It Came From Beyond

ʻOumuamua, the first known interstellar asteroid, may lead us to rethink the idea that life came here from other stars.

Artist’s impression of the interstellar asteroid Oumuamua. (ESO/M. Kornmesser)
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The recent discovery of the first interstellar asteroid is still creating a sensation among scientists, who would like to figure out—among other things—where the object now known as ʻOumuamua came from.

What we know is the following: In October, the interstellar visitor was spotted moving past the Sun at a speed of about 50 kilometers per second, following a hyperbolic path that lies mostly outside our Solar System. ʻOumuamua (Hawaiian for “a messenger from afar arriving first”) has the shape of a cigar, about 400 meters long and 40 meters in diameter. It spins around its own axis every 7.3 hours, and seems to have a rocky content rich in metal.

The panspermia hypothesis, first detailed by Svante Arrhenius in 1903, proposes that life can be transported from one planet to another via asteroids or other bodies moving through space. While recent investigations support the possibility of spreading life in this way within our own inner Solar System—for example, from Earth to Mars or vice versa—the statistical odds of this happening between star systems have been estimated to be very low.

Now that we’ve identified the first interstellar asteroid, we can use planet formation models to estimate that perhaps 10 of these objects would pass through our Solar System every year. This may in turn force us to re-assess the possibility of interstellar panspermia.

The odds are still stacked against it, however. An interstellar object would have received high doses of radiation for a very long time, effectively sterilizing its surface. If it came into contact with any body in our neighborhood, the odds are it would fall into the Sun or collide with Jupiter, the two largest gravity sinks in the Solar System, rather than small planets like Earth or Mars. And since it’s traveling much faster than asteroids and comets that originate closer to home, any impact with a rocky planet would not be gentle.

Nevertheless, now we know that these interstellar visitors exist, and this is hugely significant. Additional modeling studies should teach us more about the eventual fate of these objects when they collide with terrestrial planets.

We also should consider the idea of “directed panspermia”—the deliberate transmission of life to another planet by an advanced intelligent species—originally theorized by Francis Crick and Leslie Orgel nearly 50 years ago. At the time it was proposed, the suggestion seemed straight out of science fiction. However, we humans are close to being able to do that ourselves, by placing spores or other dormant life forms on a rocket destined for some suitable exoplanet. What we lack most is identification of a habitable world with a balmy ocean. Of the more than 3,500 known exoplanets, there surely must be suitable ones. Should we try to transmit Earthly life to another planet, even if there’s a chance it might already be inhabited by life forms? Perhaps not. Then again, maybe someone else already did.

About Dirk Schulze-Makuch
Dirk Schulze-Makuch

Dirk Schulze-Makuch is a Professor at the Technical University Berlin, Germany, and an Adjunct Professor at Arizona State University and Washington State University. He has published seven books and nearly 200 scientific papers related to astrobiology and planetary habitability. His latest book (2017) is The Cosmic Zoo: Complex Life on Many Worlds.

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