One hundred years ago, it was generally believed that our solar system was inhabited by intelligent beings who built a vast system of canals connecting the verdant regions of a drying planet. In 1877, Italian astronomer Giovanni Schiaparelli eyeballed Mars through his telescope and reported seeing lines on the planet connecting darker regions which he called “canali”, Italian for “channels”. When that word was translated into the English as “canals”, public interest was understandably piqued. Wealthy businessman Percival Lowell took up the cause, funding the observatory in Flagstaff, Arizona that bears his name. Observation of Mars became his lifelong crusade. He confirmed the existence of canals and posited that they were the product of Martian engineers. His views were so well accepted that in 1907, the Wall Street Journal called “ the most important event of the year… the proof by astronomical observation that conscious, intelligent life exists on the planet Mars.” Improved telescopes and, eventually, the 1965 Mariner 4 fly-by spacecraft shattered that image. Pictures beamed back showed a planet that resembled the barren, crater-pocked surface of the moon, rather than the comfortable home of Martian civilization. And more discouraging news was to come from the first instruments that landed on the planet. Enthusiasm about nearby extraterrestrial life waned. Now the pendulum is swinging back to motivate exploring the real possibility that our Solar System harbors life beyond our Earth, albeit of more modest microbial form.

Drawings of Mars by Percival Lowell

The nadir for finding Martian life came with the landings of the two Viking spacecraft in 1976. No longer expecting to see cities and intelligent creatures, these landers conducted remote experiments to detect organic molecules and the respiration products of resident microorganisms. The most tantalizing results came from the “labeled release” experiment. Mars soil samples were incubated with a drop of water containing a cocktail of nutrients labeled with radioactive carbon, then monitored for the evolution of radiolabeled carbon dioxide. It was detected. However, other instruments on Viking failed to detect any organic molecules in the soil. To reconcile these inconsistencies, scientists posited that the labeled release result was not caused by life forms, but by natural chemistry driven by reactive superoxides in the Martian soil which had formed in the dry, ultraviolet radiation-bathed conditions on the surface. In fairness, some scientists remain skeptical of that conclusion and hold out the possibility that Viking did indeed find life on Mars in 1976.

Although no subsequent missions have included direct experiments to detect life, there has been extensive exploration of Mars by rovers and orbiting satellites. Dramatic close-up images and tests of the composition of Martian soil and rocks reveal that Mars may not have always suffered from its current desert condition. Visible gullies may have resulted from ancient floods of water, and clay-like soils might have formed beneath ancient lakes. Theory and models suggest that Mars had a much thicker atmosphere a billion years ago that could have kept the surface warmer than its present chill, stabilized surface water and provided a feasible abode of life, before most of the atmosphere escaped the weak pull of Martian gravity (one third that of Earth). While water once flowed freely on the surface of Mars in the past, some is presently trapped in seasonal polar ice caps and is likely to remain in sub-surface permafrost. Life may have begun there. It could have left behind fossilized evidence or still be thriving in underground niches, as we know occurs beneath the surface of the Earth. A next generation Mars rover is in the works to further analyze the surface and collect and store samples to be returned by a subsequent mission. It’s only a guess when human explorers will set foot on the planet. If reality had kept pace with the marvelous movie 2001: A Space Odyssey, released in 1968, we would have been well-beyond human exploration of Mars by now. As its co-author and futurist Arthur C. Clark stated, his biggest missed prediction was that earthlings would step on the moon in 1969 but then “give up” in 1972 with the last Apollo mission.

Mars is not the only place where the search is on for extra-terrestrial life in our Solar System. Venus is the closest planet to Earth and seemed to be at a “habitable” distance from the Sun to enable liquid water and the conditions for life. But, largely from the Soviet Venera probes of the 1960s-1980s, we now know that Venus has a crushing, dense atmosphere containing toxic clouds of sulfuric acid, and surface temperatures hot enough to melt lead (~500 oC) due to a runaway greenhouse effect. Of current interest in this era of global warming, the greenhouse heating of a planet results when visible light from the Sun penetrates the atmosphere, but surface heat is re-radiated upwards in the infrared wavelengths that are blocked by carbon dioxide and other “greenhouse gasses”, trapping heat near the surface. Conditions are so intense on Venus that most robotic landing attempts failed or remained viable for less than two hours before succumbing to the heat and pressure. While there are fanciful suggestions that life might exist in more welcome regions high in its atmosphere, there is scant hope that we will find life on our neighboring planet.

Spacecraft have now travelled to the outer planets and revealed new candidates for life elsewhere in our Solar System. It had long been assumed that Jupiter, Saturn, Uranus, Neptune and Pluto were much too far from the Sun’s warming rays to support life. But flyby missions changed the focus from those planets themselves to their orbiting moons. Roughly 400 years after moons of Jupiter were first spotted by Galileo’s early telescope, the spacecraft aptly named Galileo found evidence that one of its large moons, Europa, contains a vast ocean of water underneath an icy crust about 10 miles thick. The heat necessary to sustain liquid water could not come from the sun. Likely candidates are the decay of radioactive substances in the core, and tidal friction due to the massive pull of nearby Jupiter. Like the tides on our oceans, Jupiter’s gravity gives varying tugs on regions of its moons, deforming them as they orbit, thus creating internal friction and generating sufficient heat to melt water. This effect also drives the internal heating to power copious volcanic activity seen on Jupiter’s moon Io. With any luck, the necessity of drilling through miles of Europan ice to search for sea creatures might be avoided due to the sighting of geysers spewing forth from cracks in the surface. NASA is planning the Europa Clipper mission to fly close to the surface of Europa dozens of times to sample its geysers for signs of life and to map its encrusted oceans. Is it too far-fetched to consider life in the sub-surface of Europa? Perhaps not, as we know on Earth that life thrives near hydrothermal vents miles deep in our oceans, empowered by gaseous eruptions rather than the Sun’s rays.

Saturn is even farther from the Sun’s energy source, but as with Jupiter, spacecraft have found one of its moons, Enceladus, to have an icy crust that erupts geysers of water replete with hydrocarbons and other organic molecules. And then there are The Sirens of Titan. That’s the title of a science fiction book by Kurt Vonnegut. But there is a real allure there for scientists. This largest moon of Saturn is the only moon in in our solar system known to have a substantial atmosphere plus rivers and seas on its surface. We learned this from the Cassini-Huygens mission which orbited Saturn and dropped a probe into the atmosphere of Titan in 2005. But in the frigid temperature of Titan, these surface “waters” are not composed of H2O, but of hydrocarbons such as methane and ethane. If life exists there, it would offer a stark, fascinating contrast to life as we know it here on Earth. NASA hopes to launch a rocket carrying a nuclear-powered helicopter called Dragonfly to descend to the surface of Titan in the next decade, though it wouldn’t get there until 2034. Stay tuned.

Enceladus in false color accentuating crevasses in blue

By its literal definition, SETI is seeking evidence of intelligent life elsewhere in the universe. A successful find could be the detection of a radio or optical “we are not alone” signal without interpretable messages, or, as some enthusiasts hope, receipt of a full-fledged “Encyclopedia Galactica” to advance our science and solve the problems of humanity. The detection of microbial life in our Solar System might seem less spectacular. But it would be a giant leap for science to discover an independent solution to the challenge of converting inorganic molecules to living entities that can utilize energy for metabolism, build structures against the flow of entropy, reproduce themselves and evolve into other life forms. And knowing it has happened more than once should increase the odds that full-fledged intelligent civilizations do exist beyond Earth. There is the alternate scenario that life has spread from planet to planet, known as panspermia. We know that bits of the moon and Mars splattered from asteroid-like impacts and have traversed the intervening space to Earth. This type of spread could result in all creatures in our Solar System coming from a common ancestor-quite a blast for Darwin. It is an exciting time for scientists to advance both SETI signal searches and the exploration of the Solar System in the quest to learn whether life on Earth is a unique invention in the cosmos.

---

--
Richard M. Lawn

Many thanks for an excellent post!

I have to say, though, that unless all life in our solar system shares a single origin (=is monophyletic), it is not so clear that we should be rooting for life elsewhere in our solar system.

In fact, there may be good reason to hope that planet Earth is the only planet with life in our solar system: https://www.nickbostrom.com/extraterrestrial.pdf

From said source:

"But I hope that our Mars probes will discover nothing. It would be good news if we find Mars to be completely sterile. Dead rocks and lifeless sands would lift my spirit."

Makes you think.

While I agree, in the case of Mars, (as we may need to colonize it, however that is going to take an enormous amount of resources to do starting with creating a new magnetosphere from the L1 position) I would love for there to be life elsewhere in our solar system to prove that life can be generated under many circumstances. For Mars, I'd love for us to find it lifeless now but not in the past. The ability to compare DNA, (assuming it has it pr something comparative) would be an amazing science coup.

awesome news, looking forward to reading more about et - should i phone home. keep up the great work.

---

>I would love for there to be life elsewhere in our solar system to prove that life can be
>generated under many circumstances.

But this would be bad news for us, right? If life, indeed, can be ”generated under many circumstances”, then we should hear from life beyond our solar system. Which we don’t.

An obvious interpretation is that intelligent life is exceedingly short-lived.

Finding evidence of life - past or present - on Mars would thus suggest that mankind is doomed (why not, e.g., https://www.nytimes.com/2019/11/26/climate/greenhouse-gas-emissions-carbon.html).

(Unless, like I said, Mars-life colonized Earth, or Earth-life colonized Mars – i.e. that life in our solar system is monophyletic)

Hello Sir

In front of Sirs like yourselsf Sir I am just a simple tourist admiring the surroundings but I am also a turist with a catch :))))) :p I am a Crypto Miner :))).... So do care please do tell kind Sir how much would cost a megalodon of a Huble ....I never joke when I talk serious talk and I always am faster than the laser beam when it gets to business !!!

Thank you very much for you time kind Sir and hope hope to hear from soon :)
\/ & ♡

---

The interpretation ( that intelligent life is extremely short-lived) does not strike me as obvious.
Intelligent life could be very plentiful in the galaxy, and we might very well still not have heard from it yet, for a number of reasons.

We might be purposely isolated, either to prevent harm to our cultures by too-sudden extraterrestrial contact, or because they wish to observe us in our naive state, and see what ever will we do next, or both.
Or, it might be that we simply haven't looked hard enough or long enough to detect extraterrestrial civilizations. Perhaps our making a sufficient effort in this direction is what qualifies us as ready to be contacted.

We are a dot • in the infinitness of the universes ersad but what a • We Are !!!

I please all of you dots ••• out there to not ever forget we first saw the dot • that became a ○ circle and then came m
etc !!!!MUCH LOVE & RESPECT!!!

I KNOW SOMETIMES IS EVEN HARD TO PAY FOR THE ELETRICAL BILL AND HAVE DOUBTS BUT PLEASE DO IT THIS WAY SOMEWHERE,SOMETIME WILL GIVE BRTH TO A STAR .
THEN WHE N THE STAR WILL DIES IT WILL GIVE ALL IT'S BEAUTY ONLY TO BY GIVE BIRTH TO A SUPERNOVA !!!
TO THE SUPERNOVAS LADIES AND GENTS TINY LITTLE • Dot :)

Peace & Love

The interpretation ( that intelligent life is extremely short-lived) does not strike me as obvious.

Global warming may be a limiting factor universe wide.

Those who have found out how to live with it may have done so by strictly limiting population and energy consumption. They may not build big transmitters.

What an narrow-minded asinine comment. You're basically saying that nowhere in the universe is it possible to advance beyond a carbon economy. Fusion energy is just around the corner for us. I'm sure other civilizations have figured it out. It's a big place that's been around for a long time.

FYI our planet has been warmer before. Life flourished for a span of hundreds of millions of years, from the Permian to the Paleogene.

Having just read the paper the Nick Bostrom wrote, I can see where he is coming from.
It is an eye opening piece that throws the mortality of intelligent life into sharp relief.

However, I can't help but want him to be wrong. He discusses the theory of the Great Filter. Either it is an apocalyptic event that wipes out a sufficiently advanced race, or a highly improbable chain of events that creates intelligent life. This theory is postulated due to the fact in the 50 plus years that we have been searching the skies for other intelligent life, we have heard nothing. Is it possible, how ever unlikely it maybe, that we are the first life form to reach this level of technology?

I would far prefer that the universe were teeming with life. After all, to paraphrase the 1997 film Contact, "If we are alone, it is an awful waste of space."

Agreed, SiriusC, agreed.

I find it sad that so much of importance in modern discourse is all too often overshadowed by the misguided notion of "global warming".

It has unfortunately become more of a fashionable buzz word, thrown around quite unnecessarily...

Per Aspera Ad Astra!

---

What man has discovered back then, and what we know today has changed dramatically. Just imagine what people in the future will find out next.

I can't help thinking about Charles Holland Duell when I see threads like this. The famous quote, now thought to be nothing of the sort incidently, "Everything that can be invented has been invented" is what I refer too The universe could be full of inteligent life communicating away to each other using technologies we have not discovered yet.

---

Wave upon wave of demented avengers march cheerfully out of obscurity into the dream.

A conjecture first put forward by R. N. Bracewell in 1960 as I recall, after he examined Tesla's Long Delayed Echoes. Bracewll considered it not impossible but highly unlikely.

As we continue to further our plan to explore mars and beyond, it is important we put to consideration its adverse effect on our home planet 'earth'. The irreversible climate change we experience (though arguable) here on earth is caused partly by the activities of man but majorly by the combine gravitational pull by sun and earth on mars which continually erode mars of its outermost atmospheres.

Mars is believed to have flourished with water coursing its surfaces like earth (400 million years ago). This beauty came to an end with all the surface run-off and large atmospheric gases (greenhouse gases) escaping into the vast space adjoining the red planet; going by the simple law of conservation of matter and laws of dynamics, the escaped greenhouse gases were either be flung away towards Jupiter by the centrifugal force generated by the spinning effect of the planet or pulled toward earth and sun by their combined gravitational force on the outer planets.

I believe the two likely incidents mentioned above happened to the greenhouse gases on the outermost layer of mars atmosphere. The escaped gases drift through space in a slow but continues manner such that earths gravity combs the gases thereby increasing the volume of greenhouse gases in earths atmosphere year in year out.

Until earthlings know and agree to all the causes of the increase in greenhouse gases that our planet is experiencing, our capacity to protect mother planet-earth will only be a political manifesto. The most disheartening decision on climate change is that poised by some politicians and supported by some members of the science community to blame other politicians whom they disagree with. This is unacceptable.

---

I like to point out that a the moment NASA is searching for ET life based on molecules and SETI project is searching for life based on radio signals. And I know E=mc^2 give one way to change energy into mass.

Also the famous Chanels on Mars are signals large enough to see from a long distance. The same as the big wall of china can be seen from a long distance.

Also there are idea's that ET life can be based on pure energy.

And very often is told that life that can communicate is based on physical, spirit and soul. And that communication is sending and receiving.

---

Well done!

Also the famous Chanels on Mars are signals large enough to see from a long distance.

Going to be picky here, sorry. :^) There are no Martian "canals" aka canali, channels, etc. They were a combination of optical illusion and meme (seeing what was expected or claimed by others rather than what was there) and found not to exist once high-resolution photos from orbiters were obtained. Mars does have a large, deep canyon system (Valles Marineris) which is visible from Earth-based telescopes as a dark band, but as far as I know, they were not recognized as having depth until the Mariner orbiter missions in the early 1970's identified them as canyons... this is also how and when they were named.

---