Piecing Together The Narrative of Evolution

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

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

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

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

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

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

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

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

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

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

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

She described her work and findings more specifically as follows:

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

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

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

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

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

 

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

 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Large Reservoir of Liquid Water Found Deep Below the Surface of Mars

Facebooktwittergoogle_plusredditpinterestlinkedinmail
Artist impression of the Mars Express spacecraft probing the southern hemisphere of Mars, superimposed on a radar cross section of the southern polar layered deposits. The leftmost white line is the radar echo from the Martian surface, while the light blue spots are highlighted radar echoes along the bottom of the ice.  Those highlighted areas measure very high reflectivity, interpreted as being caused by the presence of water. (ESA, INAF. Graphic rendering by Davide Coero Borga )

Far beneath the frigid surface of the South Pole of Mars is probably the last place where you might expect the first large body of Martian liquid water would be found.  It’s -170 F on the surface, there are no known geothermal sources that could warm the subterranean ice to make a meltwater lake, and the liquid water is calculated to be more than a mile below the surface.

Yet signs of that liquid water are what a team of Italian scientists detected — a finding that they say strongly suggests that there are other underground lakes and streams below the surface of Mars.  In a Science journal article released today, the scientists described the subterranean lake they found as being about 20 kilometers in diameter.

The detection adds significantly to the long-studied and long-debated question of how much surface water was once on Mars, a subject that has major implications for the question of whether life ever existed on the planet.

Finding the subterranean lake points to not only a wetter early Mars, said co-author Enrico Flamini of the Italian space agency, but also to a Mars that had a water cycle that collected and delivered the liquid water.  That would mean the presence of clouds, rain, evaporation, rivers, lakes and water to seep through surface cracks and pool underground.

Scientists have found many fossil waterways on Mars, minerals that can only be formed in the presence of water, and what might be the site of an ancient ocean.

But in terms of liquid water now on the planet, the record is thin.  Drops of water collected on the leg of NASA’s Phoenix Lander after it touched down in 2008, and what some have described as briny water appears to be flowing down some steep slopes in summertime.  Called recurrent slope lineae or RSLs, they appear at numerous locations when the temperatures rise and disappear when they drop.

This lake is different, however, and its detection is a major step forward in understanding the history of Mars.

Color photo mosaic of a portion of Planum Australe on Mars.  The subsurface reflective echo power is color coded and deep blue corresponds to the strongest reflections, which are interpreted as being caused by the presence of water. (USGS Astrogeology Science Center, Arizona State University, INAF)

The discovery was made analyzing echoes captured by the the radar instruments on the European Space Agency’s Mars Express, a satellite orbiting the planet since 2002.  The data for this discovery was collected from observation made between 2012 and 2015.

 

A schematic of how scientists used radar to find what they interpret to be liquid water beneath the surface of Mars. (ESA)

Antarctic researchers have long used radar on aircraft to search for lakes beneath the thick glaciers and ice layers,  and have found several hundred.  The largest is Lake Vostok, which is the sixth largest lake on Earth in terms of volume of water.  And it is two miles below the coldest spot on Earth.

So looking for a liquid lake below the southern pole of Mars wasn’t so peculiar after all.  In fact, lead author Roberto Orosei of the Institute of Radioastronomy of Bologna, Italy said that it was the ability to detect subsurface water beneath the ice of Antarctica and Greenland that helped inspire the team to look at Mars.

There are a number of ways to keep water liquid in the deep subsurface even when it is surrounded by ice.  As described by the Italian team and an accompanying Science Perspective article by Anja Diez of the Norwegian Polar Institute, the enormous pressure of the ice lowers the freezing point of water substantially.

Added to that pressure on Mars is the known presence of many salts, that the authors propose mix with the water to form a brine that lowers the freezing point further.

So the conditions are present for additional lakes and streams on Mars.  And according to Flamini, solar system exploration manager for the Italian space agency, the team is confident there are more and some of them larger than the one detected.  Finding them, however, is a difficult process and may be beyond the capabilities of the radar equipment now orbiting Mars.

 

Subsurface lakes and rivers in Antarctica. Now at least one similar lake has been found under the southern polar region of Mars. (NASA/JPL)

The view that subsurface water is present on Mars is hardly new.  Stephen Clifford, for many years a staff scientist at the Lunar and Planetary Institute, even wrote in 1987 that there could be liquid water at the base of the Martian poles due to the kind of high pressure environments he had studied in Greenland and Antarctica.

So you can imagine how gratifying it might be to learn, as he put it “of some evidence that shows that early theoretical work has some actual connection to reality.”

He considers the new findings to be “persuasive, but not definitive” — needing confirmation with other instruments.

Clifford’s wait has been long, indeed.  Many observations by teams using myriad instruments over the years did not produce the results of the Italian team.

Their discovery of liquid water is based on receiving particularly strong radar echoes from the base of the southern polar ice — echoes consistent with the higher radar reflectivity of water (as opposed to ice or rock.)

After analyzing the data in some novels ways and going through the many possible explanations other than the presence of a lake, Orosei said that none fit the results they had.  The explanation, then, was clear:  “We have to conclude there is liquid water on Mars.”

The depth of the lake — the distance from top to bottom — was impossible to measure, though the team concluded it was at least one meter and perhaps in the tens of meters.

Might the lake be a habitable?  Orosei said that because of the high salt levels “this is not a very pleasant environment for life.”

But who knows?  As he pointed out, Lake Vostok and other subglacial Antarctic lake, are known to be home to single-cell organisms that not only survive in their very salty world, but use the salt as part of their essential metabolism.

 

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Exoplanet Science Flying High

Facebooktwittergoogle_plusredditpinterestlinkedinmail
An artist’s concept shows what the TRAPPIST-1 planetary system may look like, based on available data about the planets’ diameters, masses and distances from the host star, as of February 2018. Credit: NASA/JPL-Caltech

 

Early this spring, the organizers of an exoplanet science gathering at Cambridge University put out the word that they would host a major meeting this summer.  Within a week, the 300 allotted slots had been filled by scientists aspiring and veteran, and within a short time the waiting list was up to 150 more.

Not the kind of reaction you might expect for a hardcore, topic-specific meeting, but exoplanet science is now in a phase of enormous growth and excitement.  With so many discoveries already made and waiting to be made, so many new (and long-standing) questions to be worked on, so much data coming in to be analyzed and turned into findings,  the field has something of a golden shine.

What’s more, it has more than a little of the feel of the Wild West.

Planet hunters Didier Queloz and Michel Mayor at the European Southern Observatory’s La Silla site. (L. Weinstein/Ciel et Espace Photos)

Didier Queloz, a professor now at Cambridge but in the mid 1990s half of the team that identified the first exoplanet, is the organizer of the conference.

“It sometimes seems like there’s not much exploration to be done on Earth, and the opposite is the case with exoplanets,” he told me outside the Cambridge gathering.

“I think a lot of young scientists are attracted to the excitement of exoplanets, to a field where there’s so much that isn’t known or understood.”

Michel Mayor of the Observatory of Geneva — and the senior half of the team that detected the first exoplanet orbiting a star like our sun, 51 Pegasi b– had opened the gathering with a history of the search for extra-solar planets.

That search had some conceptual success prior to the actual 1995 announcement of an exoplanet discovery, but several claims of having actually found an exoplanet had been made and shown to be wanting.  Except for the relative handful of scientists personally involved, the field was something of a sideshow.

“At the time we made our first discovery, I basically knew everyone in the field.  We were on our own.”

Now there are thousands of people, many of them young people, studying exoplanets.  And the young people, they have to be smarter, more clever, because the questions are harder.”

And enormous progress is being made.

The pace of discovery is charted here by Princeton University physicist and astronomer Joshua Winn. First is a graphic of all the 3,735 exoplanet discoveries made since 1995, and then the 1943 planets found just from 2016 to today.

The total number and distribution of known exoplanets, identified by the mass of the planet and their distance from their host star. A legend to the four major techniques for finding exoplanets is in the lower right The circled planets in green are those in our solar system. All the data comes from the NASA Exoplanet archive. (Joshua Winn, Princeton University)

 

Based on published papers, Winn found that the discovery of 1,943 new planets had been announced in papers between 2016 and today. Winn said the number is not formal as some debate remains whether a small number are planets or not.

Many of the planets discovered via the transit method come from the Kepler and K2 missions.  Kepler revolutionized the field with its four years of intensively observing a region of the sky for planet transits in front of their star.

The K2 mission began after the second of Kepler’s four stabilizing wheels failed. But adjustments were made and the second incarnation of Kepler has continued to find planets, though in a different way.

While a majority of exoplanets have been detected via the transit method, the first exoplanet was discovered by Mayor and Queloz via the radial velocity method — which involves ground-based measurements of the “wobble” of a star caused by the gravitational pull of a planet.

Many astronomers continue to use the technique because it provides more information about the minimum mass and orbital eccentricity of planet.  In addition, two high-precision, next-generation spectrometers for radial velocity measuring are now coming on line and are expected to significantly improve the detection of smaller planets using that method.

One is the ESPRESSO instrument (the Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic) recently installed by the European Southern Observatory on the Very Large Telescope in Chile. The other newcomer is EXPRES, developed by scientists at Yale University, with support for the National Science Foundation.  The instrument, designed go look for Earth-sized planets, has been installed on the Lowell Observatory Discovery Channel Telescope in Arizona.

 

The Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) will search for exoplanets with unprecedented precision by looking at the minuscule changes in the properties of light coming from their host stars. This picture shows the front-end structure where the light beams coming from the four Very Large Telescopes are brought together and fed into fibers. They then deliver the photons to a spectrograph in another room, which makes the radial velocity measurements. (Giorgio Calderone, INAF Trieste)

The conference, which will go through the week, focuses both generally and in great detail on many of the core questions of the field:  how exoplanets are formed, what kind of stars are likely to produce what kinds of planets, the makeup and dynamics of exoplanet atmospheres, planet migration, the architecture of planetary systems.

And, of course, where new exoplanets might be found.  (Mostly around red dwarf stars, several scientists argued, and many in the relatively near neighborhood.)

Notably, many of the exoplanet questions being studied have clear implications for better understanding our own solar system.  In fact, it is often said that we won’t really understand the workings and history of our solar system, planets, moons, asteroids and more until we know a lot more about the billions and billion of other planetary systems in our galaxy.

Also notable for this conference is the lack of emphasis on biosignatures, habitability and the search for life beyond Earth.  The conference is billed as being about “exoplanet science,” and Queloz explained the absence of habitability and life-detection talks was based on the scientific progress made, or not made, in the past two years.

When it comes to planet detection, however, theory and practice are coming together in searches for exoplanets around smaller and cooler stars, and even around young stars where planets are just forming.  Such a planet discovery was announced this week coming from the European Space Agency’s Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument.

 

The first clear image of a planet caught while being formed,around the dwarf star PDS 70. The planet is visible as a bright point to the right of center. The star at the center is blacked out by a coronagraph mask that blocks its blinding light. The SPHERE instrument is on the European Southern Observatory’s Very Large Telescope (A. Müller et al./ESO)

 

The Cambridge exoplanet conference is the second in a series begun two years ago by Queloz and Kevin Heng, an exoplanet atmosphere theoretician at the University of Bern and director of the Center for Space and Habitability.

The two had been struck by how European exoplanet conferences seemed to be dominated by senior scientists, with little time or space for the many younger men and women coming up in the field.  The presentations also seemed more long and formal than needed.

So using funds from their own institutions to seed the conferences, Heng set up the first in Davos, Switzerland and Didier the second in Cambridge.  The idea has caught on, and similar gathering are now scheduled at two year intervals in Heidelberg, Las Vegas, Amsterdam, Porto and hopefully later in Asia, too.

There is no dearth of other exoplanet gatherings around the world, and attendees report that they are also very well attended.

But given sheer amount of work now being done in the field that was so lonely only twenty years ago,  they surely appear to be warranted.

And newsworthy, though no always reportable.

Three of the papers discussed in the Cambridge conference, for instance, are under reporting embargo from the journal Nature. And information from George Ricker, principal investigator for NASA’s Transiting Exoplanet Survey Satellite (TESS), about the early days of the mission are also under embargo.  Suffice it to say, however, that Ricker reported that things are going well for the exoplanet-hunting telescope.

 

This test image from one of the four cameras aboard the Transiting Exoplanet Survey Satellite (TESS) captures a swath of the southern sky along the plane of our galaxy. TESS is designed to study exoplanets around the brightest stars, and is expected to cover more than 400 times the amount of sky shown in this image. (NASA/MIT/TESS)

While the initial discovery of an exoplanet was difficult for sure, what the much, much larger field is grappling with now is clearly even more challenging.  With that in mind, I asked Queloz what he hoped to see from exoplanets in the years ahead.

“We have reached the point where we know stars usually have planets.  But what we are still looking for is an Earth twin — a planet clearly like ours.  That we have not found.  Before I retire, what I hope for is the discovery of that Earth twin.”

 

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Breakthrough Findings on Mars Organics and Mars Methane

Facebooktwittergoogle_plusredditpinterestlinkedinmail
The Curiosity rover on Mars takes a selfie at a site named Mojave. Rock powdered by the rover drill system and then intensively heated rock and then heated to as much as 800 degrees centigrade produced positive findings for long-sought organics. (NASA/JPL-Caltech/MSSS.)

A decades-long quest for incontrovertible and complex Martian organics — the chemical building blocks of life — is over.

After almost six years of searching, drilling and analyzing on Mars, the Curiosity rover team has conclusively detected three types of naturally-occurring organics that had not been identified before on the planet.

The Mars organics Science paper, by NASA’s Jennifer Eigenbrode and much of the rover’s Sample Analysis on Mars (SAM) instrument team, was twinned with another paper describing the discovery of a seasonal pattern to the release of the simple organic gas methane on Mars.

This finding is also a major step forward not only because it provides ground truth for the difficult question of whether significant amounts of methane are in the Martian atmosphere, but equally important it determines that methane concentrations appear to change with the seasons. The implications of that seasonality are intriguing, to say the least.

In an accompanying opinion piece in Science, Inges Loes ten Kate of Utrecht University in  Netherlands wrote of the two papers: “Both these findings are breakthroughs in astrobiology.”

The clear conclusion of these (and other) recent findings is that Mars is not a “dead” planet where little ever changes.  Rather, it’s one with cycles that appear to produce not only methane but also sporadic surface water and changing dune formations.

Remains of 3.5 billion-year old lake that once filled Gale Crater. NASA scientists concluded early in the Curiosity mission that the planet was habitable long ago based on the study of mudstone remains like these. (NASA/JPL-Caltech/MSSS)

Finding organic compounds on Mars has been a prime goal of the Curiosity rover mission.

Those carbon-based compounds surely fall from the sky on Mars, as they do on Earth and everywhere else, but identifying them has proven illusive.

The consequences of that non-discovery have been significant.  Going back to the Viking missions of 1976, scientists concluded that life was not possible on Mars because there were no organics, or none that were detected.

Jen Eigenbrode, research astrobiologist at NASA’s Goddard Space Flight Center. (NASA/W. Hrybyk)

But the reasons for the disappearing organics are pretty well understood.  Without much of an atmosphere to protect it, the Martian surface is bombarded with ultraviolet radiation, which can destroy organic compounds.  Or, in the case of the samples discovered by the SAM team, large organic macromolecules — the likes of proteins, membranes and DNA — are broken up into much smaller pieces.

That’s what the team found, Eigenbrode told me. The organics were probably preserved, she said, because of exceptionally high levels of sulfur present in that part of Gale Crater.

The organics, extracted from mudstone at the Mojave and Confidence Hill sites, had bonded tightly with ancient non-organic material.  The organic material was freed to be collected as gas only after being exposed to temperatures of more than 500 to 800 centigrade in the SAM oven.

“This material was buried for billions of years and then exposed to extreme surface conditions, so there’s a limit to what we can learn about.  Did it come from life?  We don’t know.

“But the fact we found the organic carbon adds to the habitability equation.  It was in a lake environment that we know could have supported life.  Organics are things that organisms can eat.”

It will take different kinds of instruments and samples from drilling deeper into the extreme Martian surface to answer the question of whether the organics came from living microbes.  But for Eigenbrode, future answers of either “yes” or “no” are almost equally interesting.

Finding clear signs of early Martian life would certainly be hugely important, she said.  But a conclusion that Mars never had life — although it had conditions some 3.5 to 3.8 billion years ago quite similar to conditions on Earth at that time — raises the obvious question of “why not?”

NASA’s Curiosity rover raised robotic arm with drill pointed skyward while exploring Vera Rubin Ridge at the base of Mount Sharp inside Gale Crater. This navcam camera mosaic was stitched from raw images taken on Sol 1833, Oct. 2, 2017 and colorized. (NASA/JPL-Caltech/Ken Kremer, Marco Di Lorenzo)

Organic molecules are the building blocks of all known life on Earth, and consist of a wide variety of molecules made primarily of carbon, hydrogen, and oxygen atoms. However, organic molecules can also be made by chemical reactions that don’t involve life.

Examples of non-biological sources include chemical reactions in water at ancient Martian hot springs or delivery of organic material to Mars by interplanetary dust or fragments of asteroids and comets.

It needs to be said that today’s Mars organics announcement was not the first we have heard.  In 2014, a NASA team reported the presence of chlorine-based organics in Sheepbed mudstone at Yellowknife Bay, the first ancient Mars lake visited by Curiosity.

That work, led by NASA Goddard scientists Caroline Freissinet and Daniel Glavin and published in the Journal of Geophysical Research, focused on signatures from unusual organics not seen naturally on Earth.

The organics were complex and made entirely of Martian components, the paper reported.  But because they combined chlorine with the organic hydrocarbons, they are not considered to be as “natural” as the discovery announced today.

And when it comes to organics on Mars, the complicated history of research into the presence of the gas methane (a simple molecule that consists of carbon and hydrogen) also shows the great challenges involved in making these measurements on Mars.

By measuring absorption of light at specific wavelengths, the tunable laser spectrometer on Curiosity measures concentrations of methane, carbon dioxide and water vapor in the Martian atmosphere. (NASA)

 

The gold-plated Sample Analysis on Mars contains three instruments that make the measurements of organics and methane.  (NASA/Goddard Space Flight Center)

The second Science paper, authored by Chris Webster of NASA’s Jet Propulsion Lab and colleagues, reports that the gas methane has been detected regularly in recent years, with surprising seasonality.

“The history of Mars methane has been frustrating, with reports of some large plumes and spikes detected, but none have been repeatable.  It’s almost like they’re random,” he told me.  “But now we can see a large seasonal cycle in the background of these detections, and that’s extremely important.”

Over three Mars years, or almost five Earth years, Webster said there have been significant increases in methane detected during the summer, and especially the late summer. That tripling of the methane counts is considered too great to be random, especially since the count declines as predicted after the summer ends.

No definite explanation of why this happens has emerged yet, but one theory has been embraced by some scientists.

While it is still cold in the Martian summer, it can get warm enough where the sun shines directly on a collection of ice for some melting to occur.  And that melting, the paper reports, could provide an escape valve for methane collected long ago under the surface.  The process is termed “microseepage.”

 

This illustration shows the ways in which methane from the subsurface might find its way to the
surface where its release could produce the large seasonal variation in the atmosphere
as observed by Curiosity. Potential methane sources include byproducts from organisms alive or long dead, ultraviolet degradation of organics, or water-rock chemistry; and its losses include atmospheric photochemistry and surface reactions. Seasons refer to the northern hemisphere. The plotted data is from Curiosity’s TLS-SAM instrument, and the curved line through the data is to aid the eye. (NASA/JPL-Caltech)

Methane is a crucial organic in astrobiology because most of that gas found on Earth comes from biology, although various non-biological processes can produce methane as well.

Today’s paper by Webster et al is the third in Science on Mars methane as measured by Curiosity, and it is the first to find a seasonal pattern.  The first paper, in 2013,  actually reported there was no methane measured in early runs, a conclusion that led to push-back from many of those working in the field.

While the Mars methane results released today are being described as a “breakthrough,” they follow closely the findings of a Science paper in 2009 by Michael Mumma and Geronimo Villanueva, both at NASA Goddard.

The two reported then similar findings of plumes of methane on Mars, of a seasonality associated with their distribution, and a similar conclusion that the methane probably was coming from subsurface reservoirs.  Like Webster et al, Mumma and Villanueva said they were unable to determine if the source of methane was biological or geological.

The methane levels in the plumes they found were considerably higher than detected so far by Curiosity, but what they were detecting was quite different.  Using ground-based telescopes, they detected the high concentrations in two specific areas over a number of years, while Curiosity is measuring methane levels that are more global or regional.

Red areas indicate where in 2003 ground-based observers detected concentrations of methane in the Martian atmosphere, measured in parts per billion (ppb).  (NASA / M. Mumma & others)

Just as Webster was criticized for his initial paper saying there was no methane detected on Mars, the Mumma team also got sharp questions about their methodology and conclusions.  This grew as their numerous follow-up efforts to detect the Mars methane proved unsuccessful.

But now Webster says the Curiosity findings have essentially “confirmed” what Mumma and Villanueva reported nine years ago.

Still, the Curiosity results are a breakthrough because they were made on Mars rather than through a telescope. Mumma, who described the new Curiosity results as “satisfying,” agreed that they were a major step forward.

“This is how science works,” he said.  “We do our work and put out our papers and other scientists react.  We take it all in and make changes if needed.  But the big changes come when new, and maybe different, data is presented.”

And that’s exactly what will be happening soon regarding methane on Mars.  Beginning early this year, the European/Russian Trace Gas Orbiter (TGO) has been collecting data specifically on Mars gases including methane.  Unlike previous Mars methane campaigns, this one can potentially determine whether the methane being released from below the surface was formed by biology or geology — although not without great difficulty.

Mumma, who is part of that TGO team, said the first release of information is due in the fall.

 

 

 

 

 

 

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Joining the Microscope and the Telescope in the Search for Life Beyond Earth

Facebooktwittergoogle_plusredditpinterestlinkedinmail

 

Niki Parenteau of NASA’s Ames Research Center is a microbiologist working in the field of exoplanet and Mars biosignatures. She adds a laboratory biology approach to a field generally known for its astronomers, astrophysicists and planetary scientists. (Marisa Mayer, Stanford University.)

 

The world of biology is filled with labs where living creatures are cultured and studied, where the dynamics of life are explored and analyzed to learn about behavior, reproduction, structure, growth and so much more.

In the field of astrobiology, however, you don’t see much lab biology — especially when it comes to the search for life beyond Earth.  The field is now largely focused on understanding the conditions under which life could exist elsewhere, modeling what chemicals would be present in the atmosphere of an exoplanet with life, or how life might begin as an organized organism from a theoretical perspective.

Yes, astrobiology includes and learns from the study of extreme forms of life on Earth, from evolutionary biology, from the research into the origins of life.

But the actual bread and butter of biologists — working with lifeforms in a lab or in the environment — plays a back seat to modeling and simulations that rely on computers rather than actual life.

Niki Parenteau with her custom-designed LED array, can reproduce the spectral features of different simulated stellar and atmospheric conditions to test on primitive microbes. (Marc Kaufman)

There are certainly exceptions, and one of the most interesting is the work of Mary “Niki” Parenteau at NASA’s Ames Research Center in the San Francisco Bay area.

A microbiologist by training, she has been active for over five years now in the field of exoplanet biosignatures — trying to determine what astronomers could and should look for in the search for extraterrestrial life.

Working in her lab with actual live bacteria in laboratory flasks, test tubes and tanks, she is conducting traditional biological experiments that have everything to do with astrobiology.

She takes primitive bacteria known to have existed in some form on the early Earth, and she blasts them with the radiation that would have hit the planet at the time to see under what conditions the organisms can survive.  She has designed ingenious experiments using different forms of ultraviolet light and a LED array that simulate the broad range of radiations that would come from different types of stars as well.

What makes this all so intriguing is that her work uses, and then moves forward, cutting edge modeling from astronomers and astrobiologists regarding thick photochemical hazes understood to have engulfed the early Earth — making the planet significantly colder but also possibly providing some protection from deadly ultraviolet radiation.

That was a time when the atmosphere held very little oxygen, and when many organisms had to make their living via carbon dioxide and sulfur-based photosynthesis that did not use water and did not produce oxygen. This kind of photosynthesis has been the norm for much of the history of life on Earth, and certainly could be common on many exoplanets orbiting other stars as well.

So anything learned about how these early organisms survived in frigid conditions with high ultraviolet radiation — and what potentially detectable byproducts they would have produced under those conditions — would be important in the search for biosignatures and extraterrestrial life.

Parenteau has spent years learning from astronomers working to find ways to characterize exoplanet biosignatures, and she has been eager to convert her own work into something useful to them.

“These are not questions that can be answered by one discipline,” she told me.  “I certainly understand that when it comes to exoplanet biosignatures and life detection, astronomy has to be in the lead.  But biologists have a role to play, especially when it comes to characterizing what life produces.”

When haze built up in the atmosphere of Archean Earth, the young planet might have looked like this artist’s interpretation – a pale orange dot. A team led by Goddard scientists thinks the haze was self-limiting, cooling the surface by about 36 degrees Fahrenheit (20 Kelvins) – not enough to cause runaway glaciation. The team’s modeling suggests that atmospheric haze might be helpful for identifying earthlike exoplanets that could be habitable. (NASA’s Goddard Space Flight Center/Francis Reddy)

Here is the back story to Parenteau’s work:

Recent work by NASA Goddard Space Flight Center astronomer and astrobiologist Giada Arney and colleagues points to the existence of a thick haze around the early Archean Earth and probably today around some, and perhaps many, exoplanets.  This haze — which is more like pollution than clouds — is produced by the interaction of strong incoming radiation and chemicals (most commonly methane and carbon dioxide) already in the atmosphere.

The haze, Arney concluded based on elaborate modeling of those radiation-chemical interactions, would be hard on any life that might exist on the planet because it would reduce surface temperatures significantly, though probably not always fatally.

Giada Arney is an astronomer and astrobiologist at NASA’s Goddard Space Flight Center.  As with Parenteau, her general approach to science was formed at the University of Washington’s pioneering Virtual Planetary Laboratory. (NASA/Goddard Space Flight Center)

On the other hand, the haze would also have the effect of blocking 84 percent of the destructive ultraviolet radiation bombarding the planet — especially the most damaging ultraviolet-C light that would otherwise destroy nucleic acids in cells and disrupt the working of DNA.  (Ultraviolet-C radiation is used as a microbial disinfectant.)

Ozone in our atmosphere now plays the role of blocking the most destructive forms of UV radiation, but ozone is formed from oxygen and on early Earth there was very little oxygen at all.

So how did organisms survive the radiation assault?  Might it have been that haze? And might there be hazes surrounding exoplanets as well?  (None have been found so far.)

It’s difficult enough to sort through the potentially protective role of a haze on early Earth.  To do it for exoplanets requires not only an understanding of the effects of a haze on ultraviolet light, but also how the dynamics of a haze would change based on the amounts and forms of radiation emitted by different types of stars.

It’s all very complicated, but the answers needn’t be theoretical, Arney concluded. They could be tested in a lab.

And that’s where Parenteau comes in, with her desire and ability to design biological experiments that might help scientists understand better how to look for life on distant exoplanets.

“I knew that (Parenteau) had been super interested in this kind of question for a long time,” Arney said.  “She one of the few people in the world with the know-how to simulate an atmosphere, and probably the only one in the world who could do the experiment.”

The 48 LEDs (light-emitting diodes) of the board designed and created by Parenteau and Ames intern Cameron Hearne. Each one is independently controlled and can be used to simulate the amount of radiation arriving on a planetary surface — taking into account the flux from the planet’s star and some aspects of its atmosphere.  A microbe is then exposed to the radiation to see whether or how it can survive. (Niki Parenteau.)

Parenteau’s experiment at first looks pretty low-tech, but in fact it’s very much custom-designed and custom-built.

The ultraviolet bulbs include the powerful, germicidal ultraviolet-C variety, some of the glass for the experiment is made of special quartz that is transparent to that ultraviolet light, the LED array has 48 tiny bulbs that can be controlled by software to provide different amounts and kinds of light as identified and provided by Arney

Before designing and making her own LED board with Ames intern Cameron Hearne, Parenteau met with solar panel specialists who might be able to provide an instrument she could use, but it turned out they were very expensive and not nearly as versatile as she wanted.  Having grown up on a farm in northern Idaho, Parenteau is comfortable with making things from scratch, and her experiments reflect that comfort and talent.

How would Parenteau determine whether the haze does indeed protect the microbial cells after exposing them to the various radiation regimes?  This is how she explained the process, which measures the number of cells living or dead given a simulated UV and stellar bombardment:

“Imagine the cells as soap bubbles in a clear glass.  If you look through the glass, the soap bubbles prevent you from seeing through and the glass has a higher ‘optical density.’ However, if you pop or lyse the soap bubbles, suddenly you can see through the glass and the optical density decreases. 

“The latter represents dead ‘popped’ cells that were killed by the UV irradiation.   I predict that by simulating the spectral qualities of the haze, which decreases the UV flux by 84%, more cells will survive.”

The Parenteau-Arney collaboration is being funded through a National Astrobiology Institute grant to the University of Washington’s famously-interdisciplinary Virtual Planetary Laboratory.

The microbes-and-haze experiment is one of many that Parenteau is working on in the general field of biosignatures.  While the haze experiment is primarily designed to determine if microbes could survive a UV bombardment if a haze was present, she is also working on the central question of what might constitute a biosignature.

With that in mind, she is also measuring the gases produced by microbes under different radiation and atmospheric conditions, and that is directly applicable to searching for extraterrestrial life.

A densely-packed community of microbes, including oxygen-producing cyanobacteria as well as anoxygenic purple and green bacteria, being studied with Parenteau’s LED array. A central question involves what gases are emitted and might be detectable on a distant planet. (Niki Parenteau)

 

Parenteau’s lab glove box with green, purple and other bacteria that is regularly exposed to radiation conditions believed to have existed on early Earth when a photochemical haze is believed to have been present.  (Marc Kaufman)

If and when she does find particularly interesting results in the gas measurements inside the anaerobic glove box, she says, she knows where to go.

“I would hand the results to an astronomer.  We could say that if a particular kind of exoplanet with a particular atmosphere had microbial life, this is the suite of gases we would expect to be emitted.”

Those gases, Parenteau says, may be photochemically altered as they as they rise through the planet’s atmosphere to the upper levels where they could be detected by the telescopes of the future. But in the challenging and complex world of biosignatures, every bit of hard-won data is most valuable since it could some day lead to a discovery for the ages.

 

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail