It’s just you and I, Kepler−442b.
How can an extraterrestrial exoplanet support life as we know it? As it turns out, a lot.
New study published in the Monthly Notices of the Royal Astronomical Society contradicts a claim made in a report published last year that there may be 300 million planets in our galaxy that are “possibly habitable.”
This new research of known exoplanets focuses on photosynthesis and suggests that Earth-like circumstances on possibly habitable worlds may be less common than previously believed.
Photosynthesis is the process through which plants convert light, water, and carbon dioxide into oxygen and energy.
Astronomers have found 4,422 exoplanets to date, but just a few are deemed potentially habitable.
For an exoplanet to be potentially habitable, it must have an oxygen-rich atmosphere, since photosynthesis has been crucial to the development of complex biospheres like those on Earth.
The James Webb Space Telescope (JWST), which is scheduled to launch later this year, will be able to study exoplanet atmospheres as they pass their stars. The light passing through their atmospheres will disclose the types of gases present.
However, liquid water is required for photosynthesis. Only exoplanets with the ideal temperature — neither too hot nor too cold — might support such an object on their surface.
In this so-called “Goldilocks Zone,” how many rocky, Earth-sized exoplanets exist?
This research implies there are few.
Even among the few of known rocky and possibly livable exoplanets, none meet the theoretical parameters to support an Earth-like photosynthesis-based biosphere.
There is not only terrible news.
The study, which examined the quantity of radiation (sunlight) received by each prospective exoplanet from its star, finds that Kepler442b is near to getting enough sunlight to support a substantial biosphere that may be identified by JWST.
What is known regarding Kepler-442b
Kepler-442b, a rocky planet with almost twice the mass of Earth, circles a fairly hot orange dwarf star 1,120 light-years distant in the constellation Lyra.
Its existence was revealed in 2015 when the Kepler Space Telescope spotted it transiting its parent star. In 2018, the telescope ceased to function.
This exoplanet, also known as KOI-4742.01, is almost half the distance from its star as the Earth is from the Sun. It takes Kepler-442 112 days to circle the star.
It is, however, a “super-Earth,” which, despite the name, is not Earth-like.
The study suggests that stars with half the temperature of the Sun cannot support biospheres similar to Earth because they do not emit sufficient energy in the appropriate wavelength range.
That doesn’t imply photosynthesis would be impossible, but there wouldn’t be enough plant life to support a biosphere similar to Earth.
70% of stars in the Milky Way are faint red dwarf stars (also known as M-dwarfs), none of which, according to this study, provide their planets with sufficient sunlight for major photosynthesis to occur.
Even worse, stars that are hotter and brighter than the Sun may, in theory, power more photosynthesis, but the study implies that these stars do not persist long enough for sophisticated life to form.
“Since red dwarfs are by far the most common kind of star in our galaxy, our discovery suggests that Earth-like circumstances on other planets may be far less frequent than we had hoped,” said Giovanni Covone, a professor at the University of Naples and the study’s primary author. “This work imposes stringent restrictions on the parameter space for complex life, therefore it appears that the “sweet spot” for sustaining a biosphere comparable to that of Earth is not that expansive.”