Northern Arizona University researchers have developed sophisticated planetary models suggesting that 26 of the 29 nearby rocky exoplanets like those in the TRAPPIST 1 system may support extraterrestrial life that is much less evolutionarily advanced than Earth’s, even though they are billions of years older, because of limited plant energy.
“If life on those exoplanets evolved just like on Earth, most of those planets will just be filled with microbes and not advanced aliens,” explained NAU ecoinformatics professor Chris Doughty and the lead author of a study detailing the team’s findings.
The researchers also found evidence that three of the studied planets may be somewhat more biologically advanced than mere microbes, including one that may be ahead of Earth from an evolution perspective. However, they said these planets may host life more like what’s depicted in the Dune novels than in James Cameron’s Avatar films.
Search for Extraterrestrial Life on Nearby Planets to Determine “Who is Ahead”
When announcing their findings, the NAU team noted that scientists have long debated the seemingly high likelihood that intelligent life should exist versus the lack of evidence for such advanced extraterrestrial life.
“Physicist Enrico Fermi famously asked, given the high likelihood of intelligent extraterrestrial life in the galaxy, ‘Where are they?’ Doughty explained.
According to the NAU team, one possible explanation is a lack of plant energy that sophisticated lifeforms need to keep evolving. On Earth, warmer, wetter environments support more plant life, providing animals with the fuel they need to evolve. The researchers suspect this may apply on a planetary-wide scale, potentially offering a comparatively wet Earth an evolutionary boost over older, drier planets in our cosmic neighborhood.
“Who is ahead?” Doughty explained. “That is the mystery we are quantitatively trying to solve.”
TRAPPIST-1e and Other Candidates Orbiting Red Dwarf Stars
Unlike Earth, most rocky exoplanets astronomers have discovered orbit smaller, cooler stars called red dwarfs. While many such candidates are billions of years older than Earth, they receive much less solar energy.
Planets within a red dwarf’s habitable zone where liquid water can exist on the surface are also typically tidally locked, meaning one half of the planet never receives direct sunlight. Still, red dwarf stars are the most common type in our galaxy, increasing the chances of finding extraterrestrial life on planets orbiting them.
Study co-author Michael Gowanlock, a NAU associate informatics professor, said that even if photosynthetic life on a planet orbiting a red dwarf had billions of years more than Earth to evolve, it may still trail Earth life from an evolutionary standpoint.
“The total annual photosynthesis is likely lower because there is less light and half the planetary surface area available for photosynthesis,” Gowanlock explained.
To predict the amount of plant energy available for animal evolution on some of the most promising “nearby” life candidate exoplanets, the team modeled TRAPPIST-1e and 28 other exoplanets that may have water within Earth’s cosmic neighborhood. For example, TRAPPIST-1e is 40 light-years from Earth, so conventional rockets would take thousands of years to reach it.
For comparison, the team used the roughly 2.4 x 1025 grams of carbon that were “fixed” on Earth during the 3.2 billion years before more efficient vascular plants evolved. Once plant life began, the team said that 7 x 1025 grams more carbon was fixed before humans evolved.
“Advanced Life on Those Exoplanets Might be More Dune Than Avatar”
After running the simulations, the NAU team determined that TRAPPIST-1e has fixed only 21% of Earth’s carbon “despite being several billion years older than Earth.”
Study coauthor Cameron Hrabak, an NAU alumnus, said this figure, which is less than the amount fixed by the Earth before the evolution of more efficient vascular plants, suggests that TRAPPIST-1e “may only be at the microbial stage of evolution.”
“That’s well behind Earth,” Hrabak said.
When they ran the same numbers for the other 28 exoplanets on their life candidate list, they found just two where life had “potentially evolved ahead of Earth’s: GJ 1061c and K2-3d.” Notably, both Earth-like exoplanets are larger, hotter, and brighter than most Earth-like planets discovered in our solar neighborhood.
The models also revealed three other “nearby” planets that could have evolved life to a stage similar to Earth’s Mesozoic, or “roughly equivalent to the age of dinosaurs on Earth.”
When discussing the types of life that might exist on those candidates, Doughty said the expected rain-limited savannah woodland conditions could evolve something one might find Muad Dib riding through the desert rather than something out of James Cameron’s vivid imagination.
“To use two pop culture references, the ecological characteristics that shape advanced life on those exoplanets might be more ‘Dune’ than ‘Avatar,’” Doughty said.
Planets Likely Filled with Microbes “and Not Advanced Aliens”
When discussing the study’s implications, the NAU team cautioned that their figures are only estimates and “not proof” of extraterrestrial life. They also note that the atmospheres around TRAPPIST-1e and other life candidates “would profoundly affect climate, photosynthesis and how life evolved.”
Ongoing efforts by the James Webb Space Telescope may offer additional data on these 29 exoplanets that could help the team further refine their models. However, Doughty said the study’s results do suggest that life on nearby Earth-like planets may be “evolutionarily behind us and still at the microbial stage.”
Which means we can sleep well, because if life on those exoplanets evolved just like on Earth, most of those planets will just be filled with microbes and not advanced aliens,” the team leader concluded.
Christopher Plain has spent the last six years as Associate News Editor and Head Science Reporter at The Debrief. Follow and connect with him on X, learn about his novels at plainfiction.com, or email him at christopher@thedebrief.org.