Category: Astrobiology (page 1 of 10)

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.” The molecular clock is figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged.… Read more

A Unique Science Expedition to Greenland

Greenland from above, where the ice sheet is melting to form lakes and to expose rocks not visible for millennia. @Susan Oliver

It is my very good fortune to report that I have just arrived in Greenland for quite a scientific adventure.
 
Over the next days, a group of scientists (along with me and NASA videographer Mike Toillion) will be traveling to the site of the stromatolite that might, or might not, be the oldest remains of life on Earth.  In a 2016 Nature paper, it was described as having been fossilized about 3.7 billion years ago.
 
Another Nature paper two years later challenged the biological origins of the “fossil,” and the debate has been pretty vigorous since.

Vigorously debated putative stromatolite from the Isua Peninsula, Greenland.

We’ll be helicoptering about 100 miles northeast of the capital Nuuk to get to the Isua peninsula, where the oldest (or almost the oldest, depending on who you choose to follow) rock formations on Earth can be found. Three days and two nights on the ice, or what we hope is still ice. And then a day or more of scientific debate.

I will be writing about this and more (some folks involved the Mars 2020 mission will also be testing instruments at the site) for Many Worlds in the days and weeks ahead.

To me this is an important story not only because of the possible age of the stromatolite find.  If confirmed, it would move back the presence of identified life on Earth by 200 million years.

It is also important because of the fact that scientists with different views on this important issue have traveled thousands of miles to go to the site together and try to reach a consensus—or at least to vigorously argue their cases.  Doesn’t often happen in such high profile science.

Greenstone Belt formations on the Isua Peninsula where our team will be headed.

 
Greenland has, of course, been in the news of late for reasons ranging  worrisome purchase offers to far more worrisome warming.  Remarkable are the “moulin” — which drain the water running on the ice sheet and send it down thousands of feet to the water or land below. 
Kind of a ice black hole.

A “moulin” in Greenland that acts as a very deep drain for water melting on the ice sheet.

Now it’s in my news because, well, I’m here in Greenland, to learn, to report back, and to take in everything this spectacular place has to offer.
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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.”

Johnson first visited the acid salt lakes of the Yilgarn Craton of Western Australia as a graduate student at MIT, and has returned multiple with colleagues to understand mineral biosignatures as well as biomarker preservation in this analog environment for early Mars.

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Exoplanets Discoveries Flood in From TESS

NASA’s Transiting Exoplanet Survey Satellite (TESS) has hundreds of “objects of interest” waiting to be confirmed as planets in the data from the space telescope’s four cameras.  These three were the first confirmed TESS discoveries, identified last year during its first three months of observing. By the time the mission is done, TESS’s wide-field cameras will have covered the whole sky in search of transiting exoplanets around 200,000 of the nearest (and brightest) stars. (NASA / MIT / TESS)

The newest space telescope in the sky — NASA’s Transiting Exoplanet Survey Satellite, TESS — has been searching for exoplanets for less than a year, but already it has quite a collection to its name.

The TESS mission is to find relatively nearby planets orbiting bright and stable suns, and so expectations were high from the onset about the discovery of important new planets and solar systems.  At a meeting this week at the Massachusetts Institute of Technology devoted to TESS  results,  principal investigator George Ricker pronounced the early verdict.

The space telescope, he said,  “has far exceeded our most optimistic hopes.”  The count is up to 21 new planets and 850 additional  candidate worlds waiting to be confirmed.

Equally or perhaps more important is that the planets and solar systems being discovered promise important results.  They have not yet included any Earth-sized rocky planet in a sun’s habitable zone — what is generally considered the most likely, though hardly the only, kind of planet to harbor life — but they did include planets that offer a great deal when it comes to atmospheres and how they can be investigated.

This infographic illustrates key features of the TOI 270 system, located about 73 light-years away in the southern constellation Pictor. The three known planets were discovered by NASA’s Transiting Exoplanet Survey Satellite through periodic dips in starlight caused by each orbiting world. Insets show information about the planets, including their relative sizes, and how they compare to Earth. Temperatures given for TOI 270’s planets are equilibrium temperatures, (NASA’s Goddard Space Flight Center/Scott Wiessinger)

One of the newest three-planet system is called TOI-270, and it’s about 75 light years from Earth. The star at the center of the system is a red dwarf, a bit less than half the size of the sun.

Despite its small size, it’s brighter than most of the nearby stars we know host planets. And it’s stable, making its solar system especially valuable.

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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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Hayabusa2 Snatches Second Asteroid Sample

Artist impression of the Hayabusa2 spacecraft touching down on asteroid Ryugu (JAXA / Akihiro Ikeshita)

“1… 2… 3… 4…”

The counting in the Hayabusa2 control room at the Japan Aerospace Exploration Agency’s Institute of Space and Astronautical Sciences (JAXA, ISAS) took on a rhythmic beat as everyone in the room took up the chant, their eyes fixed on the large display mounted on one wall.

“10… 11… 12… 13…”

The display showed the line-of-sight velocity (speed away from or towards the Earth) of the Hayabusa2 spacecraft. The spacecraft was about 240,000,000 km from the Earth where it was studying a near-Earth asteroid known as Ryugu. At this moment, the spacecraft was dropping to the asteroid surface to collect a sample of the rocky body.

“20… 21… 22… 23…”

Asteroid Ryugu from an altitude of 6km. Image was captured with the Optical Navigation Camera – Telescopic (ONC-T) on July 20, 2018 ( JAXA, University of Tokyo & collaborators)

Asteroid Ryugu is a carbonaceous or “C-type” asteroid; a class of small celestial bodies thought to contain organic material and undergone relatively little alteration since the beginning of the Solar System. Rocks similar to Ryugu would have pelted the early Earth, possibly delivering both water and the first ingredients for life to our young planet. Where and when these asteroids formed and how they moved through the Solar System is therefore a question of paramount importance to understanding how terrestrial planets like the Earth became habitable. It is a question not only tied to our own existence, but also to assessing the prospect of life elsewhere in the Universe.

The Hayabusa2 mission arrived at asteroid Ryugu just over one year ago at the end of June 2018. The spacecraft remotely analyzed the asteroid and deployed two rovers and a lander to explore the surface. Then in February of this year, the spacecraft performed its own descent to touchdown and collect a sample. The material gathered will be analyzed back on Earth when the spacecraft returns home at the end of 2020.

Touchdown is one of the most dangerous operation in the mission. The distances involved mean that it took about 19 minutes to communicate with the spacecraft during the first touchdown and 13 minutes during the second touchdown, when the asteroid had moved slightly closer to Earth. Both these durations are too long to manually guide the spacecraft to the asteroid surface.… Read more

NASA Announces Astrobiology Mission to Titan

 

The Dragonfly drone has been selected as the next New Frontiers mission, this time to Saturn’s moon Titan.  Animation of the vehicle taking off from the surface of the moon. (NASA)

A vehicle that flies like a drone and will try to unravel some of the mysteries of Saturn’s moon Titan was selected yesterday to be the next New Frontiers mission to explore the solar system.

Searching for the building blocks of life,  the Dragonfly mission will be able to fly multiple sorties to sample and examine sites around Saturn’s icy moon.

Titan has a thick atmosphere and features a variety of hydrocarbons, with rivers and lakes of methane, ethane and natural gas, as well as and precipitation cycles like on Earth.  As a result, Dragonfly has been described as an astrobiology mission because it will search for signs of the prebiotic environments like those on Earth that gave rise to life.

“Titan is unlike any other place in the solar system, and Dragonfly is like no other mission,” said Thomas Zurbuchen, NASA’s associate administrator for science at the agency headquarters in Washington.

“It’s remarkable to think of this rotorcraft flying miles and miles across the organic sand dunes of Saturn’s largest moon, exploring the processes that shape this extraordinary environment. Dragonfly will visit a world filled with a wide variety of organic compounds, which are the building blocks of life and could teach us about the origin of life itself.”

 

Saturn’s moon Titan is significantly larger than our moon, and larger than the planet Mercury. It features river channels of ethane and methane, and lakes of liquified natural gas. It is the only other celestial body in our solar system that has flowing liquid on its surface. (NASA)

As described in a NASA release, Titan is an analog to the very early Earth, and can provide clues to how life may have arisen on our planet.

Dragonfly will explore environments ranging from organic dunes to the floor of an impact crater where liquid water and complex organic materials key to life once existed together for possibly tens of thousands of years. Its instruments will study how far prebiotic chemistry may have progressed.

They also will investigate the moon’s atmospheric and surface properties and its subsurface ocean and liquid reservoirs. Additionally, instruments will search for chemical evidence of past or extant life.

Because it is so far from the sun, Titan’s surface temperature is around -290 degrees Fahrenheit and its surface pressure is 50 percent higher than Earth’s.… Read more

Methane on Mars. Here Today, Gone Tomorrow

On the 2,440th Martian day at Gale Crater, the Curiosity rover detected a large spike in the presence of the gas methane. It was by far the largest plume detected by the rover, and parallels an earlier ground-based discovery of an even larger plume of the gas.  (NASA, JPL-Caltech, MSSS)

The presence — and absence — of methane gas on Mars has been both very intriguing and very confusing for years.  And news coming out last week and then on Monday adds to this scientific mystery.

To the great surprise of the Curiosity rover team, their Sample Analysis on Mars instrument sent back a measurement of 21 parts per billion of methane on Thursday — by far the highest measurement since the rover landed at Gale Crater.

As Paul Mahaffy, principal investigator of the instrument that made the measurement, described it yesterday at a large astrobiology conference in Seattle, “We were dumbfounded.”

And then a few days later, all the methane was gone.   Mahaffy, and NASA headquarters, reported that the readings went down quickly to below 1 part per billion.

These perplexing findings are especially important because methane could — and also could not — be a byproduct of biology.  On Earth, more than 90 percent of methane is produced via biology.  On Mars — at this point, nobody knows.  But the question has certainly gotten scientists’ attention.

The most recent finding of a return to low methane levels suggests that last week’s methane detection was one of the transient methane plumes that have been observed in the past. While Curiosity scientists have noted background levels rise and fall seasonally, they haven’t found a pattern in the occurrence of these transient plumes.

“The methane mystery continues,” said Ashwin Vasavada, Curiosity’s project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “We’re more motivated than ever to keep measuring and put our brains together to figure out how methane behaves in the Martian atmosphere.”

This image was taken by the left Navcam on the Curiosity Mars rover on June 18, 2019, the day when a methane plume was detected.  It shows part of “Teal Ridge,” which the rover has been studying within a region called the “clay-bearing unit.” (NASA/JPL-Caltech)

The nature and size of this most recent methane plume will, by chance, be the most widely observed so far.

That’s because the Mars Express orbiter happened to be performing spot tracking observations at the Gale Crater right around the time Curiosity detected the methane spike. … Read more

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