Category: The Search for Life Beyond Earth (page 1 of 6)

Using Climate Science on Earth to Understand Planets Beyond Earth

Climate expert Tony Del Genio has just retired after 41 years-plus at NASA’s Goddard Institute of Space Studies (GISS) in New York City. Here Del Genio is attending a Cubs game at Wrigley Field with (from the lower right) Dawn Gelino, Shawn Domogal-Goldman, Aaron Gronstal and Mary Voytek. All are part of the NASA NExSS initiative. (Dawn Gelino)

Anthony Del Genio started out his career expecting to become first an engineer and then a geophysicist.  He was in graduate school at UCLA and had been prepared by previous mentors to enter the geophysics field.  But a 1973 department-wide test focused on seismology, rather than fields that he understood better, and his days as a geophysicist were suddenly over.  Fortunately,  one of his professors saw that he had done very well in the planetary atmospheres and geophysical fluid dynamics sections of the exams, and suggested a change in focus.

That turned out to be a good thing for Del Genio, for the field of climate modeling, and for NASA. Because for the next four decades-plus, Del Genio has been an important figure in the field of climate science — first modeling cloud behavior and climate dynamics on Earth with ever more sophisticated atmospheric general circulation models (GCMs), and then beginning to do the same on planets beyond Earth.

His entry into the world of Venus, Saturn, Titan and distant exoplanets beyond is how I met Tony in 2015. At the same time that Many Worlds began as a column, Del Genio was named one of the founding leaders of the Nexus for Exoplanet System Science (NExSS) — the pioneering, interdisciplinary NASA initiative to bring together scientists working in the field of planetary habitability.  (NExSS also supports this column.)

Del Genio is a hard-driving scientist, but also has a self-deprecating and big-picture, poetic side.  This came across at our first diner breakfast together on Manhattan’s Upper West Side (where GISS is located), and was highlighted in a piece that Del Genio just wrote for a new series initiated by the American Geophysical Union (AGU),  Perspectives of Earth and Space Scientists.   In that series, scientists are asked to look back on their careers and write about their science and journeys.  Del Genio’s perspective is the first in this series, and I will reprint most of its bottom half because I found it so informative and interesting.

But first, a quote from Del Genio’s piece that sets the stage:  “The beauty of science, if we are patient, is that nature reveals its secrets little by little, slowly enough to keep us pressing forward for more but fast enough for us not to despair.”… Read more

How Long Were the Wet Periods on Early Mars, and Was That Water Chemically Suitable For Life?

 

An artist rendering, based on scientific findings, of Gale Crater in Mars during one of its ancient, wet periods. (NASA)

There is no doubt that early Mars had long period of warmer and much wetter climates before its atmosphere thinned too much to retain that liquid H20 on the surface.

As we know from the Curiosity mission to Gale Crater and other orbital findings, regions of that warmer and wetter Mars had flowing water and lakes periodically over hundreds of millions of years.  That’s one of the great findings of planetary science of our times.

But before approaching the question of whether that water could have supported life, a lot more needs to be known than that water was present.  We need answers to questions like how acidic or basic that water likely was?  Was it very salty? Did it have mineral and elemental contents that could provide energy to support any potential life?

And most especially, how long did those wet periods last, and the dry periods as well?

In a recent paper for Nature Communications, some more precise answers are put forward based on data collected at Gale Crater and interpreted based on geochemical modeling and Earth-based environmental science.

The water, say geochemist Yasuhito Sekine of the Earth-Life Science Institute (ELSI) in Tokyo and colleagues from the U.S. and Japan, had many important characteristics supportive of life.  It was only mildly salty, it had a near-neutral pH, it contained essential minerals and elements in state of disequilibrium — meaning that they could give and receive the electrons needed to provide life-supporting energy.   The  area was hardly lush — more like the semi-arid regions of Central Asia and Utah’s Great Salt Lake — but it contained water that was plausibly life supporting.

Based on an analysis of the patterns and quantities of salt remains, they estimate the water was present numerous times for between 10,000 to one million years each period.

Were those warm eras long enough for life to emerge, and the dry period short enough for it to survive?

“We don’t have a clear answer,” Sekine said. “But it is now more clear that the key question is which is more important:  the chemistry of the water or the duration of its presence?”

And the way to address the question, he said, is through a mix of planetary science and environmental science.

“This is a first step in the application of environmental chemistry to Mars,” Sekine said.… Read more

Icy Moons and Their Plumes

The existence of water or water vapor plumes on Europa has been studied for years, with a consensus view that they do indeed exist.  Now NASA scientists have their best evidence so far that the moon does sporadically send water vapor into its atmosphere.  (NASA/ESA/K. Retherford/SWRI)

Just about everything that scientists see as essential for extraterrestrial life — carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur and sources of energy — is now known to be pretty common in our solar system and beyond.  It’s basically there for the taking  by untold potential forms of life.

But what is not at all common is liquid water.  Without liquid water Earth might well be uninhabited and today’s Mars, which was long ago significantly wetter, warmer and demonstrably habitable,  is widely believed to be uninhabited because of the apparent absence of surface water (and all that deadly radiation, too.)

This is a major reason why the discovery of regular plumes of water vapor coming out of the southern pole of Saturn’s moon Enceladus has been hailed as such a promising scientific development.  The moon is pretty small, but most scientists are convinced it does have an under-ice global ocean that feeds the plume and just might support biology that could be collected during a flyby.

But the moon of greatest scientific interest is Europa, one of the largest that orbits Jupiter.  It is now confidently described as having a sub-surface ocean below its crust of ice and — going back to science fiction writer extraordinaire Arthur C. Clarke — has often been rated the most likely body in our solar system to harbor extraterrestrial life.

That is why it is so important that years of studying Europa for watery plumes has now paid off.   While earlier observations strongly suggested that sporadic plumes of water vapor were in the atmosphere, only last month was the finding nailed, as reported in the journal Nature Astronomy.

“While scientists have not yet detected liquid water directly, we’ve found the next best thing: water in vapor form,” said Lucas Paganini, a NASA planetary scientist who led the water detection investigation.

 

As this cutaway shows, vents in Europa’s icy crust could allow plumes of water vapor to escape from a sub-surface ocean. If observed up close, the chemical components of the plumes would be identified and could help explain the nature and history of the ocean below. ( NASA) 

The amount of water vapor found in the European atmosphere wasn’t great — about an Olympic-sized pool worth of H2O.  … Read more

Mapping Titan, the Most Earth-Like Body in Our Solar System

In an image created by NASA’s Cassini spacecraft, sunlight reflects off lakes of liquid methane around Titan’s north pole.  Cassini radar and visible-light images allowed researchers to put together the first global geological map of Saturn’s largest moon.  (NASA/JPL-Caltech/University of Arizona/University of Idaho)

Saturn’s moon Titan has lakes and rivers of liquid hydrocarbons, temperatures that hover around -300 degrees Fahrenheit, and a thick haze that surrounds it and has cloaked it in mystery.   An unusual place for sure, but perhaps what’s most unusual is that Titan more closely resembles Earth of all the planets and moons in our solar system.

This is because like only Earth it has that flowing liquid on its surface, it has a climate featuring wind and rain that form dunes, rivers, lakes, deltas and seas (probably of filled with liquid methane and ethane), it has a thick atmosphere and it has weather patterns that change with the seasons.  The moon’s methane cycle is quite similar to our water cycle.

And now astronomers have used data from NASA’s Cassini-Huygens mission to map the entire surface of Titan for the first time.  Their work has found a global terrain of mountains, plains, valleys, craters and lakes .  Again, this makes Titan unlike anywhere else in the solar system other than Earth.

“Titan has an atmosphere like Earth. It has wind, it has rain, it has mountains,” said Rosaly Lopes, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena.  She and her colleagues wove together images and radar measurements taken by the spacecraft to produce the first global map of the moon.

“Titan has an active methane-based hydrologic cycle that has shaped a complex geologic landscape, making its surface one of most geologically diverse in the solar system,” she said.  “It’s a really very interesting world, and one of the best places in the solar system to look for life,”

Cassini orbited Saturn from 2004 to 2017 and collected vast amounts of information about the ringed gas giant and its moons. The mission included more than 100 fly-bys of Titan,  which allowed researchers to study the moon’s surface through its thick atmosphere and survey its terrain in unprecedented detail.

The first global geologic map of Titan is based on radar and visible-light images from NASA’s Cassini mission.

Their work, which now adds the surface of Titan to the kind of geological mapping done of the surfaces of Mars, Mercury and our moon, was published in Nature Astronomy.Read more

PIXL: A New NASA Instrument For Ferreting Out Clues of Ancient Life on Mars

 

Extremely high definition images of the com ponents of rocks and mud as taken by PIXL, the Planetary Instrument for X-ray Lithochemistry .   On the Mars 2020 rover, PIXL  will have significantly greater capabilities than previous similar instruments sent to Mars.  Rather than reporting bulk compositions averaged over several square centimeters, it will identify precisely where in the rock each element resides. With spatial resolution of about 300 micrometers, PIXL will conduct the first ever petrology investigations on Mars, correlating elemental compositions with visible rock textures . (NASA)J

The search for life, or signs of past life beyond Earth is now a central issue in space science, is central to the mission of NASA, and is actually a potentially breakthrough discovery in the making  for humanity.    The scientific stakes could hardly be higher.

But identifying evidence of ancient microbial life – and refuting all reasonable non-biological explanations for that evidence — is stunningly difficult.

As recent wrangling over Earth’s oldest rocks in Greenland has shown, determining the provenance of a deep-time biosignature even here on Earth is extraordinarily difficult. In 2016, scientists reported discovery of 3,700 million yr-old stromatolites in the Isua geological area of Greenland.

Just three years later, a field workshop held at the Isua discovery site brought experts from around the world to examine the intriguing structures and see whether the evidence cleared the very high bar needed to accept a biological interpretation. While the scientists who published the initial discovery held their ground, not one of the other scientists felt convinced by the evidence before them.  Watching and listening as the different scientists presented their cases was a tutorial in the innumerable factors involved in coming to any conclusion.

Now think about trying to wrestle with similar or more complex issues on Mars, of how scientists can reach of level of confidence to report that a sign (or hint) of past life has apparently been found.

As it turns out, the woman who led the Greenland expedition — Abigail Allwood of NASA’s Jet Propulsion Lab — is also one of the key players in the upcoming effort to find biosignatures on Mars.  She is the principal investigator of the Planetary Instrument for X-ray Lithochemistry (PIXL) that will sit on the extendable arm of the rover, and it has capabilities to see in detail the composition of Mars samples as never before.

The instrument has, of course, been rigorously tested to understand what it can and cannot do. … Read more

On the Ground in Greenland, at the Disputed Ancient Stromatolite Site

Enlarge to full screen on lower right. A pioneering three-dimensional, virtual reality look at a Greenland outcrop earlier described as containing 3.7-billion- year-old stromatolite fossils, which would be the oldest remnant of life on Earth. The video capture, including the drone-assisted overview of the site, is part of a much larger virtual reality effort to document the setting undertaken late in August. As the video focuses in on the scientifically controversial outcrop, cuts are visible in the smooth surfaces that were made by two teams studying the rocks in great detail to determine whether the reported stromatolite fossils are actually present. (Parker Abercrombie, NASA/JPL and Ian Burch, Queensland University of Technology.)

 

Seldom does one rock outcrop get so many visitors in a day, especially when that outcrop is located in rugged, frigid terrain abutting the Greenland Ice Sheet and can be reached only by helicopter.

But this has been a specimen of great importance and notoriety since it appeared from beneath the snow pack some eight years ago. That’s when it was first identified by two startled geologists as something very different from what they had seen in four decades of scouring the geologically revelatory region – the gnarled Isua supercrustal belt – for fossil signs of very early life.

Since that discovery the rock outcrop has been featured in a top journal and later throughout the world as potentially containing the earliest signature of life on Earth – the outlines of half inch to almost two inch-high stromatolite structures between 3.7 and 3.8 billion years old.

The Isua greenstone, or supracrustal belt, which contains some of the oldest known rocks and outcrops in the world, is about 100 miles northeast of the capital, Nuuk.

If Earth could support the life needed to form primitive but hardly uncomplicated stromatolites that close to the initial cooling of the planet, then the emergence of life might not be so excruciatingly complex after all. Maybe if the conditions are at all conducive for life on a planet (early Mars comes quickly to mind) then life will probably appear.

Extraordinary claims in science, however, require extraordinary proof, and inevitably other scientists will want to test the claims.

Within two years of that initial ancient stromatolite splash in a Nature paper (led by veteran geologist Allen Nutman of the University of Wollongong in Australia), the same journal published a study that disputed many of the key observations and conclusions of the once-hailed ancient stromatolite discovery. … Read more

Exploring Early Earth by Using DNA As A Fossil

Betül Kaçar is an assistant professor at the University of Arizona, and a pioneer in the field of paleogenomics — using genetic material to dive back deep into the ancestry of important compounds. (University of Arizona)

Paleontology has for centuries worked to understand the distant past by digging up fossilized remains and analyzing how and why they fit into the evolutionary picture.  The results have been impressive.

But they have been limited.  The evolutionary picture painted relies largely on the discovery of once hard-bodied organisms, with a smattering of iconic finds of soft-bodied creatures.

In recent years, however, a new approach to understanding the biological evolution of life has evolved under the umbrella discipline of paleogenomics.  The emerging field explores ancient life and ancient Earth by focusing on genetic material from ancient organisms preserved in today’s organisms.

These genes can be studied on their own or can be synthetically placed into today’s living organisms to see if, and how, they change behavior.

The goals are ambitious:  To help understand both the early evolution and even the origins of life, as well as to provide a base of knowledge about likely characteristics of potential life on other planets or moons.

“What we do is treat DNA as a fossil, a vehicle to travel back in time,” said Betül Kaçar, an assistant professor at the University of Arizona with more than a decade of experience in the field, often sponsored by the NASA Astrobiology Program and the John Templeton Foundation.  “We build on modern biology, the existing genes, and use what we know from them to construct a molecular tree of life and come up with the ancestral genes of currently existing proteins.”

And then they ask the question of whether and how the expression of those genes — all important biomolecules generally involved in allowing a cell to operate smoothly — has changed over the eons.  It’s a variation on one the basic questions of evolution:  If the film of life were replayed from very early days, would it come out the same?

Cyanobacteria, which was responsible for the build-up of oxygen in the Earth’s atmosphere and the subsequent Great Oxidation Event about 2.5 billion years ago.  Kaçar studies and replaces key enzymes in the cyanobacteria in her effort to learn how those ancestral proteins may have behaved when compared to the same molecules today.

The possibility of such research — of taking what is existing today and reconstructing ancient sequences from it — was first proposed by Emile Zuckerkandl, a biologist known for his work in the 1960s with Linus Pauling on the hypothesis of the “molecular clock.”… Read more

Searching for the Edge of Habitability

Topographical map of Venus by NASA’s Magellan spacecraft (1990 – 1994). Color indicates height. (NASA/JPL/USGS)

How many habitable worlds like our own could exist around other stars? Since the discovery of the first exoplanets, the answer to this question has seemed tantalizingly close. But to estimate the number of Earths, we first need to understand how our planet could have gone catastrophically awry.

In other words, we need to return to Venus.

We have now discovered over 4000 planets beyond our solar system. Approximately one-third of these worlds are Earth-sized and likely to have rocky surfaces not crushed under deep atmospheres. The next step is to discover how many of these support temperate landscapes versus ones unsuitable for life.

The Earth’s habitability is often ascribed to the level of sunlight we receive. We orbit in the so-called ‘habitable zone’ where our planet’s geological cycle can adjust the level of carbon dioxide in our atmosphere to keep our seas liquid. In a closer orbit to the sun, this cycle could not operate fast enough to keep the Earth cool. Our seas would evaporate and our atmosphere fill with carbon dioxide, sending the planet temperature into an upwards spiral known as a runaway greenhouse.

If our solar system had just one Earth-sized planet, this would suggest we could simply count-up similar sized planets in the habitable zones around other stars. This would then be our set of the most likely habitable worlds.

However, this idea is shredded in a new paper posted this month to be published in the Journal of Geophysical Research: Planets. Led by Stephen Kane from the University of California, Riverside, the paper is authored by many of the top planetary scientists we have met before in this column.

Their message is simple: our sun is orbited by two Earth-sized planets but only one is habitable. To identify habitable planets around other stars, we need to explain why the Earth and Venus evolved so differently. And the data suggests this is not just a climate catastrophe.

Orbiting beyond the inner edge of the habitable zone, Venus does appear at first to be a runaway Earth. The planet’s atmosphere is 96.5% carbon dioxide, smothering the surface to escalate temperatures to a staggering 863°F (462°C). Images from NASA’s Pioneer Venus mission in the late 1970s revealed a surface of highlands and lowlands that resembled the continents of Earth. This is all consistent with a picture of an Earth-like planet with a runaway greenhouse atmosphere.… Read more

“Agnostic Biosignatures,” And the Path to Life as We Don’t Know It

Most research into signs of life in our solar system or on distant planets uses life on Earth as a starting point. But now NASA has begun a major project to explore the potential signs of life very different from what we have on Earth.  For example, groups of molecules, like those above, can be analyzed for complexity, regardless of their specific chemical constituents.  ( Brittany Klein/Goddard Space Flight Center)

Biosignatures – evidence that says or suggests that life has been present – are often very hard to find and interpret.

Scientists examining fossilized life on Earth can generally reach some sort of agreement about what is before them, but what about the soft-bodied or even single-celled organisms that were the sum total of life on Earth for much of the planet’s history as a living domain? Scientific disagreements are common.

Now think of trying to determine whether a particular outline on an ancient Martian rock, or a geochemical or surface anomaly on that rock, is a sign of life. Or perhaps an unexpected abundance of a particular compound in one of the water vapor plumes coming out of the moons Europa or Enceladus. Or a peculiar chemical imbalance in the atmosphere of a distant exoplanet as measured in the spectral signature collected via telescope.

These are long-standing issues and challenges, but they have taken on a greater urgency of late as NASA missions  (and those of other space agencies around the world) are being designed to actively look for signs of extraterrestrial life – most likely very simple life – past or present.

And that combination of increased urgency and great difficulty has given rise to at least one new way of thinking about those potential signs of life. Scientists call them “agnostic biosignatures” and they do not presuppose any particular biochemistry.

“The more we explore the solar system and distant exoplanets, the more we find worlds that are really foreign,”  said Sarah Stewart Johnson, at an assistant professor at Georgetown University and principal investigator of the newly-formed Laboratory for Agnostic Biosignatures (LAB).  The LAB team won a five-year, $7 million grant last year from NASA’s Astrobiology Program.

“So our goal is to go beyond our current understandings and find ways to explore the world of life as we don’t know it,” she told me.  “That might mean thinking about a spectrum of how ‘alive’ something might be… And we’re embracing uncertainty, looking as much for biohints as biosignatures.”… Read more

If Bacteria Could Talk

 

Hawaiian lava cave microbial mats appear to have the highest levels and diversity of genes related to quorum sensing so far.  (Stuart Donachie, University of Hawai`i at Mānoa)

Did you know that many bacteria — some of the oldest lifeforms on Earth — can talk?  Really.

And not only between the same kind of single-cell bacteria, but  back and forth with members of other species, too.

Okay, they don’t talk in words or with sounds at all.  But they definitely communicate in a meaningful and essential way, especially in the microbial mats and biofilms (microbes attached to surfaces surrounded by mucus) that constitute their microbial “cities.”

Their “words” are conveyed via chemical signaling molecules — a chemical language — going from one organism to another,  and are a means to control when genes in the bacterial DNA are turned “on” or “off.”  The messages can then be translated into behaviors to protect or enhance the larger (as in often much, much larger) group.

Called “quorum sensing,” this microbial communication was first identified several decades ago.  While the field remains more characterized by questions than definitive answers, is it clearly growing and has attracted attention in medicine, in microbiology and in more abstract computational and robotics work.

Most recently,  it has been put forward as chemically-induced behavior that can help scientists understand how bacteria living in extreme environments on Earth — and potential on Mars —  survive and even prosper.  And the key finding is that bacteria are most successful when they form communities of microbial mats and biofilms, often with different species of bacteria specializing in particular survival capabilities.

Speaking at the recent Astrobiology Science Conference in Seattle,  Rebecca Prescott, a National Science Foundation  Postdoctoral Research Fellow in Biology said this community activity may make populations of bacteria much more hardy than otherwise might be predicted.

 

Quorum sensing requires a community. Isolated Bacteria (and Archaea) have nobody to communicate with and so genes that are activated by quorum sensing are not turned “on.”

“To help us understand where microbial life may occur on Mars or other planets, past or present, we must understand how microbial communities evolve and function in extreme environments as a group, rather than single species,” said Prescott,

“Quorum sensing gives us a peek into the interactive world of bacteria and how cooperation may be key to survival in harsh environments,” she said.

Rebecca Prescott  is a National Science Foundation Postdoctoral Fellow in Biology (1711856) and is working with principal investigator Alan Decho of the University of South Carolina on a NASA Exobiology Program grant.

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