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Physicists: Ancient life might have escaped Earth and journeyed to alien stars

An illustration shows a comet passing in front of a star.
An illustration shows a comet passing in front of a star.
(Image: © NASA/JPL-Caltech)

A pair of Harvard astrophysicists have proposed a wild theory of how life might have spread through the universe.

Imagine this:

Millions or billions of years ago, back when the solar system was more crowded, a giant comet grazed the outer reaches of our atmosphere. It was moving fast, several tens of miles above the Earth's surface — too high to burn up as a fireball, but low enough that the atmosphere slowed it down a little bit. Extremely hardy microbes were floating up there in its path, and some of those bugs survived the collision with the ball of ice. These microbes ended up embedded deep within the comet's porous surface, protected from the radiation of deep space as the comet rocketed away from Earth and eventually out of the solar system entirely. Tens of thousands, maybe millions, of years passed before the comet ended up in another solar system with habitable planets. Eventually, the object crashed into one of those planets, deposited the microbes — a few of them still living — and set up a new outpost for earthly life in the universe.

Related: 5 Reasons to Care About Asteroids

You could call it "interstellar panspermia," the seeding of distant star systems with exported life.

We have no idea whether this ever actually happened –.and there's a mountain of reasons to be skeptical. But in a new paper,  Amir Siraj and Avi Loeb, both astrophysicists at Harvard University, argue that at least the first part of this story — the depositing of the microbes into a comet that gets ejected from the solar system — should have happened between one and a few dozen times in Earth's history. Siraj told Live Science that although a lot more work needs to be done to back up the finding, it should be taken seriously — and that the paper may have been, if anything, too conservative in its estimate of the number of life-exporting events.

While the study's concept may seem far-fetched, humanity is constantly confronted with seeming impossibilities, like Earth going around the sun, or quantum physics, or bacteria hitching a ride into the galaxy aboard a comet — that turn out to be true, Siraj said

And there's been reason to suspect that it might be possible. A series of experiments using small rockets in the 1970s found colonies of bacteria in the upper atmosphere. Comets really do enter and leave our solar system from time to time, and Siraj and Loeb's calculations show that it's plausible, maybe even likely, this has happened to large comets that graze Earth. Comets are porous, and might actually shield microbes from deadly radiation some microbes can survive a remarkably long time in space.

That alone is reason for scientists to take the idea seriously, Siraj said, and for researchers from fields like biology to jump in and figure out some of the details.

"It's a brand new field of science," he told Live Science

However, Stephen Kane, an astrophysicist at the University of California, Riverside, told Live Science that he was deeply skeptical of the suggestion that microbes from Earth might have actually turned up alive on alien planets through some version of this process.

The first problem would occur when the comet slammed into the atmosphere, he said. Siraj and Loeb point out that some bacteria can survive extraordinary accelerations. But the precise mechanism by which the microbes would adhere to the comet is unclear, Kane said, since the aerodynamic forces around the comet might make it impossible for any microbes to reach the surface and work their way deep enough below the surface to be protected from radiation.

It's also not clear, he said, whether any microbes would really have been up high in our atmosphere in the first place Those rocket experiments from the 1970s are old and questionable, he said, and we still don't have a good picture of what the biology of the upper atmosphere really looks like today — let alone hundreds of millions of years ago, when comet encounters were much more common.

The biggest question, though, Kane said, is what would happen to the microbes after they landed aboard the comet. It's plausible, he said, that some bacteria might survive decades in space — long enough to reach, say, Mars. But there's little direct evidence that any bacteria might survive the thousands or millions of years necessary to travel to another habitable star system. And that's really the key idea of this paper: Researchers have long suggested that debris from major collisions might blast life around between our solar system's planets and moons. But exporting life to an alien star system likely requires a more specialized scenario.

Still, Kane said, the calculations in this study of how precisely a comet might skim through the atmosphere were new to him, and "very interesting."

Siraj didn't strongly challenge any of Kane's concerns, but reframed them one by one as opportunities for further study. He wants to know, he said, precisely what the biology of the upper atmosphere looks like, and how comets might react to it. There's reason to think that at least some bacteria might survive super-long trips through deep space, he said, based on how robust they are under extreme conditions on Earth and in orbit. But for now, it's time for scientists across fields to jump in and start filling in the gaps, Saraj said.

Originally published on Live Science.

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  • Speed
    There is this: https://www.ibtimes.com/fireball-meteoroid-grazes-earths-atmosphere-returning-space-2886827And this: https://www.quora.com/Can-an-asteroid-comet-meteorite-enter-the-atmosphere-pass-reasonably-close-to-Earth-surface-and-still-exit-it-without-any-consequences-Has-it-ever-happened
    Reply
  • Anonymous010
    An awful lot would have to go exactly right for what these guys are proposing to actually happen. Even if the first part, that microbes attached to a comet as it passed through Earth's atmosphere, had happened 1000 times over Earth's history, AND we assume that the microbes can survive indefinitely in the comet, I would still be extremely surprised if even a single one of those seeded comets ever crashed into a habitable planet over the remainder of the universe's lifetime. There are just way too many random factors.
    Reply
  • molly cruz
    As we refine our 3-D copiers to create trachea's and urinary tracts, and as a species contemplate our future without the local Sun, it's easy for me to see us reducing life forms to their DNA and carting the whole shebang off to a new planet, and even easier to consider the fact that most mythology consists of some God magically producing life forms in "six something or others, like days or centuries or millennia" before He took a break, as very possibly not being the first time we did it.
    We have come up, in the process of trying to annihilate each other, with war toys enough to put us in the catbird's seat, when it comes to arguing with Armageddon, which is exactly what we're doing now, only NASA isn't the headline grabber it might be. Without this questionable past, we could not even consider how to grapple with incoming balls of fire and ice from the beyond; so in my estimation, we are Mother Nature's Grunts, the Saviors here, bound -- by our swollen cerebrums and very fashionable thumbs-- to be the default creature to take on the task of saving, first the planet from incoming Space debris, and later to do just what the article suggests: first find a planet, next seed it with the appropriate microbes, seeds, critters, and finally when the Garden is done, ourselves. I'm just hoping they'll leave out the mosquitoes! The prophets were mostly astronomers and saw this coming.

    This scenario makes the historically worst of us, the vengeful but creative warriors, from the first catapult to he atomic bomb, the actual Good Guys, in the Real Agenda, about which we have little to say, except that if we fail, nothing else much matters, the irony of which I find most fascinating. And if we succeed, when we knock that first asteroid off course, it will be an Aha! moment to outshine all others, as we look back at our seemingly reckless behavior and realize it was not our own doing, because we are on a Holy Mission to create "Life everlasting, Amen!"
    Reply
  • FN Moeller
    Might have? Most certainly has is the answer. Its a two way street also of course.
    Reply
  • Susan
    In this article, "bacteria hitching a ride into the galaxy aboard a comet" is included in a list of weird concepts that turned out to be true. Since when is a hypothesis the same thing as a true fact??
    Reply
  • egribble
    Science fact is often stranger than science fiction so I have an open mind. My thoughts are that Panspermia between Earth and Mars was highly likely due to regular large meteor impacts early in both planets existence. Also many bacterial extremophiles are extremely hardy. To me the idea of DNA spreading around the galaxy in comets and leading to new life is harder to accept. In order for new cells to reproduce the basic cell would need to be preserved. We are talking hundreds of light years distance, millions of years in a high radiation free space environment. However as I have said, science fact is often stranger than science fiction.
    Reply
  • FN Moeller
    egribble said:
    Science fact is often stranger than science fiction so I have an open mind. My thoughts are that Panspermia between Earth and Mars was highly likely due to regular large meteor impacts early in both planets existence. Also many bacterial extremophiles are extremely hardy. To me the idea of DNA spreading around the galaxy in comets and leading to new life is harder to accept. In order for new cells to reproduce the basic cell would need to be preserved. We are talking hundreds of light years distance, millions of years in a high radiation free space environment. However as I have said, science fact is often stranger than science fiction.


    You need to examine deep earth bacteria, found up to 5 km below the surface at temperatures above that of boiling water, anaerobic bacteria that would survive both impact and space travel. Yes life leaves a planet with a large impact. This is how we know that Mars still has life and that Mars and Earth most certainly shared life. Until samples are returned to earth we call it theory or hypothesis just to be polite but most definitely the Earth and Mars have both received and have both sent life into and from space. We all know life is out there but to be polite to those that don't see this we call it a hypothesis.
    Reply