One of the goals of exoplanetary science is detecting other habitable planets similar to our own Earth. A new study provides insight into the rate of these "new Earths" occurring around other stars--with some of them supporting up to seven of these planets.
A new study from astronomers and planetary scientists, published in The Astronomical Journal, looked into the possible sizes of habitable zones (HZ) based on stellar classifications. The research team is led by Astrobiology Professor Stephen Kane from the University of California, Riverside (UCR).
Professor Kane is joined by scientists from UC Berkeley, the Universities of Southern Queensland and Hawai'i, the California Institute of Technology (Caltech), and its Infrared Processing and Analysis Center. There are also researchers from Search for Extraterrestrial Intelligence (SETI) Institute's Carl Sagan Center for the Study of Life in the Universe.
Starting the HZ Analysis with the Trappist-1
The study began with Kane's study of a nearby solar system, designated as Trappist-1. At the center of this system is an ultra-cool red dwarf star slightly larger than our own Jupiter, but with 84 times the mass.
Trappist-1 is surrounded by seven terrestrial planets, making it one of the largest ever found. Three of these are Earth-sized planets within its Habitable Zone, first discovered by Belgian astronomers back in 2015.
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"This made me wonder about the maximum number of habitable planets it's possible for a star to have, and why our star only has one," Kane said in a UCR article. The lead author added: "It didn't seem fair!"
The research team then devised a model system where different simulated planets orbited a star. Running the simulated model through an algorithm that factored in gravitational forces, the team observed interplanetary interaction over billions of years.
Only Up To Seven Planets
After the simulations, the team came up with the conclusion that it is indeed possible for stars to support as much as seven planets. They also found out the stars similar to our own Sun could support up to six planets, but with liquid water.
"More than seven, and the planets become too close to each other and destabilize each other's orbits," Kane explained.
As for the Solar System currently having only one habitable planet, Kane suspects that the local gas giant Jupiter might have something to do with it. It boasts a mass of about two and a half times compared to all the other planets in our system combined. Kane explained that Jupiter has a significant effect on the habitability of other planets in the solar system, owing to its size that "disturbs" other orbits in the system.
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Another star noted in the study is Beta CVn (Beta Canum Venaticorum), located some 27 light-years from the Sun. Since it does not have a gas giant like Jupiter, it is a candidate for the next phase of the study. The team has 20 years of radial velocity data for Beta CVn taken from the Keck/High-Resolution Echelle Spectrometer and Automated Planet Finder. The team will look into the potential dynamical packing of terrestrial planets.
Future studies will also look into the effect of atmospheric composition of the planets in other star systems.
