which the world receives enough heat for ice to melt, but water does not turn into steam.
However, the question of how to calculate the boundaries of this zone for different stars is quite controversial. And in a new study, scientists have indicated that it is even more complex than previously thought. After all, the luminosity of a star changes significantly during its lifetime. For example, at the dawn of our Sun’s existence, this indicator was only 70% of its current value.
Long-term habitable zone
In accordance with changes in the luminosity of stars, the boundaries of habitable zones also change. In the case of the Sun, it is believed that the inner boundary beyond which a planet becomes similar to Venus expands at a rate of 1% per 100 million years. And at the end of its existence, our star should turn into a red giant.
At the same time, the orbits of planets change much less significantly. And evolution requires considerable periods of time. For example, photosynthesis on Earth developed 2 billion years after the first organisms appeared, and during all that time our planet was in the “habitable zone.”
Therefore, scientists have invented a new term, “Continuous Habitable Zone,” which refers to a planet’s stay in suitable conditions for a certain period of time, and have developed a mathematical apparatus that makes it possible to understand whether a particular planet is located in it or not.
Research results
Overall, the methodology was aimed at finding planets that had been continuously in habitable zones for 2 billion years. Such studies have identified 164 similar worlds. Scientists have discovered that the widest habitable zones are found around stars that are slightly younger and slightly heavier than the Sun. Therefore, in their opinion, it is worth looking for aliens near such places.
However, as they noted, the “habitability” of a planet is not limited to this parameter alone. It is also worth considering its geology, as the movement of lithospheric plates may come to a complete halt in a few billion years.
According to phys.org
