spaceSpace and Physics

How Life Might Migrate Through The Universe


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockAug 20 2020, 17:30 UTC


Two of the biggest questions humanity has asked itself are how life formed on Earth and if there is life elsewhere in the universe. The answer to both, researchers suggest, could very well be one and the same. 

We know that important organic molecules are found on asteroids, comets, and nebulae, and some of these were possibly delivered to the young Earth. However, some researchers suggest that much more might have come to our planet. Could the ancestors of all living organisms today have come from elsewhere? Sure, the depths of space don't seem very life-friendly, but certain organisms can survive these extreme conditions.


This concept is known as panspermia, and it was recently the central theme of Breakthrough Discuss – a conference held at UC Berkeley where experts in different fields presented results and ideas on the “Migration of Life in the Universe.” The conference opened with the recorded words of the late Stephen Hawking: “Life could spread from planet to planet or from stellar system to stellar system, carried on meteors.”  

Are we all Martians?

Mars is today a cold and dry planet, but for a long time it had water oceans on its surface. If life formed there, researchers think it could have escaped into space and eventually found its way to Earth. Obviously, there are caveats to the probability of this idea, but it has a lot going for it.


For life to get to space, it needs to be thrown there by an impact. This usually means high temperatures and pressures, which would kill any lifeforms in the soil. Yet researchers have estimated that some of Mars' meteorites had low enough temperatures (less than boiling water) for life to survive.

The size of the rock fragment also plays a role in this. The rocks have to be small enough to not turn into plasma as they plummet through Earth’s atmosphere but also big enough that its interior is shielded from sterilizing cosmic rays. That said, Martian meteorites the right size have reached our planet with not much difficulty before.

“I think there's good evidence,” Dr Ben Weiss, a professor of planetary science at MIT and speaker at the conference, told IFLScience. “It's certainly not a crackpot idea to suggest that within our own Solar System that some of the planets are not biologically isolated. We are confident that probably billions of tons of Martian rocks have been transferred to Earth since the two planets formed. We also know that every few hundred thousand years, a fist-sized rock gets from Mars [to Earth] in just a year.” 


In an experiment conducted on the Long Duration Exposure Facility, bacteria were able to survive in space for nearly six years. Since then, more experiments have shown that many lifeforms are capable of surviving a journey between Mars and Earth.

In general, cross-contamination is not an unlikely hypothesis. It's possible that lifeforms on Earth have experienced deep space even before humans have attempted the same feat. Conservative estimates suggest that, after an impact, most material would rain back down. However, a small percent would travel and hit terrestrial planets, and a much smaller fraction (on the order of one-millionth of a percent) would be able to reach the moons of Jupiter and Saturn.

Vadim Sadovski/Shutterstock

Good things come in small packages


Often the idea of panspermia only focuses on planets and moons; it doesn’t include the smaller bodies of the Solar System. To create life, scientists think organic materials, water, heat, and time are needed. All of these existed on planetesimals, the very earliest small bodies that formed in our Solar System.

“I think a lot of times we think about life as only arising once a planet is completed in a form that is familiar to us,” conference speaker Dr Lindy Elkins-Tanton, principal investigator of NASA's Psyche Mission and director of the School of Earth and Space Exploration at Arizona State University, told IFLScience.

“Within just 100,000 years or 200,000 years, geologically no time after the first solids in the Solar System formed, planetesimals had all those parts needed for life. They had a little gravity, they had fluid water, they were warm, and they were filled with organics. Maybe that was a possible birthplace for life.”


That life might have then spread throughout the Solar System by planetesimals is an interesting idea. In the Solar System's formative years, as planets migrated, smaller objects might have whizzed around until eventually colliding with the ancient Earth, possibly delivering the first living organisms to our planet.

It's also possible that life might have arisen on planetesimals independently and just stayed on them, never quite capable of jumping ship. If life did form on these objects, it would be extremely unlikely for it to still be there today. It would have had to survive 4.5 billion years in terrible conditions with no heat and no water.

Interstellar lifeforms are more likely to be stowaways than pilots


With the discovery of ‘Oumuamua, the idea of panspermia shifted from comets and planetary fragments in our neighborhood to the wider galaxy. ‘Oumuamua, an object moving between star systems, shows that there is an exchange of material between them. This exchange might be very small but it is not insignificant. If we assume that life could move across planets, why not assume between stars? The idea is certainly intriguing but there are several challenges when it comes to this interstellar panspermia.

Although accelerating out of a star system is not too difficult, this comes with a price. Most interstellar objects are moving at high velocity, so life on these objects would face a high-speed impact on arrival.

Another factor to consider is time. These objects might be traveling for tens of millions of years. Sure, they might be big and cold enough to preserve material in a deep freeze, but could the material withstand such a long transit?


It’s not just physics and biology that is against this hypothesis, statistics doesn't support it either. Given what we know of the universe, it is unlikely that a rock could go from the surface of one planet in a star system to the surface of a planet in another star system.

This artist’s impression shows the first interstellar comet: `Oumuamua. ESO/M. Kornmesser

While panspermia is a fascinating idea, it remains to be proven. The clearest piece of evidence would be finding life elsewhere compatible with life here on Earth. Finding alien life is the first step, but working out if we are related is not too far behind. 

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