“Life in the Milky Way” –Could Earth Have Seeded Our Galaxy? (Weekend Feature)

Milky way Center

 

In a recent blog, Harvard’s distinguished astronomer, Avi Loeb, celebrated the the launch of the space dog Laika onboard Sputnik 2 on November 3, 1957, as a historic milestone, the first contemporary demonstration that humans are capable of exporting Earth’s life out into the Milky Way. But as Loeb writes, our planet has accomplished the same task many times over, when terrestrial rocks were launched into space as a result of asteroid impacts, the most vivid being the massive impact 65 million years ago, when an object the size of Mount Everest ended the 450-million-year reign of dinosaurs, oddly paving the way for the emergence of Homo sapiens.

In Ends of the World, mass-extinction authority, Peter Brannen, dionosaur-ending Chicxulub asteroid as so large that, even at the moment of impact, the top of it might have still towered more than a mile above the cruising altitude of a 747. In its nearly instantaneous descent, it compressed the air below it so violently that it briefly became several times hotter than the surface of the sun.” When the meteorite hit ground zero, it was totally intact. It was so massive that the atmosphere didn’t even make a scratch on it.

The force of the impact was so great, speculates Brannen, that it may have littered the Moon with fragments of dinosaur bone.

Indeed, the recently discovered interstellar comet 2I/Borisov entered the last leg of its trip toward the solar system by passing the nearest star to the sun when the first humans first modern humans left Africa.

Mars-to-Earth Shuttle

A recent example of the possibility of the exportation of life, is the Mars-to-Earth shuttle of meteorites that Loeb says may have had harbored “tiny astronauts, in the form of microorganisms in their belly. Nearly two decades ago, we learned that a Martian meteorite, the famous Allen Hills meterorite, named ALH84001, which was found in Antarctica, was never heated above 40 degrees Celsius (104 degrees Fahrenheit) after being ejected from the surface of Mars. And a paper published in Science a few years prior had argued there was evidence for past biological activity inside the rock.”

The ALH84001 conjecture, however, was ultimately rejected, but the principle remains valid, raising the possibility says Loeb that if organisms were transferred from Mars to Earth billions of years ago, they could have been the original seeds of life on our own planet. If so, we could all literally be Martians. The existence of the Mars-to-Earth shuttle for biological organisms, it is natural to wonder whether a terrestrial package might have been sent not just to Mars but out of the solar system entirely long before Voyager 1 and 2 were launched.

“The Death of Mars” –Pluto-Size Asteroid Ignited Ancient Climate Change

Most asteroid impacts are not powerful enough to eject terrestrial rocks with enough speed to leave the solar system. But many solar system bodies spend most of their time in the Oort cloud, a sort of comet nursery that hovers, loosely bound to the sun, at distances up to 100,000 times farther out than Earth. Some of these bodies appear episodically as long-period comets with eccentric orbits that bring them close to the sun, where they can get gravitationally kicked by planets like a slingshot all the way out of the solar system.

Oort Cloud Comets

The comet nursery of the Oort Cloud in the outer reaches of our Solar System, spits out long-period comets with eccentric orbits that bring them close to the sun, where they can get gravitationally ejected by planets all the way out of the solar system –like a ball running through a pinball machine says Loeb.. Some of these spectaucular long-period comets (LPCs) pass just 50 to 100 kilometers above Earth’s surface, possibly scooping up life from the atmosphere before heading back out into the vast reaches of the Cosmos. Recent discoveries have provided evidence that microorganism colonies exist at altitudes of 48 to 77 kilometers.

Life Exporting Events

In a paper written with Amir Siraj, Loeb calculates that there could have been tens of such life-exportation events over the lifetime of Earth. A similar number of events are expected to be associated with asteroids that came from outside the solar system before they grazed our planet’s atmosphere. “This number,” he writes, ” would increase by orders of magnitude if life existed above an altitude of 100 kilometers during points in Earth’s history as a result of enhanced atmospheric turbulence or volcanic activity. Of course, these bodies cannot pass too close to the ground because air friction would slow them down and either force them to crash or burn them up”.

“The Death Star” Event That Ejected Life Into the Solar System

These Earth-grazing objects would scoop microbes at accelerations of millions of gs. Microbes such as Bacillus subtilis, Caenorhabditis elegans, Deinococcus radiodurans, Escherichia coli and Paracoccus denitrificans have been shown to live through accelerations just one order of magnitude smaller. these mini astronauts, says Loeb, are perfetly suited for ride through the Interstellar medium of the Milky Way.

In 2019, an Anthropocene-Epoch example of Earth seeding the Cosmos occurred when the planet’s most indestructible species, the tardigrade, an eight-legged micro-animal that will survive until the Sun dies, according to a 2017 Oxford University collaboration, likely made it out alive following a crash landing on the Moon’s surface by Israel’s Beresheet probe in April, according to the US-based organization responsible for their trip.

“We believe the chances of survival for the tardigrades… are extremely high,” Nova Spivack, co-founder and chairman of the Arch Mission Foundation, told AFP, adding that the diminutive creatures, which are under a millimeter (0.04 inches) in size, had been dehydrated to place them in suspended animation, then “encased in an epoxy of artificial amber, and should be revivable in the future.”

Who knows what else may be out there?

The Daily Galaxy via Science, Avi Loeb Blog Scientific American, Cambridge.org