The search for Life on earth-like worlds orbiting distant stars is part of the age-old quest to learn whether or not we are alone in the Universe. But forget about green extra-terrestrials with tiny antennae or cocoon-shaped aliens. Everything from rocky-like creatures to shapeless ectoplasm can be the much sought after form of Life you aspire to find on distant planets!
Absence of evidence doesn’t equate evidence of absence (Donald Rumsfeld, speaking about Saddam Hussein’s weapons of mass destruction, but perfectly fitting the topic of Life among the Stars)
We do not share the same Sun
Are we alone in the Universe? When we gaze up at the night sky filled with wonderful comets, stars and planets, it comes natural to wonder what those worlds might look like. Would they have forests and lowlands, lakes and rivers, herds and swarms, predators and prey, day and night? Would creatures there speak, write and use tools? Would they resent our presence? Would they love us?
The possibility of answering a question that had intrigued philosophers, theologians and scientists since the time of ancient Greeks seems not a far-fetched perspective today. But beware, the life thriving out there is perhaps not the one that meets your expectations or suits your aesthetic taste.
With a perennial lack of credible radio signals from extra-terrestrial intelligences, à la Jodie Foster in the movie Contact, screen adaptation of scientist Carl Sagan’s book of the same name, it is difficult to foresee how long we have to wait for an interplanetary meaningful message. Therefore, the only way to actively find life in the Universe is to watch out for extra-solar planets circling around sun-like stars, with potentiality for life based on their distance from the star and evidence of oxygen, water and, possibly, organisms.
Space telescopes can detect extra-solar planets by recording the minute difference in brightness that originates when a planet passes behind its host star. To know more about exoplanets, NASA is planning to launch an increasingly powerful number of space telescopes in the near future. A huge orbiting telescope, named Terrestrial Planet Finder Interferometer (TPFI), will be launched in the 2020s to study the exoplanet atmospheres. Until then we can only vaguely guess which exoplanet is a suitable land to call home.
Types of Life
How many types of life can reasonably find place in the Universe? Based on current scientific advances, the tree of Life consists of 3 different bushes that have differentiated over the course of billions of years. One bush contains bacteria, whereas viruses are not considered really living organisms. The second group encompass the multicellular life, from men to porcupines and sequoia. The third line includes unicellular complex organisms such as amebae.
The question is: how do we know that there isn’t a fourth bush, waiting to be discovered, perhaps on distant planets, made of a combination of the above forms or others?
Life can be weird and multiform. Don’t assume that with different atmospheres and nutritional sources, life’s quality and shape will meet your every day experience! Actually, it might have surprising and unexpected appearances that we can only barely imagine: giant unicellular protoplasm, half plant-half-animal beasts, supremely intelligent stone-like creatures, macro-organisms just made of bacteria! Will we be able to interact with them, and how?
Old Aliens
Before looking for traces of life in the distant Universe, we should ask ourselves a simple question: do aliens visited our planet? According to popular myths, reverberated in unnumbered books and TV series, extra-terrestrial intelligences are familiar with the Blue Planet. They visited Earth since the deep mist of time and secretly intervened at some key points during the human history, based on evidence of numerous archaeological artifacts whose scientific explanation is unsatisfactory for alien enthusiasts.
Why aliens did not introduce themselves instead of performing weird activities such as kidnapping harmless farmers, killing cows and tracing circles in the fields?
It seems that ETs are not great communicators and show-biz talents. It is rumoured that they are extremely shy and avoid publicity as scourge.
The end of the Maya calendar, in December 21, 2012, preconized their return but they failed to materialise, despite the mass-media resonance. If they actually came back on Earth, definitely their visit passed fully unnoticed. May be they maliciously despise our planet as depicted in the H.G. Well’s novel War of the Worlds (1898) and cannot tolerate our unpleasant and vile company.
Piecing evidences
On the lid of the sarcophagus of the Mayan King Pakal in Mexico, there is an image strongly evocative of a rocket with a man on board that alien–friendly minds pretend is the Maya ruler in a spaceship.
They justify the opinion with the observation that:” He is at an angle like modern-day astronauts upon take off of the rocket. He is manipulating some controls and has some type of telescope in front of him. His feet are on a kind of pedal. On the back of the flying machine there is an apparatus that looks like an exhaust with flames.
Archaeologists, however, think that this image shows the king sitting on the Sun idol and descending into the underworld, where the sun goes at night, within the classical mythological symbolic frame of a ‘world tree’ with branches stretched into the sky and roots immersed into the underworld.
Argument from Ignorance
The myth surrounding an ancient alien intervention in human life pretends that ETs used acoustic stone levitation to build the pyramids, supernatural powers to trace the Nazca lines in Peru and their abnormal strength to raise the Easter Island statues. Why they did these wonders, leaving our curiosity unsatisfied?
If there is no evident terrestrial explanation for a phenomenon or artwork then the theory of alien intervention from the outer space must be true, according to a logical fallacy know as argumentum ad ignorantiam or ‘argument from ignorance’. Proponents of the out-of –this-world theory should first make sure that something is not in this world, before assuming that it comes from the outer space!
Short history of Aliens
Disputation over the existence of alien creatures did no start with 1950’ science-fiction rave neither with New Age myths. Two thousand years ago prophet Ezekiel while walking along the Chebar River in Chaldea saw four human-like creatures emerging from a tempestuous wind accompanied by four flying wheels shining like silver that after a while disappeared in the sky.
Traditional cosmologic myths recount of one or more extremely powerful agents who created the Cosmos and that periodically return to visit Earth. Hebrews thought that humanity was just one of the many form of life present in the Universe. In most ancient cultures, deities, angels, demons and spirits were considered real entities who lived somewhere behind the sky.
The idea that human beings share the Cosmos with other sentient creatures was not only the result of a religious will, but the subject of philosophical diatribes. In the fifth century B.C. philosopher Democritus devised the atomic theory, speculating that the Universe is made of microscopically tiny indestructible particles moving in the vacuum. Democritus predicted that if atoms work in this way on Earth, they work similarly in other parts of the Cosmos:” There are infinite words different in size, and some have no sun and no moon, others are bigger and in other Universes they are more numerous…The worlds crash in their collisions. Some worlds do not have plants, animals and water, too”.
Latin poet Tito Lucrezio resumes the theme in his book De Rerum Natura:”If the number of atoms is so immense, that the full human life cannot count them all and the same strength and nature that connect them on Earth persists everywhere with the same power, it is necessary to admit that somewhere else in the empty space, on other terrestrial globes, different human and animals races exist. ”
Crowded Cosmos
The search for planets around distant suns hit the headlines these days. Soon astronomers will find the 1000th exoplanet in our cosmic neighbourhood. According to a recent paper, there are 8.8 billion planets similar in size and temperature to Earth waiting to be discovered.
At a pace so rapid that resembles a race, scientists hunting exoplanets are multiplying their observations and efforts. Since 2011 they have discovered 3 exoplanets per week, a precious few of which lie in the ‘habitable zone’ where water could be present in a liquid form! Astronomers estimate that our Milky Way Galaxy holds more than 100 billion planets.
I know it’s a little hard to swallow at first when you think that for decades, astronomers scanned the skies unsuccessfully searching for planets around other stars. At some point the search was stacked. Then, something really unusual happened in 1991.
That year, truly out of the blue, astronomers Alexander Wolszcan and Dale Frail who were studying a totally different astral phenomenon, the millisecond pulsars, found a system of 3 orbiting planets circling around an exotic pulsar named PSR B1257+12. Two of these planets are few times bigger than Earth and one is approximately the size of the Moon. A pulsar is quite different from our Sun. So the two scientists were shocked to find that the first exoplanets ever discovered were orbiting an unsuspected star totally unlike the Sun.
Hunting Life
But it was not until four years later, in 1995, that the fourth exoplanet, 51 Pegasi B, was discovered by Didier Queloz and Michel Mayor of the University of Geneva, Switzerland. It is a completely different Jupiter-size world orbiting a normal star, 51 Pegasi, every 4.2 days!
Soon afterward, in January 1996, Geoffrey W. Mercy, an observer at the San Francisco State University, and his colleague Paul Butler presented exoplanets number 5 and 6 found orbiting a sun-like star to an audience of jaw-dropped astrophysicists at a Press Conference of the American Astronomical Society in San Antonio, Texas. Six exoplanets discovered in 5 years is a great achievement. The announcements shook the world of astronomy because scientists were convinced that such planets were too rare and difficult to find. They were definitely wrong.
Most planet hunters, like Jim Kasting, who wrote a book on what makes a world habitable, or Geoffrey W. Mercy, the best planet-discoverer on this Planet, think that life is thriving in thousand forms out there because extra-solar planets aren’t rare after all. Each and every planet with some water and a decent atmosphere, orbiting at the right distance from his sun, is a suitable candidate as interstellar cradle of Life!
Timothy W. Brown, a graduate student at Harvard University, saw in 1999 an exoplanet transiting his star for the first time ever, through a tiny amateur-size telescope allocated in a parking lot in Colorado. Weeks later the transit was confirmed by scientists in Tennessee.
When the number of exoplanets glimpsed in the space started to rise, astronomers realized that they were totally different from each other and also nothing like what they expected or even imagined as possible cradles of Life! Some are partly made of pure diamond, good as a girl’s best friends, but unsuitable as life culture.
Only 20 years ago, nobody could dream of listing 1000 extra-solar planets. Thinking that some of them can host their peculiar form of life is reinvigorating the now widely shared scientific opinion that we are not alone in this cosmic silence.
Small Traces
Since 2001 scientists have detected traces of sodium, carbon dioxide, methane, carbon monoxide and water in the atmosphere of some exoplanets. The presence of such elements is an indirect, but remote and not definitive signature of life.
Only 30 to 50 exoplanets so far have revealed secrets of their atmosphere. Some of these worlds are conspicuously large and hot and embrace their star more tightly than Mercury hugs our Sun. Therefore, they are not suitable candidates for life.
However, a number of small super-Earth-size planets, which are between 2 and 10 times bigger than our home planet, are placed in orbits that might permit life to survive. This confirms the original suspect that pioneering astrophysicist Frank Drake, inventor of SETI (Search for Extraterrestrial Intelligence) is trying to prove since 1960s: worlds thriving with life are probably more abundant that what scientists initially thought or can imagine.
Water worlds
Consider for example the twin planets Kepler 62e and 62 f: they are less than twice the Earth’s size and orbit at a distance from their star that may capable of supporting life as we know it. However, this is not enough to make a living planet. Detection of bio-signatures, such as methane or oxygen in the atmosphere is essential to demonstrate that life exists there!
Nonetheless Kepler 62e and 62f twin planets are the most life-friendly planets yet seen outside our solar system. They were discovered by a team working with the NASA’s Kepler Space Telescope, observing gaps in luminescence to confirm the presence of planets passing in front of their star.
Actually the team discovered five planets orbiting around Kepler 62 but only e and f are in the habitable zone and according to a theoretical model they are completely covered with water, implying that if there are inhabited, creatures there might have evolved in marine environments and adapted to a life in the water. To make it sure we might travel the 1200 light years that separate us from Kepler 62 to have a direct look.
Finding a planet the size of Earth orbiting a star similar to the Sun has been the Holy Grail of the last generation of astrophysicists. When Xavier Dumusque and colleagues of the Geneva Observatory in Switzerland pinpointed in 2012 a planet named Alpha Centauri Bb at only 4.36 light-years from Earth in the star system closest to our own, it was like finding the right candidate. Alpha Centauri Bb is about 10% heavier of Earth and orbit around a star with 93% of Sun’s mass. Unfortunately it lies in the uninhabitable zone, where water cannot exist in liquid form due to the surface temperature that likely reaches the 1200° Celsius.
The search of life in the Cosmos got close to a Big Bang in June 2013 when astronomers found three planets in the habitable zone around the star Giese 667C.
May be they are not inhabited, but water can exist in liquid form on them. Their mere existence raises the hopes of finding other worlds behind our solar system that support life.
Over time the Kepler Space Telescope will find more planets in distant orbits and it is only a matter of time before astronomers detect the first true alien Earth, a planet the size of our own located in its star’s habitable zone.
A theoretic model
Lichens and algae could be the first life forms we will find on Earth-like planets. The assumption is based on the signature colour of the light they emit. Most of worlds are rocky, with extreme dryness and acidity, characteristics that limit the life to the hardier forms. Seen from a distance, each type of simple organism creates a unique colour pattern. Lichens appear yellow. Bacteria and algae appear green.
Earth, seen from the space, radiates a “red edge” of near infrared light, signature of chlorophyll in plants. Distant planets with a lot of green vegetation are also expected to show a similar ‘red edge”.
A matter of matter
The elementary bricks of the ordinary matter of which people, bacteria and dogs are made of are protons, neutrons and electrons, the same stuff out of which stars and planets are composed, too. This observation inevitably leads to the conclusion that life has a common base in the cosmos. Size and shape do matter, though energy is also important.
Traces of methane are particularly intriguing because this compound could be an indicator of biological activity: think about the methane produced by cow burps, for instance. Methane can also originate from geophysical processes, such as volcanic and geyser activities.
So the scientists are shifting from methane to the search of oxygen, and particularly of ozone (O3) a highly reactive molecule made of three oxygen atoms, that is far more likely to represent a sign of life on exoplanets. The only problem is that ozone is difficult to detect unless the planet atmosphere is thick at least twice that of Earth. Subtle signatures of ozone in the distant space might be detectable by the big space telescopes due to be launched during the 2020s. Now it is not observable from Earth and it not clear whether with the Terrestrial Planet Finder it will be possible to spot the ozone signature unambiguously.
Nonetheless, it is interesting that a molecule so important for respiration of animals and plants on Earth, the oxygen, will also tell if life is present out there!
Martian Life
There is a long standing belief of life on Mars. Martians have repeatedly invaded our home planet perhaps on the favouring occasion of wars, famine and scourges. At least this is what tens of movies, books, songs and legends suggest. Nineteen century artist Bizarro (Les mondes perdus) foresaw humanity building bridges between worlds, from Earth to Mars perhaps, a desire deeply rooted in our soul.
It is most probable that between 2030s and -40s humanity will settle on Mars. While waiting for that achievement it is possible to admire the beauty of the landscapes of the Red Planet thanks to photographs taken from the NASA spatial probes. Dunes of black sands, arabesques of dried rivers, extended glaciers and deep canyons: everything seems to evoke the presence of life. The examination of sampled specimens will tell us if martial life is possible.
Finding amino acids and other biologically significant molecules on Mars would be important but not evidence of living organisms. However, it would confirm that the necessary ingredients for the formation of life are present in the neighbouring planet.
Microorganisms have been found in meteorites accidentally falling on Earth, indicating that Life on Earth may originate from the outer space. A new line of research indicates that life came on Earth from an alien source. Meteorites crashing on our planet could have supplied early organisms with essential molecules that allowed them to store energy, survive, multiply, thrive and evolve to give rise to all terrestrial life we see today.
The presence of extreme conditions on Mars suggests lack of life. Good Mars analogues such as a Peruvian lake in the Atacama’s desert or Lake Magic in Western Australia share similar extreme conditions, such as the acidity at pH 1.7, about the same as the stomach content, but nonetheless they are hosting simple forms of life: algae, single cell organisms that lack a nucleus, and a type of fungi.
Life can exist in such harsh acid brines, and this fact reveals that life might be found elsewhere, including on Mars, which rocks may contain minerals that host microorganisms in fluid inclusions.
Pampering Mars
The Red Planet contamination with terrestrial bacteria may have dramatic consequence for its environment, NASA’s computer simulations suggest. We do not know what Earth organisms can do out of the Blue planet, but, believe it or not, the United Nations Outer Space Treaty bans the contamination of potentially fertile worlds with earthly bacteria
Protecting Mars with an Intergalactic Reserve will not worth the expense and the effort because Earth bacteria are probably already there, catapulted by NASA’s Viking probes or delivered by debris of ancient meteorites! More likely, terrestrial bacteria launched in the space do not survive the journey because of Sun radiations!
Risky trip
Humans travelling to Mars will face a hidden risk: solar radiation. Scientists recently assessed radiation doses in units of Sieverts (Sv) which give the amount of ionizing energy per unit of mass. A CT scan of the head delivers about 2 milliSieverts (mSv) and one the abdomen about 8 mSv.
A jetliner pilot typically receives about 5 mSv per year whereas an astronaut aboard the International Space Station receives about 200 mSv per year.
A round trip to Mars would take 360 days, thus it has been calculated that Mars astronauts would receive a total dose of 662 mSv from galactic cosmic rays in addition to the radiation from solar events, such as solar flares and coronal mass ejections.
The journey will increase a male astronaut’s chance of getting a fatal cancer by about 4% and a female’s astronaut chance by about 5%. A human exploration to Mars appears a dangerous trip!
New Hope from Radio-signals
Powerful and extremely rapid signals lasting for few milliseconds captured by the radio-telescope Parkes in Australia made headlines in June 2013. What is amazing is that they arrived from the abysses of time: 8 billion light years ago. The signals started their journey through the space when the Universe was about half of his current age and the solar system did not exist yet!
Were these signals sent by aliens? It is not easy to tell but the probable source of emission is a neutron star or a black hole, objects in which the matter is pushed to extreme conditions. Signals generated by electrons spiralling violently in a magnetic field created by a black hole of a neutron star are sometimes so regular and predictable to resemble intelligent radio signals.
In a 1959’s article physicists Giuseppe Cocconi and Philip Morris speculated that the ideal frequency for interstellar radio-transmission would be the 1,420 Mega Hertz, emitted by the neutral hydrogen. Followers of the SETI project called it watering hole, the place where all animals (planetary signals, in this case) gather to drink.
In 1974, SETI sent a signal of 1679 bits to the globular cluster M13. The message was simple like the electronic game Space Invaders and contained all the basic information on Earth and the human race in a simplified drawing. Nobody reply.
The mind behind SETI, the astrophysicist Frank Drake, now 82, in April 1960 tuned the National Radio Astronomy Observatory of Green Ban, West Virginia, on the 1,420 MHz radio wave and pointed it to the star Tau Ceti, 11 light-years away, getting a repetitive signal that later revealed to be originating from a secret military radar. The failure was not going to demolish the expectances of Frank Drake.
In 2013, after fifty years of space silence, Drake admits:” A lot of young people come up and say they want to be part of SETI, but then they discover there are no jobs. No company is hiring anyone to search for messages from aliens. Most people don’t’ seem to think there is much benefit of it.”
Why we obstinately desire to find someone else to chat with on distant stars? It is a feature of the human soul the tendency to search similitudes everywhere. The most visionary intuition, perhaps, is due to the fervid imagination of Frank Herbert, father of the Dune saga, who described the race of Calebans, alien intelligences living in another dimension, that in our Universe are perceived as stars!
Epilogue
Watching the night sky filled with brilliant stars we cannot refrain from thinking that this marvel is not out there only for us. Somewhere else, creatures similar or completely diverse are waiting for a contact. Despite the frustration due to the lack of radio signals, we continue to nurture the unearthly hope that we are not alone in the Universe.
Mars is not the richly populated planet we once guessed at. The icy seas of the outer region of our solar system may support life but almost certainly no more than bacteria. So maybe we need to look further to distant exoplanets and search for alien artefacts. In fact astrobiologists are no longer waiting for an audacious signal from an alien civilization but actively exploring the depths of skies for signs indicating that somewhere else there is a place somebody calls home.
Along this line, astronomers are looking for waste heat from ‘Dyson spheres’ and galaxies darkened by millions of Dyson spheres. In 1960, physicist Freeman Dyson pointed out that if alien civilisations exist, almost certainly they are far older and far more advanced than our, due to a statistic calculation. Civilizations spanning many thousands or millions of years inevitably keep expanding and need a lot of energy.
The best source of energy in any solar system is the star itself. Therefore, Dyson’s conclusion was that after millions of years the star might be entirely surrounded by planet-size solar power plants that would appear in the distance like a gigantic sphere. A Dyson’s sphere would emit waste heat in the form of infrared waves.
Carl Sagan intervened on the question in 1966 suggesting that if an infrared telescope detects a warm object lacking visible wavelengths, almost certainly the light form the star is blocked and it could be a Dyson sphere. A colonized galaxy would quickly turn from looking ordinary to very red.
The search for artefacts and waste should not be separated from the normal exploration of the Universe, but again, an enormously advanced and spacefaring civilization might be just too weird for us to spot.
Indisputably though, when scientists will find traces of life out there, this fact alone will have an enormous impact on our life and side effects that we cannot foresee but the stepping-stone of a New Age. Believe it or not: life just wants to be.
Further reading:
1). Paul Davies (2010) The Eerie Silence – Renewing our search for alien intelligence. Houghton Muffin Harcourt Eds.
2). Lee Billings (2013) Five billions years of solitude. The search for life among the stars. Current, New York USA.
3) Richard Talcott (2013) Top ten exoplanets. 2013 October, Astronomy.