Technosignatures and the Search for Extraterrestrial Intelligence

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A rendering of a potential Dyson sphere, named after Freeman A. Dyson. As proposed by the physicist and astromomer decades ago, they would collect solar energy on a solar system wide scale for highly advanced civilizations. (SentientDevelopments.com)

The word “SETI” pretty much brings to mind the search for radio signals come from distant planets, the movie “Contact,” Jill Tarter, Frank Drake and perhaps the SETI Institute, where the effort lives and breathes.

But there was a time when SETI — the Search for Extraterrestrial Intelligence — was a significantly broader concept, that brought in other ways to look for intelligent life beyond Earth.

In the late 1950s and early 1960s — a time of great interest in UFOs, flying saucers and the like — scientists not only came up with the idea of searching for distant intelligent life via unnatural radio signals, but also by looking for signs of unexpectedly elevated heat signatures and for optical anomalies in the night sky.

The history of this search has seen many sharp turns, with radio SETI at one time embraced by NASA, subsequently de-funded because of congressional opposition, and then developed into a privately and philanthropically funded project of rigor and breadth at the SETI Institute.  The other modes of SETI went pretty much underground and SETI became synonymous with radio searches for ET life.

But this history may be about to take another sharp turn as some in Congress and NASA have become increasingly interested in what are now called “technosignatures,” potentially detectable signatures and signals of the presence of distant advanced civilizations.  Technosignatures are a subset of the larger and far more mature search for biosignatures — evidence of microbial or other primitive life that might exist on some of the billions of exoplanets we now know exist.

And as a sign of this renewed interest, a technosignatures conference was scheduled by NASA at the request of Congress (and especially retiring Republican Rep. Lamar Smith of Texas.)  The conference took place in Houston late last month, and it was most interesting in terms of the new and increasingly sophisticated ideas being explored by scientists involved with broad-based SETI.

“There has been no SETI conference this big and this good in a very long time,” said Jason Wright, an astrophysicist and professor at Pennsylvania State University and chair of the conference’s science organizing committee.  “We’re trying to rebuild the larger SETI community, and this was a good start.”

 

At this point, the search for technosignatures is often likened to that looking for a needle in a haystack. But what scientists are trying to do is define their haystack, determine its essential characteristics, and learn how to best explore it. (Wiki Commons)

 

During the three day meeting in Houston, scientists and interested private and philanthropic reps. heard talks that ranged from the trials and possibilities of traditional radio SETI to quasi philosophical discussions about what potentially detectable planetary transformations and by-products might be signs of an advanced civilization. (An agenda and videos of the talks are here.)

The subjects ranged from surveying the sky for potential millisecond infrared emissions from distant planets that could be purposeful signals, to how the presence of certain unnatural, pollutant chemicals in an exoplanet atmosphere that could be a sign of civilization.  From the search for thermal signatures coming from megacities or other by-products of technological activity, to the possible presence of “megastructures” built to collect a star’s energy by highly evolved beings.

Michael New is Deputy Associate Administrator for Research within NASA’s Science Mission Directorate. He was initially trained in chemical physics. (NASA)

All but the near infrared SETI are for the distant future — or perhaps are on the science fiction side — but astronomy and the search for distant life do tend to move forward slowly.  Theory and inference most often coming well before observation and detection.

So thinking about the basic questions about what scientists might be looking for, Wright said, is an essential part of the process.

Indeed, it is precisely what Michael New, Deputy Associate Administrator for Research within NASA’s Science Mission Directorate, told the conference. 

He said that he, NASA and Congress wanted the broad sweep of ideas and research out there regarding technosignatures, from the current state of the field to potential near-term findings, and known limitations and possibilities.

“The time is really ripe scientifically for revisiting the ideas of technosignatures and how to search for them,” he said.

He offered the promise of NASA help  (admittedly depending to some extent on what Congress and the administration decide) for research into new surveys, new technologies, data-mining algorithms, theories and modelling to advance the hunt for technosignatures.

 

Crew members aboard the International Space Station took this nighttime photograph of much of the Atlantic coast of the United States. The ability to detect the heat and light from this kind of activity on distant exoplanets does not exist today, but some day it might and could potentially help discover an advanced extraterrestrial civilization. (NASA)

 

Among the several dozen scientists who discussed potential signals to search for were the astronomer Jill Tarter, former director of the Center for SETI Research, Planetary Science Institute astrobiologist David Grinspoon and University of Rochester astrophysicist Adam Frank.  They all looked at the big picture, what artifacts in atmospheres, on surfaces and perhaps in space that advanced civilizations would likely produce by dint of their being “advanced.”

All spoke of the harvesting of energy to perform work as a defining feature of a technological planet, with that “work” describing transportation, construction, manufacturing and more.

Beings that have reached the high level of, in Frank’s words, exo-civilization produce heat, pollutants, changes to their planets and surroundings in the process of doing that work.  And so a detection of highly unusual atmospheric, thermal, surface and orbital conditions could be a signal.

One example mentioned by several speakers is the family of chemical chloroflourohydrocarbons (CFCs,)  which are used as commercial refrigerants, propellants and solvents.

Astronomner Jill Tarter is an iconic figure in the SETI world and led the SETI Institute for 30 years. (AFP)

These CFCs are a hazardous and unnatural pollutant on Earth because they destroy the ozone layer, and they could be doing something similar on an exoplanet.  And as described in the conference, the James Webb Space Telescope — once it’s launch and working — could most likely detect such an atmospheric compound if it’s in high concentration and the project was given sufficient telescope time.

A similar single finding described by Tarter that could be revolutionary is the radioactive isotope tritium, which is a by-product of the nuclear fusion process.  It has a short half-life and so any distant discovery would point to a recent use of nuclear energy (as long as it’s not associated with a recent supernova event, which can also produce tritium.)

But there many other less precise ideas put forward.

Glints on the surface of planets could be the product of technology,  as might be weather on an exoplanet that has been extremely well stabilized, modified planetary orbits and chemical disequilibriums in the atmosphere based on the by-products of life and work.  (These disequilibriums are a well-established feature of biosignature research, but Frank presented the idea of a technosphere which would process energy and create by-products at a greater level than its supporting biosphere.)

Another unlikely but most interesting example of a possible technosignature put forward by Tarter and Grinspoon involved the seven planets of the Trappist-1 solar system, all tidally locked and so lit on only one side.  She said that they could potentially be found to be remarkably similar in their basic structure, alignment and dynamics. As Tarter suggested, this could be a sign of highly advanced solar engineering.

 

Artist rendering of the imagined Trappist-1 solar system that had been terraformed to make the planets similar and habitable.  The system is one of the closest found to our own — about 40 light years.

 

Grinspoon seconded that notion about Trappist-1, but in a somewhat different context.

He has worked a great deal on the question of today’s anthroprocene era — when humans actively change the planet — and he expanded on his thinking about Earth into the galaxies.

Grinspoon said that he had just come back from Japan, where he had visited Hiroshima and its atomic bomb sites, and came away with doubts that we were the “intelligent” civilization we often describe ourselves in SETI terms.  A civilization that may well self destruct — a fate he sees as potentially common throughout the cosmos — might be considered “proto-intelligent,” but not smart enough to keep the civilization going over a long time.

Projecting that into the cosmos, Grinspoon argued that there may well be many such doomed civilizations, and then perhaps a far smaller number of those civilizations that make it through the biological-technological bottleneck that we seem to be facing in the centuries ahead.

These civilizations, which he calls semi-immortal, would develop inherently sustainable methods of continuing, including modifying major climate cycles, developing highly sophisticated radars and other tools for mitigating risks, terraforming nearby planets, and even finding ways to evolve the planet as its place in the habitable zone of its host star becomes threatened by the brightening or dulling of that star.

The trick to trying to find such truly evolved civilizations, he said, would be to look for technosignatures that reflect anomalous stability and not rampant growth. In the larger sense, these civilizations would have integrated themselves into the functioning of the planet, just as oxygen, first primitive and then complex life integrated themselves into the essential systems of Earth.

And returning to the technological civilizations that don’t survive, they could produce physical artifacts that now permeate the galaxy.

 

MeerKAT, originally the Karoo Array Telescope, is a radio telescope consisting of 64 antennas now being tested and verified in the Northern Cape of South Africa. When fully functional it will be the largest and most sensitive radio telescope in the southern hemisphere until the Square Kilometre Array is completed in approximately 2024. (South African Radio Astronomy Observatory)

 

This is exciting – the next phase Square kilometer Array (SKA2) will be able to detect Earth-level radio leakage from nearby stars. (South African Radio Astronomy Observatory)

 

While the conference focused on technosignature theory, models, and distant possibilities, news was also shared about two concrete developments involving research today.

The first involved the radio telescope array in South Africa now called MeerKAT,  a prototype of sorts that will eventually become the gigantic Square Kilometer Array.

Breakthrough Listen, the global initiative to seek signs of intelligent life in the universe, would soon announce the commencement of  a major new program with the MeerKAT telescope, in partnership with the South African Radio Astronomy Observatory (SARAO).

Breakthrough Listen’s MeerKAT survey will examine a million individual stars – 1,000 times the number of targets in any previous search – in the quietest part of the radio spectrum, monitoring for signs of extraterrestrial technology. With the addition of MeerKAT’s observations to its existing surveys, Listen will operate 24 hours a day, seven days a week, in parallel with other surveys.

This clearly has the possibility of greatly expanded the amount of SETI listening being done.  The SETI Institute, with its radio astronomy array in northern California and various partners, have been listening for almost 60 years, without detecting a signal from our galaxy.

That might seem like a disappointing intimation that nothing or nobody else is out there, but not if you listen to Tarter explain how much listening has actually been done.  Almost ten years ago, she calculated that if the Milky Way galaxy and everything in it was an ocean, then SETI would have listened to a cup full of water from that ocean.  Jason Wright and his students did an updated calculation recently, and now the radio listening amounts to a small swimming pool within that enormous ocean.

 

The NIROSETI team with their new infrared detector inside the dome at Lick Observatory. Left to right: Remington Stone, Dan Wertheimer, Jérome Maire, Shelley Wright, Patrick Dorval and Richard Treffers. (Laurie Hatch)

The other news came from Shelley Wright of the University of California, San Diego, who has been working on an optical SETI instrument for the Lick Observatory.

The Near-Infrared Optical SETI (NIROSETI) instrument she and her colleagues have developed is the first instrument of its kind designed to search for signals from extraterrestrials at near-Infrared wavelengths. The near-infrared regime is an excellenr spectral region to search for signals from extraterrestrials, since it offers a unique window for interstellar communication.

The NIROSETI instrument utilizes two near-infrared photodiodes to be able to detect artificial, very fast (nanosecond) pulses of infrared radiation.

The NIROSETI instrument, which is mounted on the Nickel telescope at Lick Observatory, splits the incoming near-infrared light onto two channels, and then checks for coincident events, which indicate signals that are identified by both detectors simultaneously.

Jason Wright is an assistant professor of astronomy and astrophysics at Penn State. His reading list is here.

Wright of Penn State was especially impressed by the project, which he said can look at much of the sky at once and was put together with on very limited budget.

Wright, who teaches a course on SETI at Penn State and is a co-author of a recent paper trying to formalize SETI terminology, said his own take-away from the conference is that it may well represent an important and positive moment in the history of technosignatures.

“Without NASA support, the whole field has lacked the normal structure by which astronomy advances,” he said.  “No teaching of the subject, no standard terms, no textbook to formalize findings and understandings.

“The Seti Institiute carried us through the dark times, and they did that outside of normal, formal structures. The Institute remains essential, but hopefully that reflex identification will start to change.”

 

Participants in the technosignatures conference in Houston last month, the largest SETI gathering in years.  And this one was sponsored by NASA and put together by the NExSS for Exoplanet Systems Science (NExSS,)  an interdisciplinary agency initiative. (Delia Enriquez)
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Time-Traveling in the Australian Outback in Search of Early Earth

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This story was written by Nicholas Siegler, Chief Technologist for NASA’s Exoplanet Exploration Program at the Jet Propulsion Laboratory with the help of doctoral student Markus Gogouvitis, at the University of New South Wales, Australia and Georg-August-University in Gottingen, Germany.

 

These living stromatolites at Shark Bay, Australia are descendants of similar microbial/sedimentary forms once common around the world.  They are among the oldest known repositories of life.  Most stromatolites died off long ago, but remain at Shark Bay because of the high salinity of the water. (Tourism, Western Australia)

 

This past July I joined a group of geologists, geochemists, microbiologists, and fellow astronomers on a tour of some of the best-preserved evidence for early life.

Entitled the Astrobiology Grand Tour, it was a trip led by Dr. Martin Van Kranendonk, a structural geologist from the University of New South Wales, who had spent more than 25 years surveying Australia’s Pilbara region. Along with his graduate students he had organized a ten-day excursion deep into the outback of Western Australia to visit some of astrobiology’s most renowned sites.

The trip would entail long, hot days of hiking through unmaintained trails on loose surface rocks covered by barb-like bushes called spinifex.  As I was to find out, nature was not going to give up its secrets easily.  And there were no special privileges allocated to astrophysicists from New Jersey.

 

The route of our journey back in time.  (Google Earth/Markus Gogouvitis /Martin Van Kranendonk)

The state of Western Australia, almost four times the size of the American state of Texas but with less than a tenth of the population (2.6 million), is the site of many of astrobiology’s most heralded sites. For more than three billion years, it has been one of the most stable geologic regions in the world.

It has been ideal for geological preservation due to its arid conditions, lack of tectonic movement, and remoteness. The rock records have in many places survived and are now able to tell their stories (to those who know how to listen).

 

The classic red rocks of the Pilbara in Western Australia, with the needle sharp spinifex bushes in the foreground. (Nick Siegler, NASA/JPL-Caltech)

Our trip began with what felt like a pilgrimage. We left Western Australia’s largest city Perth and headed north for Shark bsy. It felt a bit like a pilgrimage because the next morning we visited one of modern astrobiology’s highlights – the living stromatolites of Shark Bay.

Stromatolites literally mean “layered rocks”. It’s not the rocks that are alive but rather the community of microbial mats living on top. They are some of the Earth’s earliest ecosystems.

We gazed over these living microbial communities aloft on their rock perches and marveled at their exceptional longevity — the species has persisted for over three billion years. Their ancestors had survived global mass extinctions, planet-covering ice glaciers, volcanic activity, and all sorts of predators. Once these life forms took hold they were not going to let go.

 

The stromatolites forming today in the shallow waters of Shark Bay, Australia are built by colonies of microbes that capture ocean sediments. (University of Wisconsin-Madison)

The photosynthetic bacteria that built ancient stromatolites played a central role of our trip for three reasons:

  • Their geological footprints allowed scientists to date the evolution of early life and at times gain insight into the environments in which they grew.
  • They eventually harbored the first oxygen-producing bacteria and played a central role in creating our oxygen-rich atmosphere.
  • By locating ever-increasingly older microbial fossils we observed a lower limit to the age of the first life forms.. Given photosynthesis is not a simple process, the first life forms must have been simpler. Speculating, perhaps a few hundred million years earlier so that the first life form on Earth may have originated at four billion years ago.

When viewed under a microscope, you can see the mats are made of millions of single cell bacteria and archaea, among the simplest life forms we know. Within these relatively thin regions are multiple layers of specialized microbial communities that live interdependently.

Bacteria in the top layer evolved to harvest sunlight to live and grow via photosynthesis. Their waste products include oxygen as well as important nutrients for many different bacterial species within underlying layers. And this underlying layer’s waste product would do the same for the layer beneath it, perfectly recycling each other’s waste. The oldest forms of life that we know of had learned to co-exist together in a chemically interdependent environment.

 

Broken piece of a living stromatolite, which was was remarkably spongy and smelled slightly salty, indicative of the hypersaline bay that has contributed to their survival by making bacteria and other organisms undesirable. What was actually most remarkable of the visit to Hamelin pool was how quiet it was. There were no seagulls and other birds because of the hypersaline environment. They had gone elsewhere for their meals. (Nick Siegler, NASA/JPL-Caltech)

 

We saw ripped up portions of the mats that washed upon the shore at Hamelin pool in Shark Bay. A whole ecosystem held in one’s hand. Thousands of millions of years ago ancient relatives of these microbes thrived in shallow waters all around our planet, and left behind fossilized remains. But due to the evolution of grazing organisms these microbial structures are nowadays constrained to very specific environments. In the case of Shark Bay, the very high salt contents of this inlet have warded off most predators providing the microbes with a safe haven to live.

Ironically, the rocks, which help identify these ancient life forms, at the time were just a nuisance for the living microbes.

Small fine grains of sedimentary rock carried along in the daily tides would occasionally get stuck in the sticky mucus the microbes would secrete. In addition, the photosynthetic bacteria found at Shark Bay may have been inadvertently making their own rock by depleting the carbon dioxide in the surrounding water as part of photosynthesis and precipitating carbonate, adding to the grains of sediment trapped within the sticky top layer.

Over time, the grains from both the sedimentary and precipitated rocks would  cover the surface and block the sunlight for which these organisms had evolved to depend on. As an evolutionary tour de force, the photosynthetic microbes learned to migrate upward, leaving the newly formed rock layers behind.

These secondary rock fossils today showcase visually observable crinkly, frequently conical shapes, in stark contrast to abiotic sedimentary rocks. These ancient life forms left behind geological footprints reminding us they were here first.

Nick Siegler of JPL on his Australian Magical Origins Tour.  (Markus Gogouvitis)

Now to the most important contribution of stromatolites – terraforming the Earth.

Living in shallow water, the top most layer of the Shark Bay microbial mats are known to host cyanobacteria, photosynthetic bacteria that produce oxygen as a byproduct. Scientists don’t know what the first bacteria produced as they harnessed the energy of the Sun. But they do know that they eventually started producing oxygen.

In the evolution of life that eventually led to all plants and animals, this was one of the great events. More than 2.5 billion years ago, ancient bacteria began diligently producing oxygen in the oceans. Earth’s atmosphere began to irreversibly shift from its original, oxygen-free existence, to an oxic one, initiating the formation of our ozone layer and paving the way for the evolution of more complex life. Our planet has been terraformed by micro-organisms!

It was in the Karijini National Park where we went back in time (2.4 billion years) and observed an extraordinary piece of evidence for the early production of oxygen in Earth’s oceans, a time before oxygen made a strong presence in our atmosphere.

 

Banded iron formation at Karajini National Park.  (Nick Siegler, NASA-JPL/Caltech)

 

We saw a massive gorge with steep vertical walls carved out by flowing water. As oxygen production by early bacteria increased below the water surface it would react with dissolved iron ions (early oceans were iron-rich) causing iron oxides to precipitate and settle to the bottom.

For reasons not entirely understood — perhaps related to seasonal or temperature effects– the amount of new oxygen temporarily decreased and iron ion remained soluble in the oceans and other types of sediments accumulated, carbonates, slate, and shale. And then, just as before, the oxygen reappeared creating a new layer of precipitated iron.

The result was a banded sedimentary rock, a litmus test to a changing world, where oxygen would be the reactive ingredient leading to larger and more complex life forms. As the oxygen production no longer cycled, the oxygen went on to saturate the ocean and then accumulated in the Earth’s atmosphere eventually to the levels we have today.

 

Banded iron formation at Karajini. (Nick Siegler, NASA-JPL/Caltech)

After a day of looking down at rocks and spinifex it was both a relief and a joy to look up at the glorious Western Australian night sky. Far away from the light pollution of modern cities, each night would greet us with an awe-inspiring starlit sky. It never got old to remember we are part of a vast network of stars suspended in an infinite space.

The nights would start with the appearance of Venus well before sundown followed shortly by the innermost planet Mercury and then Jupiter and Saturn. It didn’t take long after sunset to see the renowned Southern Cross. Mars joined the evening as well, perfectly appearing on the arc called the ecliptic.

But nothing stirred the group more than the emergence of the swath of stars of the Milky Way, the disk of our home galaxy where its spiral arms all lie. The nights would be so clear that one could actually see the dark clouds of gas and dust that block large portions of the galaxy’s stars from shining through. We partook in the well-known tradition connecting individual points of light to form exotic creatures like scorpions and centaurs. But we also we followed the inverted approach of the Aborigines and connected the dark patches. Only then did we see the emu of the Milky Way. I would never have thought of connecting the darkness.

 

Australian night sky, with campfire below.  (Maëva Millan/NASA-GSFC/Georgetown University)

The night sky appeared even more special knowing that each of its stellar members likely host planetary systems like our own. How many of them host life? Maybe even civilizations? The numbers are in their favor.

At the half-way point of our trip we hiked to an ancient granite region in the red rocks of the Pilbara which contain the world’s largest concentration of Pleistocene rock art also known as petroglyphs. These etchings are believed to be 6,000 to 20, 000 years old.

The artists used no pigments, but rather rocks to pound/chisel shapes into the desert varnish, a thin dark film (possibly of microbial origin) that typically covers exposed rock surfaces in hyper arid regions. We came across many stylized male and female figures with highlighted genitalia as well as animals such as emus and kangaroos. Little is known about the people who created these art works. They left no clues to their origin or fate.

 

Rock art by aboriginal people done 6,000 to 20,000 years ago. The shapes were etched into an existing varnish on the rock. (Nick Siegler, NASA-JPL/Caltech)

Pilbara is also where the oldest mineral on Earth –a zircon dated at 4.4 billion years old — was discovered four years ago in the Jack Hills region.  Because of the geological history of the region, it is a frequent (if hardscrabble) site where many geologists and geochemists specializing in ancient Earth do their work.

In the last several days of the tour we encountered ever-increasing older evidence of stromatolites extending out to circa 3.5 billion years, about 75% of the history of the Earth. I expected the quality of the stromatolites to degrade as we went back in time and it looked like I was right until I saw a remarkably large rock in a locality called the Strelley Pool Formation. The rock measuring approximately 1.5 meters in all three directions gave a rare view of ancient stromatolites from all sides and an unequivocal interpretation of past life.

Large and ancient fossil stromatolite at the Strelley Pool Formation, with Siegler and Gogouvitis.  (Nick Siegler, NASA-JPL/Caltech)

The shapes of the embedded rocks formed by the microbial mats from the top view clearly show the elliptical areas where the bacteria inched upwards to acquire sunlight. Regions between the conical stromatolites were filled in by carbonate sediments in ancient shallow waters. These were later chemically altered to silica-rich rocks through alteration and etching of minerals by fluids. Silicified rocks are very weather-resistant, making them a great medium to preserve fossils for billions of years.

The side views of the stromatolite-laden rock revealed the expected conical layered shapes we saw in younger rocks (and in the living stromatolites of Shark Bay). Everything we had learned about stromatolite structures was clearly visible in this circa 3.43 billion year old example. It is astounding to realize that complex phototrophic (light-eating) organisms, even if not yet oxygen producing, were around during the deposition of the Strelley Pool Formation.

 

Detail of Strelley Pool stromatolite fossil.  (Nick Siegler, NASA-JPL/Caltech)

It is not unreasonable to speculate that the earliest life forms are even older by perhaps a few more hundred million years or so. There is evidence for even more ancient stromatolites in Greenland (3.7 billion years old) and isotope carbon evidence, with considerable controversy, in Nuvvuagittuq greenstone belt in northern Quebec, Canada (4.28 billion years old). Hence, life on Earth may have emerged within 500 million years from its formation. That is astonishingly rapid.

Was Earth an exception or the rule? What does that say for possible life on exoplanets?

Our tour came to an end on July 11. We had traveled over 1,600 miles through Australia’s outback, from Western Australia’s biggest city Perth, all the way up to Port Hedland at the north coast. We were privileged to see the country in ways that very few people get a chance to, and to be steeped in the multidisciplinary sciences of astrobiology while seeing some of its iconic ground.

I had seen some of the earliest evidence for life and the pivotal effect it had on our environment. For those 10 days I learned what it was like to be a time traveler.

 

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Water Worlds, Aquaplanets and Habitability

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This artist rendering may show a water world — without any land — or an aquaplanet with lots of more shallow water around a rocky planet. (NASA)

 

The more exoplanet scientists learn about the billions and billions of celestial bodies out there, the more the question of unusual planets — those with characteristics quite different from those in our solar system — has come into play.

Hot Jupiters, super-Earths, planets orbiting much smaller red dwarf stars — they are all grist for the exoplanet mill, for scientists trying to understand the planetary world that has exploded with possibilities and puzzles over the past two decades.

Another important category of planets unlike those we know are the loosely called “water worlds” (with very deep oceans) and their “aquaplanet” cousins (with a covering of water and continents) but orbiting stars very much unlike our sun.

Two recent papers address the central question of habitability in terms of these kind of planets — one with oceans and ice hundreds of miles deep, and one particular and compelling planet (Proxima Centauri b, the exoplanet closest to us) hypothesized to have water on its surface as it orbits a red dwarf star.

The question the papers address is whether these watery worlds might be habitable.  The conclusions are based on modelling rather than observations, and they are both compelling and surprising.

In both cases — a planet with liquid H20 and ice many miles down, and another that probably faces its red dwarf sun all or most of the time — the answers from modelers is that yes, the planets could be habitable.   That is very different from saying they are or even might be inhabited.  Rather,  the conclusions are based on computer models that take into account myriad conditions and come out with simulations about what kind of planets they might be.

This finding of potential watery-world habitability is no small matter because predictions of how planets form point to an abundance of water and ice in the planetesimals that grow into planets.

As described by Eric Ford, co-author of one of the papers and a professor of astrophysics at Pennsylvania State University, “Many scientists anticipate that planets with oceans much deeper than Earths could be a common outcome of planet formation. Indeed, one of the puzzling properties of Earth is that it has oceans that are just skin deep” compared to the radius of the planet.

“While some planets very close to their star might loose all their water, it would take a delicate balancing act to remove many ocean’s worth of water and to leave a planet with oceans as shallow as those on Earth.”

An interesting place to start.

 

Artist’s conception of a planet covered with a global ocean. A new study finds that these wate rworlds could maintain stable climates and perhaps sustain life under certain conditions. (ESO/M. Kornmesser)

 

It should first be said that many scientists are dubious that extreme water worlds can support life or can support detectable life.  My colleague Elizabeth Tasker wrote a column — Can You Overwater a Planet? — focused on this view last year.

The first of the two new exoplanets/ocean papers involves planets with very deep oceans. Written by Edwin Kite of the University of Chicago and Ford of Penn State, the paper in the Astrophysical Journal concludes that even a planet with such super deep oceans could — under certain conditions — provide habitable conditions.

This finding is at odds with previous simulations, and Kite says that is part of its significance. The scientific community has largely assumed that planets covered in a deep ocean would not support the cycling of minerals and gases that keeps the climate stable on Earth, and thus wouldn’t be friendly to life.

But the Kite and Ford study found that ocean planets (with 10 to 1000 times as much water as Earth) could remain habitable much longer than previously assumed. The authors performed more than a thousand simulations to reach that conclusion.

Eric Ford is a professor astrophysics at Penn State and a specialist in planet formation. (Penn State)

“This really pushes back against the idea you need an Earth clone—that is, a planet with some land and a shallow ocean,” said Edwin Kite, assistant professor of geophysical sciences at the University of Chicago and lead author of the study.

Edwin Kite is an assistant professor of planetary sciences at the University of Chicago. (Univ. of Chicago)

Because life needs an extended period to evolve — and because the light and heat on planets can change as their stars age — scientists usually look for planets that have both some water and some way to keep their climates stable over time. The method for achieving this steady state that we know is, of course, how it works on Earth. Over eons, our planet has cooled itself by drawing down atmospheric greenhouse gases into minerals and warms itself up by releasing them via volcanoes.

But this model doesn’t work on a water world, with deep water covering the rock and suppressing volcanoes.

Kite and Ford wanted to know if there was another way to achieve a balance. They set up a simulation with thousands of randomly generated planets, and tracked the evolution of their climates over billions of years.

“The surprise was that many of them stay stable for more than a billion years, just by luck of the draw,” Kite said. “Our best guess is that it’s on the order of 10 percent of them.”

These planets sit in the right location around their stars. They happened to have the right amount of carbon present, and they don’t have too many minerals and elements from the crust dissolved in the oceans that would pull carbon out of the atmosphere. They have enough water from the start, and they cycle carbon between the atmosphere and ocean only, which in the right concentrations is sufficient to keep things stable.

None of this means that such a planet exists — our ability to detect oceans worlds is in its infancy.  The issue is rather that Kite and Ford conclude that a deep ocean planet could potentially be habitable if other conditions were met.

 

Artist rendering of Proxima Centauri b orbiting its red dwarf host star. (ESO/L.Calçada/Nick Risinger)

 

Anthony Del Genio and his team of modelers at NASA’s Goddard Institute for Space Studies in New York used their state-of-the-art climate simulations to look at another aspect of the exoplanet water story, and they chose Proxima Centauri b as their subject.  The roughly Earth-sized planet was discovered in 2016 and is the closest exoplanet to Earth.

Scientists determined early on that it is a rocky (as opposed to gaseous) planet and that it orbits its host star every 11 days.  If that star was as powerful as our sun, there would be no talk of possible habitability on close-in Proxima b.  But the star is a red dwarf and puts out only a fraction of the radiation coming from a host star like our sun.

Still, the case for habitability on Proxima b was initially considered to be weak, in part because the planet is tidally locked by its closeness to the host star.  In other words, it would most likely not spin to create days and nights as it orbits, but rather would have a sun-facing side and a space-facing side — making the temperature differences great.

Our ability to characterize a small planet like Proxima b remains very limited, and so it is unknown whether the planet has water or whether it has an atmosphere.  So those two essential components of the habitability question are missing.

But Del Genio’s team decided to model the dynamics of Proxima b with a presumed ocean, though not one that is many miles deep.  In Earth science parlance, what Del Genio referred to as an “aquaplanet.” And using their sophisticated models, they would simulate “dynamic” oceans with currents like our own, rather than the stationary oceans modeled earlier on exoplanets.

And rather to their surprise, they reported in the journal Astrobiology that their model of ocean behavior showed that the planet would not have only small areas of potential habitability — the earlier proposed habitable “eyeball” scenario — but rather much of the planet could be habitable.  That could include some of the normally space-facing side.

 

One type of possible water world is an “eyeball” planet, where the star-facing side is able to maintain a liquid-water ocean, while the rest of the surface is ice. (Image via eburacum45/DeviantArt)

 

“Our group said let’s hook up an atmosphere to a dynamic ocean rather than a static one,” Del Genio said.  “That way you get ocean currents like those on our coasts, and they move water of different temperatures around.

“If you have a real and dynamic ocean in your model, then we found that the eyeball goes away.  Usually the currents go west to east and they carry warmer water even to the night side.”

Anthony Del Genio, leader of NASA’s GISS team that  uses cutting edge Earth climate models to better understand conditions on exoplanets.

So using this more sophisticated model, not insignificant areas of Proxima b, or any other planet like it orbiting a red dwarf star, could be habitable, they concluded.  But again, that is assuming some pretty big “ifs” — the presence of an ocean and an atmosphere.

And then the team added variables such as a thick nitrogen and carbon atmosphere or a thin one, fresh water or salty water, a planet that is firmly locked and never rotating, or one that rotates a modest amount — giving the dark side some light.  Del Genio said that with all these added factors, a substantial portion of the surface of Proxima b, or a planet like it, would have liquid water and potentially habitable conditions.

This focus on watery worlds — including those that would be extreme compared with Earth today — makes sense in the context of the history of Earth.

While there is no direct evidence of this, many scientists think that the very early Earth was covered for a period of time with water with little or no land.

And then after land appeared, it still took some three billion years for any life form — bacteria, early planets — to colonize the land, and another half billion years for animals to come ashore.  Yet the oceans were long habitable and inhabited, as early a 3.8 billion years ago.

So until astronomy and exoplanet science develop the needed instruments and scientists acquire the observed knowledge of conditions on water worlds, progress will come largely from modelling that tells us what might be possible.

 

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Curiosity Rover Looks Around Full Circle And Sees A Once Habitable World Through The Dust

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An annotated 360-degree view from the Curiosity mast camera.  Dust remaining from an enormous recent storm can be seen on the platform and in the sky.  And holes in the tires speak of the rough terrain Curiosity has traveled, but now avoids whenever possible. Make the screen bigger for best results and enjoy the show. (NASA/JPL-Caltech/MSSS)

 

When it comes to the search for life beyond Earth, I think it would be hard to point to a body more captivating, and certainly more studied, than Mars.

The Curiosity rover team concluded fairly early in its six-year mission on the planet that “habitable” conditions existed on early Mars.  That finding came from the indisputable presence of substantial amounts of liquid water three-billion-plus years ago, of oxidizing and reducing molecules that could provide energy for simple life, of organic compounds and of an atmosphere that was thick enough to block some of the most harmful incoming cosmic rays.

Last year, Curiosity scientists estimated that the window for a habitable Mars was some 700 million years, from 3.8 to 3.1 billion years ago.  Is it a coincidence that the earliest confirmed life on Earth appeared about 3.8 billion years ago?

Today’s frigid Mars, which has an atmosphere much thinner than in the planet’s early days, hardly looks inviting, although some scientists do see a possibility that primitive life survives below the surface.

But because it doesn’t look inviting now doesn’t mean the signs of a very different planet aren’t visible and detectable through instruments.  The Curiosity mission has proven this once and for all.

The just released and compelling 360-degree look (above) at the area including Vera Rubin Ridge brings the message home.

Those fractured, flat rocks are mudstone, formed when Gale Crater was home to Gale Lake.  Mudstone and other sedimentary formations have been visible (and sometimes drilled) along a fair amount of the 12.26-mile path that Curiosity has traveled since touchdown.

 

An image of Vera Rubin Ridge in traditional Curiosity color, and the same view below with filters designed to detect hematite, or iron oxide. That compound can only be formed in the presence of water. (NASA/JPL-Caltech)

 

The area the rover is now exploring contains enough hematite — iron oxide — that its signal was detectable from far above the planet, making this area a prized destination since well before the Mars Science Laboratory and Curiosity were launched.

Like Martian clays and sulfates that have been identified and explored, the hematite is of great interest because of its origins in water.  Without H2O present many eons ago, there would be no hematite, no clay, no sulfates.  But as Mars researchers have found, there is a lot of all three.

I like to return to Mars and especially Curiosity because it provides something unique in the cosmos:  an environment where scientists today have ground-truthed the hypothesis that early Mars was once habitable, and found unambiguous results that it was.

That doesn’t mean that the planet necessarily ever gave rise to, or supported, living organisms.  But it’s a lot more than can be said for other targets for life beyond Earth.

NASA’s Europa Clipper may determine some day that beneath the ice crust of that moon of Jupiter is an ocean that is, or was, habitable.  But that determination is still years away.  Same with Saturn’s moon Enceladus, which some see as habitable beneath its ice, but no mission is currently approved to determine that.

And when it comes to exoplanets and possible life on them, it is both a logical and alluring conclusion that some support living organisms — there are, after all, billions and billions of exoplanets, and the cosmos is filled with the elements and compounds we find on Earth.

But we remain quite far away from consensus on what an exoplanet biosignature might be, and much further away from being able to confidently detect the probable biosignature elements and compounds on distant exoplanets.

And so for now we have Mars as our most plausible target for life beyond Earth.

 

Vera Rubin Ridge, with its high concentration of both red and green hematite. (NASA/JPL-Caltech)

 

It wasn’t that long ago that the NASA exploration mantra for Mars was “follow the water,”  under the assumption that life needed water to survive.

But Curiosity and satellites orbiting Mars have found abundant proof that water did play a major role in the planet’s early times.  Not only has Curiosity found that a lake existed on and off for hundreds of millions of years at Gale Crater, but researchers recently announced the presence of a large reservoir of liquid water beneath the southern polar region.

What’s more, evidence of briny surface streams on steep Martian cliffs in their warm season has grown stronger, though it remains a much-debated finding.

But with the water story well established, researchers are focused more on organics, minerals and what can be found beneath the radiation-baked surface.

Curiosity has been working for months around Vera Rubin Ridge, though for much of that time with a big handicap — the rover’s long-armed drill wasn’t working.  Important internal mechanisms stopped performing in late 2016, and it wasn’t until late spring of 2018 that a workaround was ready.

After one successful drilling, the next two failed.  But there was no drill problem with those two; the rock on the ridge was just too hard to penetrate.  It makes sense that the rock would be very hard because it has withstood millions of years of powerful winds blowing across Gale Crater, while other nearby rock and sediments were carried away.

The best way to discover why these rocks are so hard is to drill them into a powder for the rover’s two internal laboratories. Analyzing them might reveal what’s acting as “cement” in the ridge, enabling it to stand despite wind erosion.

Most likely, said Curiosity project scientist Ashin Vasavada, groundwater flowing through the ridge in the ancient past had a role in strengthening it, perhaps acting as plumbing to distribute this wind-proofing “cement.” In this case, it would be some variation of hematite, which in crystal form can be pretty hard on its own.

On its third attempt — and after a prolonged search for a “soft” spot in the ridge — the Curiosity drill did succeed in digging a hole and bringing back some precious powdered contents for study in the two onboard labs.

After the exploration of Vera Rubin Ridge and its hematite will come explorations of large deposits of sulfates and phyllosilicates (clays) — both formed in water as well — further up Mt. Sharp.

 

Curiosity’s pathway over the past six years, from near the Bradbury Landing site to the successful drilling at Vera Rubin Ridge. The route has gone through fossil lake beds, dune fields, the underlying rock formation of Mt. Sharp and now up to the hematite concentrations. (NASA/JPL=Calgtech)

 

I find the landscape of Mars that Curiosity shows us to be captivating, but also sobering when it comes to the search for life beyond Earth.

Here is the planet closest to Earth (during some orbits, at least), one that has been determined to be habitable 3 to 4 billion years ago,  one that can be studied with rovers on the ground and orbiting satellites — and still we can’t determine if it ever actually supported life, and probably won’t be able to for decades to come.

The big confounding factor on Mars really is time.  Life could have come and gone billions of years ago, and intense surface radiation could have erased that history and made it appear as if life was never there.  (This is one reason why Mars scientists want to dig deeper below the surface, where the effects of radiation would be much reduced.)

Time may be a powerful obstacle when it comes finding signs of life on exoplanets as well.  If life exists elsewhere in the cosmos, it surely comes and goes, too.  The odds of us catching it when it’s present may be low, despite all those billions and billions of planets. (Given the way that exoplanet biosignatures work, the life needs to be present at the time of observation.)

Or maybe the time for life in the cosmos has really just begun.

Harvard-Smithsonian astrophysicist Avi Loeb argued several years ago that life on Earth may be a premature flowering, compared with what may well happen later and elsewhere. (Column on his intriguing ideas is here.)

A majority of stars in the cosmos are red dwarfs, or M stars.  They take eons to stabilize and then generally continue in a steady state for much longer than a G star like our sun.  So, he argued,  life in the cosmos around red dwarfs may not become widespread for some time, and then could last for a very long time if and when it did arise.

But enough about time — other than to perhaps take a little more time to enjoy the 360-degree view of Mars and Curiosity that brings thoughts like these to mind.

 

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Piecing Together The Narrative of Evolution

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A reconstruction of the frond-like sea creature Stromatoveris psygmoglena, which lived during the Cambrian explosion of life forms on Earth.  Newfound fossils of Stromatoveris were compared with Ediacaran fossils, and researchers concluded they were all very early animals and that this animal group survived the mass extinction event that occurred between the Ediacaran and Cambrian periods. (Jennifer Hoyal Cuthill.)

An essential characteristic of life is that it evolves. Whether on Earth or potentially Mars, Europa or distant exoplanets, we can assume that whatever life might be present has the capacity and the need to change.

Evolution is intimately tied to the origin-of-life question, which this column often explores.  Having more answers regarding how life might have started on Earth can no doubt help the search for life elsewhere, just as finding life elsewhere could help understand how it started here.

The connection between evolution and exoplanets has an added and essential dimension when it comes to hunting for signatures of distant extraterrestrial life.

Searching for a planet with lots of oxygen and other atmospheric compound in disequilibrium (as on Earth) is certainly a way forward. But it is sobering to realize that those biosignatures would not have been detectable on Earth for most of the time that life has been present.  That’s because large concentrations of oxygen are a relative newcomer to our planet,  product of biological evolution.

With all this in mind, it seems both interesting and useful to look at the work of a researcher studying the fossil record to better understand a particular transition on Earth — the one from simpler organisms to multicellular creatures that can be considered animals.

The surprising, large transitional life of the Ediacaran period, which just preceded the Cambrian explosion of complex life. This grouping is termed the Ediacara assemblage, and existed late in the period.  (John Sibbick)

The researcher is Jennifer Hoyal Cuthill of the University of Cambridge, who I first met at the Earth-Life Science Institute in Tokyo, a unique place where scientists research the origin of Earth and of life on Earth.

She had been included in a group of twelve two-year fellows recruited from around the world who specialized in fields ranging from the microbiology of extreme environments to the current and past dynamics of the deep Earth and the digital world of chemo informatics.  And then there was Hoyal Cuthill, whose field is paleobiology, with a heavy emphasis on evolution.

Now Hoyal Cuthill has published a paper in the journal Paleontology that describes findings in the fossil record that shed light on that transition from less complex organisms like bacteria, algae and fungi to  to animals.

Her specialty is the Ediacaran period some 635 to 541 million years ago.  This transitional period came after a snowball Earth event and was followed by the Cambrian explosion, when ocean life of all sorts grew and changed at an unprecedented rate.  But as she and others have found, the Ediacaran also had large and unique lifeforms, and she is working to make sense of them.

She described her work and findings more specifically as follows:

“When did animals originate? What were the bizarre, early fossils known as the Ediacaran biota?

“We show that both questions are answered by a frond-like sea creature called Stromatoveris psygmoglena known from exceptionally preserved, Cambrian fossils from Chengjiang County, China.

“Originally described from only eight specimens, we examined over 200 new fossils since discovered by researchers from Northwest University (in Xian.) Stromatoveris was compared to earlier Ediacaran fossils in a computer analysis of anatomy and evolutionary relationships.

“This showed that Stromatoveris and seven key members of the Ediacaran biota share detailed anatomical similarities, including multiple, radiating, branched fronds that unite them as a phylum of early animals, originating by the Ediacaran Period and surviving into the early Cambrian.”

Fossil of Stromatoveris psygmoglena, turned on its side.  New research suggests that Stromatoveris and related Ediacaran lifeforms could be among the earliest creatures that can be described as an animal. Ediacaran fossils have been found from Australia to arctic Siberia, Canada to southern Africa.  (Jennifer Hoyal Cuthill)

 

Dickinsonia is a genus of iconic fossils of the Ediacaran biota. While a bilaterian affinity had been previously suggested by some researchers, this study suggests that it is closely related to other members of the Ediacaran biota as well as Cambrian Stromatoveris.  (Jennifer Hoyal Cuthill)

 

More broadly, Hoyal Cuthill told me that “the story of the origin of life and the evolution of life are so interwoven.”

“Looking back as far as we can, we see important patterns emerging from the very start.  All things learn.  If possible, they add to complexity… And evolution does not result in a complete replacement.  When transitions happen -– even big ones – important life patterns continue.  And so do some creatures.”

This continuity within change is what she has focused on, in the transitional Proterozoic Eon when bacterial and plant life evolved into the more complex ocean animal life of the Cambrian explosion.

She has traveled the world and scoured the fossil record to come up with this conclusion:  that creatures that can be called “animals” existed at least as far back as the early days of the Ediacaran, some 630 million years ago, when many macro-fossils quite suddenly appeared following that early epoch of global freezing.

The Ediacaran period gets its name from the Ediacara Hills in Australia, where famous fossils of this age were found. Known also as the Vendian, the Ediacaran was the final stage of Pre-Cambrian time. During this time, large (up to meter-sized) organisms, often shaped like fronds with holdfast discs, lived on thick mats of bacteria which, unlike today, coated the sea floor. The slimy mats acted as a barrier between the water above and the sediments below, preventing oxygen from reaching under the sea floor and making it less habitable.

During this time, large (up to meter-sized) organisms, often shaped like discs or fronds,  lived on or in shallow horizontal burrows beneath thick mats of bacteria which, unlike today, coated the sea floor. The slimy mats acted as a barrier between the water above and the sediments below, preventing oxygen from reaching under the sea floor and turning it largely uninhabitable.

And then when the Cambrian explosion occurred beginning some 540 million years ago, most of those lifeforms were thought to have gone extinct. Some paleobiologists hold that Earth’s first mass extinction actually took place during this period, when newly evolved animals transformed the environment.

Biota from the Ediacaran period through the Cambrian explosion. (Proceedings of the Royal Academy; B M. Gabriela Mángano, Luis A. Buatois)

Hoyal Cuthill says that her research leads her to a very different view: that there was a broad but not mass extinction, and that Ediacaran animals survived well after the Cambrian Explosion.

And in the journal paper published this week, Hoyal Cuthill and co-author Jian Han of Northwest University in Xian present fossil evidence from southern China of Cambrian creatures that she argues are unquestionably animal.

She said they have characteristics such as radial symmetry, differentiated bodies and an animal type organization. These fossils date from the early Cambrian, she said, yet they are similar in important ways to creatures found during the earlier Ediacaran period.

In other words, this group of animals not only persisted from the onset of the Ediacaran period, but also after the often-invoked mass extinction that came along with the Cambrian Explosion.

Jennifer Hoyal Cuthill, paleobiologist with a focus on Ediacaran period when life began to grow substantially in size. (Julieta Sarmiento Photography).

Hoyal Cuthill says that while the fossil record from the Ediacaran is sparse, flora and fauna are known to have included some of the oldest definite multicellular organisms. The organisms, she said, resembled fractal fronds but bear little resemblance to modern lifeforms.

The world’s first ever burrowing animals also evolved in the Ediacaran, though we don’t know what they looked like. The only fossils that have been found are of the burrows themselves, not the creatures that made them.

In an earlier paper, she described how and why many of the Ediacaran lifeforms got as large as they did.

“All organisms need nutrients simply to survive and grow, but nutrients can also dictate body size and shape.

“During the Proterozoic, there seem to have been major changes in the Earth’s oceans which may have triggered this… growth to the macro-scale. These include increases in oxygen and, potentially, other nutrients such as organic carbon.”

In other words, the surrounding atmosphere, oceans, perhaps reversing magnetic fields, tectonic and volcanic activity and the resulting menu of chemical compounds available and climatic conditions are essential drivers of biological evolution.  Just as they are now considered some of the important indicators of a potentially habitable exoplanet.

And on a currently far more fanciful note, wouldn’t it be wonderful if scientists could some day not only find life beyond Earth, but to learn to study how that life, too, might have evolved.

 

 

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