Growing evidence points to a once-habitable world—and recent findings suggest that life could exist on Mars today.

MARTIAN MISSION: Since landing on the Red Planet on August 5, 2012, NASA’s Curiosity rover has roamed the environment collecting samples and taking photos in search of signs of life, both past and present.

NASA/JPL-Caltech/MSSS

This September, tech mogul Elon Musk unveiled his updated plans for colonizing Mars. By 2024, he said, his aerospace company SpaceX plans to deliver people to our neighboring planet in massive rocket ships, which he hopes to start constructing within the next year. Although perhaps the boldest declaration yet (outside of science fiction) of intent to actually spearhead extraterrestrial habitation, Musk’s ambition reflects an age-old curiosity: Can the Red Planet support life? Has it ever before?

In 1976, NASA’s Viking 1 and 2 set down on Mars with the primary mission of answering those questions. While the two landers discovered no clear signs of living microorganisms on the planet’s barren surface, photographs taken from orbit revealed geological features that suggested a once-watery environment—dry valleys that resembled those created by rivers on Earth. “If you assume that liquid water is all life needs, then this could count as the first evidence that life might have been possible on Mars in the past,” says Alfonso Davila, a research scientist at NASA Ames Research Center in California.

Subsequent missions to the planet started to paint a clearer picture of its potential biological history. For example, in the early 2000s, NASA rovers Spirit and Opportunity discovered sediments and minerals that couldn’t have formed without water, as well as materials, such as patches of silica, typically found in hot springs and steam vents, where extremophiles thrive on Earth. Most recently, the rover Curiosity, which landed on the planet in August 2012, has detected simple carbon-based organic compounds in the Gale Crater, a large cavity near the Martian equator.

Despite growing evidence that Mars might have been teeming with life eons ago, exploration of the planet has painted a bleak image of its contemporary environment.

Despite growing evidence that Mars might have been teeming with life eons ago, exploration of the planet has painted a bleak image of its contemporary environment. Because it lacks a thick atmosphere and a magnetic field, which are essential for making Earth a hospitable place to live, Mars is exposed to harmful ultraviolet (UV) light and ionizing radiation from cosmic rays. Those features, along with low temperature and pressure, “make the environment pretty hostile to life as we know it,” says Manish Patel, a senior lecturer in planetary sciences at the Open University in the U.K.

Nevertheless, scientists are uncovering aspects of the planet that indicate Mars could still be harboring isolated pockets of life. Although the chances may be small, these findings have major implications for continued missions to the Red Planet—and, of course, its potential future colonization by humans. (See “A Hostile Planet.”)

MARTIAN MALADIES: Humans may have grand dreams of colonizing Mars, but before that happens, scientists and engineers will need to devise ways to protect travelers from the planet’s hostile environment. Spacesuits can help protect against most environmental harms, such as frigid temperatures and low oxygen. However, high levels of space radiation, which is the biggest concern, will be the most difficult to avoid.
See full infographic: WEB | PDF© SYLVAIN SARRAILH

Water marks

Remnants of a wet Mars remain the clearest hint that the planet once could have harbored life. Data gathered by Curiosity point to the existence of a massive freshwater lake in the Gale Crater billions of years ago, and scientists’ analyses suggest this environment had habitable conditions: a relatively neutral pH, low salinity, and elements that make up the building blocks of life—carbon, oxygen, hydrogen, sulfur, nitrogen, and phosphorus.¹

Curiosity has also detected evidence of simple organic molecules in this region, including methane,²chlorobenzene,³ and hints of longer-chain molecules resembling fatty acids⁴—all of which have primarily biological origins on Earth. “The consensus is that Mars had a lot of water in its ancient past, and that life could have existed and grown then,” Patel says. (See “Ancient Microbes on Mars.”)

Nowadays, however, confirmed sources of Martian water exist solely as ice, primarily in the planet’s polar regions, with very recent evidence pointing to the possibility of ice patches at much lower latitudes, near the planet’s equator.⁵ And life—at least as we know it—needs liquid water to survive.

In 2000, scientists detected Martian gullies, channels traversing the landscape that appear similar to those created by flowing water on Earth.⁶ Images that the Mars Global Surveyor spacecraft captured along the sides of craters, pits, and valleys suggested that these formations are relatively young, as they lack geological features such as impact craters or dusty dunes. These images hinted at the possibility that liquid water might have existed in the planet’s recent past—and might still sometimes be present on the planet’s surface. More evidence for this idea emerged a few years later when researchers reported that new, light-colored streaks in the form of fingerlike branches had appeared in some of the gullies, further signaling recent activity.⁷

Subsequent analyses, however, revealed that the streaks could have been produced through other processes. In 2010, based on images from the Mars Reconnaissance Orbiter (MRO), scientists reported that the streaks appeared only during the Martian winters. During that time of year, water stays frozen and dry ice builds up on the planet’s surface, meaning that carbon dioxide, a gas that makes up more than 90 percent of the planet’s atmosphere, may have been the cause.⁸

Sure enough, when Patel and his colleagues tested this hypothesis last year, they found it to be a likely explanation. In the Open University’s Mars Chamber, which simulates the temperature, pressure, and atmospheric composition of the Red Planet, the researchers deposited carbon dioxide frost onto the surface of soil, then warmed the chamber with a heat lamp to mimic what happens when the sun rises. The resulting process of sublimation—where a solid transitions directly into gas—was enough to create very similar formations.⁹ And in another 2016 study, an independent group of researchers reported that data from MRO supplied no evidence of minerals associated with flowing water in those structures.¹⁰

Meanwhile, another feature of the steep Martian slopes, dubbed recurring slope lineae (RSLs), has provided more-tantalizing evidence that the planet could occasionally host liquid water. Unlike gullies, RSLs are dark streaks that appear during the warmest parts of the year, growing in the summer, when ice is most likely to melt, and fading in the winter.¹¹ And although scientists have never directly detected liquid water, it may not take as much of it as some researchers expect to generate these features. In another Mars Chamber experiment, published last year in Nature Geoscience, Patel and colleagues placed a block of ice in the simulated Martian environment and found that a small amount of water, which boiled at much lower temperatures due to low pressure, was able to kick up the soil to create streak-like features.¹² “That showed that if there is water, you need a lot less than originally [thought],” Patel says. Altogether, the presence of liquid H2O on the planet remains up for debate.

Two features of Mars’s surface suggest that water may, at times, flow on the planet. Channels known as gullies (top two images) that appear on steep slopes look comparable to formations created by flowing water on Earth, although recent analyses indicate that these were likely formed by other processes. More recently, researchers have identified recurring slope lineae (RSLs; lower two images), seasonal streaks also suggestive of flowing water. The primary theory, based on the identification of perchlorates, is that RSLs are formed by brine, or very salty water. Where the water would come from is still a mystery, and alternative theories challenge the idea that water is needed to form such structures. For example, some scientists have posited that dry sand avalanches could result in the same streaking pattern.NASA/JPL-CALTECH/UNIV OF ARIZONA

Salty surfaces

The case for contemporary water on Mars has been bolstered by signs of perchlorates, a type of salt, in the seasonal streaks.¹³ Perchlorates lower the freezing point and evaporation rate of water, which would allow H2O to exist as a liquid in Martian conditions. On Earth, perchlorates also act as an energy source for some microorganisms.

“People were getting really excited because they were thinking, well, bacteria can metabolize perchlorates, so perhaps these are potential habitats that we could maybe explore on future missions,” says Jennifer Wadsworth, a PhD student in astrobiology at the University of Edinburgh. “So we thought, okay, well let’s look at perchlorates and see [whether] bacteria could survive under Martian conditions.”

As it turned out, when bathed in UV light, these salts can actually be lethal. When Wadsworth and her advisor exposed the soil bacterium Bacillus subtilis to perchlorates while irradiating the cells with UV levels typical for the Martian surface, the microbes died within minutes.¹⁴ “Perchlorate seems to be quite abundant everywhere, and the radiation penetrates quite a few meters [beneath the planet’s surface], according to models,” Wadsworth says. “So it could mean that the top few meters of soil are in fact uninhabitable.” However, she adds, this finding does not rule out the possibility that there might be extremophiles that could survive these conditions, or that more-conventional microbes live farther underground.

Deep below the surface, UV and ionizing radiation are significantly reduced, while pressure and temperature begin to increase. “You can reach a point where you’re shielded from all the nasty things, and the temperature and pressure could be high enough to allow a habitable environment,” Patel says. “The evidence is piling up that if we want to find these signs of life on Mars, we really need to get down below the surface to get away from nasty oxidants and environmental influences.”

Experiments in the Open University’s Mars chamber, which simulates the environment on the planet, could help determine the conditions that form these geological structures.MANISH PATEL/OU

ANCIENT MICROBES ON MARS?

A LIVING LAKE?: More than 3 billion years ago, a massive meteor hit Mars, creating an approximately 155-km-wide crater in the planet’s surface. Data from NASA’s Curiosity rover suggest that this area, known as the Gale Crater, was once filled with water, and may even have hosted life. Analysis of the sediments also points to once-habitable conditions, with evidence of simple organic molecules that may have originated from biological sources.NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSSThe chances of finding life on Mars today may be slim, but many scientists believe that the planet hosted living organisms at some point during its history. One of the most promising regions for ancient Martian life is the Gale Crater, a large region near the planet’s equator. Data gathered from the crater by rovers and orbiters have revealed evidence both of past (and possibly present) water and of simple organic molecules—two essential ingredients for life.

Recently, while examining data collected by the rover Curiosity, a group of researchers discovered boron, a chemical element that can stabilize the sugars used to make RNA (Geophys Res Lett, 44:8739-48, 2017). Some scientists believe that this element may have even contributed to the origin of life on Earth. “Boron, when it’s dissolved in water, has very special properties—it can react with organic molecules to form other types of organic molecules,” says Patrick Gasda, a postdoc at Los Alamos National Laboratory. “We found boron in this area [that used to have] lots of water; if there were organics there, that could actually mean that you could do these types of reactions on Mars.”

Scientists currently only have speculative estimates about when the Red Planet was last amenable to life. For example, NASA researcher Alfonso Davila and his colleagues have proposed that parts of Mars may have been habitable as recently as 5 million to 10 million Earth years ago (Astrobiology, 13:334-53, 2013). They estimate that during that period, the planet was tilted at an angle that may have provided polar regions with enough solar energy to melt the subsurface ice. After completing additional analyses, the researchers also posited that the water composition in the atmosphere during these periods was similar to that seen in the driest parts of the Atacama Desert in Chile, where microbes have been found living in extremely arid soil (Astrobiology, 16:159-68, 2016).

“While this does not necessarily mean that Mars was as habitable as the Atacama during those periods, it does suggest that the habitability window near the surface might have closed not billions of years ago, but perhaps tens of millions to several hundred million years ago,” Davila says. And the current conditions on the planet, while probably not conducive to modern microbial activity, are promising for researchers searching for signs of living organisms in the planet’s history, he adds. “Those same conditions, extreme dryness and extreme cold, that prevent life from being active in the environment are also very good at preserving evidence of life.”

Curbing contamination

Of course, the most definitive way to confirm life on Mars would be to collect live or previously living specimens. ExoMars, a rover that the European Space Agency plans to send to Mars in 2020, will be equipped with a drill that can extract soil samples from depths down to two meters, the deepest of any Mars sampling to date. The robot’s onboard laboratory will carry out tests on collected specimens. Another upcoming rover expedition, NASA’s Mars 2020, plans to collect samples to set aside for future missions to ferry back to Earth.

Without knowing exactly what life-forms, if any, exist on our red, dusty neighbor, it is difficult to predict what people might encounter when they eventually get there. “How do you look for something that you don’t know [about]?” Patel asks. “It’s a real problem that we face. All we can do is look for what we do know—and even then, it’s incredibly difficult to measure everything.”

Directly probing for life on the Red Planet takes some finesse, as scientists must ensure that they do not accidently misidentify organisms that hitched a ride from Earth as Martian. Although it is not possible to reduce the risk of contamination to zero, researchers can take measures to lower the chances that they will introduce Earthly organisms into their experiments. Curiosity, for example, is barred from exploring the RSLs, due to concerns that the rover, which was not completely sterilized prior to launch, might contaminate the suspected water in those regions.

The evidence is piling up that if we want to find these signs of life on Mars, we really need to get down below the surface to get away from nasty oxidants and environmental influences.—

Manish Patel,
Open University

“Being able to clean [spacecraft] well enough to identify Mars microbes if they might be present and distinguish them from the residual contamination from Earth is an extremely challenging problem,” says Cassie Conley, NASA’s planetary protection officer. Future rovers will be subjected to various sterilization strategies before launch, including wiping down surfaces with sterilizing solutions, baking heat-resistant components at high temperatures, and using highly sensitive biosensors to identify the presence of microbes.

Researchers are also trying to ensure that the human explorers NASA plans to send to Mars by the 2030s do not contaminate the planet—a much more difficult task, as most of the methods used to clean spacecraft cannot be applied to people. “We can be confident about how much contamination we sent on [robots], because we can measure it before launch and be confident that it won’t increase,” Conley says. “Once humans start landing on Mars, there will be associated microbes that come along.”

Monitoring microbial migrants within astronaut communities is also important for managing human health. In a study published earlier this year, Kasthuri Venkateswaran, a senior research scientist at NASA’s Jet Propulsion Laboratory who is involved in the Planetary Protection Program, and colleagues found that after four people spent 30 days in an enclosed habitat that mirrored conditions on the International Space Station, the diversity of certain fungi—including those associated with allergies and asthma—in their surroundings increased.¹⁵ In another recent investigation, researchers reported that bacterial communities in a simulated spacecraft changed after hosting six crew members for 520 days.¹⁶In this case, cleaning agents were able to keep the microbial populations under control, pointing to the importance of maintaining strict sterilization protocols in space.

Keeping any potential life-forms native to Mars from hitching a ride back to Earth is another concern. Scientists and policy makers want to ensure that samples brought back by rovers or human explorers—or living organisms that accidently hitch a ride—will not endanger species on Earth. Such Mars-to-Earth contamination, Conley says, presents “a much more complicated set of questions about public health and the potential for invasive species.”

A HOSTILE PLANT

NASA hopes to send humans to Mars by the 2030s, and private companies, such as SpaceX, Mars One, and Lockheed Martin, have grand plans to establish human settlements on the planet. But big questions remain about the plausibility and safety of such missions.

People who land on the Red Planet will face harsh conditions, such as frigid temperatures, low pressure, and an atmosphere with precious little oxygen. Micron-size dust particles may also be a major factor, as they could cause respiratory problems and contain toxic materials. In addition, Martian soil contains abundant amounts of perchlorates, a type of salt that can impair the functioning of the human thyroid, which could be hazardous to scientists digging in the dirt.

On the other hand, perchlorates might actually be extremely useful during a mission to the Red Planet. Not only are they a component of rocket fuel, the compounds could also be a source of oxygen for human consumption: many microbes metabolize perchlorates, generating this element as a by-product, and some scientists have proposed prototypes of portable emergency systems that exploit these microbial pathways to generate breathable air (Int J Astrobiol, 12:321-25, 2013).

A much more serious concern about living on Mars is radiation. Without a protective magnetic field like that surrounding the Earth, the surface of the Red Planet is constantly bombarded with galactic cosmic rays—high-energy particles from space that can lead to a variety of health problems. At the doses of cosmic radiation that humans would receive on a trip to the Red Planet, one of the primary problems they will face is cancer. According to analyses by Francis Cucinotta, a radiation biologist at the University of Nevada, Las Vegas, astronauts on the International Space Station can exceed their lifetime limits of radiation, based on NASA’s radiation standards, in just 18 months for women and two years for men (PLOS ONE, 9:e96099, 2014). And radiation levels would likely be even higher on a trip to Mars, which is far beyond the Earth’s protective magnetosphere. (The cancer risk is slightly higher in women because they have the added concerns of breast and ovarian cancer plus a greater risk of developing lung cancer, although the latter association is not well understood, Cucinotta says.)

Rodent experiments have revealed that exposure to radiation akin to that experienced on Mars can lead to an increased risk of cancer in “bystander” cells close to those damaged by radiation, which can release “oncogenic signals” (Sci Rep, 7:1832, 2017). Radiation exposure can also alter the tumor microenvironment in ways that promote cancer. Using mouse models of breast cancer, Mary Helen Barcellos-Hoff, a radiation oncologist at the University of California, San Francisco, and her colleagues discovered that when healthy epithelial cells were transplanted into an animal that had been exposed to Mars-like radiation, tumors developed from those unirradiated cells (Cancer Cell, 19:640-51, 2011). “You create the seed of the cancer with mutations, but they still have to be in the appropriate soil for the cancer to actually develop,” Barcellos-Hoff says. “[We’ve found that] the kind of radiation found in space likely perturbs [the tumor microenvironment] in a more profound way than radiation that’s found on Earth.”

More recently, scientists have amassed evidence suggesting that cosmic radiation may have worrisome effects on the brain. Specifically, Charles Limoli of the University of California, Irvine, and colleagues have shown in animal experiments, mostly with rodents, that these galactic particles can cause deficits in learning and memory, reduce the complexity and density of dendritic spines, and lead to persistent neuroinflammation (Sci Adv, 1:e1400256, 2015; Sci Rep, 6:34774, 2016). “The data suggests that the irradiated brain is never normal,” says Limoli. “Now, how precisely these cognitive deficits will manifest and impact astronaut performance is another important question that’s very difficult to pinpoint.”

While radiation risks are concerning, they are not deal breakers for future Mars travel, Limoli says, and researchers are now working on ways to mitigate these issues. For example, NASA is exploring ways to protect astronauts from radiation with compounds that repair damaged DNA. One such compound is nicotinamide mononucleotide, which scientists recently reported could reverse aging in mice by activating processes involved in DNA repair (Science, 355:1312-17, 2017).

In addition, Limoli and his colleagues are developing drugs that could help alleviate radiation effects in the brain. “We’re working on a variety of pharmacologic interventions,” Limoli says. “[And] we can always hope that our engineering colleagues come up with better and better shielding.”

Diana Kwon is a freelance science journalist living in Berlin, Germany.

References

J.P. Grotzinger et al., “A habitable fluvio-lacustrine environment at Yellowknife Bay, Gale Crater, Mars,” Science, 343:1242777, 2014.
P.R. Mahaffy et al., “The imprint of atmospheric evolution in the D/H of Hesperian clay minerals on Mars,” Science, 347:412-14, 2015.
C. Freissinet et al., “Organic molecules in the Sheepbed Mudstone, Gale Crater, Mars,” J Geophys Res: Planets, 120:495-514, 2015.
E. Hand, “Mars rover finds long-chain organic compounds,” Science, 347:1402-03, 2015.
J.T. Wilson et al., “Equatorial locations of water on Mars: Improved resolution maps based on Mars Odyssey Neutron Spectrometer data,” Icarus, 299:148-60, 2018.
M.C. Malin, K.S. Edgett, “Evidence for recent groundwater seepage and surface runoff on Mars,” Science, 288:2330-35, 2000.
M.C. Malin et al., “Present-day impact cratering rate and contemporary gully activity on Mars,” Science, 314:1573-77, 2006.
S. Diniega et al., “Seasonality of present-day Martian dune-gully activity,” Geology, 38:1047-50, 2010.
M.E. Sylvest et al., “Mass wasting triggered by seasonal CO2 sublimation under Martian atmospheric conditions: Laboratory experiments,” Geophys Res Lett, 43:12,363-70, 2016.
J.I. Núñez et al., “New insights into gully formation on Mars: Constraints from composition as seen by MRO/CRISM,” Geophys Res Lett, 43:8893-902, 2016.
A.S. McEwen et al., “Seasonal flows on warm Martian slopes,” Science, 333:740-43, 2011.
M. Massé et al., “Transport processes induced by metastable boiling water under Martian surface conditions,” Nat Geosci, 9:425-28, 2016.
L. Ojha et al., “Spectral evidence for hydrated salts in recurring slope lineae on Mars,” Nat Geosci, 8:829-32, 2015.
1J. Wadsworth, C.S. Cockell, “Perchlorates on Mars enhance the bacteriocidal effects of UV light,” Sci Rep, 7:4662, 2017.
1A. Blachowicz et al., “Human presence impacts fungal diversity of inflated lunar/Mars analog habitat,” Microbiome, 5:62, 2017.
P. Schwendner et al., “Preparing for the crewed Mars journey: Microbiota dynamics in the confined Mars500 habitat during simulated Mars flight and landing,” Microbiome, 5:129, 2017.

We have accomplished a lot in our (relatively) short time on Earth. We’ve sent humans to the Moon and to live in space, developed massive and sophisticated telescopes to see the farthest reaches of the cosmos, and even rocketed rovers to Mars and probes to the edge of our solar system. However, a number of organizations have taken humanity’s voyage into the final frontier a step farther. NASA, the European Space Agency, and the research collective behind the Search for Extraterrestrial Intelligence (SETI) have been working tirelessly to find out if we are alone, once and for all.

Already, a number of projects exist that scan the stars for signs of intelligent life. And despite the fact that many of them have been looking to the skies for decades, we have yet to make contact. And that’s a bit of a problem.

0. The Paradox That Started It All

To put it mildly, our solar system is very old. In fact, scientists are still figuring out just how old — clues gathered from meteorites suggest it is almost 5 billion years old, and surrounding star systems are likely billions of years older. While interstellar travel still seems to be a distant dream, new technology is born every year that allows us to scan the skies for signals from civilizations in the most distant corners of the cosmos. The number of known alien worlds and star systems discovered through these technologies continues to rise, but our creative methods of listening to space have not yet revealed anything that resembles extraterrestrial communications or civilizations.

Given the size and age of our universe, it seems like we should have made contact. We, of course, have not.

In the early 20th century, physicist Enrico Fermi asked himself a now-famous question: Given the scope of our universe, why haven’t we found intelligent extraterrestrial life yet (or why haven’t they found us)? This is sometimes called the Fermi Paradox or the Great Silence. Scientists have floated many possible answers in the century since Fermi first asked this question. Here are some of the most plausible reasons why he haven’t made first contact.

Image Credit: NASA

1. #GreatFilter

Basic probability asserts that alien life must exist. Since we haven’t made contact yet, one theory goes, there must be something barring life from interstellar travel or, at least, barring it from communicating with other alien species. This barrier is known as the “Great Filter,” and it is a force or event that stops a civilization from getting to the aforementioned point of interstellar travel or communication.

If the theory holds true, there are two primary reasons that we haven’t made contact: Because societies kill themselves off before they reach a state advanced enough to explore the stars or interstellar travel is simply not possible on a technological scale. Neither option is particularly pleasing.

And according to the experts behind the work, the filter event is of equal or greater probability than the existence of alien life itself. This is the point argued by Robin Hanson, a research associate at the Future of Humanity Institute at Oxford University, in his discussion of the topic.

No alien civilizations have substantially colonized our solar system or systems nearby. Thus among the billion trillion stars in our past universe, none has reached the level of technology and growth that we may soon reach. This one data point implies that a Great Filter stands between ordinary dead matter and advanced exploding lasting life.

Since we have not been able to detect alien life (or leave the solar system much, for that matter), how far are we from being caught up in some event that would bar us from ever finding aliens? “The easier it was for life to evolve to our stage, the bleaker our future chances probably are,” Hanson writes. In other words, the more life there is in the cosmos, the greater the likeliness that we are about to reach a cataclysmic, life-ending event or reach the cosmic limits of technological advancement.

2. Do Not Disturb the Aliens

Another hypothesis asserts that alien civilizations certainly exist, but they’re simply inactive. That’s the “aestivation hypothesis” (aestivation refers to an organism’s state of prolonged inactivity, similar to a bear hibernating or a frog that buries itself in sand during hot weather), which was put forth by researchers from Oxford’s Future of Humanity Institute and the Astronomical Observatory of Belgrade.

The theory, published in a paper in the Journal of the British Interplanetary Society in 2017, states that aliens may be “hibernating” until the environmental conditions are just right to become active and build their super society. The researchers argue that the laws of thermodynamics directly limit computation, as computing technologies need to be cooled in order to function. This makes it exceedingly difficult to create advanced technologies, as keeping them cool at scale quickly becomes prohibitively difficult. So the aliens are falling into a dormant until, to be blunt, the universe cools.

But distilling the development of a civilization to the kinds of conditions that our current, and somewhat imperfect, models can predict could be reductive. What if intelligent extraterrestrial life has found a way around the thermodynamic conditions that limit its ability to compute? “What if there are other forms of value that can be generated?” the study authors write. If they’re wrong about the relationship between thermodynamics and technology, the aestivation hypothesis would be moot. In this case, perhaps one of the other ideas here holds true.

3. A “Gaian”-tic Bottleneck

Image Credit: Creative Commons

According to the “Gaian Bottleneck” hypothesis, life needs particular environmental conditions to develop, and they’re not so common. Astrobiologists at the Australian National University penned their explanation to the Fermi Paradox in 2016.

Extinction is “the cosmic default for most life that has ever emerged on the surfaces of wet rocky planets in the Universe,” the researchers wrote. That’s because a planet has to be actually inhabited for it to be habitable, because organisms change the concentration of greenhouse gases in the atmosphere. A Catch-22 emerges: no life without habitability, no habitability without life.

For alien life to persist, the researchers write, it must hang on: “like trying to ride a wild bull. Most life falls off.” Life can only take place with the presence of an unlikely feedback loop. In this case, Earth is the exception to the rule.

4. Trapped in Deep Oceans

In 2015, after nearly a decade in transit, NASA’s New Horizons spacecraft became the first to do a close flyby of Pluto. It offered humanity its first look at its icy surface and raised questions about the possibility of subsurface oceans of water, and lots of methane and nitrogen. These questions put Pluto on a short but growing list of worlds with buried oceans trapped under a thick crust of ice and rock (some of the other worlds are Saturn’s moons Europa, Callisto, Enceladus and Ganymede, as well as Jupiter’s moon Titan).

Those oceans figure prominently into another theory of where life might be lurking, one that Alan Stern, the principal investigator for New Horizons, touches on. Since buried oceans form a much more stable ecosystem than flowing surface streams, changes such as altering tides and dissipation take place over a longer time period. A hard outer shell protects hypothetical life in the oceans from a harsh climate and a lethal mix of gases on the surface. “Impacts and solar flares, and nearby supernovae, and what orbit you’re in, and whether you have a magnetosphere, and whether there’s a poisonous atmosphere — none of those things matter,” Stern told Space.com.

Any intelligent alien life that forms in these deep oceans would have to overcome a big hurdle to reach inhabitants of other worlds: drilling through that thick, protective crust. All that work would only get them to the surface — sending signals to other planets become even more unlikely.

5. Missed Signals

The Allen Telescope Array,

Image Credit: National Science Foundation

For the past eighty years or so, we’ve been listening for signs of extraterrestrial life with radio technology. The Allen Telescope Array, situated 470 km (290 miles) northeast of San Francisco, is one of the biggest — since 2007, 42 dishes have stood at the ready to scan the skies regularly in the hope of receiving radio signals from extraterrestrial life.

But what if extraterrestrial life doesn’t operate on those frequencies? Attempts at contact could simply be passing us by simply because we don’t comprehend the right wavelengths.

Instead of using telescope arrays and scanning the skies for radio signals, Duncan Forgan at the University of St. Andrews in Scotland suggests creating a galactic communications network. The same way we blink our high beams to send a signal to other drivers, we could use the shadow that Earth creates when it passes in front of the Sun to send a message to our fellow inhabitants of the universe. Forgan suggests that we build powerful lasers that contain those encoded messages, which are sent out as we pass in front of the Sun.

“If you want to communicate with someone on the other side of the galactic centre, there’s lots of stuff in the way – dust, stars, a big black hole – so you can take the long way around using the network,” Forgan tells New Scientist. Rather than letting intergalactic messages get lost in the vastness of space, civilizations in different galaxies could agree to use this “galactic communications network” to ensure their messages get to their intended recipients – a unified system to cut through the chatter.

6. We are Being Impatient

We’ve only been actively reaching out for alien life for about a century — a mere blip in the long history of the solar system and of the universe overall. Evan Solomonides, an astrophysics and mathematics undergrad and researcher at Cornell University, suggests that it could take a while — about 1,500 years from now, to be precise — before we hear from any extraterrestrials.

In a paper submitted to the American Astronomical Society, Solomonides examines the probability of finding life. “We predict that under 1 percent of the galaxy has been reached at all thus far, and we do not anticipate to be reached until approximately half of the stars/planets have been reached.” Solomonides believes that we will have explore around half of the Milky Way galaxy before we hear anything, which will take a while since we’ve barely explored our own galactic neighborhood.

Solomonides is careful to note that the 1,500 years is not a deadline. “This is not to say that we must be reached by then or else we are, in fact, alone. We simply claim that it is somewhat unlikely that we will not hear anything before that time.”

'Alien cover up': Nearly 2,000 UFOs tracked by radar system but details suppressed

RADAR operatives patrolling the skies over the US and Canada track an average of 1,800 UFOS every five years it has emerged.

02-12-2017 om 19:32 geschreven door peter

Jurassic Park in China: een waar prehistorisch paradijs - HNL.be

Bob van Huet

Bron: AD.nl

Vers uit het ei

Vliegen niet bijzonder

02-12-2017 om 19:07 geschreven door peter

Alles is met elkaar verbonden en er is iets groters dan dit lichaam. Deze film is een bedreiging voor overheden en religies

The Reality of Truth is een zeer provocerende film waarin wordt gekeken naar de mysterieuze relatie tussen spiritualiteit en kruidengeneeskunde.

Ontwaking

Verbonden

Bedreiging

02-12-2017 om 18:40 geschreven door peter

Barack Obama will share secret files on Aliens if you support him in the fight against AIDS

02-12-2017 om 18:25 geschreven door peter

Weird Colored Cloud and Black Sphere Suddenly Appear Over Fields in Ontario, Canada

02-12-2017 om 18:18 geschreven door peter

shutterstock

Clinical Trials of a New “Cancer Vaccine” Show That It May Actually Work

IN BRIEF

A THERAPY FOR EACH PATIENT

NEOANTIGENS TO THE RESCUE

02-12-2017 om 12:38 geschreven door peter

Elon Musk: We Must Leave Earth For One Critical Reason

WHY WE NEED TO LEAVE EARTH

02-12-2017 om 12:25 geschreven door peter

Google’s Artificial Intelligence Built an AI That Outperforms Any Made by Humans

IN BRIEF

An AI That Can Build AI

A View of the Future

02-12-2017 om 12:13 geschreven door peter

02-12-2017 om 01:46 geschreven door peter

Search for Life on the Red Planet

Water marks

Salty surfaces

ANCIENT MICROBES ON MARS?

Curbing contamination

A HOSTILE PLANT

References

Tags

02-12-2017 om 01:34 geschreven door peter

Former SETI director Jill Tarter: ‘An alien signal isn’t coming to the US, it’s coming to planet Earth’

02-12-2017 om 01:13 geschreven door peter

Related

We Just Beamed A Signal At Space Aliens. Was That A Bad Idea?

Is traveling at light speed possible?

02-12-2017 om 01:02 geschreven door peter

ALIEN LIFE COULD FIND A HOME IN HIDDEN OCEANS ON FROZEN WORLDS AT THE EDGES OF OUR SOLAR SYSTEM

02-12-2017 om 00:45 geschreven door peter

Where Is Alien Life? Six Of The Top Theories

0. The Paradox That Started It All

1. #GreatFilter

2. Do Not Disturb the Aliens

3. A “Gaian”-tic Bottleneck

4. Trapped in Deep Oceans

5. Missed Signals

6. We are Being Impatient

02-12-2017 om 00:33 geschreven door peter

Bright moon and aurora borealis

01-12-2017 om 22:43 geschreven door peter

Legendary female Soviet pilot and UFO hunter, Marina 'Madam MIG' Popovich, dies at 86

01-12-2017 om 22:14 geschreven door peter

01-12-2017 om 21:55 geschreven door peter

Supervolcano eruptions might be more common than we thought — but there’s still no need to panic

01-12-2017 om 21:36 geschreven door peter

Huge exoplanet ten times more massive than Jupiter has unique carbon monoxide atmosphere

What's a Hot Jupiter

01-12-2017 om 21:26 geschreven door peter

01-12-2017 om 21:10 geschreven door peter

MUFON’s New Social Network