Super-Earths Are Bigger and More Habitable Than Earth, and Astronomers Are Discovering More of the Billions They Think Are Out There
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.
Common and Easy to Find
Most super-Earths orbit cool dwarf stars, which are lower in mass and live much longer than the sun.
Based on current projections, about a third of all exoplanets are super-Earths, making them the most common type of exoplanet in the Milky Way. The nearest is only six light-years away from Earth. You might even say that our solar system is unusual since it does not have a planet with a mass between that of Earth and Neptune.
Another reason super-Earths are ideal targets in the search for life is that they’re much easier to detect and study than Earth-sized planets. There are two methods astronomers use to detect exoplanets. One looks for the gravitational effect of a planet on its parent star and the other looks for brief dimming of a star’s light as the planet passes in front of it. Both of these detection methods are easier with a bigger planet.
Super-Earths Are Super Habitable
It turns out that Earth is not the best of all possible worlds.
Due to Earth’s tectonic activity and changes in the brightness of the sun, the climate has veered over time from ocean-boiling hot to planet-wide, deep-freeze cold. Earth has been uninhabitable for humans and other larger creatures for most of its 4.5-billion-year history. Simulations suggest the long-term habitability of Earth was not inevitable, but was a matter of chance. Humans are literally lucky to be alive.
Researchers have come up with a list of the attributes that make a planet very conducive to life. Larger planets are more likely to be geologically active, a feature that scientists think would promote biological evolution. It would have an atmosphere thicker than Earth’s that would act as an insulating blanket. Scientists think that these attributes combined will make a planet super habitable.
By definition, super-Earths have many of the attributes of a super habitable planet.
Recently, there’s been an exciting addition to the inventory of habitable planets. Astronomers have started discovering exoplanets that have been ejected from their star systems, and there could be billions of them roaming the Milky Way. If a super-Earth is ejected from its star system and has a dense atmosphere and watery surface, it could sustain life for tens of billions of years, far longer than life on Earth could persist before the sun dies.
Detecting Life on Super-Earths
But it is able to do some of this science and is scheduled to target two potentially habitable super-Earths in its first year of operations. Another set of super-Earths with massive oceans discovered in the past few years, as well as the planets discovered this summer, are also compelling targets for James Webb.
These telescopes are all under construction and set to start collecting data by the end of the decade.
Astronomers know that the ingredients for life are out there, but habitable does not mean inhabited. Until researchers find evidence of life elsewhere, it’s possible that life on Earth was a unique accident. While there are many reasons why a habitable world would not have signs of life, if, over the coming years, astronomers look at these super habitable super-Earths and find nothing, humanity may be forced to conclude that the universe is a lonely place.
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