Astrobiology Archives

August 10, 2009December 24, 2015 by Anne Minard

Sun, Earth Are Unlikely Pair to Support Life

The violent youth of solar proxies. Courtesy of IAU.

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We don’t know how lucky we are — really.

We know the interaction between Earth and Sun is a rarity in that it allowed life to form. But scientists working to understand the possibility that it could have happened elsewhere in the Universe are still far from drawing conclusions.

What is becoming clearer is that life probably shouldn’t have formed here; the Earth and Sun are unlikely hosts.
A series of presentations at this year’s meeting of the International Astronomical Union meeting, in Brazil last week, focused on the role of the Sun and Sun-like stars in the formation of life on planets like Earth.

Edward Guinan, a professor of astronomy and astrophysics at Villanova University in Pennsylvania, and his collaegues have been studying Sun-like stars as windows into the origin of life on Earth, and as indicators of how likely life is elsewhere in the cosmos. The work has revealed that the Sun rotated more than ten times faster in its youth (over four billion years ago) than today. The faster a star rotates, the harder the magnetic dynamo at its core works, generating a stronger magnetic field, so the young Sun emitted X-rays and ultraviolet radiation up to several hundred times stronger than it does today.

A team led by Jean-Mathias Grießmeier from ASTRON in the Netherlands looked at another type of magnetic fields — that around planets. They found that the presence of planetary magnetic fields plays a major role in determining the potential for life on other planets as they can protect against the effects of both stellar particle onslaughts.

“Planetary magnetic fields are important for two reasons: they protect the planet against the incoming charged particles, thus preventing the planetary atmosphere from being blown away, and also act as a shield against high energy cosmic rays,” Grießmeier said. “The lack of an intrinsic magnetic field may be the reason why today Mars does not have an atmosphere.”

All things considered, the Sun does not seem like the perfect star for a system where life might arise, added Guinan.

“Although it is hard to argue with the Sun’s ‘success’ as it so far is the only star known to host a planet with life, our studies indicate that the ideal stars to support planets suitable for life for tens of billions of years may be a smaller slower burning ‘orange dwarf’ with a longer lifetime than the Sun — about 20-40 billion years,” he said.

Such stars, also called K stars, “are stable stars with a habitable zone that remains in the same place for tens of billions of years,” he added. “They are 10 times more numerous than the Sun, and may provide the best potential habitat for life in the long run.”

Not are planets like Earth the best places to harbor life, he said. Planets double or triple the size of Earth would do a better job of hanging onto an atmosphere and maintaining a magnetic field: “Furthermore, a larger planet cools more slowly and maintains its magnetic protection.”

Manfred Cuntz, an associate professor of physics at the University of Texas at Arlington, and his collaborators have examined both the damaging and the favorable effects of ultraviolet radiation from stars on DNA molecules. This allows them to study the effect on other potential carbon-based extraterrestrial life forms in the habitable zones around other stars. Cuntz says: “The most significant damage associated with ultraviolet light occurs from UV-C, which is produced in enormous quantities in the photosphere of hotter F-type stars and further out, in the chromospheres, of cooler orange K-type and red M-type stars. Our Sun is an intermediate, yellow G-type star. The ultraviolet and cosmic ray environment around a star may very well have ‘chosen’ what type of life could arise around it.”

Rocco Mancinelli, an astrobiologist with the Search for Extraterrestrial Life (SETI) Institute in California, observes that as life arose on Earth at least 3.5 billion years ago, it must have withstood a barrage of intense solar ultraviolet radiation for a billion years before the oxygen released by these life forms formed the protective ozone layer. Mancinelli studies DNA to delve into some of the ultraviolet protection strategies that evolved in early life forms and still persist in a recognizable form today. As any life in other planetary systems must also contend with radiation from their host stars, these methods for repairing and protecting organisms from ultraviolet damage serve as models for life beyond Earth. Mancinelli says “We also see ultraviolet radiation as a kind of selection mechanism. All three domains of life that exist today have common ultraviolet protection strategies such as a DNA repair mechanism and sheltering in water or in rocks. Those that did not were likely wiped out early on.”

The scientists agree that we do yet know how ubiquitous or how fragile life is, but as Guinan concludes: “The Earth’s period of habitability is nearly over — on a cosmological timescale. In a half to one billion years the Sun will start to be too luminous and warm for water to exist in liquid form on Earth, leading to a runaway greenhouse effect in less than 2 billion years.”

Why is the Sun yellow?

Source: International Astronomical Union (IAU). A link to the meeting is here.

July 30, 2009December 24, 2015 by Brian Ventrudo

Sub-surface Oceans In Early Comets Suggest Possible Origin of Life

A view of NASA's Deep Impact probe colliding with comet Tempel 1, captured by the Deep Impact flyby spacecraft's high-resolution instrument.

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A new study claims early comets contained vast interior oceans of liquid water that may have provided the ideal conditions for early life to form.

In a paper published in the International Journal of Astrobiology, Professor Chandra Wickramasinghe and his colleagues at the Cardiff Centre for Astrobiology suggest the watery environment of early comets, together with the vast quantity of organics already discovered in comets, would have provided ideal conditions for primitive bacteria to grow and multiply during the first 1 million years of a comet’s life.

The Cardiff team has calculated the thermal history of comets after they formed from interstellar and interplanetary dust approximately 4.5 billion years ago. The formation of the solar system itself is thought to have been triggered by shock waves that emanated from the explosion of a nearby supernova. The supernova injected radioactive material such as Aluminium-26 into the primordial solar system and some became incorporated in the comets. Professor Chandra Wickramasinghe together with Drs Janaki Wickramasinghe and Max Wallis claim that the heat emitted from radioactivity warms initially frozen material of comets to produce subsurface oceans that persist in a liquid condition for a million years.

Professor Wickramasinghe said: “These calculations, which are more exhaustive than any done before, leaves little doubt that a large fraction of the 100 billion comets in our solar system did indeed have liquid interiors in the past.

Comets in recent times could also liquefy just below their surfaces as they approach the inner solar system in their orbits. Evidence of recent melting has been discovered in recent pictures of comet Tempel 1 taken by the “Deep Impact” probe in 2005.”

The existence of liquid water in comets gives added support for a possible connection between life on Earth and comets. The theory, known as cometary panspermia, pioneered by Chandra Wickramasinghe and the late Sir Fred Hoyle argues the case that life was introduced to Earth by comets.

Source: University of Cardiff

July 17, 2009December 24, 2015 by Anne Minard

Ancient Domes Reveal 3.45-billion-year-old Life History

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Ancient, dome-like rock structures contain clues that life was active on Earth 3.45 billion years ago, according to new research — and the findings could help shed light on life’s history on Earth and other planets, including Mars.

Abigail Allwood, who studies planetary habitability at NASA’s Jet Propulsion Laboratory, led the research. She and her colleagues studied stromatolites, which are dome- or column-like sedimentary rock structures formed in shallow water, layer by layer, over long periods of geologic time.

Geologists have long known that the large majority of the relatively young stromatolites they study—those half a billion years old or so—have a biological origin; they’re formed with the help of layers of microbes that grow in a thin film on the seafloor.

The microbes’ surface is coated in a mucilaginous substance to which sediment particles rolling past get stuck.

“It has a strong flypaper effect,” said John Grotzinger, a Caltech geologist and a study co-author. In addition, the microbes sprout a tangle of filaments that almost seem to grab the particles as they move along. “The end result,” Grotzinger explains, “is that wherever the mat is, sediment gets trapped.”

So in a young stromalite, dark bands like those seen in the close-up cross section at left indicate organic material. But 3.45 billion years ago, in the early Archean period of geologic history, things weren’t quite so simple.

“Because stromatolites from this period of time have been around longer, more geologic processing has happened,” Grotzinger says. Pushed deeper toward the center of Earth as time went by, these stromatolites were exposed to increasing, unrelenting heat. This is a problem when it comes to examining the stromatolites’ potential biological beginnings, he explains, because heat degrades organic matter. “The hydrocarbons are driven off,” he says. “What’s left behind is a residue of nothing but carbon.”

As such, geologists debate whether or not the carbon found in these ancient rocks is diagnostic of life.

Allwood and her team turned to the texture and morphology of the rocks themselves, from samples gathered in Western Australia. The samples, says Grotzinger, were “incredibly well preserved.” Dark lines of what was potentially organic matter were “clearly associated with the lamination, just like we see in younger rocks. That sort of relationship would be hard to explain without a biological mechanism.”

Allwood set about trying to find other types of evidence. She looked at what she calls the “microscale textures and fabrics in the rocks, patterns of textural variation through the stromatolites and—importantly—organic layers that looked like actual fossilized organic remnants of microbial mats within the stromatolites.”

She saw “discrete, matlike layers of organic material that contoured the stromatolites from edge to edge, following steep slopes and continuing along low areas without thickening.” She also found pieces of microbial mat incorporated into storm deposits, which disproved the idea that the organic material had been introduced into the rock more recently, rather than being laid down with the original sediment.

“In addition,” Allwood notes, “Raman spectroscopy showed that the organics had been ‘cooked’ to the same burial temperature as the host rock, again indicating the organics are not young contaminants.”

Allwood said she, Grotzinger, and their team have collected enough evidence that it’s no longer a great leap to accept the stromatolites as biological in origin. And the researchers say the implications of the findings don’t stop at life on Earth.

“One of my motivations for understanding stromatolites,” Allwood says, “is the knowledge that if microbial communities once flourished on Mars, of all the traces they might leave in the rock record for us to discover, stromatolite and microbial reefs are arguably the most easily preserved and readily detected. Moreover, they’re particularly likely to form in evaporative, mineral-precipitating settings such as those that have been identified on Mars. But to be able to interpret stromatolitic structures, we need a much more detailed understanding of how they form.”

Both images courtesy of Abigail Allwood.

Source: Eurekalert, a media service of the American Association for the Advancement of Science (AAAS). The research appeared in online June 10 and in print June 16 in the Proceedings of the National Academy of Sciences (PNAS).

June 24, 2009December 24, 2015 by Anne Minard

Does Enceladus Harbor a Liquid Ocean? Reasonable Minds Disagree

Image of Enceladus from Cassini. Credit: NASA/JPL/Space Science Institute

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Two papers in the journal Nature this week come down on opposite sides of the question about whether Saturn’s moon Enceladus contains a salty, liquid ocean.

One research team, from Europe, says an enormous plume of water spurting in giant jets from the moon’s south pole is fed by a salty ocean. The other group, led out of the University of Colorado at Boulder, contends that the supposed geysers don’t have enough sodium to come from an ocean. The truth could have implications for the search for extraterrestrial life, as well as our understanding of how planetary moons are formed.

The Cassini spacecraft first spotted the plume on its exploration of the giant ringed planet in 2005. Enceladus ejects water vapor, gas and tiny grains of
ice into space hundreds of kilometers above the moon’s surface.

The moon, which orbits in Saturn’s outermost “E” ring, is one of only
three outer solar system bodies that produce active eruptions of dust
and vapor. Moreover, aside from the Earth, Mars, and Jupiter’s moon
Europa, it is one of the only places in the solar system for which
astronomers have direct evidence of the presence of water.

The European researchers, led by Frank Postberg of the University of Heidelberg in Germany, are reporting the detection of sodium salts among the dust ejected in the Enceladus plume. Postberg and colleagues have studied data from the Cosmic Dust Analyzer (CDA) onboard the Cassini
spacecraft and have combined the data with laboratory experiments.

They say the icy grains in the Enceladus plume contain
substantial quantities of sodium salts, hinting at the salty ocean
deep below.

The results of their study imply that the concentration of sodium chloride in the ocean can be as high as that of Earth’s oceans and is about 0.1-0.3 moles of salt per kilogram of water.

But the Colorado study suggests a different interpretation.

Nicholas Schneider, of CU-Boulder’s Laboratory for Atmospheric and Space Physics, and his colleagues say high amounts of sodium in the plume should give off the same yellow light that comes off street lights, and that the world’s best telescopes can detect even a small number of sodium atoms orbiting Saturn.

Schneider’s team usied the 10-meter Keck 1 telescope and the 4-meter Anglo-Australian telescope, and demonstrated that few if any sodium atoms existed in the water vapor. “It would have been very exciting to support the geyser hypothesis. But it is not what Mother Nature is telling us,” said Schneider.

One suggested explanation for the contrasting results, said Schneider, is that deep caverns may exist where water evaporates slowly. When the evaporation process is slow the vapor contains little sodium, just like water evaporating from the ocean. The vapor turns into a jet because it leaks out of small cracks in the crust into the vacuum of space.

“Only if the evaporation is more explosive would it contain more salt,” he said. “This idea of slow evaporation from a deep cavernous ocean is not the dramatic idea that we imagined before, but it is possible given both our results so far.”

But Schneider also cautions that several other explanations for the jets are equally plausible. “It could still be warm ice vaporizing away into space. It could even be places where the crust rubs against itself from tidal motions and the friction creates liquid water that would then evaporate into space,” he said.

“These are all hypotheses but we can’t verify any one with the results so far,” said Schneider. “We have to take them all with, well, a grain of salt.”

Lead photo caption: Image of Enceladus from Cassini. Credit: NASA/JPL/Space Science Institute

Sources: Press releases from CU Boulder and the University of Leicester, via Nature and Eurekalert (a news service through the American Association for the Advancement of Science).

June 15, 2009December 24, 2015 by Anne Minard

Tiny, Deep-Frozen Greenland Bacterium May Hold Extra-Terrestrial Clues

Courtesy of Pennsylvania State University

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Researchers have breathed new life into a bacterium trapped deep under glacial ice in Greenland — for over 120,000 years.

The researchers, who hail from Pennsylvania State University, say the newly discovered bacterium may hold clues as to what life forms might be frozen on other planets.

Jennifer Loveland-Curtze and her team of scientists at Penn State report finding the novel microbe, which they have called Herminiimonas glaciei, in the current issue of the International Journal of Systematic and Evolutionary Microbiology.

From samples recovered nearly two miles (more than 3 kilometers) in a Greenland glacier, the team coaxed the dormant microbe back to life, first incubating their samples at 2 degrees C (35 degrees F) for seven months and then at 5 degrees C (41 degrees F) for four and a half months more, after which colonies of very small purple-brown bacteria were seen.

H. glaciei is small even by bacterial standards – it is 10 to 50 times smaller than E. coli. Its small size probably helped it to survive in the liquid veins among ice crystals and the thin liquid film on their surfaces. Small cell size is considered to be advantageous for more efficient nutrient uptake, protection against predators and occupation of micro-niches and it has been shown that ultramicrobacteria are dominant in many soil and marine environments.

Most life on our planet has always consisted of microorganisms, so it is reasonable to consider that this might be true on other planets as well. Studying microorganisms living under extreme conditions on Earth may provide insight into what sorts of life forms could survive elsewhere in the solar system.

“These extremely cold environments are the best analogues of possible extraterrestrial habitats,” Loveland-Curtze said. “The exceptionally low temperatures can preserve cells and nucleic acids for even millions of years. H. glaciei is one of just a handful of officially described ultra-small species and the only one so far from the Greenland ice sheet; studying these bacteria can provide insights into how cells can survive and even grow under extremely harsh conditions, such as temperatures down to -56 degrees C (-68 degrees F), little oxygen, low nutrients, high pressure and limited space.”

The tiny bacteria also provide a warning about more common bacteria on Earth, Loveland-Curtze pointed out.

“H. glaciei isn’t a pathogen and is not harmful to humans,” she said, “but it can pass through a 0.2 micron filter, which is the filter pore size commonly used in sterilization of fluids in laboratories and hospitals. If there are other ultra-small bacteria that are pathogens, then they could be present in solutions presumed to be sterile.”

Source: Eurekalert

June 5, 2009December 24, 2015 by Brian Ventrudo

So Where Is ET, Anyway?

While having lunch with colleagues at Los Alamos National Labs in 1950, physicist Enrico Fermi mused about the likelihood of intelligent life existing elsewhere in the Universe. Fermi, one of the most astute scientists of his day, thought the size and age of the Universe means many advanced civilizations should have already colonized the galaxy, just as humans colonized and explored the Earth. But if such galaxy-wide extraterrestrial civilizations exist, he wondered, where are they?

Some believe this problem, called the Fermi Paradox, means advanced extraterrestrial societies are rare or nonexistent. Others suggest they must destroy themselves before they move on to the stars.

But this week, Jacob D. Haqq-Misra and Seth D. Baum at Penn State University proposed another solution to the Fermi Paradox: that extraterrestrial civilizations haven’t colonized the galaxy because the exponential growth of a civilization required to do so is unsustainable.

The researchers call their idea the “Sustainability Solution”. It states: “The absence of ETI (extra-terrestrial intelligence) observation can be explained by the possibility that exponential or other faster growth is not a sustainable development pattern for intelligent civilizations.”

The researchers base their conclusions on a study of civilizations on Earth. Historically, rapid growth of societies means rapid resource depletion and environmental degradation, usually with dire results. They cite the example of Easter Island, where resource depletion likely caused a collapse of the local population. And they conclude that while there are examples of sustainable growth like the !Kung San people of the Kalahari Desert, exponential growth in population and spatial expansion of a society is almost always linked to unsustainable growth and eventual collapse.

This principle has implications for our current global civilization. Since Earth’s resources are finite and it receives solar radiation at a constant rate, human civilization cannot sustain an indefinite, exponential growth. But even if we survive and advance as a civilization, we may have trouble colonizing the galaxy should we ever decide to do so. And if this limitation applies to us, it may apply to other civilizations as well.

But the Sustainability Solution doesn’t mean ET is not out there. Slower-growth extraterrestrial societies might still communicate by radio or other wavelengths, so current SETI programs still make sense. Or ETI may result in chemical bio-markers in planetary atmospheres which may leave spectroscopic signatures detectable with upcoming generations of Earth and space-based planet-hunting telescopes.

The Sustainability Solution also allows that advanced civilizations may indeed colonize the galaxy, then collapse as resources are consumed at an unsustainable rate.

And some civilizations may send small messenger probes to other stars, which suggests a search for extraterrestrial artifacts (SETA) within our own solar system might be just as fruitful as radio-based SETI. Searches might involve radio or visible detection of extraterrestrial probes orbiting the sun. Or artifacts may even be embedded within planets or moons of our solar system, just like the giant black monoliths in Arthur C. Clarke’s 2001: A Space Odyssey.

In any case, the discovery of artifacts from a slow-growth extraterrestrial civilization would be an example “sustainable development” on a galactic scale.

You can read the original article here.

April 9, 2009December 24, 2015 by Anne Minard

Without Nickel, Life on Earth Could Finally Breathe

Caption: Banded iron formations like this from northern Michigan contain evidence of a drop in dissolved nickel in ancient oceans. Credit: Carnegie Institution for Science

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Researchers have long puzzled over why oxygen flourished in Earth’s atmosphere starting around 2.4 billion years.

Called the “Great Oxidation Event,” the transition “irreversibly changed surface environments on Earth and ultimately made advanced life possible,” said Dominic Papineau of the Carnegie Institution’s Geophysical Laboratory.

Now, Papineau has co-authored a new study in the journal Nature, which reveals new clues to the mystery in ancient sedimentary rocks.

The research team, led by Kurt Konhauser of the University of Alberta in Edmonton, analyzed the trace element composition of sedimentary rocks known as banded-iron formations, or BIFs, from dozens of different localities around the world, ranging in age from 3,800 to 550 million years. Banded iron formations are unique, water-laid deposits often found in extremely old rock strata that formed before the atmosphere or oceans contained abundant oxygen. As their name implies, they are made of alternating bands of iron and silicate minerals.

They also contain minor amounts of nickel and other trace elements. And the history of nickel, the researchers think, may reveal a secret to the origin of modern life.

Nickel exists in today’s oceans in trace amounts, but was up to 400 times more abundant in the Earth’s primordial oceans. Methane-producing microorganisms, called methanogens, thrive in such environments, and the methane they released to the atmosphere might have prevented the buildup of oxygen gas, which would have reacted with the methane to produce carbon dioxide and water.

A drop in nickel concentration would have led to a “nickel famine” for the methanogens, who rely on nickel-based enzymes for key metabolic processes. Algae and other organisms that release oxygen during photosynthesis use different enzymes, and so would have been less affected by the nickel famine. As a result, atmospheric methane would have declined, and the conditions for the rise of oxygen would have been set in place.

The researchers found that nickel levels in the BIFs began dropping around 2.7 billion years ago and by 2.5 billion years ago was about half its earlier value.

“The timing fits very well. The drop in nickel could have set the stage for the Great Oxidation Event,” Papineau said. “And from what we know about living methanogens, lower levels of nickel would have severely cut back methane production.”

As for why nickel dropped in the first place, the researchers point to geology. During earlier phases of the Earth’s history, while its mantle was extremely hot, lavas from volcanic eruptions would have been relatively high in nickel. Erosion would have washed the nickel into the sea, keeping levels high. But as the mantle cooled, and the chemistry of lavas changed, volcanoes spewed out less nickel, and less would have found its way to the sea.

“The nickel connection was not something anyone had considered before,” Papineau said. “It’s just a trace element in seawater, but our study indicates that it may have had a huge impact on the Earth’s environment and on the history of life.”

Source: Carnegie Institution for Science, via Eurekalert.

April 7, 2009December 24, 2015 by Nancy Atkinson

Would Life Form Differently Around Cool Stars?

This artist's conception shows a young, hypothetical planet around a cool star. Credit: JPL

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“Life as we know it” seems to be the common caveat in our search for other living things in the Universe. But there’s also the possibility of life “as we don’t know it.” A new study from NASA’s Spitzer Space Telescope hints that planets around stars cooler than our sun might possess a different mix of potentially life-forming, or “prebiotic,” chemicals. While life on Earth is thought to have arisen from a hot soup of different chemicals, would the same life-generating mix come together around other stars with different temperatures? (And should we call it ‘The Gazpacho Effect?’) “Prebiotic chemistry may unfold differently on planets around cool stars,” said Ilaria Pascucci, lead author of the new study.

Pascussi and her team used Spitzer to examine the planet-forming disks around 17 cool and 44 sun-like stars. The stars are all about one to three million years old, an age when planets are thought to be forming. The astronomers specifically looked for ratios of hydrogen cyanide to a baseline molecule, acetylene. Using Spitzer’s infrared spectrograph, an instrument that breaks light apart to reveal the signatures of chemicals, the researchers looked for a prebiotic chemical, called hydrogen cyanide, in the planet-forming material swirling around the stars. Hydrogen cyanide is a component of adenine, which is a basic element of DNA. DNA can be found in every living organism on Earth.

The researchers detected hydrogen cyanide molecules in disks circling 30 percent of the yellow stars like our sun — but found none around cooler and smaller stars, such as the reddish-colored “M-dwarfs” and “brown dwarfs” common throughout the universe.

Cool Stars May Have Different Prebiotic Chemical Mix

The team did detect their baseline molecule, acetylene, around the cool stars, demonstrating that the experiment worked. This is the first time that any kind of molecule has been spotted in the disks around cool stars.

“Perhaps ultraviolet light, which is much stronger around the sun-like stars, may drive a higher production of the hydrogen cyanide,” said Pascucci.

Young stars are born inside cocoons of dust and gas, which eventually flatten to disks. Dust and gas in the disks provide the raw material from which planets form. Scientists think the molecules making up the primordial ooze of life on Earth might have formed in such a disk. Prebiotic molecules, such as adenine, are thought to have rained down to our young planet via meteorites that crashed on the surface.

“It is plausible that life on Earth was kick-started by a rich supply of molecules delivered from space,” said Pascucci.

The findings have implications for planets that have recently been discovered around M-dwarf stars. Some of these planets are thought to be large versions of Earth, the so-called super Earths, but so far none of them are believed to orbit in the habitable zone, where water would be liquid. If such a planet is discovered, could it sustain life?

Astronomers aren’t sure. M-dwarfs have extreme magnetic outbursts that could be disruptive to developing life. But, with the new Spitzer results, they have another piece of data to consider: these planets might be deficient in hydrogen cyanide, a molecule thought to have eventually become a part of us.

Said Douglas Hudgins, the Spitzer program scientist at NASA Headquarters, Washington, “Although scientists have long been aware that the tumultuous nature of many cool stars might present a significant challenge for the development of life, this result begs an even more fundamental question: Do cool star systems even contain the necessary ingredients for the formation of life? If the answer is no then questions about life around cool stars become moot.”

Or, could life form differently around cooler stars from anything we know?

Source: JPL

March 17, 2009December 24, 2015 by Nancy Atkinson

Molecules From Space May Have Affected Life On Earth

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A decade ago researchers analyzed amino acids from space, brought to Earth in meteorite which landed in Australia, finding a prevalence of “left-handed” amino acids over their “right-handed” form. Now, a new study of dust from meteorites supports this finding, and offers new clues to a long-standing mystery about how life works on its most basic, molecular level. “We found more support for the idea that biological molecules, like amino acids, created in space and brought to Earth by meteorite impacts help explain why life is left-handed,” said Dr. Daniel Glavin of NASA’s Goddard Space Flight Center in Greenbelt, Md. “By that I mean why all known life uses only left-handed versions of amino acids to build proteins.”

20 different amino acids arrange themselves in a variety of ways to build millions of different proteins. Amino acid molecules can be built in two ways that are mirror images of each other, like your hands. Although life based on right-handed amino acids would presumably work fine, “you can’t mix them,” says Dr. Jason Dworkin of NASA Goddard, co-author of the study. “If you do, life turns to something resembling scrambled eggs — it’s a mess. Since life doesn’t work with a mixture of left-handed and right-handed amino acids, the mystery is: how did life decide — what made life choose left-handed amino acids over right-handed ones?”

Over the last four years, a team lead by Glavin, carefully analyzed samples of meteorites with an abundance of carbon, called carbonaceous chondrites. The researchers looked for the amino acid isovaline and discovered that three types of carbonaceous meteorites had more of the left-handed version than the right-handed variety – as much as a record 18 percent more in the often-studied Murchison meteorite. “Finding more left-handed isovaline in a variety of meteorites supports the theory that amino acids brought to the early Earth by asteroids and comets contributed to the origin of only left-handed based protein life on Earth,” said Glavin.

All amino acids can switch from left-handed to right, or the reverse, by chemical reactions energized with radiation or temperature, according to the team. The scientists looked for isovaline because it has the ability to preserve its handedness for billions of years, and it is extremely rarely used by life, so its presence in meteorites is unlikely to be from contamination by terrestrial life. “The meteorites we studied are from before Earth formed, over 4.5 billion years ago,” said Glavin. “We believe the same process that created extra left-handed isovaline would have created more left-handed versions of the other amino acids found in these meteorites, but the bias toward left-handed versions has been mostly erased after all this time.”

The team’s discovery validates and extends the research first reported a decade ago by Drs. John Cronin and Sandra Pizzarello of Arizona State University, who were first to discover excess isovaline in the Murchison meteorite, believed to be a piece of an asteroid. “We used a different technique to find the excess, and discovered it for the first time in the Orgueil meteorite, which belongs to another meteorite group believed to be from an extinct comet,” said Glavin.

The team also found a pattern to the excess. Different types of meteorites had different amounts of water, as determined by the clays and water-bearing minerals found in the meteorites. The team discovered meteorites with more water also had greater amounts of left-handed isovaline. “This gives us a hint that the creation of extra left-handed amino acids had something to do with alteration by water,” said Dworkin. “Since there are many ways to make extra left-handed amino acids, this discovery considerably narrows down the search.”

If the bias toward left-handedness originated in space, it makes the search for extraterrestrial life in our solar system more difficult, while also making its origin a bit more likely, according to the team. “If we find life anywhere else in our solar system, it will probably be microscopic, since microbes can survive in extreme environments,” said Dworkin. “One of the biggest problems in determining if microscopic life is truly extra-terrestrial is making sure the sample wasn’t contaminated by microbes brought from Earth. If we find the life is based on right-handed amino acids, then we know for sure it isn’t from Earth. However, if the bias toward left-handed amino acids began in space, it likely extends across the solar system, so any life we may find on Mars, for example, will also be left-handed. On the other hand, if there is a mechanism to choose handedness before life emerges, it is one less problem prebiotic chemistry has to solve before making life. If it was solved for Earth, it probably has been solved for the other places in our solar system where the recipe for life might exist, such as beneath the surface of Mars, or in potential oceans under the icy crust of Europa and Enceladus, or on Titan.”

The team’s paper appears in the March 16 Proceedings of the National Academy of Sciences.

Source: Astrobiology Magazine

March 16, 2009December 24, 2015 by Anne Minard

Indian Balloon Experiment Nets Three New Bacteria

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Indian scientists flying a giant balloon experiment have announced the discovery of three new species of bacteria from the stratosphere.

In all, 12 bacterial and six fungal colonies were detected, nine of which, based on gene sequencing, showed greater than 98 percent similarity with reported known species on earth. Three bacterial colonies, however, represented totally new species. All three boast significantly higher UV resistance compared to their nearest phylogenetic neighbors on Earth.

The experiment was conducted using a balloon that measures 26.7 million cubic feet (756,059 cubic meters) carrying 1,000 pounds (459 kg) of scientific payload soaked in liquid Neon. It was flown from the National Balloon Facility in Hyderabad, operated by the Tata Institute of Fundamental Research (TIFR).

An onboard cryosampler contained sixteen evacuated and sterilized stainless steel probes. Throughout the flight, the probes remained immersed in liquid Neon to create a cryopump effect. The cylinders, after collecting air samples from different heights ranging from 20 km to 41 km (12 to 25 miles) above the Earth’s surface, were parachuted down and retrieved. The samples were analyzed by scientists at the Center for Cellular and Molecular Biology in Hyderabad as well as the National Center for Cell Science in Pune for independent confirmation.

One of the new species has been named as Janibacter hoylei, after the astrophysicist Fred Hoyle, the second as Bacillus isronensis recognizing the contribution of ISRO in the balloon experiments which led to its discovery, and the third as Bacillus aryabhata after India’s celebrated ancient astronomer Aryabhata (also the name of ISRO’s first satellite).

The researchers have pointed out in a press release that precautionary measures and controls operating in the experiment inspire confidence that the new species were picked up in the stratosphere.

“While the present study does not conclusively establish the extra-terrestrial origin of microorganisms, it does provide positive encouragement to continue the work in our quest to explore the origin of life,” they added.

This was the second such experiment conducted by ISRO, with the first one in 2001. Even though the first experiment had yielded positive results, the researchers decided to repeat the experiment while exercising extra care to ensure that it was totally free from any terrestrial contamination.

Source: Indian Space Research Organisation

Additional links: Center for Cellular and Molecular Biology, National Center for Cell Science, Tata Institute of Fundamental Research