Impact Survival of Microbes Highlights the Feasibility of Panspermia
Through five peer-reviewed papers, published here, here, here, here and here, I have explored with my students and postdocs the possibility of the transfer of life, so-called panspermia, in exoplanetary systems like TRAPPIST-1 as well as throughout the Milky-Way galaxy -including in the dense stellar environment of the Galactic center.
An interstellar gardener could enhance the cross-fertilization of planets beyond the random chance of impacts by microbe-carrying rocks. As I proposed here, our civilization could choose to seed the Milky-Way galaxy with life from Earth by launching a capsule with microbes, nutrients and a power source, on a collision course with an interstellar object like 3I/ATLAS which will carry our package to interstellar space and potentially disperse its content once it arrives to the habitable zone of another star.
This deliberate life-delivery system would be far more consequential than the Golden Record sent onboard the Voyager spacecraft, which only contained an advertisement message about our civilization for anyone out there who might care to read it.
The possibility that an interstellar object might serve another purpose was supported by the discovery of organic molecules on 3I/ATLAS by the SPHEREx Space Observatory (as discussed here). The five letters of DNA were recently found here in material from the asteroid Ryugu. Some interstellar objects might be Trojan Horses, appearing as natural comets from the outside but carrying a technological package inside.
The natural transfer of microbial life within rocks is certainly possible. A Martian rock named ALH84001 arrived to Earth’s surface without being heated to more than 40 degrees Celsius since its ejection from the surface of Mars (as reported here). Microbes could have survived in the interior of this rock. In fact, Mars and Earth exchanged numerous such rocks in their early history and could have shared the same forms of life in liquid water given their similar surface conditions and composition. Life transfer could have happened among adjacent members of other tightly-packed planetary systems, such as the seven rocky planets of the star TRAPPIST-1 (as I discussed here).
A new paper published this month here subjected microorganisms to controlled extreme pressures for short periods and assessed their survival. The study found that microbes can survive extreme pressures of up to 20,000 times larger than the atmospheric pressure on Earth (corresponding to about 2 giga-pascals), that may arise in asteroid impacts. This means that microbes could stay alive as rocks are ejected from the surface of planets as a result of spallation triggered by a meteor impact.
The complementary question is how long could microbes survive in the harsh conditions of space, which include freezing temperatures and bombardment by cosmic-rays and UV radiation without essential nutrients. Their lifespan under these extreme conditions would determine how far they can travel in space before landing on the fertile ground of a new planet. Would these microbes fertilize the new ground on which they land with their genetic material like undamaged dandelion seeds carried by the wind?
The new paper demonstrates that the specific extremophile Deinococcus radiodurans has an outstanding ability to survive the extreme transient pressures associated with impact-induced ejection from Mars. Earlier work has demonstrated that this microorganism can survive the radiation, cold, and desiccation associated with interplanetary transport.
Mars is a smaller body than Earth which therefore cooled to habitable conditions before Earth. Given the above experimental results, it is possible that we are all Martians since life was delivered to Earth by Martian rocks in the form of the Last Universal Common Ancestor (LUCA) about 4.2 billion years ago (as reported here).
In that case, the first humans to go to Mars might feel as if we are returning to their childhood home.
By now, Mars is a desert without any liquid water on its surface. The loss of its vitality at the middle of its history, triggered by the loss of its atmosphere a few billion years ago, might not have been totally fatal because its descendants might visit it back deliberately on a human-made spacecraft. What started as a random fluke of nature, panspermia, may come full circle as a deliberate transfer of life on technological equipment, directed panspermia.
The story of life on Mars and Earth carries an important lesson. Sometimes when your life turns miserable at an old age, it is your children from long ago who may come to visit you on your deathbed and revive your prospects to thrive all over again.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
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