We are the Aliens

THE PANSPERMIA THEORY OF LIFE ON EARTH

INTRO

Life began on Earth around 3.8 billion years ago. Before that, no life. Then, life. Scientists call it abiogenesis. Life from non living matter. And not just any non-living matter — it had to be only stuff found on primordial Earth. How that happened is one of the greatest mysteries of all time. Generations of scientists devoted entire careers to find the answer. And here’s the surprising thing: they kind of figured it out.

The first step was breaking life down to its key building blocks.

<HECKLEFISH> Cool car, cool house, hot wife.

Of course I mean lipids, proteins, and RNA. For life to exist, you need these three things. So if you can explain how each of these elements could form and combine on Primordial Earth, you have a path to life. And here’s how it goes.

<HECKLEFISH> Wait - are you about to solve the greatest mystery of all time?

Pretty much. 

First, lipids can form if you combine carbon monoxide and hydrogen around a heat source. Turns out, all these ingredients were present on Primordial Earth. The current theory is lipids formed underwater in areas where heat from the Earth’s crust  - which contained carbon monoxide and hydrogen - escaped through hydrothermal vents.

Now this would all happen in salt water, because that’s what you have on Primordial Earth.

In salt water, lipids need amino acids to survive. And when amino acids combine, you get the second building block to life: proteins.

The formation of RNA - which would evolve into DNA - is trickier, but Scientists at the Rensselaer Polytechnic Institute in New York had a break through in 2009. They showed that the elements needed for RNA could collect and combine on certain kinds of clay surfaces. 

The last piece of the puzzle is time. This didn’t happen in an instant. Nobody flipped a switch. The precursors to life developed into the first living cells over millions of years. The elements are all there. Given the right combinations and conditions, life from the primordial soup is possible.

But what if it was much simpler than that?

What if life on Earth didn’t need all those chemical and geological elements to come together in unlikely combinations? 

What if life didn’t begin on Earth at all?

THE SEEDS OF PANSPERMIA

The theory is called Panspermia, meaning the seeds of life are everywhere. And they propagate through space, from one location to another. 

It’s not a new idea. It can be traced all the way back to Ancient Greece. Around 450 BCE Greek philosopher Anaxagoras of Clazomenae suggested life came from animal and plant seeds - or in the original Greek, “spermata” - that floated everywhere in the mixture of stuff that was the Universe. 

The Panspermia theory gained support in the 18th Century. French historian Benoit de Maillet theorized the cosmos was “full of seeds of everything which can live in the Universe”. 

At the same time, the Aristotelian idea that life spontaneously arose on Earth from non-living stuff was facing some big challenges.

First, in 1796, French mathematition Pierre-Simon Laplace developed a theory that the Solar System was formed from a nebula of gas and dust orbiting the sun which became widely accepted. And if this theory was true, Primordial Earth was way too hot for the development of life as we understood it.

Then, in 1859, Darwin rocked the scientific world by publishing “On the Origin of Species”. Suddenly there was a solid theory of how life on Earth became so diverse over time. 

<HECKLEFISH> I still don’t buy that I came from a monkey.

You didn’t. That’s not what Darwin’s theory says.

<HECKLEFISH> Really? I gotta re-read that thing.

But Darwin’s theory only explained how we evolved from the first living cell. It didn’t explain what happened before that. Suddenly there was a bigger focus on that final mystery: where did life come from in the first place?

In the late 19th century, the prestigious French Academy of Sciences offered 500 francs for any scientist who could prove spontaneous generation of life was possible. 

A young, relatively unknown chemist named Louis Pasteur took the challenge. He customized flasks with tall necks, where he could store sterilized cultures without any chance of outside contamination. And nothing happened. There was no generation of new microorganisms like there would be if they were left in the air to collect contamination. That was good enough to win the contest and create serious doubt life could grow from anything but other life.

These events opened the door for Panspermia’s popularity.  After all, life was here. It had to come from somewhere. 

The first of these Panspermia theories to gain traction came from Nobel prize winning scientist Svante Arrhenius in 1908. He published an article called “Die Verbreitung des Lebens im Weltenraum” - “the Distribution of Life in Space”. His idea was that microscopic forms of life, like spores, can be propagated in space, driven by the radiation pressure from the sun, and seed life from one planet to another. His theory became known as Radiopanspermia.

For this to work, bacterial spores would need to survive long periods of time in space. But Arrhenius was encouraged by experiments done by chemist Emile Roux - one of Pasteur’s close c0llaberators. Roux proved anthrax could survive UV radiation in an airless environment.

There was only one small problem with this.

Emile Roux was wrong.

It took French plant physiologist Paul Becquerel to demonstrate Roux’s results were due to experimental error. In fact, microbes would not survive under the extreme ultraviolet radiation found in space.

For Panspermia to work, biological matter would need to hitch a ride through space on something that can survive the harsh conditions.  

Does such a vehicle exist? Turns out, the answer is yes. And they arrive on Earth all the time.

LITHOPANSPERMIA

A new theory of Panspermia took hold, expressed in a speech to the British Society for the Advancement of Science in 1871 by  scientist Sir William Thompson - better known as Lord Kelvin.

<HECKLEFISH> Why does that name sound familiar?

He ended up inventing a temperature scale.

<HECKLEFISH> The Lord scale?

I’m going to pretend you’re joking.

<HECKELFISH> Lord it’s cold. Hey - I bet that’s how it started!

Lord Kelvin suggested biological matter was buried in meteoric rock moving through space. The rock would provide protection for the microbes inside until it landed on Earth and provided the seed for life.

The process was called Lithopanspermia - adding the Greek word Litho, meaning rock.

Kelvin wrote, “Hence and because we all confidently believe that there are at present, and have been from time immemorial, many worlds of life besides our own, we must regard it as probable in the highest degree that there are countless seed-bearing meteoric stones moving about through space. If at the present instant no life existed upon this Earth, one such stone falling upon it might, by what we blindly call natural causes, lead to its becoming covered with vegetation”

Renowned physicist Hermann Helmholtz joined the growing number of scientists supporting Kelvin.

 He added that meteorites did contain organic molecules. And even at the time they had a sense comets were composed of hydrogen and carbon. It seemed like the right theory at a time when life from non-living matter seemed ridiculous.

And the promotion of Lithopanspermia continued into the modern age, most notably with Astronomer Sir Fred Hoyle. Hoyle devoted his career to proving organic matter pervades our Universe and challenging the idea life originated on Earth in a primordial soup. 

He didn’t buy the idea life originated from inorganic molecules and found it ridiculous not to think of life as everywhere in the Universe.  Hoyle was often dismissed by mainstream science, since he believed our biosphere extended well beyond our planet and into the Milky Way, and that it was impossible to prevent the exchange of biological material between star systems. 

He claimed victory when organic material was discovered in Halley’s Comet in 1986. His frequent collaborator Chandra Wickramasinghe felt vindicated again when the Rosetta Mission to Comet 67P/C-G found a mix of compounds thought to be essential precursors to life - including slats of ammonium and hydrocarbons.

But for Lithopanspermia to be the answer to life on Earth, it doesn’t matter if meteors hit the Earth today. They had to have hit the planet 4 billion years ago, before life began.

Turns out, back on Primordial Earth, there were more than a few meteorites. We had an all out bombardment.

PRIMORDIAL EARTH

They say the Universe started with a bang.

<HECKELFISH> A big one.

Exactly. But our planet had its own big bang when it formed 4.6 billion years ago. A meteor the size of the planet Mars made a direct hit.

<HECKLEFISH> No way.

It’s true.

<HECKELFISH> Must have caused serious damage.

It did. A big chunk got knocked out.

<HECKLEFISH> Wish someone had saved it in a bucket of ice or something. We could sew it back on.

Oh, it’s still there. We call it the moon.

<HECKLEFISH> Maybe just leave it, then. We need it for werewolf movies.

This big meteor impact was followed by a hailstorm of comets, which caused craters on the moon and likely on the young Earth as well.

But what about smaller meteors that might actually land safely and deliver biological matter? Seems logical they were around. 

In 2013, a team from the Geological Survey of Denmark and Greenland found the evidence.

The Isua greenstone belt is a stretch of volcanic rock in Southwest Greenland. And it’s old. Like, really old.

Scientists divide the Earth’s live span into four Geological eons. First is the Hadean Eon, which starts at the formation of the Earth and ends 4 billion years ago. It’s named after Hades, the Greek God who was in charge of Hell, because conditions back then were, well — it wasn’t a good time to visit Earth. Next is the Archean Eon which spans 4 billion years ago to 2.5 billion years ago. This is followed by the Proterozoic and  Phanerozoic eons, but our focus is on the Archean. This is when life begins. And miraculously, the rocks on the Isua greenstone belt date all the way back to this time. 

This makes the greenstone belt a great place to gain insights into Earth’s very early history. 

The survey team visiting in 2013 took rock samples and discovered they were some of the oldest ever found — going back 4.1 billion years. That placed the rocks in the timeline after the Mars-sized meteor impact but before the barrage of comets. 

And there was something else: the rocks contained the chemical elements osmium and iridium. These elements were heavy metals, which should have disappeared into the Earth’s core when the planet was liquid. But there they were. And the team knew comets don’t contain these heavy metals. The rocks they found were meteorites.

And maybe even the exact meteorites that transported the seeds of life into Primordial Earth.

ROCKS FROM MARS

Of course, the Lithopanspermia theory isn’t about just any meteorite landing on Earth. It requires rocks with viable biological matter buried inside. These rocks have to originate from somewhere habitable. 

Throughout human history, people witnessed thousands of meteorites falling from the sky. In Ancient Greece, these sightings were often associated with supernatural events, and considered omens from the Gods. But really, they were most often pieces of an asteroid belt located between the orbits of Mars and Jupiter.  They were lifeless rocks, occasionally containing metallic elements - like the samples found in Greenland. They did not launch from a habitable zone abundant with the building blocks of life.

We need proof that matter from another habitable planet could make it here. 

And in 1815, that’s exactly what we got.

It was 10:00am on October 3 - yes, this was such a big deal we know the exact time. A farmer was tending to his vineyard in Chassigny, France. First he heard the terrifying “boom” in the sky, like a cannon from the Napoleonic Wars. Only there were no cannons around. It was a sonic boom, not something farmers in 1815 would know about. But very soon he would see the cause - a nine pound object falling from the sky, coming fast. And close - making impact 400 meters from where he stood.

The meteorite exploded on impact, spreading fragments everywhere, sending stones in all directions. 

Villagers collected pieces around the impact site. A larger piece was found 160 meters away. 

A doctor from Langres, Mr. Pistollet, arrived two days later to make an official field investigation of the site. He was able to retrieve 4 grams of the meteor for study. 

And it’s from examining the composition of that fragment we learned that, for the first time, we were hit with something from a planet different from our own. This rock was from Mars.

Since that time, NASA has identified over 60,000 meteorites on Earth, including 175 that originated from the planet Mars.

And one of them looked like it contained the remains of ancient life. It was a piece of a meteorite found in Antartica, labelled 84001. It remains the most well-known meteorite ever found. In fact, on August 7, 1996, President Bill Clinton announced to the world this rock may contain evidence of life on Mars. 

The President stood on the South lawn of the White House that afternoon and said, “today rock 84001 speaks to us across all those billions of years and millions of miles. It speaks of the possibility of life. If this discovery is confirmed, it will surely be one of the most stunning insights into our universe that science has ever uncovered.” He could have stopped there, but he didn’t. He went on to say, “Its implications are as far-reaching and awe-inspiring as can be imagined.”

The meteorite was found in Antartica, in the Far Western Icefield called Allan Hills. It was December 27, 1984. Scientists riding snowmobiles on their annual survey of the area took samples from a rocky outcrop protruding from the blue ice. The first spark of excitement happened when they got it back to the lab. Oxygen isotope analysis revealed a Martian origin. Scientists got more excited when they noticed unusual structures in the rock: fine-grained round areas called “rosettes”. They proposed that these structures were caused by organic matter, carbonate spheroids with a biological origin. If true, this would be the first signs ever of extraterrestrial life. 

In 1996, they published their theory in the journal Science. Word was out - we may have discovered evidence of past biological activity on Mars. The biological matter lived in the outermost black rims of the carbonate globules in rock 84001.

But after further examination, scientists did not accepted this theory as true. One key issue was the abundance of contamination from terrestrial materials - the rock had been sitting on Earth for over 30 million years. Another was the speculative nature of the inferences made from shapes in the rocks  - in other words, there was no conclusive evidence of biological matter.

 Turns out, 84001 - the world’s most famous meteorite - was probably not the ancient home to extraterrestrial life. President Clinton’s “stunning insights into our universe” would have to wait.

But the public won’t let the fascination with this meteorite die. The disproven paper has been sited more than 2,000 times.

Truth is, we have yet to find living biological matter on Mars. But we’re pretty sure it was there. We’ve discovered water in the form of ice on Mars - a requirement for life as we know it - at the poles and beneath the surface. Incredibly, in 2008 the Phoenix Lander actually dug into the Mars surface and “saw” the water-ice first hand.  

The surface suggest this water was once flowing everywhere. We’ve found ancient river valleys, lakebeds and minerals that would only form with the presense of water. Mars may not be teeming with life now, but 3.8 billion years ago it was much closer to an Earth-like environment.

So Mars is a possible source for Lithopanspermia in our Solar System. But it turns out, if you follow the water, there’s a lot more.

FOLLOW THE WATER

Around the same time the media was going crazy about alien life in meteor 84001, the Galileo mission made a much bigger discovery. Because this one was true.

In 1995, NASA’s Galileo spacecraft began its orbit around Jupiter. And for the next eight years we got stunning details about the planet. Of course, Jupiter - the largest planet in our solar system - isn’t habitable at all.  First, there’s no solid surface. It’s made of hydrogen and helium gas, with traces of methane and ammonia among other unpleasant compounds. There’s also intense heat and radiation. So not only will we not get biological matter from Jupiter, there are no rocks to break off and transport it our way.

But the Galileo spacecraft found something else during its time orbiting Jupiter. 

One of the moons, Europa, appeared to have a bright, icy crust. And the patterns of ridges and cracks on the surface were consistent with the presence of a subsurface ocean beneath the ice shell. Scientists now believe there is an ocean under that surface, a key ingredient for life.  

Turns out, moons are the most likely sources of life in our Solar System.

Saturn is another gas giant with extreme atmospheric pressures. Nothing could live there either. But similar to Jupiter, one of Saturn’s moons might be hiding its own ocean.

The moon is called Enceladus. 

NASA’s Cassini spacecraft discovered geysers erupting on Enceladus’s South Pole suggesting a subsurface ocean beneath the icy surface. And chemical analysis of the atmosphere contained complex organic molecules. Including many building blocks needed to support life, like carbon dioxide methane, ammonia, and hydrogen. Scientists think this is likely due to hydrothermal activity on the ocean floor, similar to hydrothermal vents in our oceans. 

Cassini also discovered a key molecule on Enceladus: hydrogen cyanide. Yes, that is poison to us, but scientists actually think the molecule plays a big role in the origins of life. According to Jonah Peter, a biophysicist at Harvard, “it’s sort of the Swiss Army knife of prebiotic chemistry.”

Saturn has another moon that holds possible life, it’s largest one, aptly named Titan.

The Cassini spacecraft did more than just fly by this moon. On Christmas Day in 2004 a separate lander called Huygens launched from Cassini, passed through the Titan atmosphere, and landed on the surface. So we have more than just chemical readings or atmospheric tests from Titan. We have actual pictures.

At the landing site, we can see pebbles of water ice all around. We’ve got arial photos as Huygens landed of areas consistent with large bodies of water. There appeared to be large drainage channels crossing the mainland and flowing into what might have been a dark sea. The atmosphere is rich in organic molecules and complex hydrocarbons. The surface is too cold for life, but there’s complex chemistry happening, with lakes and rivers of liquid hydrocarbons. And again, there is evidence of subsurface oceans. Of all the moons, Titan is most similar to primordial Earth.

And there is more. Jupiter has two other moons that likely have subsurface oceans: Ganymede and Callisto. 

A computer model of Ganymede’s interior created in 2014 indicated the moon’s rocky sea bottom might be in contact with salt water. This opens up the possibility of primitive life forming there.

Turns out, our Solar System is full of hidden oceans.

<HECKLEFISH> Man, I picked the wrong planet.

You’d rather be somewhere with an underground ocean?

<HECKLEFISH> Heck yeah. I may just panspermia my way over to Europa.

Well there’s one problem with that. You wouldn’t survive the trip.

<HECKELFISH> I’ll be fine. I’ll bring my tunes, I got snacks.

This actually brings up another challenge to the Lithospermia theory. In our solar system, the journey from one habitable place to another is really long. For example, the distance from Earth to Europa is about 480 million miles. If you got in a car and drove there at 100 miles an hour, it would take you over 500 years to get there.

<HECKLEFISH> Is that with or without traffic?

The point is, that’s well beyond our life span. Rocks can survive that long. But what about biologic matter?

It turns out, for certain bacteria, 500 years ain’t nothing.

ANCIENT BACTERIA

A disaster was about to happen on Lake Peigneur in southern Louisiana. 

It was 1980. The Diamond Crystal Salt Company operated a mine on the Lake to extract rock salt from the rich soil on the lake floor. 

But underground salt deposits have another characteristic - they often have large pockets of space that trap oil. So at the same time, Texaco had a drilling rig moving about the surface of the lake, trying to get at that oil. 

On the morning of November 20, the crew of the oil rig was probing the lake bed when their 14 inch drill bit got stuck at a depth of about 1,230 feet. They attempted to free the drill, and heard a series of disturbing pops from below - and then the entire rig started to tip. The crew evacuated the rig in time to watch the entire thing get swallowed up into the lake.

Turns out, they had accidentally penetrated three levels deep into the salt mine below and opened up a giant sink hole that began sucking in everything around it. No fewer than eleven barges, a tugboat, and an entire lake house were pulled into the swirling man-made vortex.

Even more spectacularly, the canal that drained the lake into the Gulf of Mexico began flowing backwards as the water level fell. So they created a 164 foot waterfall - the tallest in the State for its brief existence. 

Somehow, all 50 people working in the mine escaped before the waters flooded the tunnels.

Eventually, the whirlpool calmed down and the lake refilled itself.

But the disaster caught the attention of Dr. Russel Vreeland of the University of New Orleans. He knew that all that lake water flowing into the mine was only 2% salt. But rock salt dissolves readily in water. So inside those flooded mines was water suddenly saturated with salt. Maybe as high as 32%, higher even than our oceans. And for a biologist, this was exciting.

The disaster created an entirely new environment.

In 1987, Dr. Vreeland was allowed access to the mines. And his suspicions panned out.  Most creatures would find the concentrations of salt in those mines lethal. But he found a new species of bacteria called Halobacteriales that thrived in it. This bacteria had been trapped in water pockets in the salt crystals, set free in the oil rig disaster. 

But those weren’t just any salt crystals. The salt beneath Lake Peigneur was formed by the evaporation of a previous body of salt water some 125 million years ago. This new species of bacteria - which Dr. Vreeland was able to revive from its stasis state - came from the heyday of the dinosaurs.

How could a biological organism survive so long? The unique conditions in the salt mine ended up protecting the bacteria from elements that would normally damage an organism. Oxygen would normally be one source of damage, but that didn’t exist inside the rock-salt crystals. Ultraviolet radiation would be another danger, but none penetrated so deep in the ground. And it turns out, these extreme species of bacteria contain dan-protecting proteins of their own that prevent damage over time.

The discovery of 125 million year old halophilic bacteria was a boost to the Lithopanspermia theory. It meant biological matter was viable even on galactic time scales.

But there’s one last issue with the theory. These microbes had to travel from one habitable zone to another through space. And space is a “zone” that is not habitable at all.

EXTREMOPHILES

Space is about the harshest environment you can imagine.  

If you step out into space, you likely won’t survive even a few seconds.

First, it is mostly a vacuum, which means there is no atmosphere. With no pressure from air or other gases, water in your body quickly turns to vapor. Which leads to desiccation - the complete dehydration of all matter.

Second, it’s either really hot or really cold. The temperature can vary between -400 to +400 degrees Fahrenheit depending on if you’re facing the sun - which by the way is nearly 10,000 degrees Fahrenheit on its surface. So don’t face the sun.

Lastly, deadly radiation is everywhere. Ultra violet, cosmic rays and high-energy particles break chemical bonds and alter the structure of organic molecules. Which could really hurt.

So what biological material could possibly survive out there? And survive long enough to make a journey across the Solar System to seed new life on Earth?

Dr. Thomas Brock wasn’t trying to answer this when he lead a team of researchers into Yellowstone park in 1964. He was just fascinated by the microbes living in the hot springs. But his findings would have profound implications for the field of astrobiology. Because Brock was about to discover a new type of biological matter called the extremophile - a microbe that could exist in the harshest environments.

Brock and his team lowered microscope slides into the boiling springs. A few days later they brought the slides back to the lab. And there were living microorganisms on every one.

These would be called Thermophilic Bacterium and they thrived in boiling waters - nearly 200 degrees Fahrenheit. Once they published their seminal paper describing the find, a new world opened up to researchers. Areas that were considered uninhabitable now became worthy of study.

Microorganisms called Hyperthermophilic archaea were found that can survive up to 298 degrees Fahrenheit. And Deinococcus Geothermal were discovered, microbes able to grow at temperatures a low as -13 degrees Fahrenheit.

Of course the ultimate environment considered uninhabitable was space.

And we sent microorganisms into space every chance we got. They hitched a ride into low Earth orbit on rockets in 1965. Then in 1966,  samples of bacteriophage were attached to the Gemini IX mission and exposed to outer space for 16.8 hours. A similar experiment was done on Gemini XII, this time with an exposure of 6.5 hours. In both cases, well, not much survived. The Gemini experiments ended up proving the strong killing power of the full space environment.

But the tests continued - this time with more sophisticated exposure devices providing various levels of optical filters to protect from UV rays.

You’ve probably heard of Neil Armstrong and Buzz Aldrin. But just a few years after they landed on the moon in Apollo 11, John Young and Charles Duke accomplished the same feat in Apollo 16. For supporters of panspermia, their landing was much more exciting, because they carried microorganisms outside the Earth’s magnetic shield for the first time.

Apollo 16 was outfitted with a sophisticated exposure device called the MEED (microbial ecology equipment device).   It held a tray of 798 microorganism samples mounted on the end of a TV boom on the command module. And it exposed samples to space vacuum for 1.3 hours, including direct exposure to the sun. While we learned a bit about varying levels of UV radiation, ultimately the microorganisms did not fare well.

In 1983 and then again ten years later,  the Spacelab missions launched - these were modular labs for scientific experimentation that would be launched into orbit. The mission was controlled for the first time by the German Space Operations center. Both of these missions exposed microbes to space for 10 full days. But they had a unique goal. They set out to show the implications of progressive ozone depletion for life on Earth. To simulate this process, they exposed the microbes to increasing levels of UV radiation. It gave us a look into a future with no ozone - and since the microbes didn’t survive this trip either, the future didn’t look good. Turns out we really need our ozone.

Beginning in 1994, the experiments moved onto robotic Earth-orbiting ships, including Russian made Foton satellites. And with these missions, a significant change was made to better simulate the Lithopanspermia environment: the microbes were shielded from UV rays as they would be if buried in a meteorite.

The first mission exposed the samples for 15 days. The next, in 1997, exposed them for 10 days. In 1999, the Russian Foton exposed the spores and bacteriophage for 12.7 days. And in all cases, a significant amount of  biological matter survived.

In 2005, Scientists added unique organisms called Lichens to the Russian Foton M2 mission. These creatures are actually a symbiotic combination of fungi and algae. 

<HECKLEFISH> Kinda like you and me.

Which one are you?

<HECKLEFISH> I ain’t the fungi.

In the case of Lichens, the fungal partner provides a protective structure and absorbs water and nutrients. The algae contributes photosynthesis, which makes organic compounds benefiting both partners. Scientists collected the lichen from two extreme places on Earth. Half were from 2000 meters high in the mountains of Spain. The other half were sourced from the Antarctic Dry valleys. And they proved to be nearly indestructable.

They were exposed to space for 16 days on the Russian Foton M2 satellite. The results were impressive.

All the exposed lichens showed the same photosynthetic activity after the flight as measured before the flight. The findings indicated that lichenized fungal and algal cells can survive in space after full exposure to massive UV and cosmic radiation - conditions proven to be lethal to bacteria and other microorganisms. 

The lichen upper cortex seems to provide adequate protection against solar radiation. Moreover, after extreme dehydration induced by high vacuum, the lichens were able to recover their full metabolic activity in 24 hours.

When the International Space Station became operational in 2008, the length of the testing went from days to years. A variety of biologiocal samples, from spores to microbes to viruses, were given a permanent home on the space station on a device called the EXPOSE-E. This contains one tray for experiments on prebiotic chemical evolution. Another tray tests outer space conditions like surviving the vacuum and intense solar UV spectrum. A third tray simulates the Mars surface climate. 

Through all this testing, scientists found over and over again that extraterrestrial solar UV radiation was the most dangerous factor facing microbes in their efforts to survive in space. In fact, if shielded against solar UV,  spores of  the bacterium bacillus subtitles were cabable of surviving in space for up to 6 years.

The Japanese contributed new insights in the Lithopanspermia debate with their Tanpopo project. They added their own module to the International Space Station called the Japanese Experiment Module Exposed Facility. Here they tested the effect of space exposure on microbes to test their survival time. And they found evidence that some microbes can survive for at least a year in space. In one case, the top layer of a radioactivity-resistant bacteria Deinococcus radiodurans did not survive the year long exposure, but the cells underneath this layer survived. This suggests that - in addition to meteorites - clusters of microorganisms could be a viable way for life to spread from planet to planet, if the layers of cells are thick enough.

Bottom line, given the right conditions, the strongest biological spores and lichens can survive a trip through the solar system.

But when we think of life coming to us from space, we’re probably thinking beyond the Solar System.

It’s not all that exciting to think we came from one of Jupiter’s moons.

Could life have been delivered here from somewhere further? Some Earth-like planet in the Milky Way Galaxy?

To date, we’ve discovered thousands of exoplanets - meaning planets orbiting a star other than our own sun.

And of those, at least 59 are potentially habitable. This includes 1 the size of Mars, 20 the size of Earth, and 30 that are, well, really big. And if we’ve identified 59, you know there are a lot more.

Could pieces of these planets ever travel all the way to our Solar System carrying biological matter?

Until recently, the answer was no. We logged over 750,000 known asteroids and comets, and not one of them originated outside our solar system.

Then, in 2017, that all changed.

OUMUAMUA

On October 19, 2017, the Pan-STARRS telescope on the summit of mount Haleakala on the island of Maui signaled an alert. It was in the middle of a nightly pre-programmed survey of the skies contracted by NASA. It was looking for near-Earth objects of note. Most every night, it found nothing new. But this night would be different.

Pan-STARRS was tracking an object moving rapidly west across the sky at 6.2 degrees per day.  Rob Weryk, a researcher for the University of Hawaii Institute for Astronomy, identified the object and submitted it to the Minor Planet center. He knew right away the object was unusual. “Its motion could not be explained using a normal solar system asteroid or comet orbit.” He contacted Marco Micheli, a fellow graduate from the Institute who worked at the European Space Agency’s telescope in the Canary Islands. Marco saw the same issue with the motion. The object’s trajectory was extreme. It was not on any sort of loop that would take it around the sun. They searched the Pan-STARRS image archive and found photos of the object on previous days. And that gave them the additional data to confirm it: this object came from outside our solar system.

For the first time in recorded history, they were looking at an interstellar object.

NASA’s Center for Near Earth Objects team plotted the object’s trajectory. It came from the direction of the constellation Lyra. And it was cruising through space at 15.8 miles per second.

The object approached the solar system from “above” the elliptical. Then it did a quick plunge toward the sun before making a hairpin turn, passing Earth at a distance of 15 million miles on its way toward the constellation Pegasus.

Astronomers at the Hubble and Spitzer telescopes found that the object had an odd, cigar like shape. And it was around 400 meters long. It also sped up slightly as it left the solar system, which alarmed some who worried it was an alien spaceship. Comets can accelerate as they recoil from material they emit. But this visitor was not emitting much at all - and ultimately was classified an asteroid.

Maybe it was knocked into space by collisions of other planets, or gravitational tides. But however it got here, the fact remains, it was now feasible that interstellar objects could travel our way.

The Minor Planet Center in Cambridge, Massachusetts designated the object A/2017 U1. But the team on Haleakala that first discovered it gave it the name Oumuamua. Which roughly translates to “messenger from a distant past.”

Unfortunately, NASA lacks a rapid response mission team ready to investigate objects that suddenly appear. So we couldn’t get close to Oumuamua and will likely never see it again.

But in case more objects like it do appear, there is a European mission planned called Comet Interceptor. This will park itself in orbit beyond the moon, ready to investigate the next interstellar object that pays us a visit.

ONE LAST POSSIBILITY

Since the 1800’s, when the theory of Panspermia seemed like the more likely theory of life on Earth, things have shifted. We now know about DNA and RNA. The potential of combining elements to create a living cell from organic compounds on Primordial Earth is much better understood - and feels much more possible. 

Meanwhile, the reality of an interstellar rock small enough to land safely on Earth but big enough to protect living microbes inside, just randomly arriving here from a habitable world millions of miles away - well, that’s starting to feel more complicated than necessary. Space travel is long, harsh and difficult, making life transfers unlikely and complex. Most important, we have yet to actually find biological matter living in meteorites. Occam’s razor suggests the simpler answer - life originating right here - might be the right one.

Although, there is another type of Panspermia that is the simplest answer of all.

It’s called Directed Panspermia.

It was suggested by Francis Crick and Leslie Orwell - the team that co-discovered the structure of DNA with James Watson. Reputable and respected scientific minds. They put forth their theory at a conference on Communication with Extraterrestrial Intelligence organized by Carl Sagan in 1971. Their idea? Organisms were deliberately transmitted to the Earth by intelligent beings from another planet. 

It certainly solves all the problems of rocks randomly getting here and miraculously containing life. If intelligent beings inserted the biological matter and directed the meteorites at Earth, this avoids all the work trying to explain the Galactic-scaled logistics.

But our instinct is to dismiss the idea - it sounds like a bad science fiction movie and there’s no evidence for it.

Except . . . there is. 

Crick points out in his paper on Directed Panspermia that the chemical composition of living organisms “must  reflect to some extent the composition of the environment in which they evolved”. He goes on to point out that human beings have a trace element in their bodies called molybdenum, which is actually crucial to our organic processes, and plays an important role in enzymatic actions. But here’s the thing: molybdenum is very rare on Earth.

Maybe the origin of life did indeed begin on another planet.

Which makes us the aliens.