All About Emergence

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A swarm of birds act as an emergent whole as opposed to a collection of individual birds. The workings of swarms have been fruitfully studied by artificial life scientists, who look for abstracted insights into life via computers and other techniques. (Walerian Walawski)

 

If there was a simple meaning of the often-used scientific term “emergence,” then 100-plus scientists wouldn’t have spent four days presenting, debating and not infrequently disagreeing about what it was.

But as last month’s organizers of the Earth-Life Science Institute’s “Comparative Emergence” symposium in Tokyo frequently reminded the participants, those debates and disputes are perfectly fine and to be expected given the very long history and fungibility of the concept.

At the same time, ELSI leaders also clearly thought that the term can have resonance and importance in many domains of science, and that’s why they wanted practitioners to be exposed more deeply to its meanings and powers.

Emergence is a concept commonly used in origins of life research, in complexity and artificial life science; less commonly in chemistry, biology, social and planetary sciences; and — originally – in philosophy. And in the 21st century, it is making a significant comeback as a way to think about many phenomena and processes in the world.

So what is “emergence?” Most simply, it describes the ubiquitous and hugely varied mechanisms by which simple components in nature (or in the virtual or philosophical world) achieve more complexity, and in the process become greater than the sum of all those original parts.

The result is generally novel, often surprising, and sometimes most puzzling – especially since emergent phenomena involve self-organization by the more complex whole.

Think of a collection of ants or bees and how they join leaderless by the many thousands to make something – a beehive, an ant colony – that is entirely different from the individual creatures.

 

The Eagle nebula is an intense region of star formation, an emergent phenomenon
that clearly creates something novel out of simpler parts. (European Space Observatory.)

Think of the combination of hydrogen and oxygen gases which make liquid water. Think of the folding of proteins that makes genetic information transfer possible. Think of the processes by which bits of cosmic dust clump and clump and clump millions of times over and in time become a planetesimal or perhaps a planet. Think of how the firing of the billions of neurons in your brain results in consciousness.

All create complexity out of component parts, produce something irreducible from those original parts, and all have been resistant to a full explanation using the usual reductionist tools of the scientific world. This doesn’t mean that something magical or divine is going on – rather, that either humans have not figured out what happens or that what happens is not comprehensible given our understanding of the laws of nature and physics.

Heady stuff, which is why the study and use of the concept of emergence has become increasingly widespread as a tool, or perhaps a pathway, to address complex problems.

Luis Campos is a historian of science and was Baruch S. Blumberg NASA/Library of Congress Chair in Astrobiology. (Nerissa Escanlar)

Before going on, a little history is in order. Luis Campos, a historian of science at the University of New Mexico and the most recent Baruch S. Blumberg NASA/Library of Congress Chair in Astrobiology, described the concept of philosophical and scientific emergence – though not the word — as going back to the Greeks, at least.

The term “emergence” comes from the Latin verb emergo which means to arise, to rise up. Its meaning and importance have ebbed and flowed, with a major flowering in the United Kingdom in the 1920s.

It is seldom discussed, Campos said at the ELSI symposium, but the modern concepts of emergence flow to some extent from dialectics of Hegel, Marx and Engels, as well as the holism of South Africa’s controversial leader and thinker, Jan Smuts.

Campos said the “emergence” of today is quite different from those iterations. His point, he said, is that major scientific approaches grow from the societal bedrock of their times – and today that means a willingness to consider possible limits to the strict scientific reductionism of the modern era.

In philosophical terms, and generally in the history of science, there are several basic forms of emergence.

The first involves surprising complexity that arises unexplained and remains so at a particular scale, though science may catch up some day and provide plausible explanations. The formation of stars and galaxies and black holes would all be considered emergent phenomena, but astrophysics is gradually learning many of the processes that allow immeasurable complexity to appear throughout the cosmos – all from the simplest of components.

The other involves complex phenomena that appear to be beyond the capacity of physical or natural laws to ever explain. The quantum world, for instance, includes the phenomenon called quantum entanglement – a physical sensation which occurs when

The endlessly different symmetrical and fractal patterns of snowflakes are an emergent phenomenon given that each starts with the same basic material and ends up looking different. (Wilson Bentley)

pairs or groups of particles cannot be described independently of the state of the other, even when the particles are separated by a large distance.

So while emergence may be, as information scientist Francis Heylighen of the Vrije Universiteit in Brussel argued at the ELSI symposium, “simple, common and natural,” it also comes in innumerable forms that can seem mysterious or, as described in the quantum world, “spooky.”

David Pines, a co-founder of the Santa Fe Institute, which specializes in complexity studies, illustrated the dimensions of the emergence debate when he wrote about it several years ago for the online publishing site “Medium.”

“We live in an emergent universe,” he wrote, “in which it is difficult, if not impossible, to identify any existing interesting scientific problem or study any social or economic behavior that is not emergent.”

In the presence of claims like this, emergence has become a phenomenon where scientific consensus – or even agreement – can be difficult to achieve. Is it a trite “buzzword,” as some argue?  Or is it a profound and important pathway to understand underlying phenomena of the world that cannot be adequately described by reductionist, deterministic science?

Some of the modern pioneers in thinking about emergence come from the world of Artificial Life, or ALife. Using computer simulations, ALife researchers study essential properties of living systems such as evolution and adaptive behavior. Since the evolutionary clock cannot go backwards to see the what attributes are inevitable and what is more random, ALife analyzes these kinds of processes by simulating lifelike behaviors and patterns within computers.

As described at the ELSI symposium by University of Tokyo ALife and complex systems specialist Takashi Ikegami, decades of work in the ALife field have led to the conclusion that the pathways to life and consciousness are created by a cascade of emergent phenomena possessing the capability for “open-ended evolution.”

 

Takashi Ikegami and an android he helped build as part of his decades of work in the field of Artificial Life. (Bloomberg News)

 

And with computing power still increasing steadily, he said that the scale at which emergent properties can be identified and traced will similarly increase. As an example of how faster and larger computers can and will scale up ALife experiments and research, he told the story of the Rubik’s cube and what became known as “God’s algorithm.”

For 30 years, mathematicians and others working to solve the famous cube puzzle concluded that the minimum number of moves needed to complete the task was 22. This was not based on the experience of some Rubik’s cube fans, but rather of sustained mathmatical analysis.

But then in 2010 a teams of computer scientists and mathemeticians with access to Google’s supercomputers found that the minimum number of moves for any of the 43 quadrillion Rubik’s position was actually a very surprising 20. This result, Ikegami argues, is a reflection of the emergence of new technological capabilities in the last decade that are changing the world.

Some other classic artificial life simulations involve virtual birds or fish that are given some very simple rules to follow about how close individuals can approach each other and how they should steers in relation to other flock or schoolmates. Those simple instructions lead to the formation of virtual swarms and schools of enormous complexity that emerge from the individual-to-group transition.

An example of the unexpected behavior that can emerge: A flock splits to avoid an obstacle and then reunite once passed.

ALife is virtual, but emergence is everywhere in the natural world as well once you know what to look for. Bénard cells, for instance, are geometrically regular convection structures that spontaneously form in water or other thicker fluids when it is heated from below and/or cooled from above.

 

Benard cells formed spontaneously by convection in fluids.

The cells are formed as the hotter fluid rises and the cooler sinks, a process that results in spontaneous self-organization into a regular pattern of cells. The cells would be considered to be emergent phenomena.

John Hernlund is a geophysicist and vice director ELSI, and was the lead science organizer for the conference.

“Bénard convection is a composite phenomenon that arises from the combination of simpler processes: thermal expansion, Archimedes principle, thermal conduction, and viscous resistance to shearing motion in a fluid,” he said. “Nothing about those basic constituent processes alone would enable you to predict that their combination would yield the beautiful regular geometric patterns seen in Bénard cells, and this is why these are often used as an example of emergent behavior.”

Astrophysicist Elizabeth Tasker, a professor and communicator for the Japanese Space Agency JAXA, chaired an early session on emergence which focused on how the universe and planets were formed. She said her field has generally not described that 13.7 billion year process that followed the Big Bang in terms of emergent phenomenon, but that over the week she gradually saw the usefulness and did so in particularly compelling terms.

“As an astrophysicist,” she said. “I began to see the history of the universe as a manga, with examples of emergence forming the individual frames: matter strewn around the cosmos was drawn by gravity into structures that became galaxies, gas collapsed until fusion birthed a star, rocky boulders accreted and then began to melt and circulate to produce plate tectonics.

“Each manga frame represented the introduction of a new property of the universe, one that could not be exhibited by the individual pieces that had created it. A lone gas molecule could not show the spinning spiral of a galactic disc, nor begin to fuse elements within a star. Likewise, the rocky pieces that formed a planet could not start the circulation of plate tectonics by themselves. Neighboring interactions created a system that could spawn an entirely new process.”

Alex Penn, a complexity scientist at the University of Surrey.

 

While emergence is most often understood in terms of physical systems, and then virtual systems that try to capture their patterns and laws, the concept also has a presence in the social and economic sciences as well.

Alex Penn of the University of Surrey, in fact, introduced emergence in the social spheres and humanities as emergent on a scale similar to what Daniel Pines said about science. “Basically, almost everything of significance that arises in the social world is emergent,” she said.

Those phenomena ranged from the rise of different kinds of economic levels of development to political movements, cultures and down to the raising of children and residential segregation.

That housing segregation has been studied sufficiently that it has been determined that when a self-identifying group becomes less than one-third of the neighborhood population, they will begin to move to move out to be closer to those they identify with. Within a relatively short period of time, a mixed neighborhood will emerge into a segregated community via self-organization.

 

The Schelling model of what happens as neighborhoods self-segregate.

 

Other examples of emergence put forward from the social and cultural worlds include traffic jams, improv jazz performances and marriage. (A married person remains themselves, but also become part of a larger and more complex entity, from which novelty and surprise are sure to arise.)

Since the emergence symposium was taking place at an institute focused on how our planet formed and how life later appeared, it was only natural that emergence in that realm was a frequent topic. How a world without biology became one with biology is emergence writ large, with simplicity transforming to complexity innumerable times in innumerable ways.

While scientists speak of the Last Universal Common Ancestor (LUCA) as the source from which all life today arose, it is also widely held that other proto-life existed and disappeared because it could not compete successfully.

The ELSI model of that process is often presented as a kind of hourglass, where evolution of all kinds — in minerals, in prebiotic polypeptides, in simple organisms – creates new systems that take over and expand until they reach a bottleneck that stops the advance. Only a newly evolved version of the entity can make it through to the next step.

Participants including evolutionary biologist Simonetta Gribaldo of the Institut Pasteur argued that there is good reason to conclude that these processes were playing out wherever they could on the early Earth, doubtless resulting in many versions of prebiotic and proto-life before the Last Universal Common Ancestor (LUCA). In other words, the path to and beyond LUCA was not only messy but had many failed efforts along the way.

It fell to geochemist and geomicrobiologist Karyn Rogers of Rensselaer Polytechnic Institute to put it all into the context of emergence.

Long active in origin of life science, she said that she has become very uncomfortable with that description of what the field is trying to understand. Like many others, she does not see the “origin of life” as a singular phenomenon and so she moved to “origins of life.”

But “origins,” too, didn’t seem right because it seemed to focus too narrowly on the compounds and processes directly associated with life. She (and others) saw a larger picture.

Rogers said she doesn’t think scientists can talk about how biology appeared and prospered without also talking about the the mineral and geochemical world from which it arose

Karyn Rogers’ research focuses on the relationships between microbial communities and environmental conditions in extreme ecosystems. (Nerissa Escanlar)

Her conclusion, then, about how to describe what happened on prebiotic Earth so long ago:

“It’s the emergence of life,” she said at the end of the symposium, not the “origin”.

“One of interesting things about emergence is that it’s that smudgy place in between that we can’t quite describe. We know it’s necessary to go from an abiotic planet to a biotic planet, but can’t quite really wrap our minds on it.

“It’s not even a series of events, it’s a series of events that led to life plus all the stuff around it as well that didn’t lead to life…all the surrounding processes. I think you need all that for life to emerge.”

She said she came into the symposium convinced that the “emergence of life” was the way to see the our biological beginnings, but that hearing about the many other understandings of emergence led her to think she didn’t understand the concept and would have to revise her views. But by the end she was back to emergence, but with a difference.

Perhaps, she said, the group could consider having “emergence” and “smudginess” become synonyms for that cross-discipline arena of simple-to-significantly more-complex transitions they had been discussing all week.

The idea was embraced by many of the other scientists.

 

A Livestream of the symposium is available here.

 

 

 

 

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Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to marc.kaufman@manyworlds.space.

The Gale Winds of Venus Suggest How Locked Exoplanets Could Escape a Fate of Extreme Heat and Brutal Cold

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Two images of the nightside of Venus captured by the IR2 camera on the Akatsuki orbiter in September 2016 (JAXA).

 

More than two decades before the first exoplanet was discovered, an experiment was performed using a moving flame and liquid mercury that could hold the key to habitability on tidally locked worlds.

The paper was published in a 1969 edition of the international journal, Science, by researchers Schubert and Whitehead. The pair reported that when a Bunsen flame was rotated beneath a cylindrical container of mercury, the liquid began to flow around the container in the opposite direction at speeds up to four times greater than the rotation of the flame. The scientists speculated that such a phenomenon might explain the rapid winds on Venus.

On the Earth, the warm equator and cool poles set up a pressure difference that creates our global winds. These winds are deflected westward by the rotation of the planet (the so-called Coriolis force) promoting a zonal (east-west) air flow around the globe. But what would happen if our planet’s rotation slowed? Would our winds just cycle north and south between the equator and poles?

The Moon is tidally locked to the Earth, so only one hemisphere is visible from our planet (Smurrayinchester / wikipedia commons).

Such a slow-rotating scenario may be the lot of almost all rocky exoplanets discovered to date. Planets such as the TRAPPIST-1 system and Proxima Centauri-b all orbit much closer to their star than Mercury, making their faint presence easier to detect but likely resulting in tidal lock. Like the moon orbiting the Earth, planets in tidal lock have one side permanently facing the star, creating a day that is equal to the planet’s year.

The dim stars orbited by these planets can mean they receive a similar level of radiation as the Earth, placing them within the so-called “habitable zone.” However, tidal lock comes with the risk of horrific atmospheric collapse. On the planet side perpetually facing away from the star, temperatures can drop low enough to freeze an Earth-like atmosphere. The air from the dayside would then rush around the planet to fill the void, freezing in turn and causing the planet to lose its atmosphere even within the habitable zone.

The only way this could be prevented is if winds circulating around the planet could redistribute the heat sufficiently to prevent freeze-out. But without a strong Coriolis force from the planet’s rotation, can such winds exist?

A planet whose wind speeds exceed the rotation speed of the planet is said to have a “super-rotating” atmosphere. Global climate models of tidally locked planets have suggested that temperate conditions might be maintained by winds circulating between the night and day side in the same way as the Earth’s winds are generated between the equator and poles.

However, global climate models are extremely tricky, being computationally expensive and sensitive to a multitude of factors that are unmeasurable for exoplanets. As a result, it has not been possible to test if the climates produced by the computer could really exist, leaving the fate of tidally locked worlds uncertain.

 

Orbiting close to their star, the TRAPPIST-1 Earth-sized worlds are probably tidally locked, rotating just once per orbital period. This is an artist’s concept of the system, based on available data about the planets’ diameters, masses and distances from the host star, as of February 2018 (NASA/JPL-Caltech).

 

But there is a slowly rotating planet where one mechanism for super rotation can be explored. Venus is the only other Earth-sized planet we can reach by spacecraft and the planet has super rotating winds whose origin has been hotly debated for decades.

While Venus is not in tidal lock with the sun, its rotation is extremely slow. Our neighboring world takes 225 days to orbit the sun and rotates once every 243 Earth days, making the Venusian day (one rotation) longer than its year.

The planet’s thick carbon dioxide atmosphere provides Venus with the most powerful greenhouse effect in the solar system. This prevents nights on Venus from freezing and the planet maintains a fairly uniform surface temperature that is hot enough to melt lead. Yet despite the lack of a temperature gradient to drive winds, the upper atmosphere of Venus is a blistering gale. Winds whip around the planet with speeds that exceed 100 m/s (224 mph), traveling sixty times faster than the surface rotation. What could be driving this weather system?

 

A false color image of Venus with the IR2 camera on Akatsuki. 2.26 micron radiation (used in this work) is shown in red.

It is a question that returns us to the Bunsen flame experiment. Schubert and Whitehead speculated that the sun could replace the Bunsen flame in driving the Venusian winds rapidly around the planet. However, skeptics to this claim argued that the sun could only influence the cloud tops of Venus, whereas super-rotation had been observed to extend much deeper into the planet’s thick cloak of gases.

The alternative theory was that small contrasts in heat on the planet’s surface could set up circulations to drive the super-rotating winds. A challenge here was that such models appeared very sensitive to the exact starting conditions, suggesting that Venus’s super-rotating winds were a rare outcome for the planet. If true, the same mechanism was not likely to be acting on tidally locked worlds around other stars.

At the end of last year, a paper in the Astrophysical Journal Supplement Series was published that provided a heap of new data about Venus’s atmosphere. The research was led by Javier Peralta, a postdoctoral fellow at the Japan Aerospace Exploration Agency (JAXA). Using data from JAXA’s Venus orbiter, Akatsuki, Peralta had painstakingly tracked the Venusian winds.

The IR2 camera onboard Akatsuki captures images in the infrared at a wavelength of 2.26 microns. On the dayside of Venus, clouds in the upper atmosphere sitting at 60 – 70 km (37 – 44 miles) above the planet’s surface strongly reflect ultraviolet and infrared from the Sun. However, the nightside illumination comes from infrared heat emanating from Venus’s hot surface. This is partially blocked by clouds deeper in the atmosphere at altitudes between 48 – 60 km (30 – 37 miles). As the clouds have a varying transparency to this infrared glow, their shapes become visible when viewed through Akatsuki’s IR2 camera. It was these deeper, nightside clouds, that Peralta tracked.

Dr Javier Peralta, lead author of this work, is a postdoctoral researcher at JAXA.

By comparing results from 2,947 wind measurements, Peralta spotted a pattern. The winds acceleration was tied to the position of the sun, suggesting that the giant Bunsen-flame of our nearest star was indeed driving super-rotation deep in the Venusian atmosphere. It was a result that suggested this super-rotation mechanism could be common on many more planets, as it required only the heat from the star.

Yet, Peralta was quick to note that this was not a “case closed” for the Venusian winds. While they had not detected a north-south component to the winds that would have supported the alternative theory of a surface-driven origin for the super-rotating, it might have just been below the level they could detect.

“This was one reason why we made our wind measurements publicly available,” Peralta said. “Sharing measurements is critical nowadays since the new generation of computer models are able to incorporate this observational data to predict how an atmosphere will evolve.”

Peralta hopes that results from Venus can used with climate models for slow rotating worlds, helping scientists understand both our nearest neighbor and the conditions that might be present on tidally locked planets by providing comparative measurements for at least one type of super rotation generation.

 

Artist’s impression of JAXA’s Akatsuki Venus Climate Orbiter at Venus (JAXA / Akihiro Ikeshita)

As well as using results from Akatsuki, Peralta also looked at wind speed measurements from previous missions and ground observations of Venus. Comparing data since the late 1970s, his team noted a variation in the recorded wind speeds. While it is challenging to compare results from different instruments (which have different error estimates), this might suggest that the Venusian weather pattern has varied over time scales of decades.

Such variation could also support the sun being the main driver for the winds. Changes in the cloud’s reflectivity would alter how much solar radiation is absorbed, adjusting the efficiency of this driving force. If true, this could be used to calibrate models further for different reflectivity conditions.

Peralta’s results underline the importance of our solar system in understanding exoplanets. The comparison of the weird and wonderful climates among our neighboring worlds can help us explore the next Earth-sized discovery and these worlds are within the reach of our spaceships.

 

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Elizabeth Tasker
Elizabeth Tasker is an astrophysicist and science communicator at the Japan Aerospace Exploration Agency (JAXA). Her research explores the formation of stars and planets, while her science articles have covered topics from Egyptian coffins to deep sea drilling (but mainly focus on exoplanets and space missions!). While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

The Moon-Forming Impact And Its Gifts

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Rice University petrologists have found Earth most likely received the bulk of its carbon, nitrogen and other life-essential volatile elements from the planetary collision that created the moon more than 4.4 billion years ago. (Rice University)

 

The question of how life-essential elements such as carbon, nitrogen and sulfur came to our planet has been long debated and is a clearly important and slippery scientific subject.

Did these volatile elements accrete onto the proto-Earth from the sun’s planetary disk as the planet was being formed?  Did they arrive substantially later via meteorite or comet?  Or was it the cataclysmic moon-forming impact of the proto-Earth and another Mars-sized planet that brought in those essential elements?

Piecing this story together is definitely challenging,  but now there is vigorous support for one hypothesis — that the giant impact brought us the elements would later be used to enable life.

Based on high pressure-temperature experiments, modeling and simulations, a team at Rice University’s Department of Earth, Environmental and Planetary Sciences makes that case in Science Advances for the central role of the proto-planet called Theia.

“From the study of primitive meteorites, scientists have long known that Earth and other rocky planets in the inner solar system are volatile-depleted,” said study co-author Rajdeep Dasgupta. “But the timing and mechanism of volatile delivery has been hotly debated. Ours is the first scenario that can explain the timing and delivery in a way that is consistent with all of the geochemical evidence.”

“What we are saying is that the impactor definitely brought the majority supply of life-essential elements that we see at the mantle and surface today,” Dasgupta wrote in an email.

 

A schematic depicting the formation of a Mars-sized planet (left) and its differentiation into a body with a metallic core and an overlying silicate reservoir. The sulfur-rich core expels carbon, producing silicate with a high carbon to nitrogen ratio. The moon-forming collision of such a planet with the growing Earth (right) can explain Earth’s abundance of both water and major life-essential elements like carbon, nitrogen and sulfur, as well as the geochemical similarity between Earth and the moon. (Rajdeep Dasgupta; background photo of the Milky Way galaxy is by Deepayan Mukhopadhyay)

 

Some of their conclusions are based on the finding of a similarity between the isotopic compositions of nitrogen and hydrogen in lunar glasses and in the bulk silicate portions of the Earth.  The Earth and moon volatiles, they conclude, “have a common origin.”

Carbon, nitrogen and sulfur are deemed “volatile” elements because they have a relatively low boiling point and can easily fly off into space from planets and moons in their early growing stages.  A number of other life-important chemicals, including water, are volatiles as well.

The recent findings are grounded in a series of experiments by study lead author and graduate student Damanveer Grewal, who works in the Dasgupta lab.  Grewal gathered evidence to test the theory that Earth’s volatiles arrived when the embryonic planet Theia — that had a sulfur-rich core — crashed into very early Earth.

The sulfur content of the donor planet’s core matters because of the puzzling evidence about the carbon, nitrogen and sulfur that exist in all parts of the Earth — other than the core.  The team needed to test the conditions under which a core with sulfur could, in effect, exclude other volatiles, thus making them more common in the planet’s mantle and above — and as a result more available to a planet it might crash into.  

The high temperature and pressure tests led to a computer simulation to find the most likely scenario that produced Earth’s volatiles. Finding the answer involved varying the starting conditions, running approximately 1 billion scenarios and comparing them against the known conditions in the solar system today.

 

Carbonaceous chondrites include some of the most primitive known meteorites, including the iconic Allende meteorite. Some scientists have proposed they delivered volatiles to Earth, but this latest paper disputes that conclusion.

“What we found is that all the evidence — isotopic signatures, the carbon-nitrogen ratio and the overall amounts of carbon, nitrogen and sulfur in the bulk silicate Earth — are consistent with a moon-forming impact involving a volatile-bearing, Mars-sized planet with a sulfur-rich core,” Grewal said.

Another often-cited explanation about how Earth received its volatiles is the “late veneer” theory, which holds that volatile-rich meteorites, leftover chunks of primordial matter from the outer solar system, arrived after Earth’s core formed.

And while the isotopic signatures of Earth’s volatiles match these primordial objects, known as carbonaceous chondrites, the elemental ratio of carbon to nitrogen is off. Earth’s non-core material, which geologists call the bulk silicate Earth, has about 40 parts carbon to each part nitrogen, approximately twice the 20-1 ratio seen in carbonaceous chondrites. 

This led to their conclusion that the late veneer theory could not explain the conditions they had found.

Although the Rice team’s paper does not go in depth into the question of how water got to Earth, Dasgupta wrote that the team’s conclusion that the moon-forming impact brought with it other volatiles, “it is likely that the impactor would contain and bring some water too. This is especially likely because this impactor needs to form in part from oxidized carbonaceous chondritic materials (that is the condition our experiments simulated as well).

“So although we did not factor in matching the water budget in our model, it is entirely possible that this impactor brought Earth’s water budget too, if the proto-Earth was water-poor.”

 

A study by Rice University scientists (from left) Gelu Costin, Chenguang Sun, Damanveer Grewal (sitting), Kyusei Tsuno, and Rajdeep Dasgupta found Earth most likely received the bulk of its carbon, nitrogen, and other life-essential elements from the planetary collision that created the moon more than 4.4 billion years ago. The findings appear in the journal Science Advances. (Jeff Fitlow/Rice University)

 

Dasgupta, the principal investigator on a NASA-funded effort called CLEVER Planets that is exploring how life-essential elements might come together on distant rocky planets, said better understanding the origin of Earth’s life-essential elements has implications beyond our solar system.

“This study suggests that a rocky, Earth-like planet gets more chances to acquire life-essential elements if it forms and grows from giant impacts with planets that have sampled different building blocks, perhaps from different parts of a protoplanetary disk,” Dasgupta said.

“This removes some boundary conditions,” he said. “It shows that life-essential volatiles can arrive at the surface layers of a planet, even if they were produced on planetary bodies that underwent core formation under very different conditions.”

Dasgupta said it does not appear that Earth’s initial composition of bulk silicate, on its own,  could have attained the concentrations of those life-essential volatiles needed to produce our atmosphere and hydrosphere and biosphere.

This all has great implications for exoplanet studies, he said.  It means that “we can broaden our search for pathways that lead to volatile elements coming together on a planet to support life as we know it.”

CLEVER Planets is part of the Nexus for Exoplanet System Science, or NExSS, a NASA astrobiology research coordination network that is dedicated to the study of planetary habitability. CLEVER Planets involves more than a dozen research groups from Rice, NASA’s Johnson Space Center, UCLA, the University of Colorado Boulder and the University of California, Davis.

 

 

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Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to marc.kaufman@manyworlds.space.

A Hubble Spectacular

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This image of the Triangulum galaxy is the second-largest image ever taken by Hubble. (NASA, ESA, and M. Durbin, J. Dalcanton, and B. F. Williams, University of Washington)

 

As you may have noticed, there haven’t been Many Worlds columns of late.  The reason, as you can no doubt guess, is that the column is supported to some extent by NASA, and the agency is caught in the government shutdown.  So I have gotten a STOP WORK order and will not be writing much for now. But I do want to continue with my Facebook postings, with some stories or images.

As a starter, this lovely picture is the second largest Hubble image ever taken.  The result of shooting by the space observatory’s iconic Advanced Camera for Surveys, it is made up of 665 million pixels.  It features the Triangulum spiral galaxy, some 3 million light-years from Earth.
The Triangulum is small by cosmic standards, at about half the diameter of the Milky Way and a quarter of the diameter of the Andromeda galaxy. Still, astronomers estimate there are anywhere between 10 and 15 millions stars contained in this image.
Also known as Messier 33, the full galaxy is made up of 40 billion stars, which is faintly visible by naked eye under a dark sky as a small smudge in the constellation Triangulum (the triangle.)
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Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to marc.kaufman@manyworlds.space.

Weird Planets

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Artist rendering of an “eyeball world,” where one side of a tidally locked planet is always hot on the sun-facing side and the back side is frozen cold.  Definitely a tough environment, but  might some of the the planets be habitable at the edges?  Or might winds carry sufficient heat from the front to the back?  (NASA/JPL-Caltech)

The very first planet detected outside our solar system powerfully made clear that our prior understanding of what planets and solar systems could be like was sorely mistaken.

51 Pegasi was a Jupiter-like massive gas planet, but it was burning hot rather than freezing cold because it orbited close to its host star — circling in 4.23 days.  Given the understandings of the time, its existence was essentially impossible. 

Yet there it was, introducing us to what would become a large and growing menagerie of weird planets.

Hot Jupiters, water worlds, Tatooine planets orbiting binary stars, diamond worlds (later downgraded to carbon worlds), seven-planet solar systems with planets that all orbit closer than Mercury orbits our sun.  And this is really only a brief peak at what’s out there — almost 4,000 exoplanets confirmed but billions upon billions more to find and hopefully characterize.

I thought it might be useful — and fun — to take a look at some of the unusual planets found to learn what they tell us about planet formation, solar systems and the cosmos.

 


Artist’s conception of a hot Jupiter, CoRoT-2a. The first planet discovered beyond our solar system was a hot Jupiter similar to this, and this surprised astronomers and led to the view that many hot Jupiters may exist. That hypothesis has been revised as the Kepler Space Telescope found very few distant hot Jupiters and now astronomers estimate that only about 1 percent of planets are hot Jupiters. (NASA/Ames/JPL-Caltech)

 

Let’s start with the seven Trappist-1 planets.  The first three were detected two decades ago, circling a”ultra-cool” red dwarf star a close-by 40 light years away.  Observations via the Hubble Space Telescope led astronomers conclude that two of the planets did not have hydrogen-helium envelopes around them, which means the probability increased that the planets are rocky (rather than gaseous) and could potentially hold water on their surfaces.

Then in 2016 a Belgian team, using  the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, found three more planets, and the solar system got named Trappist-1.  The detection of an additional outer planet was announced the next year, and in total three of the seven planets were deemed to be within the host star’s habitable zone — where liquid water could conceivably be present.

So, we have a most interesting 7-planet solar system quite close to us, and not surprisingly it has become the focus of much observation and analysis.

But consider this:  all seven of those planets orbits Trappist-1 at a distance much smaller than from our sun to the first planet, Mercury. The furthest out planets orbits the star in 19 days, while Mercury orbits in 88 days.

 

 

The Trappist-1 solar system, with the transit data used to detect the presence of seven planets, each one blocking the light curve at different locations. (NASA/JPL-Caltech)

 

Given this proximity, then, why are the Trappist-1 planets so interesting, especially in terms of habitability?  Because Trappist-1 puts out but .05 percent as much energy as our sun, and the furthest out planet (though very close to the star by the standards of our solar system) is nonetheless likely to be frozen.

So Trappist-1 a mini-system, with seven tidally-locked (never-rotating) planets that happen to orbit in resonance to each other.  Just because it is so different from our system doesn’t mean it isn’t fascinating, instructive, and even possibly the home of planets that could potentially support life.

And since red dwarf stars are the most common type of star in the Milky way (by lot), red dwarf solar system research is an especially hot field.

So there are mini planets and systems and massive planets in what used to be considered the impossibly wrong place.  And then there are planets with highly eccentric orbits — very different from the largely circular orbits of planets in our system.

The eccentricity of HD20782b superimposed onto our circular-orbiting inner solar system planets. (Stephen Kane)

The most extreme eccentric orbit found so far is HD 20782, measured at an eccentricity of .96. This means that the planet moves in a nearly flattened ellipse, traveling a long path far from its star and then making a fast and furious slingshot around the star at its closest approach. 

Many exoplanets have eccentricities far greater than what’s found in our solar system planets but nothing like this most unusual traveler, which has a path seemingly more like a comet than a planet.

Researchers have concluded that the eccentricity of a planet tends to relate to the number of planets in the system, with many-planeted systems having far more regularly orbiting planets.  (Ours and the Trappist-1 system are examples.)

Unusual planets come in many other categories, such as the chemical makeup of their atmospheres, surfaces and cores.  Most of the mass of stars, planets and living things consists of hydrogen and helium, with oxygen, carbon, iron and nitrogen trailing far behind.

Solid elements are exceptionally rare in the overall scheme of the solar system. Despite being predominant on Earth, they constitute less than 1 percent of the total elements in the solar system, primarily because the amount of gas in the sun and gas giants is so great.  What is generally considered the most important of these precious solid elements is iron, which is inferred to be in the core of almost all terrestrial planet.

The amount of iron or carbon or sulfur or magnesium on or around a planet generally depends on the amount of these “metals” present in the host star, and then in molecular protoplanetary disc remains of the star’s formation.  And this is where some of the outliers, the apparent oddities, come in.

A super-Earth, planet 55 Cancri e, was reported to be the first known planet to have huge layers of diamond, due in part to the high carbon-to-oxygen ratio of its host star. That conclusion has been disputed,  but the planet is nonetheless unusual.  Above is an artist’s concept of the diamond hypothesis. (Haven Giguere/Yale University)

The planet 55 Cancri e, for instance, was dubbed a “diamond planet” in 2012 because the amount of carbon relative to oxygen in the star appeared to be quite high.  Based on this measurement, a team hypothesized that the surface presence of abundant carbon likely created a graphite surface on the scalding super-Earth, with a layer of diamond beneath it created by the great pressures.

“This is our first glimpse of a rocky world with a fundamentally different chemistry from Earth,” lead researcher Nikku Madhusudhan of Yale University said in a statement at the time. “The surface of this planet is likely covered in graphite and diamond rather than water and granite.”

As tends to happen in this early phase of exoplanet characterization, subsequent measurements cast some doubt on the diamond hypothesis.  And in 2016, researchers came up with a different scenario — 55 Cancri e was likely covered in lava.  But because of heavy cloud and dust cover over the planet, a subsequent group raised doubts about the lava explanation. 

But despite all this back and forth, there is a growing consensus that 55 Cancri e has an atmosphere, which is pretty remarkable given its that its “cold” side has temperatures that average of 2,400 to 2,600 degrees Fahrenheit (1,300 to 1,400 Celsius), and the hot side averages 4,200 degrees Fahrenheit (2,300 Celsius). The difference between the hot and cold sides would need to be more extreme if there were no atmosphere.

 

Could super-Earth HD 219134 b be a sapphire planet? (Thibaut Roger/University of Zurich)

And then there’s another super-earth, HD 219134, that late last year was described as a planet potentially featuring vast collections of different precious stones.

To back up for a second, researchers study the formation of planets using theoretical models and compare their results with data from observations. It is known that during their formation, stars such as the sun were surrounded by a disc of gas and dust in which planets were born. Rocky planets like the Earth were formed out of the solid bodies left over when the protoplanetary gas disc cooled and dispersed.

Unlike the Earth however, HD 219134 most likely does not have a massive core of iron — a conclusion flowing from measurements of its density.  Instead, through modeling of formation scenarios for a scalding super-Earth close to its host star, the researchers conclude the planet is likely to be rich in calcium and aluminum, along with magnesium and silicon.

This chemical composition would allow the existence of large quantities of aluminum oxides. On Earth, crystalline aluminum oxide forms the mineral corundum. If the aluminum oxide contains traces of iron, titanium, cobalt or chromium, it will form the noble varieties of corundum, gemstones like the blue sapphire and the red ruby.

“Perhaps it shimmers red to blue like rubies and sapphires, because these gemstones are aluminum oxides which are common on the exoplanet,” said Caroline Dorn, astrophysicist at the Institute for Computational Science of the University of Zurich.

 

 

A variation on the “eyeball planet” is a water world where the star-facing side is able to maintain a liquid-water ocean, while the rest of the surface is ice. (eburacum45/DeviantArt)

 

Super-Earths, which are defined as having a size between that of Earth and Neptune, are also inferred to be the most likely to be water worlds.

At a Goldschmidt Conference in Boston last year, a study was presented that suggests that some super-Earth exoplanets are likely extremely wet with water – much more so than Earth. Astronomers found more specifically that exoplanets which are between two and four times the size of Earth are likely to have water as a dominant component.  Most are thought to be rocky and to have atmospheres, and now it seems that many have ocean, as well.

The new findings are based on data from the Kepler Space Telescope and the Gaia mission, which show that many of the already known planets of this type (out of more than 4,000 exoplanets confirmed so far) could contain as much as 50 percent water. That upper limit is an enormous amount, compared to 0.02 percent of the water content of Earth.

This potentially wide distribution of water worlds is perhaps not so surprising given conditions in our solar system, where Earth is wet, Venus and Mars were once wet, Neptune and Uranus are ice giants and moons such as Europa and Enceladus as global oceans beneath their crusts of ice.

 

Might this be the strangest planet of all? (NASA)

 

As is apparent with the planetary types described so far, whether a planet is typical or atypical is very much up in the air.  What is atypical this year may be found to be common in the days ahead.

The Kepler mission concluded that small, terrestrial planets are likely more common than gas giants, but our technology doesn’t let us identify and characterize many of those smaller, Earth-sized planets.

Many of the planets discovered so far are quite close to their host stars and thus are scalding hot. Planets orbiting red dwarf stars are an exception, but if you’re looking for habitable planets — and many astronomers are — then red dwarf planets come with other problems in terms of habitability.  They are usually tidally locked and they start their days bathed in very high-energy radiation that could stertilize the surface for all time.

A prime goal of the Kepler mission had been to find a planet close enough in character to Earth to be considered a twin.  While they have some terrestrial candidates that could be habitable, no twin was found.  This may be a function of lacking the necessary technology, or it’s certainly possible (if unlikely) that no Earth twins are out there.  Or at least none with quite our collection of conditions favorable to habitability and life. 

With this in mind, my own current candidate for an especially unusual planet is, well, our own.   Planet-hunting over the past almost quarter-century leads to that conclusion — for now, at least.

And it may be that solar systems like ours are highly unusual, too.  Pretty surprising, given that not long ago it was considered the norm.

 

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Marc Kaufman
Marc Kaufman is the author of two books about space: "Mars Up Close: Inside the Curiosity Mission” and “First Contact: Scientific Breakthroughs in the Search for Life Beyond Earth.” He is also an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer. While the “Many Worlds” column is supported and informed by NASA’s Astrobiology Program, any opinions expressed are the author’s alone.

To contact Marc, send an email to marc.kaufman@manyworlds.space.