Astronomers now routinely discover planets orbiting stars outside of the solar system— they’re called exoplanets. But in summer 2022, teams working on NASA’s Transiting Exoplanet Survey Satellite found a few particularly interesting planets orbiting in the habitable zones of their parent stars.
One planet is 30 percent larger than Earth and orbits its star in less than three days. The other is 70 percent larger than Earth and might host a deep ocean. These two exoplanets are super-Earths—more massive than Earth but smaller than ice giants like Uranus and Neptune.
I’m a professor of astronomy who studies galactic cores, distant galaxies, astrobiology, and exoplanets. I closely follow the search for planets that might host life.
Earth is still the only place in the universe scientists know to be home to life. It would seem logical to focus the search for life on Earth clones—planets with properties close to Earth’s. But research has shown that the best chance astronomers have of finding life on another planet is likely to be on a super-Earth similar to the ones found recently.
Most super-Earths orbit cool dwarf stars, which are lower in mass and live much longer than the sun. There are hundreds of cool dwarf stars for every star like the sun, and scientists have found super-Earths orbiting 40 percent of cool dwarfs they have looked at. Using that number, astronomers estimate that there are tens of billions of super-Earths in habitable zones where liquid water can exist in the Milky Way alone. Since all life on Earth uses water, water is thought to be critical for habitability.