When we look at outer space, we see a vast cosmos. The universe we live in is massive, and its limits are far from the reach of human civilization. We are in our infancy when it comes to exploring the stars. Earth, our home, is the only planet, so far, that is capable of hosting life as we know it.
Therefore, we see Earth as a special place in the universe. However, a new study has shown that Earth may not be so unique after all; other stars in the universe could have many places nearly identical to Earth, capable of hosting life in the absence of gas giant planets like Jupiter.
According to a study led by UC Riverside astrobiologist Stephen Kane and published this week in the Astronomical Journal, a surprising number of exoplanets in the universe could host life as we know it.
The search for life in outer space generally focuses on what scientists call the “habitable zone,” which is the area around a star in which an orbiting planet is just at the right distance for water in a liquid state to exist on its surface. The general rule followed by astronomers when looking at potentially habitable planets is that if a planet has liquid water on its surface, chances are it can host life.
Kane had been studying a nearby solar system called Trappist-1, which has three Earth-like planets in its habitable zone.
“This made me wonder about the maximum number of habitable planets a star can have and why our star only has one,” Kane said. “It didn’t seem fair!”
That’s why Kane and his colleagues created a model system in which they simulated planets of various sizes orbiting their stars.
An algorithm took gravitational forces into account and helped test how planets interacted with each other over millions of years.
They discovered that it is possible for some stars to support up to seven habitable planets and that a star like our sun could support six planets with liquid water, and many of these exoplanets could host alien life.
“More than seven, and the planets get too close and destabilize each other’s orbits,” Kane said in a statement.
Why then does our solar system only have one habitable planet if it is capable of supporting six?
It helps if the movement of the planets is circular rather than oval or irregular, minimizing any close contact and maintaining stable orbits.
Kane also suspects that Jupiter, which has a mass two-and-a-half times that of all the other planets in the solar system combined, limited the habitability of our system.
As revealed by Kane and his colleagues, a gas giant like Jupiter has a more significant effect on the habitability of our solar system, mostly because it is supermassive, and this causes it to disrupt the orbits of other bodies within the solar system.
Only a handful of stars are known to have multiple planets in their habitable zones. In the future, Kane plans to search for additional stars surrounded by smaller planets.
These stars will be prime targets for direct imaging with NASA telescopes like the Jet Propulsion Laboratory’s Habitable Exoplanet Observatory.
Kane’s study identified one of those stars, Beta Canum Venaticorum (Beta CVn), which is a relatively nearby star system located around 27 light-years away.
Because it does not have a Jupiter-like planet, it will be included as one of the verified stars for multi-habitable zone planets.
“Although we know Earth has been habitable for most of its history, many questions remain regarding how these favorable conditions evolved with time, and the specific drivers behind those changes,” Kane revealed.
“By measuring the properties of exoplanets whose evolutionary pathways may be similar to our own, we gain a preview into the past and future of this planet — and what we must do to main its habitability.”