7 Alien 'Earths' May Be Swapping Life via Meteorites

December 14, 2017

Tiny life-forms can move easily between these recently described planets, according to a study of the travel times between worlds.

The discovery of alien life would be revolutionary. But what if we uncovered it on two—or even seven—planets all orbiting the same star?

That’s the tantalizing possibility offered by the cosmic grouping called TRAPPIST-1, where seven Earth-size worlds circle a star roughly 39 light-years away. According to a new study, those planets are packed so tightly around their stellar host that the seeds of life could be hopping between them with ease.

The study, conducted by Manasvi Lingam and Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics, is based on a theory known as panspermia, which in turn is based on the fact that planetary debris can be swapped between the worlds in our solar system. This is especially true for neighboring rocky planets—for instance, asteroid strikes have sent fragments of Mars crash-landing onto Earth.

Panspermia takes this a step further and suggests that life could catch a ride on that debris, hitchhiking from one planet to the next. It might sound wild, but recent research shows that some extreme forms of life can survive conditions akin to an interplanetary journey. Some scientists even argue that the seeds of life on Earth could have come from Mars.

In the TRAPPIST-1 system, all seven planets are nestled within a region that’s more than 20 times smaller than the distance between Mars and Earth. Such close proximity raises the tantalizing possibility that panspermia could take place in this system with ease.


Of course, right now there’s no direct evidence that panspermia happens in our solar system or beyond. And some astronomers are doubtful that hitchhikers could survive such a traumatic journey.

First, the building blocks of life would have to endure extreme heat and pressure from the impact that spewed them into space. Out in the open void, they would be subjected to harsh ultraviolet radiation from their host star for potentially millions of years. Finally, they would once again face blazing temperatures as they fell from the sky and crash-landed in yet another violent impact.

“The poor organism would be fried twice and would be radiated by ultraviolet photons,” says Brice-Olivier Demory of the University of Bern, a co-author on the study that announced the TRAPPIST-1 discovery last month.

Amaury Triaud, a University of Cambridge astronomer who also co-discovered the TRAPPIST-1 planets, is on the fence: “I'm a skeptic about this,” he says. “But I also have to remind myself that life has managed to survive in extreme conditions.”

Bacteria have persevered inside nuclear reactors and on the outer rim of the International Space Station. Tardigrades—tiny water-dwelling invertebrates that look like chubby bears—have endured the vacuum of space for up to 10 days. And organisms frozen in Antarctic ice for centuries have been revived in labs. (Also see “Weird Life Found Trapped in Giant Underground Crystals.”)

“We might find forms of life that survive under conditions that we haven't anticipated,” says Loeb. “That's why it's exciting. We shouldn't have any prejudice, but should look at all seven planets in TRAPPIST-1.”

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