The TRAPPIST-1 worlds orbit so close to one another that microbes from one world could be transported to the others through meteors in a process known as panspermia.
Most organisms cannot survive in the vacuum and radiation of space. But travel time for meteors between TRAPPIST-1’s habitable worlds is about 100 times less than it is between Earth and Mars, increasing the chances that some microbes could complete the trip.
Some scientists believe life on Earth got started through microbes transported via meteorites from Mars.
According to Manasvi Lingam and Avi Loeb, both of Harvard University, the chances of microbes migrating from one TRAPPIST-1 world to another via panspermia are 1000 times greater than those of their migrating between Mars and Earth.
“Because these distances are so close, a lot more different kinds of species, microbial or otherwise, could migrate from one planet to another,” Lingam said.
Comparing the TRAPPIST-1 planets to a series of islands, the researchers state that if there is life on any one of the habitable worlds, it likely exists on all three, having migrated much like life on Earth migrates from one island to another.
“It would not be surprising to find the same forms of life on all three habitable planets near TRAPPIST-1,” Loeb said.
Some biologists reject the comparison, arguing that planets are very different from islands. On Earth, life forms that survive the journey from one island to another often evolve differently from those in their original habitats.
Panspermia may not have to occur for life to start on any worlds. Rather than carrying the organisms themselves, meteors could transport the building blocks of life, such as water and simple proteins, from one planet to another.
Finding life on more than one TRAPPIST-1 planet would give scientists a living laboratory where they could compare the beginnings and evolution of life on multiple worlds.
“The fascinating story in science really would be that life evolved on all of these planets individually, and you could see the diversity of what nature could come up with,” emphasized Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University in Ithaca, NY.