First Mapping of Interstellar Clouds in Three Dimensions; a Key Breakthrough for Better Understanding Star Formation

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This snakelike gas cloud (center dark area) in the constellation Musca resembles a skinny filament. But it’s actually a flat sheet that extends about 20 light-years into space away from Earth, an analysis finds.
(Dylan O’Donnell, deography.com/WikiCommons)

When thinking and talking about “astrobiology,” many people are inclined to think of alien creatures that often look rather like us, but with some kind of switcheroo.  Life, in this view, means something rather like us that just happens to live on another planet and perhaps uses different techniques to stay alive.

But as defined by NASA, and what “astrobiology” is in real scientific terms, is the search for life beyond Earth and the exploration of how life began here.  They may seem like very different subjects but are actually joined at the hip;  having a deeper understanding of how life originated on Earth is surely one of the most important set of clues to how to find it elsewhere.

Those con-joined scientific disciplines — the search for extraterrestrial life and the extraordinarily difficult task of analyzing how it started here — together raise another most complex challenge.

Precisely how far back do we look when trying to understand the origins of life?  Do we look to Darwin’s “warm little pond?” To the Miller-Urey experiment’s conclusion that organic building blocks of life can be formed by sparking some common gases and water with electricity?  To an understanding the nature and evolution of our atmosphere?

The answer is “yes” to all, as well as to scores of additional essential dynamics of our galaxies.  Because to begin to answer those three questions, we also have to know how planets form, the chemical make-up of the cosmos, how different suns effect different exoplanets and so much more.

This is why I was so interested in reading about a breakthrough approach to understanding the shape and nature of interstellar clouds.  Because it is when those clouds of gas and dust collapse under their own gravitational attraction that stars are formed — and, of course, none of the above questions have meaning without preexisting stars.

In theory, the scope of astrobiology could go back further than star-formation, but I take my lead from Mary Voytek, chief scientist for astrobiology at NASA.  The logic of star formation is part of astrobiology, she says, but the innumerable cosmological developments going back to the Big Bang are not.

So by understanding something new about interstellar clouds — in this case determining the 3D structure of such a “cloud” — we are learning about some of the very earliest questions of astrobiology, the process that led over the eons to us and most likely life of some sort on the billions of exoplanets we now know are out there.

Cepheus B, a molecular cloud located in our Milky Galaxy about 2,400 light years from the Earth, provides an excellent model to determine how stars are formed. This composite image of Cepheus B combines data from the Chandra X-ray Observatory and the Spitzer Space Telescope.The Chandra observations allowed the astronomers to pick out young stars within and near Cepheus B, identified by their strong X-ray emission.
Credits X-ray: NASA/CXC/PSU/K. Getman et al.; IRL NASA/JPL-Caltech/CfA/J. Wang et al.

So, what is an interstellar cloud?

It’s the generic name given to an accumulation of gas, plasma, and dust in our and other galaxies, left over from galaxy formation.  So an interstellar cloud is a denser-than-average region of the interstellar medium.

Hydrogen is its primary component, and that hydrogen exists in a wide variety of states depending on the density, the age, the location and more of the cloud.

Until recently the rates of reactions in interstellar clouds were expected to be very slow, with minimal products being produced due to the low temperature and density of the clouds. However, organic molecules were observed in the spectra that scientists would not have expected to find under these conditions, such as formaldehyde, methanol, and vinyl alcohol.

The reactions needed to create such substances are familiar to scientists only at the much higher temperatures and pressures of earth and earth-based laboratories. The fact that they were found indicates that these chemical reactions in interstellar clouds take place faster than suspected, likely in gas-phase reactions unfamiliar to organic chemistry as observed on earth.

What was newly revealed this week is that it is possible to determine the 3D structure of an interstellar cloud. The advance not only reveals the true structure of the molecular cloud Musca, which differs from previous assumptions in looking more like a pancake than a needle.

But the two authors, astrophysicist Konstantinos Tassis of the University of Crete and Aris Tritsis, now a postdoctoral fellow at Australian National University, say their discovery will lead to a better understanding of the evolution of interstellar clouds in general. This, in turn, which will help astronomers answer the longstanding questions of how and why the enormous number and wild variety of stars exists in our galaxy and beyond.

Here is a video put together to help explain the science of Musca and its dimensions.   The work was published in the journal Science, and here is their description of what the video shows:

“The first part of the movie gives an overview of the problem of viewing star-forming clouds in 2D projection. The second part of the video shows the striations in Musca, and the process through which the normal mode spatial frequencies are recovered. The third part of the movie demonstrates how the apparently complex profiles of the intensity cuts through striations are reproduced by progressively summing the theoretically predicted normal modes. At this part of the video (1:30-1:52) the spatial frequencies are scaled to the frequency range of human hearing and are represented by the musical crescendo.”

Credit: Aris Tritsis, Nick Gikopoulos, Valerio Calisse, Kostas Tassis

In an email, Tritsis said that this is the first time that the 3-dimensional coordinates of an interstellar cloud have been measured.

“There have been other crude estimates of the 3D sizes of clouds that relied on many assumptions so this is the first time we were able to determine the size with such accuracy and certainty,” he wrote.

“What we are after is the physics that controls the nature of the stars that will form. This physics will dictate how many star will form and with what masses, but it will also be responsible for shaping the cloud. Thus, this physics is encoded in the shape and that is why we are so interested about it.”

Their pathway in to mapping a 3D cloud was the striations (wispy stripe-like patterns) they detected within the cloud. They show that these striations form by the excitation of fast magnetosonic waves (longitudinal magnetic pressure waves) – the cloud is vibrating, like a bell ringing after it has been struck.

“What we have actually found is that the entire cloud oscillates just like waves on the surface of a pond,” he wrote in his email.

Aris Tritsis, a postdoctoral student at the Australian National University.

“However, in this instance is not the surface of the water that is oscillating but the magnetic field that is threading the cloud. Furthermore, because these waves get trapped, they act like a fingerprint. They are unique and by studying their frequencies we can deduce the sizes of the boundaries that confined them.

“It is the same concept as a violin and a cello making very different sounds. In a similar fashion, clouds with different shapes and sizes will vibrate differently. After having identify the frequencies of these oscillations we scaled them to the frequency range of human hearing to get the ‘song of Musca’!”

By analyzing the frequencies of these waves the authors produce a model of the cloud, showing that Musca is not a long, thin filament as once thought, but rather a vast sheet-like or pancake structure that stretches 20 light-years away from Earth.  (The cloud is some 27 light 490 and 650 light-years from Earth.)

With the determination of its 3D nature, the scientists modeled a cloud that is ten times more spacious than earlier thought.

Konstantinos Tassis of the University of Crete is a star formation specialist. He received his doctorate in theoretical astrophysics at the University of Illinois at Urbana Champaign.

From the 3D reconstruction, the authors were able to determine the cloud’s density. Tritsis and Tassis note that, with its geometry now determined, Musca can be used to test theoretical models of interstellar clouds.

“Because of the fact that Musca is isolated and it is very ordered, it was the obvious choice for us to test our method,” Tritis wrote. “However, other clouds out there could also vibrate globally.

“Knowing the exact dimensions of Musca, we can simulate it in great detail, calculate many different properties of this particular cloud based on different star formation models, and compare them with observations.

“We believe that, with its 3D structure revealed, Musca will now act as a prototype laboratory to study star formation in greater detail than ever before. The Musca star formation saga is only now beginning, and this is a very exciting development that goes beyond this particular discovery.”

And in that way, the discovery is very much a part of the long and broad sweep of astrobiology.

 

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Putting Together a Community Strategy To Search for Extraterrestrial Life

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I regret that the formatting of this column was askew earlier; I hope it didn’t make reading too difficult.  But now those problems are fixed.

The scientific search underway for life beyond Earth requires input from many disciplines and fields. Strategies forward have to hear and take in what scientists in those many fields have to say. (NASA)

Behind the front page space science discoveries that tell us about the intricacies and wonders of our world are generally years of technical and intellectual development, years of planning and refining, years of problem-defining and problem-solving.  And before all this, there also years of brainstorming, analysis and strategizing about which science goals should have the highest priorities and which might be most attainable.

That latter process is underway now in regarding the search for life in the solar system and beyond, with numerous teams of scientists tackling specific areas of interest and concern and turning their group discussions into white papers.  In this case, the white papers will then go on to the National Academy of Sciences for a blue-ribbon panel review and ultimately recommendations on which subjects are exciting and mature enough for inclusion in a decadal survey and possible funding.

This is a generally little-known part of the process that results in discoveries, but scientists certainly understand how they are essential.  That’s why hundreds of scientists contribute their ideas and time — often unpaid — to help put together these foundational documents.

With its call for extraterrestrial habitability white papers, the NAS got more than 20 diverse and often deeply thought out offerings.  The papers will be studied now by an ad hoc, blue ribbon committee of scientists selected by the NAS, which will have the first of two public meetings in Irvine, Calif. on Jan. 16-18.

Shawn Domagal-Goldman, a leader of many NASA study projects and a astrobiologist at NASA’s Goddard Space Fight Center. (NASA)

Then their recommendations go up further to the decadal survey teams that will set formal NASA priorities for the field of astronomy and astrophysics and planetary science.  This community-based process that has worked well for many scientific disciplines since they began in the late 1950s.

I’m particularly familiar with two of these white paper processes — one produced at the Earth-Life Science Institute (ELSI) in Tokyo and the other with NASA’s Nexus for Exoplanet System Science (NExSS.)  What they have to say is most interesting.

This is what Shawn Domagal-Goldman, an astrobiologist at the Goddard Space Flight Center, had to say about their effort, which began 16 months ago with a workshop in Seattle:

Chaitanya Giri, a research scientist and the Earth-Life Science Institute in Tokyo. (Nerissa Escanlar)

“This is an ‘all-hands-on-deck’ problem, and we held a workshop to start drawing a wide variety of scientists to the problem. Once we did, the group gave itself an ambitious goal – to quantify an assessment of whether or not an exoplanet has life, based on remote observations of that world.

“Doing that will take years of collaboration of scientists like the ones at the meeting, from diverse backgrounds and diverse experiences.”

Chaitanya Giri, a research scientist at ELSI with a background in organic planetary chemistry and organic cosmochemistry, said that his work on the European Rosetta mission to a comet convinced him that it is essential to “develop technological capacities to explore habitable niches on various planetary bodies and find unambiguous signatures of life, if present.”  There is some debate about the organic molecules — the chemical building blocks of life — identified by Rosetta.

“Over the years there have been scattered attempts at building such instruments, but a coherent collaborative network was missing,” Giri said. “This necessity inspired me to put on this workshop,” which led to the white paper.

We’ll discuss the conclusions of the papers, but first at little about the decadal surveys:

NASA Decada:

Here are the instruction from the NAS to potential white paper teams working on life beyond Earth projects and issues:

  • Identify promising key research goals in the field of the search for signs of life in which progress is likely in the next 20 years.
  • Identify key technological challenges in astrobiology as they pertain to the search for life in the solar system and extrasolar planetary systems.
  • Identify key scientific questions in astrobiology as they pertain to the search for life in the solar system and extrasolar planetary systems
  • Discuss scientific advances that can be addressed by U.S. and international space missions and relevant ground-based activities in operation or funded and in development
  • Discuss how to expand partnerships (interagency, international and public/private) in furthering the study of life’s origin, evolution, distribution, and future in the universe

Quite a wide net, from specific issues to much broader ones.  But the teams submitting their papers are not expected to address all the issues, but only one or perhaps a related second.

The papers range from a SETI Institute call for a program to increase the use of artificial intelligence and machine learning to address a range of astrobiology issues; to tempting possibilities offered by teams already in the running for future missions to Europa or Enceladus or elsewhere; to recommendations from the Planetary Science Institute about studying and searching for microbialites, living carbonate rock structures once common on Earth and possibly on Mars as well.

 

Proposed White Paper Subjects

Saturn’s moon Enceladus and plume of water vapor flowing out from its South Pole. (NASA)

 

Microbialites are fresh water versions of the organic and carbonate structures called stromatolites — which are among the oldest signs of life detected on Earth.

 

The white paper from ELSI focuses how to improve and discover technology that can detect potential life on other planets and moons. It calls for an increasingly international approach to that costly and specialized effort.

The paper from Giri et al begins with a disquieting conclusion that only “lately, scattered efforts are being undertaken towards the R&D of the novel and as-yet space unproven ‘life-detection’ technologies capable of obtaining unambiguous evidence of extraterrestrial life, even if it is significantly different from {Earth} life. As the suite of space-proven payloads improves in breadth and sensitivity, this is an apt time to examine the progress and future of life-detection technologies.”

The paper points to one discovery in particular as indicative of what the team feels is necessary — an ability to search for life in regions theoretically devoid of life and therefore requiring novel detection
techniques or probes.

“For example,” they write, “air sampling in Earth’s stratosphere with a novel scientific cryogenic payload has led to the isolation and identification of several new species of bacteria; this was an innovative technique analyzing a region of the atmosphere that was initially believed to be devoid of life.”

Other technologies they see as promising and needing further development are high-sensitivity fluorescence microscopy techniques that may be able to detect extraterrestrial organic compounds with catalytic activity surrounded by membranes, i.e., extraterrestrial cells.  In addition, they support on-going and NASA-funded work on genetic samplers that could go to Mars and — if present — actually identify nucleic acid-based life.

“With back-to-back missions under development and proposed by various space agencies to the potentially habitable Mars, Enceladus, Titan, and Europa, this is a right time for a detailed envisioning of the technologies needed for detection of life,” Giri said in an e-mail.

 

Yellowknife Bay on Mars, where the rover Curiosity first found conditions that were habitable to life. The rover subsequently found many more habitable spots, but no existing or fossil microbial life so far. (NASA)

The NExSS white paper on potentially detectable biosignatures from distant exoplanets– one of four submitted by the group– is an especially ambitious one.  The NASA-sponsored effort brought in many top scientists working in the field of biosignatures, and in the past year has already resulted in the publication or submission of five major science papers in addition to the white paper.

In keeping with the interdisciplinary mission of NExSS, the paper brought in people from many fields and ultimately advocates for a Bayesian approach to exoplanet life detection (named after 18th century statistician and philosopher Thomas Bayes. )

In most basic terms, the Bayes approach describes the probability of an event based on prior knowledge of conditions that might be related to the event. A simple example:  Runners A and B have competed four times, and runner A won three times.  So the probability of A winner is high, right?  But what if the two competed twice on a rainy track and each won one race.  If the forecast for the day of the next race is rain, the probability of who will be the winner would change.

This  approach not only embraces probability as an essential way forward, but it is especially useful in terms of weighing probabilities involving many measurements and fields.   Because the factors involved in finding a biosignature are so complex and potentially confounding, they argue, the field has to think in terms of the probability that a number of biosignatures together suggest the presence of life, rather than a 100 percent certain detection (although that may some day be possible.)

Nancy Kiang of the Goddard Institute for Space Studies in New York, explores (among other subjects) the possibility of using photosynthetic pigments as biosignatures on exoplanets.

Nancy Kiang of the Goddard Institute for Space Studies in New York, explores (among other subjects) the possibility of using photosynthetic pigments as biosignatures on exoplanets.

 

Both Domagal-Goldman and collaborator Nancy Kiang of NASA’s Goddard Institute for Space Studies are eager to adopt climate modeling and it’s ability to use known characteristics of divergent sub-fields to put together a big picture. (Those two, along with Niki Parenteau of NASA Ames Research Center led the NExSS effort.)

“For instance,” Kiang said, “the general circulation model (GCM) at GISS simulates the global circulation patterns of a planet’s wind, heat, moisture, and gases, providing statistical behaviors of the simulated climate.”  She sees a similar possibility with exoplanets and biosignatures.

 

Such a computer model can take in data from different fields and come up with some probabilities.  The model “might tell us that a planet is habitable over a certain percent of its surface,” she said.

“A geochemist or planetary formation person might then tell us that if certain chemistry exists on that planet, it has good potential for prebiotic compounds to form. A biologist and geologist might tell us that certain surface signatures on the planet are plausible for either life or mineral background.” That’s not a robust biosignature, but the probability that it could be life is not zero, depending on origin of the signature.

“These different forms of information can be integrated into a Bayesian analysis to tell us the likelihood of life on the planet,” she wrote.

One arm of the NExSS team is already using the tools of climate modeling to predict how particular conditions on exoplanets would play out under different circumstances.

 

This is a plot of what the sea ice distribution could look like on a synchronously rotating ocean world. The star is off to the right, blue is where there is open ocean, and white is where there is sea ice.  (NASA/GISS/Anthony Del Genio)

I will return to the NExSS biosignatures white paper later, since it is so rich with cutting edge thinking about this upcoming stage in space science.  But I do want to include one specific recommendation made by the group, which calls itself the Exoplanet Biosignatures Workshop Without Walls (EBWWW).

What they say is necessary now is for more biologists to join the search for extraterrestrial life.

“The EBWWW revealed that the search for exoplanet life is still largely driven by astronomers and planetary scientists, and that this field requires more input from origins of life researchers and biologists to advance a process-based understanding for planetary biosignatures.

“This includes assessing the {already assessed probability} that a planet may have life, or a life process evolved for a given planet’s environment. These advances will require fundamental research into the origins and processes of life, in particular for environments that vary from modern Earth’s. Thus, collaboration between origins of life researchers, biologists, and planetary scientists is critical to defining research questions around environmental context.”

The recommendation, it seems to me, illustrates both the youth and a maturing of the field.

 

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SETI Reconceived and Broadened; A Call for Community Proposals

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A screenshot from a time lapse video of radio telescopes by Harun Mehmedinovic and Gavin Heffernan of Sunchaser Pictures was shot at several different radio astronomy facilities—the Very Large Array (VLA) Observatory in New Mexico, Owens Valley Observatory in Owens Valley California, and Green Bank Observatory in West Virginia. All three of these facilities have been or are still being partly used by the SETI (Search for the Extraterrestrial Intelligence) program. You can watch the video at: https://www.youtube.com/watch?v=SrxpgUJoHRc
A screenshot from a time lapse video of radio telescopes by Harun Mehmedinovic and Gavin Heffernan of Sunchaser Pictures that was shot at several different radio astronomy facilities—the Very Large Array (VLA) Observatory in New Mexico, Owens Valley Observatory in Owens Valley California, and Green Bank Observatory in West Virginia. All three of these facilities have been or are still being partly used by the SETI (Search for the Extraterrestrial Intelligence) program.

Earlier this summer, Natalie Cabrol, the director of the Carl Sagan Center of the SETI Institute, described a new direction for her organization in Astrobiology Magazine, and I wrote a Many World column about the changes to come.

Cabrol’s Alien Mindscapes – Perspective on the Search for Extraterrestrial Intelligence” laid out a plan for the new approach to SETI that would take advantage of the goldmine of new exoplanet discoveries in the past decade, as well as the data from fast-advancing technologies.  These fresh angles and masses of information come, she wrote,  from the worlds of astronomy and astrophysics, as well as astrobiology and the biological, geological, environmental, cognitive, mathematical, social, and computational sciences.

In her article,  Cabrol said that a call would be coming for community input on how to develop of a Virtual Institute for SETI Research. Its primary goal, she said, would be to “understand how intelligent life interacts with its environment and communicates.”

That call for white papers has now gone out in a release from SETI, which laid out the questions the organization is looking to address:

Question 1: How abundant and diverse is intelligent life in the Universe?

The Virtual Institute will use data synergistically from astrobiology, biological sciences, space and planetary exploration, and geosciences to quantitatively characterize the potential abundance and diversity of intelligent life in the Universe. The spatiotemporal distribution of potential intelligent life will be considered using models of the physicochemical evolution of the Universe.

Question 2: How does intelligent life communicate?

By drawing from a combination of cognitive sciences, neuroscience, communication and information theory, mathematical sciences, bio-neural computing, data mining, and machine learning (among others), we will proactively explore and analyze communication in intelligent terrestrial species. Building upon these analyses, we will consider the physiochemical and biochemical models of newly discovered exoplanet environments to generate and map probabilistic neural and homolog systems, and infer the resulting range of viable alien sensing systems.

Question 3: How can we detect intelligent life?

Using the results (data and databases) of research conducted under Questions 1 and 2, we will consider the design and promising exploration strategies, instruments, exploration strategies, instruments, experimental protocols, technologies, and messaging (content and support) that may optimize the probabilities of detecting intelligent life beyond Earth.

And here is what SETI hopes interested scientists will do:

To support the goals and address the questions outlined above, we seek white papers that will serve as a foundation for the intellectual framework of the Virtual Institute’s roadmap – and that specifically describe: (a) scientific rationales (theories, hypotheses) as foundations for investigations; (b) concepts of experimental designs (methods, protocols, and metrics); (c) universal markers, signals, instruments, systems, technologies for communication; (d) target identification; and (e) ground- and space-based instrumentation, observing scenarios, instrument requirements, and exploration strategies.

To better understand the possible existence of intelligence and technology in the universe, and to learn how to detect it, we expect that proposals may draw from diverse scientific fields. These include astrobiology, astronomy/astrophysics, cognitive sciences, epistemology, geo- and environmental sciences, biosciences, mathematical sciences, social sciences, space sciences, communication theory, bioneural computing, machine learning, big data analytics, technology, instrument and software development, and other relevant fields.

White papers should be submitted in electronic form as PDF files to Dr. Nathalie Cabrol at ncabrol@seti.org. They should be no more than three pages in length, with a minimum 10-point font size. A figure can be included if of critical importance. It is anticipated that there will be an opportunity for interested respondents to present their contribution in person during a planned workshop in the summer of 2017.

Notification of opportunities to present will be made after the white paper deadline of February 17, 2017, and those most responsive to this call will be published in the Astrobiology Journal. Questions related to this call should be addressed to SETI Institute President and CEO Bill Diamond at bdiamond@seti.org

Here is the column I wrote when the Astrobiology Magazine paper came out in August:

Allen Telescope Array
SETI’s partially-built Allen Telescope Array in Northern California, the focus of the organization’s effort to collect signals from distant planets, and especially signals that just might have been created by intelligent beings.  (SETI)

For decades, the Search for Extraterrestrial Intelligence (SETI)  and its SETI Institute home base have been synonymous with the search for intelligent, technologically advanced life beyond Earth.  The pathway to some day finding that potentially sophisticated life has been radio astronomy and the parsing of any seemingly unnatural signals arriving from faraway star system — signals that just might be the product of intelligent extraterrestrial life.

It has been a lonely five decade search by now, with some tantalizing anomalies to decipher but no “eurekas.”  After Congress defunded SETI in the early 1990s — a Nevada senator led the charge against spending taxpayer money to look for “little green men” — the program has also been chronically in need of, and looking for, private supporters and benefactors.

But to those who know it better, the SETI Institute in Mountain View, California has long been more than that well-known listening program.  The Institute’s Carl Sagan Center for Research is home to scores of respected space, communication, and astrobiology scientists, and most have little or nothing to do with the specific message-analyzing arm of the organization.

And now, the new head of the Carl Sagan Center has proposed an ambitious effort to further re-define and re-position SETI and the Institute.  In a recent paper in the Astrobiology Journal, Nathalie Cabrol has proposed a much broader approach to the search for extraterrestrial intelligence, incorporating disciplines including psychology, social sciences, communication theory and even neuroscience to the traditional astronomical approach.

“To find ET, we must open our minds beyond a deeply-rooted, Earth-centric perspective, expand our research methods and deploy new tools,” she wrote. “Never before has so much data been available in so many scientific disciplines to help us grasp the role of probabilistic events in the development of extraterrestrial intelligence.

“These data tell us that each world is a unique planetary experiment. Advanced intelligent life is likely plentiful in the universe, but may be very different from us, based on what we now know of the coevolution of life and environment.”

The galaxay as viewed by the Hubble Space Telescope
With billions upon billions of galaxies, stars and exoplanets out there, some wonder if the absence of a SETI signal means none are populated by intelligent being.  Others say the search remains in its infancy, and needs new approaches.  The galaxy as viewed by the Hubble Space Telescope. (NASA/STScI)

She also wants to approach SETI with the highly interdisciplinary manner found in the burgeoning field of astrobiology — the search for signs of any kind of life beyond Earth. And in a nod to NASA’s Astrobiology Institute, which has funded most of her work, Cabrol went on to call for the establishment of a SETI Virtual Institute with participation from the global scientific community.

I had the opportunity recently to speak with Cabrol, who is a French-American astrobiologist with many years of research experience working with the NASA Mars rover program and with extremophile research as a senior SETI scientist.  She sees the SETI search for technologically advanced life as very much connected with the broader goals of the astrobiology field, which are focused generally on signs of potential microbial extraterrestrial life.  Yes, she said, SETI has thus far a distinctive and largely separate role in the overall astrobiology effort, but now she wants that role to be significantly updated and broadened.

“The time is right for a new chapter for us,” she said. “The origins of SETI were visionary — using the hot technology of the day {radio astronomy} to listen for signals.  But we don’t exactly know what to look and listen for.  We don’t know the ways that ET might interact with its own environment, and that’s a drawback when looking for potential communications we might detect.”

Cabrol foresees future SETI Institute research into neural systems and how they interact with the environment (“bioneural computing,”) much more on the theory and mechanisms of communication, as well as on big data analysis and machine learning.  And, of course, into how potential biosignatures might be detected on distant planets.

The ultimate goal, however, remains the same:  detecting intelligent life (if it’s out there.)

Nathalie Cabrol, director of SETI's Carl Sagan Institute, wants to expand and update SETI's approach to searching for intelligent life beyond our solar system. (NASA)
Nathalie Cabrol, director of SETI’s Carl Sagan Center, wants to expand and update SETI’s approach to searching for intelligent life beyond our solar system. (NASA)

But with so much progress in the sciences that could help improve the chances of finding evolved extraterrestrial life, she said, it’s time for SETI to focus on them as a way to expand the SETI vision and its strategies.

“The purpose is to expand the vision and strategies for SETI research and to break through the constraints imposed by imagining ET to be similar to ourselves,” she wrote. The new approach will “probe the alien landscapes and mindscapes, and generally further understanding of life in the universe.”

The Institute will soon put out a call for white papers on how to expand the SETI search beyond radio astronomy, with an emphasis on “life as we don’t know it.”  After getting those white papers — hopefully from scientists ranging from astronomers to evolutionary biologists — the Sagan Center  plans a workshop to create a roadmap.

Cabrol was emphatic in saying that the SETI search is not turning away from the original vision of its founders — especially astrophysicists Frank Drake, Jill Tarter and Carl Sagan — who were looking for a way to quantify the likelihood of intelligent and technologically-proficient life on distant planets.  Rather, it’s an effort to return to and update the initial SETI formulation, especially as expressed in the famed Drake Equation.

Drake Equation
The Drake Equatio,, as first presented in 1961 to a gathering of scientists at the National Radio Astronomy Observatory in Green Bank, W. Va.

“What Frank proposed was actually a roadmap itself,” Cabrol said.  “The equation takes into account how suitable stars are formed, how many planets they might have, how many might be Earth-like planets, and how many are habitable or inhabited.”

Drake’s equation was formulated for the pioneering Green Bank Conference more than 50 years ago, when basically none of the components of his formula had a number or range that could be associated with it.  That has changed for many of those components, but the answer to the original question — Are We Alone? — remains little closer to being answered.

“I’ve talked a great deal with my colleagues about what type of life can be out there,” she said.  “How different from Earth can it be?”

“Now we’re looking for habitable environments with life as we know it. But it’s time to add life as we don”t know it, too.  And that can help augment our targeting, help pinpoint better what we’re looking for.”

“We think one of the key issues is how ET communicates with its environment, and the great advances in neuroscience can help inform what we do.  The same with evolutionary biology.  Given an environment with life, we want to know, what kind of evolution might be anticipated.”

Connectivity network between disciplines showing the bridges and research avenues that link together space, planetary, and life sciences, geosciences, astrobiology, and cognitive and mathematical sciences. This representation is an expanded version of the Drake equation. It integrates all the historical factors now broken down in measurable terms and expanded to include the search for life we do not know using universal markers, and the disciplines, fields, and methods that will allow us to quantify them.
A diagram of the proposed SETI  “connectivity network” between disciplines showing the bridges and research avenues that link together space, planetary, and life sciences, geosciences, astrobiology, and cognitive and mathematical sciences. Cabrol describes it as  an expanded version of the Drake equation.  (Astrobiology Journal/SETI Institute.)

These are, of course, very long-term goals.  No extraterrestrial life has been detected, and researchers are just now beginning to debate and formulate what might constitute a biosignature on a faraway exoplanet or, what has more recently been coined, a “bio-hint.”

In her paper, Cabrol is also frank about the entirely practical, real-world reasons what SETI needs to change.

“Decades of perspective on both astrobiology and the Search for Extraterrestrial Intelligence (SETI) show how the former has blossomed into a dynamic and self-regenerating field that continues to create new research areas with time, whereas funding struggles  have left the latter starved of young researchers and in search of both a long-term vision and a development program.

“A more foundational reason may be that, from the outset, SETI is an all-or-nothing venture where finding a signal would be a world-changing discovery, while astrobiology is associated with related fields of inquiry in which incremental progress is always being made.”

Whatever changes arrive at the SETI Institute, it will continue with its trademark efforts — most importantly operating the Allen Telescope Array in Northern California and collaborations with numerous other SETI groups.  The array began its work in 2007 with 42 interconnected small radio telescopes, and  continues its constant search for incoming signals.  The SETI Institute had hoped to build the array up to 350 telescopes, but the funding has not been forthcoming.

Cabrol is clearly a scientific adventurer and risk taker.  During her extremophile research in Chile, she went scuba diving and free diving — that is, diving without scuba equipment — in the Licancabur Lake, some 20,000 feet above sea level.  It is believed to be an unofficial altitude record high-altitude for both kinds of diving.

With this kind of view of life, she is a logical candidate to bring substantial change to SETI.  The new primary questions for SETI and the institute to probe are: How abundant is intelligent life in the universe?  How does it communicate? How can we detect intelligent life?

As she concluded in her Astrobiology Journal article:

‘Ultimately, SETI’s vision should no longer be constrained by whether ET has technology, resembles us, or thinks like us. The approach presented here will make these attributes less relevant, which will vastly expand the potential sampling pool and search methods, ultimately increasing the odds of detection.

“Advanced, intelligent life beyond Earth is most likely plentiful, but we have not yet opened ourselves to the full potential of its diversity.”

 

 

 

 

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Waiting on Enceladus

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NASA's Cassini spacecraft completed its deepest-ever dive through the icy plume of Enceladus on Oct. 28, 2015. Credits: NASA/JPL-Caltech
NASA’s Cassini spacecraft completed its deepest-ever dive through the icy plume of Enceladus on Oct. 28, 2015. (NASA/JPL-Caltech)

Of all the possible life-beyond-Earth questions hanging fire, few are quite so intriguing as those surrounding the now famous plumes of the moon Enceladus:  what telltale molecules are in the constantly escaping jets of water vapor, and what dynamics inside the moon are pushing them out?

Seldom, if ever before, have scientists been given such an opportunity to investigate the insides of a potentially habitable celestial body from the outside.

The Cassini mission to Saturn made its closest to the surface (and last) plume fly-through a year ago, taking measurements that the team initially said they would report on within a few weeks.

That was later updated by NASA to include this guidance:  Given the important astrobiology implications of these observations, the scientists caution that it will be several months before they are ready to present their detailed findings.

The reference to “important astrobiology implications” certainly could cover some incremental advance, but it does seem to at least hint of something more.

I recently contacted the Jet Propulsion Lab for an update on the fly-through results and learned that a paper has been submitted to the journal Nature and that it will hopefully be accepted and made public in the not-too-distant future.

All this sounds most interesting but not because of any secret finding of life — as some might infer from that official language.  Cassini does not have the capacity to make such a detection, and there is no indication at this point that identifiable byproducts of life are present in the plumes.

What is intriguing is that the fly-through was only 30 miles above the moon’s surface — the closest pass through a plume ever by Cassini — and so presumably its instruments produced some new and significant findings.

The scientists writing the paper could not, of course, discuss their findings before publication.  But Jonathan Lunine, a Cornell University planetary scientist and physicist on the Cassini mission with a longtime and deep interest in Enceladus, was comfortable discussing what is known about the moon and what Cassini (and future missions) still have to explain.

And thanks to that briefing, it became apparent that whatever new findings are coming, they will not make or break the case for the moon as a habitable place. Rather, they will essentially add to a strong case that has already been made.

“I think the evidence shows that Enceladus is the most promising target (for finding life beyond Earth) in the solar system,” Lunine told me.

enceladus geyser
Icy cyrogeysers erupt at the southern pole of Enceladus. (NASA/JPL-Caltech/Space Science Institute)

Any new findings from the October 28, 2015 fly-through would certainly be useful in terms of understanding the habitability of the moon, but he said that the logical question to ask now takes the story much further.  “Is the moon inhabited? That’s what I want to know now.”

That Lunine is such an enthusiastic supporter of a habitable Enceladus is not surprising:  He is concept principal investigator for the Enceladus Life Finder, probably the most advanced of several proposed missions looking for NASA support.

What is surprising, at least to those who have not followed Enceladus developments with the intensity they seem to deserve, is how much is already known about the moon and its potential for supporting life.

I’ll lay out Lunine’s case, but first a little background:

Enceladus is one of the 53 (or more) moons of Saturn, and is roughly the width of Colorado– about 310 miles in diameter.  It is one of Saturn’s major inner moons, is covered in ice and as a result reflects a lot of light and is one of the brightest objects in the sky.   But it didn’t attract much scientific attention until 2005 when those water vapor and dust plumes were detected shooting out from its south pole by Cassini.

Further study strongly suggests that Enceladus has a global liquid ocean between its rocky core and its icy surface, and the plumes, or geysers, consist of water pushed out through cracks in that surface.  The ocean is small in comparison to that of Jupiter’s watery moon Europa — the first is roughly the volume of Lake Superior while the latter has more water than all the oceans of the Earth put together — but as Lunine put it, “bacterium could do just fine in a Lake Superior-sized ocean.”

The history of Enceladus and its ocean are little understood in comparison with Europa, which Lunine said has probably had a stable ocean under its ice cover for billions of years.  But unlike Europa, Enceladus has that singular advantage of constantly spitting out its insides for us to study and gradually understand.  (Yes, researchers using the Hubble Space Telescope have detected what they concluded could be some water vapor plumes on Europa, too, but that finding is not confirmed.)

The equatorial surface of Enceladus is a beyond frigid  -340 degrees Fahrenheit,  but the temperatures around the southern polar fractures are a still cold but much warmer -100 to -130 degrees Fahrenheit. What’s important is the huge difference in temperatures — in the range of 200 degrees Fahrenheit.

The presumed sources of the heat are friction caused by gravitational forces from Saturn, and scalding heat from the core that enters the water through hydrothermal vents.

enceladus has a large -- 60/40 or 70/30
Scientists estimate that the ratio of rock to water and ice on Enceladus is in the range of 65 percent rock to 35 percent H2O..  NASA

So, what is known about the geysers being pushed out of Encedadus, and about the dynamics causing the phenomenon?

Already published papers report that the water vapor, which can extend out three times the diameter of the moon, is salty, filled with fine dust particles, and contains molecules including carbon dioxide, methane, molecular nitrogen, propane, acetylene, formaldehyde and traces of ammonia.  While none of these compounds are a biosignature per se, many are associated with life.

Recent analysis of some of the dust particles concluded that they were from the floor of the Enceladus ocean, and based on their characteristics appear to have been formed by the interaction of water and rock.  The most logical site for this kind of interaction is at hydrothermal vents, where heat from the core makes its way up into the water.  Some have argued that life on Earth may well have started at potentially similar hydrothermal vents on early Earth.

Jonathan Lunine is the David C. Duncan Professor of xxx at Cornell University, and Director, Center for Radiophysics and Space Research. He's also a member of the Cassini team.
Jonathan Lunine is the David C. Duncan Professor in the Physical Sciences at Cornell University, and Director of the Cornell Center for Astrophysics and Planetary Science. He’s also a longtime member of the Cassini team. (Cornell)

One of the primary goals of that final close fly-through was to collect data that would allow the Cassini scientists to measure how much hydrothermal activity is occurring within Enceladus.

If substantial amounts can be detected, that increases the chances for the existence around of vents of simple forms of life.  Measurements for hydrothermal activity depend on the detection of methane (which has already occurred) and of molecular hydrogen (which scientists were looking for in that final fly-through.)  Measurements for molecular hydrogen can be difficult to make, which might explain some of the time lag.

At the low altitude, the team also expected to be more sensitive to the possible presence of heavier and more massive molecules — including organics — that would not be observed during previous, higher-altitude passes through the plume.

One potentially complicating issue is that measurements of the pH of the water has come back with quite high alkaline levels.  If that is limited to areas around hydrothermal vents then it isn’t a problem for life, Lunine said.  But if it was far more widespread, it could be.

So these are some of the results we are now awaiting.  But to Lunine (and others on and off the Cassini team) the case for habitability and a possible home for life on Enceladus has already been made.

“What we already know is that the ocean has the general characteristics of habitability.  Obviously, it has liquid water and so there’s an energy source keeping it from all freezing.  It appears to have varied thickness but is still global. It’s salty and has organic molecules, as well as those small grains of silica.  The simplest model for why they exist is that water is cycling through quite warm rock at the base of the ocean, dissolving silica and delivering it to the ocean.

“Put this and more together and you have a signal, a big red arrow pointing to this moon saying it may well support life, and needs to be explored more and soon.”

The plumes of Enceladus originate in the long tiger stripe fractures of the south polar region pictured here. Detailed models support conclusions that the plumes arise from near-surface pockets of liquid water at temperatures of 273 kelvins (0 degrees Celsius). (Cassini Imaging Team, SSI, JPL, ESA, NASA)
The plumes of Enceladus originate in the long tiger stripe fractures of the south polar region pictured here. Detailed models support conclusions that the plumes arise from near-surface pockets of liquid water at temperatures of 273 kelvins (0 degrees Celsius). (Cassini Imaging Team, SSI, JPL, ESA, NASA)

But even if the upcoming Enceladus paper adds significantly to the habitable moon story, another mission to study the plumes may be long in coming.  Limited resources are the major reason why but so too is the congressionally-mandated mission to Europa, a target not dissimilar to Enceladus.

Texas congressman John Culberson has pushed long and hard for the Europa mission (or missions), arguing that the Jovian moon offers our best chance of finding extraterrestrial life in the solar system.  That huge and stable ocean is such a tempting target that the miles of ice encasing it are not seen as an deal-breaking obstacle. (“Thick-icers” and “thin-icers” are in constant debate about how deep that ice might go.)

That Europa is promising in terms of astrobiology is a conclusion that many scientists agree with, and NASA seems eager to cooperate. But it is nonetheless quite unusual to have Congress require NASA to mount a specific and costly mission and to set a timetable for doing it — as Congress did for Europa in 2015.

The congressional requirement follows years of waiting for a Europa mission.  The Galileo mission to Jupiter produced convincing information starting in 1998 that the moon had a large ocean under its ice surface, but almost two decades have gone by without an Europa-specific mission.

Lunine, and others, are pressing to make sure that doesn’t happen with Enceladus.  Last year he proposed a NASA Discovery mission to the moon that wasn’t selected, and has ideas for other sorts of NASA efforts.

“It was a sixteen or seventeen year odyssey to get a mission planned for Europa, and we just hope that doesn’t happen with Enceladus,” he told me.  “We could be testing for bio-activity there and really, where else would that make so much sense?”

 

 

 

 

 

 

 

 

 

 

 

 

 

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Coming to Terms With Biosignatures

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Exoplanets are much too far away for missions to visit and explore, so scientists are learning about them remotely.  That includes the question of whether they might support life — an aspect of exoplanet science that is getting  new attention. This is artist Ron Miller’s impression of an exoplanet.
Exoplanets are much too far away for missions to visit and explore, so scientists are learning about them remotely. That includes the question of whether they might support life — an aspect of exoplanet science that is getting new attention. This is artist Ron Miller’s impression of an exoplanet.

The search for life beyond our solar system has focused largely on the detection of an ever-increasing number of exoplanets, determinations of whether the planets are in a habitable zone, and what the atmospheres of those planets might look like.  It is a sign of how far the field has progressed that scientists are now turning with renewed energy to the question of what might, and what might not, constitute a sign that a planet actually harbors life.

The field of “remote biosignatures” is still in its early stages, but a NASA-sponsored workshop underway in Seattle has brought together dozens of researchers from diverse fields to dig aggressively into the science and ultimately convey its conclusions back to the exoplanet community and then to the agency.

While a similar NASA-sponsored biosignatures workshop put together a report in 2002, much has changed since then in terms of understanding the substantial complexities and possibilities of the endeavor.  There is also a new sense of urgency based on the observing capabilities of some of the space and ground telescopes scheduled to begin operations in the next decade, and the related need to know with greater specificity what to look for.

“The astrobiology community has been thinking a lot more about what it means to be a biosignature,” said Shawn Domogal-Goldman of the Goddard Space Flight Center, one of the conveners of the meeting.  Some of the reason why is to give advice to those scientists and engineers putting together space telescope missions, but some is the pressing need to maintain scientific rigor for the good of one of humankind’s greatest challenges.

“We don’t want to spend 20 years of our lives and billions in taxpayer money working for a mission to find evidence of life, and learn too late that our colleagues don’t accept our conclusions,” he told me.  “So we’re bringing them all together now so we can all learn from each other about what would be, and what would not be, a real biosignature.”

 

How to measure the chemical signatures in the atmosphere of a transiting exoplanet. The total light measured off-transit (B in the lower left figure) decreases during the transit, when only the light from the star is measured (A). By subtracting A from B, we get the planet counterpart, and from this the “chemical fingerprints” of the planet atmosphere can be revealed. Credits: NASA/JPL-Caltech.
How to measure the chemical signatures in the atmosphere of a transiting exoplanet. The total light measured off-transit (B in the lower left figure) decreases during the transit, when only the light from the star is measured (A). By subtracting A from B, we get the planet counterpart, and from this the “chemical fingerprints” of the planet atmosphere can be revealed. ( NASA/JPL-Caltech)

The three-day workshop is bringing together some 50 scientists ranging from astronomers, astrobiologists and planetary scientists to microbiologists and specialists in photosynthesis.  Organized by NASA’s Nexus for Exoplanet System Science (NExSS) — an initiative created to encourage interdisciplinary collaboration — it has been tasked with putting together a report for the larger exoplanet community and ultimately for NASA.

The first day of the workshop featured a review of previous work on biosignatures, which initially put forward the presence of oxygen in an exoplanet atmosphere as a strong and almost certain sign that biology was at work below. This is because oxygen, which is a byproduct of much life, bonds quickly with other molecules and so would be undetectable unless it was continuously replenished.

But as outlined by Victoria Meadows, director of the Virtual Planet Laboratory at the University of Washington, more recent research has shown large amounts of oxygen can be produced without biology under a number of (usually extreme)  conditions.  There has been a resulting focus on potential false positive signals regarding oxygen and other molecules.

From another perspective, Tim Lyons, a biogeochemist from the University of California, Riverside, used the early and middle Earth as an example how easy it is to arrive at a false negative result.

He said that current thinking is that for as long as two billion years, Earth was inhabited but the lifeforms produced little oxygen.  If analyzed from afar for all those years, the result would be a complete misreading of life on Earth.

With these kinds of false positives and negatives in mind, Meadows said that the current approach to understanding biosignatures is to look beyond a single molecule to the broader planetary and solar environment.

“We have to look not just at single biosignatures, but at their their context on the planet. How might life have modified an environment in a potentially detectable way?  And having stepped back a bit, does the biosignature make sense?”

As one example, while oxygen alone is no longer considered a sure biosignature, oxygen in an atmosphere in the presence of methane would be convincing because of the known results of the chemical interactions of the two.

 

Schematic for the concept of considering all small molecules in the search for biosignature gases. The goal is to start with chemistry and generate a list of all small molecules and filter them for the set that is stable and volatile in temperature and pressure conditions relevant for exoEarth planetary atmospheres. Further investigation relates to the detectability: the sources and sinks that ultimately control the molecules’ accumulation in a planetary atmosphere of specific conditions as well as its spectral line characteristics. Geophysically or otherwise generated false positives must also be considered. In the ideal situation, this overall conceptual process would lead to a finite but comprehensive list of molecules that could be considered in the search for exoplanet biosignature gases. Figure credit: S. Seager and D. Beckner.
Schematic for the concept of considering all small molecules in the search for biosignature gases.
The goal is to start with chemistry and generate a list of all small molecules and filter them for the set that is stable and volatile in temperature and pressure conditions relevant for exoEarth planetary atmospheres. In the ideal situation, this overall conceptual process would lead to a finite but comprehensive list of molecules that could be considered in the search for exoplanet biosignature gases. (S. Seager and D. Beckner)

 

In part because of the false positive/false negative issues involving oxygen, some have begun a concerted effort to produce a list of additional possible biosignatures.  William Bains, a member of Sara Seager’s team at the Massachusetts Institute of Technology, described the blunderbuss approach they have adopted:  examining some 14,000 compounds simple (fewer than six non-hydrogen atoms) and stable enough to exist in the atmosphere of an exoplanet.

In their Astrobiology Journal article, Seager, Bains and colleagues wrote that “To maximize our chances of recognizing biosignature gases, we promote the concept that all stable and potentially volatile molecules should initially be considered as viable biosignature gases.”

Elaborating during the workshop, Bains asked:  “Why does life produce the gases that it does? We really don’t know, so we’re bringing in everything as a possibility.”   Not surprisingly, he said, “The more you search, the more you find.”

And as for the possibility of life existing in extreme environments, Bains referred to the microbes known to live in radioactive environments, in plastic, and virtually everywhere else on Earth.

Because the science of remote biosignatures is still in its early stages, the unknowns can seem to overwhelm the knowns, making the whole endeavor seem near impossible.  After all, it’s proven extremely difficult to determine whether there was ever life on “nearby” Mars, and scientists have Martian meteorites to study and rovers sending back information about the geology, the geochemistry, the weather, the atmospheric conditions and the composition of the planet.

By comparison, learning how to probe the atmospheres of faraway exoplanets and assess what might or might not be a biosignature will have to be done entirely with next generation space telescopes and the massive ground telescopes in development.  The information in the photons they collect will tell scientists what compounds are present, whether liquid water is present on the surface, and potentially whether the surface is changing with seasons.  And then the interpretation begins.

That’s why Mary Voytek, the originator of NExSS and the head of the NASA astrobiology program, said at the workshop that the goal was to test and ultimately provide as many biosignatures as possible.  She wants many molecules potentially associated with life to be identified and then studied and restudied in the same critical way that oxygen has been — embraced for the biosignature possibilities it offers, and understood for the false positives and false negatives that might mislead.

“What we need is an arsenal,” she said, as many ways to sniff out the byproducts of exoplanet life as that daunting task demands.

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