cosmic hitchhike

New study tests the feasibility of life traveling from one planet to another

A new study could help resolve the biggest mystery of the cosmos: panspermia.

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When: 6-1-2020
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The hunt for extraterrestrial life has kicked into high gear with NASA’s Perseverance rover roaming the Martian surface in search of ancient microbial life.

After scouring the Red Planet, should scientists find evidence of past life on Mars, then there’s a chance you may be related to that long-dead, bacterial Martian. Think of 23andMe, but on a universal level.

The controversial theory of panspermia suggests that life may have traveled from one planet to another, like from Mars to Earth.

Recently, a team of scientists created a model to test the feasibility of life-carrying microbes piggybacking on space rocks between planets and across the cosmos. Their work suggests that pairs of neighboring, inhabited planets such as Earth and Mars could be the result of interstellar panspermia depending on the velocity at which the life-bearing material was ejected into space.

So, if we were to find life on Mars, then there is a high probability that it may have traveled to Earth at some point since there was an exchange of matter between the two planets.

Claudio Grimaldi, a researcher at the Swiss Federal Institute of Technology in Lausanne and lead author of the new study, thinks back to the asteroid that led to the extinction of dinosaurs on Earth 66 million years ago.

“A lot of material was ejected from our planet, and this material could leave the Solar System,” Grimaldi tells Inverse. “If some of that material harbored some microscopic form of life like bacteria, it's very possible that such microscopic life could survive 1-2 million years if they were shielded by these rocks.”

Could life have traveled from Mars to Earth onboard interstellar space rock?


The theory of panspermia suggests that life originated somewhere in the cosmos, and was transported between planets through interstellar objects that traveled through interstellar space — including the asteroids that smashed into Earth during its early years.

Mounting evidence suggests that Mars may have once been habitable billions of years ago, way before life began sprouting on Earth. Some scientists suggest that life may have traveled from Mars to Earth at some point, and that we owe our existence to our Martian ancestors.

WHAT’S NEW — The authors behind the recent study created a model that factored in how long microbes would survive during their space trip, the rates at which the particles disperse, and the velocities of the ejected material.

“The idea is that on average, each planet is somehow bombarded by small asteroids, meteorites,” Grimaldi says. “There is a small probability that during this bombardment, some fragments could be ejected into space.”

The model estimated the probability for different star systems, finding that so long as the velocity of the ejected material is greater than the velocities of the stars, then life-bearing material could survive the journey to another planet.

“If these bacteria can survive the trip in principle, then why not give life to other planets?” Grimaldi says.

HERE’S THE BACKGROUND — The theory of panspermia is often met with some skepticism, mainly concerning whether life-bearing material could survive a bumpy trip through space.

Oumuamua was the first interstellar comet observed from Earth, meaning that it came to us from beyond the Solar System. Some scientists suggest that life-bearing compounds may hitch a ride on interstellar objects like Oumuamua.

European Southern Observatory / M. Kornmesser

Keith Noll, chief for the Planetary Systems Laboratory at NASA’s Goddard Space Flight Center, who was not involved in the new study, says that while the theory of panspermia is not impossible, it is still highly unlikely.

“You would have to make the assumption that the environments were similar enough and that whatever life form this was could survive the radiation for however long it was in transit,” Noll tells Inverse.

Even if early space rocks carried different life forms to other planets, the right conditions would still have to be present on that planet for those life forms to survive and duplicate.

On the other hand, Earth and Mars did exchange a fair amount of material early on, with meteorites landing from Mars on our planet. Some of these meteorites were found to contain organic compounds essential for life such as nitrogen.

Jonathan Lunine, chair of the Department of Astronomy at Cornell University, who was not involved in the new study, explains that during the early Solar System, the planet Mars cooled down a lot faster than Earth did.

“Mars might have been habitable earlier and transported material to the Earth,” Lunine tells Inverse. “So it's more likely that things came from Mars to the Earth rather than from the Earth to Mars.”

Lunine also adds that since Mars is only about half the size of Earth, then Earth’s gravity would’ve made it easier for life-bearing rocks to travel to our planet rather than the other way around. And the material on those rocks could potentially survive the trip.

Evidence suggests that amino acids, the first organic molecules to appear on Earth, could survive the impact on another planet if they were traveling on board a comet. Other studies also show that bacteria could survive the impact, as well as the entry into Earth’s atmosphere.

WHY IT MATTERS — Finding out if life originated elsewhere in the cosmos and later traveled to Earth helps humans resolve their origin story and where we fit into the larger universe. If life is somehow connected across the universe, then it puts our own existence into perspective.

“I think it creates a conundrum, which is if we go elsewhere in the Solar System to try to find places where life had an independent origin from the Earth,” Lunine says. “What we want to know is whether the origin of life is a common outcome of the evolution of habitable environments, or is this something extremely rare.”

Abstract: The proposition that life can spread from one planetary system to another (interstellar panspermia) has a long history, but this hypothesis is difficult to test through observations. We develop a mathematical model that takes parameters such as the microbial survival lifetime, the stellar velocity dispersion, and the dispersion of ejecta into account in order to assess the prospects for detecting interstellar panspermia. We show that the correlations between pairs of life-bearing planetary systems (embodied in the pair-distribution function from statistics) may serve as an effective diagnostic of interstellar panspermia, provided that the velocity dispersion of ejecta is greater than the stellar dispersion. We provide heuristic estimates of the model parameters for various astrophysical environments, and conclude that open clusters and globular clusters appear to represent the best targets for assessing the viability of interstellar panspermia.
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