\u201cPhysicist\u00a0Enrico\u00a0Fermi\u00a0famously\u00a0asked,\u00a0given the high likelihood of intelligent life\u00a0in the galaxy, \u2018Where are they?\u2019\u00a0Doughty said. \u201cThis paper suggests that\u00a0our exoplanet stellar neighborhood\u00a0may be quiet because most Earth-like\u00a0planets\u00a0near us are likely to be evolutionarily behind us and still\u00a0at the microbial stage.\u00a0Which 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\u00a0microbes\u00a0and not advanced aliens.\u201d<\/p>\n
The study\u00a0was\u00a0published Sept. 22 in\u00a0the International Journal of Astrobiology<\/a>.<\/p>\n It\u00a0doesn\u2019t\u00a0say\u00a0there\u2019s not\u00a0highly advanced extraterrestrial life that could lead to a real-life reenactment of \u201cThe Three-Body Problem.\u201d\u00a0What\u00a0the study\u00a0says,\u00a0according to\u00a0the researchers, is that\u00a0such a species nearby is unlikely, as the cumulative photosynthesis on nearby potentially habitable exoplanets would be lower.<\/p>\n And here\u2019s why: If life ever evolved on a planet, its continued evolution wouldn\u2019t just automatically happen over time. Rather, it would be dependent on the cumulative plant energy of a planet, the study authors hypothesize. Looking at Earth, warm, wet places have more plant growth and species than cold, dry places. Scientists believe this is because there is more plant growth and ecological space for animals to exist. Thus, a young, warm, wet exoplanet may have more evolutionary development than an older, colder, drier exoplanet.<\/p>\n In their paper, Doughty and his coauthors explore the implications of this hypothesis for exoplanets. The planets that are most likely to have life revolve around red dwarfs, the most common star type in our galaxy. These planets, which are often billions of years older than Earth, have dimmer light and are often tidally locked, meaning only one side of the planet faces its sun.<\/p>\n \u201cIf photosynthetic life evolved on these planets, that life has been photosynthesizing for potentially billions of years longer than on Earth,\u201d said coauthor Michael Gowanlock<\/strong>, an associate informatics professor at NAU said. \u201cHowever, the total annual photosynthesis is likely lower because there is less light and half the planetary surface area available for photosynthesis. Who is ahead? That is the mystery we are quantitatively trying to solve.\u201d<\/p>\n Recent work\u00a0by coauthor Denis Sergeev, a\u00a0lecturer at the\u00a0University of Bristol\u00a0in the United Kingdom,\u00a0has\u00a0simulated\u00a0possible climate patterns\u00a0on\u00a0exoplanets\u00a0including\u00a0maps of temperature, light and precipitation, which\u00a0are the main variables needed to predict plant growth on Earth.\u00a0 In the current paper, the authors used those maps to predict potential plant growth and evolutionary rates over their lifetimes for TRAPPIST-1e and 28 other nearby exoplanets\u00a0that potentially have liquid water. (\u201cNearby\u201d is relative; TRAPPIST-1e is 40 light-years from Earth.)<\/p>\n Here\u2019s\u00a0how it works on Earth.\u00a0Roughly\u00a02.4\u00a0x\u00a01025<\/sup>\u00a0grams of\u00a0carbon\u00a0were\u00a0fixed during the 3.2 billion years before more efficient vascular plants evolved. Then\u00a07\u00a0x\u00a01025<\/sup>\u00a0grams\u00a0more carbon was fixed before\u00a0humans\u00a0evolved.\u00a0The researchers\u00a0estimated\u00a0that\u00a0TRAPPIST-1e\u00a0<\/strong>has fixed only 21% of Earth\u2019s carbon despite being several billion years older than Earth.<\/p>\n \u201cSince this is less than the\u00a0Earth had fixed before the evolution of more efficient vascular plants, we estimated that TRAPPIST-1e\u00a0<\/strong>may only\u00a0be at the microbial stage\u00a0of evolution,\u201d said coauthor Cameron Hrabak<\/strong>, an NAU alumnus. \u201cThat\u2019s well\u00a0behind Earth.\u201d<\/p>\n The researchers made similar calculations for the 29 exoplanets in Earth\u2019s stellar neighborhood that are most likely to have life and found only two planets whose life has potentially evolved ahead of Earth\u2019s: GJ 1061c and K2-3d. Both are bigger, hotter, brighter and older than most Earth-like planets in our solar neighborhood. Three other planets could be at the Mesozoic life stage, which is roughly equivalent to the age of dinosaurs on Earth.<\/p>\n These are estimates, not proof. The atmosphere around TRAPPIST-1e\u00a0and other exoplanets would profoundly affect climate, photosynthesis and how life evolved; future work with the James Webb Space Telescope could provide\u00a0additional\u00a0data that will allow the researchers to hone their estimates.<\/p>\n This technique can help predict the evolutionary constraints that shape life on those exoplanets that might surpass life on Earth, the researchers said. On Earth, plant growth can be limited by light, temperature or precipitation. For instance, deserts get plenty of light, but growth is inhibited by lack of precipitation. These constraints also shape how life evolves differently\u2014the life in tropical forests has little overlap with desert life. On exoplanets, the planets most likely to surpass Earth\u2019s total carbon fixed and evolutionary stage are mainly precipitation-limited.<\/p>\n Put simply, if there is an alien civilization in Earth\u2019s stellar neighborhood, the ecosystems shaping those intelligent creatures would be more like deserts or temperate ecosystems\u2014much like humans on Earth, as we likely evolved in rain-limited savanna woodlands.<\/p>\n \u201cTo use two pop culture references,\u00a0the ecological characteristics that shape\u00a0advanced life on\u00a0those\u00a0exoplanets might be more\u00a0\u2018Dune\u2019\u00a0than\u00a0\u2018Avatar,\u2019\u201d Doughty said.<\/p>\n <\/p>\n Heidi Toth | NAU CommunicationsWhat\u00a0the study says<\/strong><\/h3>\n
But TRAPPIST-1e\u00a0isn\u2019t\u00a0Earth. How do they compare?<\/strong><\/h3>\n
![\"Joke](\"https:\/\/in.nau.edu\/wp-content\/uploads\/sites\/402\/2026\/09\/Picture2-208x300.png\")
<\/a>What\u2019s\u00a0next, and is it an alien invasion?<\/strong><\/h3>\n
![\"Northern](\"https:\/\/in.nau.edu\/wp-content\/uploads\/sites\/402\/2019\/06\/NAU_primary-281_3514-300x213.png\")
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\n(928) 523-8737 | heidi.toth@nau.edu<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"