Posted on by Nancy Atkinson

Life in the Universe, Reflected by the Moon

This view shows the thin crescent Moon setting over ESO’s Paranal Observatory in Chile. Credit: ESO/B. Tafreshi/TWAN

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Earthshine – a poetic, fanciful word for the soft, faint glow on the Moon when the light from the Sun is reflected from the Earth’s surface, onto the dark part of the Moon. And as unlikely as it might seem, astronomers have used Earthshine to verify there’s life in the Universe: Us. While we already know about life on our own world, this technique validates that faint light from distant worlds could also be used to find potential alien life.

“We used a trick called earthshine observation to look at the Earth as if it were an exoplanet,” said Michael Sterzik from the European Southern Observatory. “The Sun shines on the Earth and this light is reflected back to the surface of the Moon. The lunar surface acts as a giant mirror and reflects the Earth’s light back to us — and this is what we have observed with the VLT (Very Large Telescope).”

Sterzik and his team said the fingerprints of life, or biosignatures, are hard to find with conventional methods, but they have now pioneered a new approach that is more sensitive. The astronomers used Earth as a benchmark for the future search for life on planets beyond our Solar System. They can analyze the faint planetshine light to look for indicators, such as certain combinations of gases in the atmosphere – as they found looking at earthshine – to find telltale signs of organic life.

Looking at earthshine, they found strong bio-signatures such as molecular oxygen and methane, as well as the presence of a ‘red edge’ caused by surface vegetation.

By observing earthshine astronomers can study the properties of light reflected from Earth as if it were an exoplanet and search for signs of life. The reflected light is also strongly polarised and studying the polarisation as well as the intensity at different colours allows for much more sensitive tests for the presence of life. Credit: ESO/L. Calçada

Instead of just looking at the planet’s reflected light, astronomers can also use spectropolarimetry, which looks at the polarization of the light. Using this approach, the biosignatures in the reflected light from Earth show up very strongly.

“The light from a distant exoplanet is overwhelmed by the glare of the host star, so it’s very difficult to analyze — a bit like trying to study a grain of dust beside a powerful light bulb,” said co-author Stefano Bagnulo from Armagh Observatory in Northern Ireland. “But the light reflected by a planet is polarised, while the light from the host star is not. So polarimetric techniques help us to pick out the faint reflected light of an exoplanet from the dazzling starlight.”

By looking at earthshine, the team was able to deduce that the Earth’s atmosphere is partly cloudy, that part of its surface is covered by oceans and — crucially — that there is vegetation present. They could even detect changes in the cloud cover and amount of vegetation at different times as different parts of the Earth reflected light towards the Moon.

“These observations allow us to determine the fractional contribution of clouds and ocean surface, and are sensitive to Spectropolarimetry unveils strong biosignatures, visible areas of vegetation as small as 10%,” the team wrote in their paper.

“Finding life outside the Solar System depends on two things: whether this life exists in the first place, and having the technical capability to detect it,” said co-author Enric Palle from Instituto de Astrofisica de Canarias, Tenerife, Spain. “This work is an important step towards reaching that capability.”

“Spectropolarimetry may ultimately tell us if simple plant life — based on photosynthetic processes — has emerged elsewhere in the Universe,” said Sterzik. “But we are certainly not looking for little green men or evidence of intelligent life.”

The astronomers said that future telescopes such as the E-ELT (the European Extremely Large Telescope), could provide more detail about the type of life beyond planets that may exists on another world.

Read the team’s paper, (pdf) which was published in Nature.

Source: ESO

Posted on by Nancy Atkinson

Salty Soil on Mars Could Be Slurping Water from the Atmosphere

This image provided by NASA shows a scraped area on Mars known as "Snow White," photographed on July 8. Two samples from Snow White were delivered to the Phoenix Mars Lander's wet-chemistry lab, and tests turned up evidence of perchlorate. Credit: NASA/JPL/University of Arizona

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It happens every summer in humid air: the salt in your salt shaker clumps together as the salt draws in the water from the air. Researchers have found this happens even in the frigid but dry McMurdo Dry Valley in Antarctica, a cold, polar desert. The sandy, salty soils there are frequently dotted with moist patches in the spring despite a lack of snowmelt and no possibility of rain. What was discovered is that the salty soils in the region actually suck moisture out of the atmosphere. Salty soils were found on Mars’ polar region by the Phoenix lander, so could the same thing be happening on the Red Planet, creating a salt brine within Mars’ soil? And if so what are the implications for life forming there?

Joseph Levy, a post-doctoral researcher from Oregon State University said it takes a combination of the right kinds of salts and sufficient humidity to make the process work. But those ingredients are present on Mars.

“If you have sodium chloride, or table salt, you may need a day with 75 percent humidity to make it work,” he added. “But if you have calcium chloride, even on a frigid day, you only need a humidity level above 35 percent to trigger the response.”

The soils in Antarctica have salt from sea spray and from ancient fjords that flooded the region. With enough humidity, those salty soils suck the water right out of the air, forming a brine, Levy said, that will keep collecting water vapor until it equalizes with the atmosphere.

Levy and his colleagues, from Portland State University and Ohio State University, found that the wet soils created by this phenomenon were 3-5 times more water-rich than surrounding soils – and they were also full of organic matter, including microbes, which they said could enhance the potential for life on Mars. The elevated salt content also depresses the freezing temperature of the groundwater, which continues to draw moisture out of the air when other wet areas in the valleys begin to freeze in the winter.

Though Mars, in general, has lower humidity than most places on Earth, studies have shown that it is sufficient to reach the thresholds that Levy and his colleagues have documented in Antarctica.

The parallels of what was found by the Mars Phoenix team is striking. The salty perchlorates found on Mars by the Phoenix lander also strongly attracts water and makes up a few tenths of a percent of the composition in all three soil samples analyzed by Phoenix’s wet chemistry laboratory. Principal investigator of the Phoenix mission, Peter Smith from the University of Arizona, Tucson, said the perchlorates could pull humidity from the Martian air.

A paper about Phoenix water studies, led by Smith, cites clues supporting an interpretation that the soil has had films of liquid water in the recent past. The evidence for water and potential nutrients “implies that this region could have previously met the criteria for habitability” during portions of continuing climate cycles.

At higher concentrations, it might combine with water as a brine that stays liquid at Martian surface temperatures. Some microbes on Earth use perchlorate as food, and future human explorers on Mars might find it useful as rocket fuel or for generating oxygen.

Levy and his team discovered the mysterious patches of wet soil in Antarctica, and then explored the causes. Through soil excavations and other studies, they eliminated the possibility of groundwater, snow melt, and glacial runoff. Then they began investigating the salty properties of the soil, and discovered that the McMurdo Dry Valleys weather stations had reported several days of high humidity earlier in the spring, leading them to their discovery of the vapor transfer.

“It seems kind of odd, but it really works,” Levy said. “Before one of our trips, I put a bowl of the dried, salty soil and a jar of water into a sealed Tupperware container and left it on my shelf. When I came back, the water had transferred from the jar to the salt and created brine.

“I knew it would work,” he added with a laugh, “but somehow it still surprised me that it did.”

The salty soils also are present on the Red Planet, which makes the upcoming landing of the Mars Science Laboratory this summer even more tantalizing.
Evidence of the salty nature of the McMurdo Dry Valleys is everywhere, Levy said. Salts are found in the soils, along seasonal streams, and even under glaciers. Don Juan Pond, the saltiest body of water on Earth, is found in Wright Valley, the valley adjacent to the wet patch study area.

“The conditions for creating this new water source into the permafrost are perfect,” Levy said, “but this isn’t the only place where this could or does happen. It takes an arid region to create the salty soils, and enough humidity to make the transference work, but the rest of it is just physics and chemistry.”

The study by Levy and his team was published online this week in the journal Geophysical Research Letters.

Sources: University of Oregon, previous article about the Phoenix Lander

Posted on by Paul Scott Anderson

Tidal Heating on Some Exoplanets May Leave Them Waterless

Venus as photographed by the Pioneer spacecraft in 1978. Some exoplanets may suffer the same fate as this scorched world. Credit: NASA/JPL/Caltech

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As the number of exoplanets being discovered continues to increase dramatically, a growing number are now being found which orbit within their stars’ habitable zones. For smaller, rocky worlds, this makes it more likely that some of them could harbour life of some kind, as this is the region where temperatures (albeit depending on other factors as well) can allow liquid water to exist on their surfaces. But there is another factor which may prevent some of them from being habitable after all – tidal heating, caused by the gravitational pull of one star, planet or moon on another; this effect which creates tides on Earth’s oceans can also create heat inside a planet or moon.

The findings were presented at the January 11 annual meeting of the American Astronomical Society in Austin, Texas.

The habitability factor is determined primarily by the amount of heat coming from the planet’s star. The closer a planet is to its star, the hotter it will be, and the farther out it is, the cooler it will be. Simple enough, but tidal heating adds a new wrinkle to the equation. According to Rory Barnes, a planetary scientist and astrobiologist at the University of Washington, “This has fundamentally changed the concept of a habitable zone. We figured out you can actually limit a planet’s habitability with an energy source other than starlight.”

This effect could cause planets to become “tidal Venuses.” In these cases, the planets orbit smaller, dimmer stars, where in order to be in that star’s habitable zone, they would need to orbit much closer in to the star than Earth does with the Sun. The planets would then be subjected to greater tidal heating from the star, enough perhaps to cause them to lose all of their water, similar to what is thought to have happened with Venus in our own solar system (ie. a runaway greenhouse effect). So even though they are within the habitable zone, they would lack oceans or lakes.

What’s problematic is that these planets could subsequently actually have their orbits altered by the tidal heating so that they are no longer affected by it. They would then be more difficult to distinguish from other planets in those solar systems which may still be habitable. While technically still within the habitable zone, they would have effectively been sterilized by the tidal heating process.

Planetary scientist Norman Sleep at Stanford University adds: “We’ll have to be careful when assessing objects that are very near dim stars, where the tides are much stronger than we feel on present-day Earth. Even Venus now is not substantially heated by tides, and neither is Mercury.”

In some cases, tidal heating can be a good thing though. The tidal forces exerted by Jupiter on its moon Europa, for example, are thought to create enough heat to allow a liquid water ocean to exist beneath its outer ice crust. The same may be true for Saturn’s moon Enceladus. This makes these moons still potentially habitable even though they are far outside of the habitable zone around the Sun.

By design, the first exoplanets being found by Kepler are those that orbit closer in to their stars as they are easier to detect. This includes smaller, dimmer stars as well as ones more like our own Sun. The new findings, however, mean that more work will need to be done to determine which ones really are life-friendly and which ones are not, at least for “life-as-we-know-it” anyway.

Posted on by Paul Scott Anderson

Do Alien Civilizations Inevitably ‘Go Green’?

Beautiful view of our Milky Way Galaxy. If other alien civilizations are out there, can we find them? Credit: ESO/S. Guisard

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In the famous words of Arthur C. Clarke, “Any sufficiently advanced technology is indistinguishable from magic.” This phrase is often quoted to express the idea that an alien civilization which may be thousands or millions of years older than us would have technology so far ahead of ours that to us it would appear to be “magic.”

Now, a variation of that thought has come from Canadian science fiction writer Karl Schroeder, who posits that “any sufficiently advanced technology is indistinguishable from nature.” The reasoning is that if a civilization manages to exist that long, it would inevitably “go green” to such an extent that it would no longer leave any detectable waste products behind. Its artificial signatures would blend in with those of the natural universe, making it much more difficult to detect them by simply searching for artificial constructs versus natural ones.

The idea has been proposed as an explanation for why we haven’t found them yet, based on the premise that such advanced societies would have visited and colonized our entire galaxy by now (known as the Fermi Paradox). The question becomes more interesting in light of the fact that astronomers now estimate that there are billions of other planets in our galaxy alone. If a civilization reaches such a “balance with nature” as a natural progression, it may mean that traditional methods of searching for them, like SETI, will ultimately fail. Of course, it is possible, perhaps even likely, that civilizations much older than us would have advanced far beyond radio technology anyway. SETI itself is based on the assumption that some of them may still be using that technology. Another branch of SETI is searching for light pulses such as intentional beacons as opposed to radio signals.

But even other alternate searches, such as SETT (Search for Extraterrestrial Technology), may not pan out either, if this new scenario is correct. SETT looks for things like the spectral signature of nuclear fission waste being dumped into a star, or leaking tritium from alien fusion powerplants.

Another solution to the Fermi Paradox states that advanced civilizations will ultimately destroy themselves. Before they do though, they could have already sent out robotic probes to many places in the galaxy. If those probes were technologically savvy enough to self-replicate, they could have spread themselves widely across the cosmos. If there were any in our solar system, we could conceivably find them. Yet this idea could also come back around to the new hypothesis – if these probes were advanced enough to be truly “green” and not leave any environmental traces, they might be a lot harder to find, blending in with natural objects in the solar system.

It’s an intriguing new take on an old question. It can also be taken as a lesson – if we can learn to survive our own technological advances long enough, we can ultimately become more of a green civilization ourselves, co-existing comfortably with the natural universe around us.

Posted on by Paul Scott Anderson

600 Million Year Drought Makes Life on Surface of Mars Unlikely

View of Mars' surface near the north pole from the Phoenix lander. Polygon shapes can be seen in the soil. Credit: NASA/JPL-Calech/University of Arizona

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Mars is often referred to as a desert world, and for good reason – its surface is barren, dry and cold. While water was abundant in the distant past, it has long since disappeared from the surface, although ice, snow, frost and fog are still common. Other than liquid brines possibly trickling at times, all of Mars’ remaining water is now frozen in permafrost and in the polar ice caps. It has long been thought that the harsh conditions would make current life unlikely at best, and now a new study reaffirms that view.

The results come from continued analysis of the data from the Phoenix lander mission, which landed in the arctic region near the north pole of Mars in 2008. They suggest that Mars has experienced a prolonged drought for at least the past 600 million years.

According to Dr. Tom Pike from Imperial College London, “We found that even though there is an abundance of ice, Mars has been experiencing a super-drought that may well have lasted hundreds of millions of years. We think the Mars we know today contrasts sharply with its earlier history, which had warmer and wetter periods and which may have been more suited to life. Future NASA and ESA missions that are planned for Mars will have to dig deeper to search for evidence of life, which may still be taking refuge underground.”

The team reached their conclusions by studying tiny microscopic particles in the soil samples dug up by Phoenix, which had been photographed by the lander’s atomic-force microscope. 3-D images were produced of particles as small as 100 microns across. They were searching specifically for clay mineral particles, which form in liquid water. The amount found in the soil would be a clue as to how long the soil had been in contact with water. It was determined that less than 0.1 percent of the soil samples contained clay particles, pointing to a long, arid history in this area of Mars.

Since the soil type on Mars appears to be fairly uniform across the planet, the study suggests that these conditions have been widespread on the planet, and not just where Phoenix landed. It’s worth keeping in mind though that soil particles and dust on Mars can be distributed widely by sandstorms and dust devils (and some sandstorms on Mars can be planet-wide in size). The study also implies that Mars’ soil may have only been exposed to liquid water for about 5,000 years, although some other studies would tend to disagree with that assessment.

It should also be noted that more significant clay deposits have been found elsewhere on Mars, including the exact spot where the Opportunity rover is right now; these richer deposits would seem to suggest a different history in different regions. Because of this, and for the other reasons cited above, it may be premature then to extrapolate the Phoenix results to the entire planet, similar soil types notwithstanding. While this study is important, more definitive results might be obtained when physical soil samples can actually be brought back to Earth for analysis, from multiple locations. More sophisticated rovers and landers like the Curiosity rover currently en route to Mars, will also be able to conduct more in-depth analysis in situ.

The Phoenix soil samples were also compared to soil samples from the Moon – the distribution of particle sizes was similar between the two, indicating that they formed in a similar manner. Rocks on Mars are weathered down by wind and meteorites, while on the airless Moon, only meteorite impacts are responsible. On Earth of course, such weathering is caused primarily by water and wind.

As for the life question, any kind of surface dwelling organisms would have to be extremely resilient, much like extremophiles on Earth. It should be kept in mind, however, that these results apply to surface conditions; it is still thought possible that any early life on the planet could have continued to thrive underground, protected from the intense ultraviolet light from the Sun, and where some liquid water could still exist today.

Given Mars’ much wetter early history, the search for evidence of past or present life will continue, but we may have to dig deep to find it.

Posted on by Paul Scott Anderson

New Study Shows How Trace Elements Affect Stars’ Habitable Zones

Comparison of the habitable zone around the Sun in our solar system and around the star Gliese 581. Credit: ESO

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Habitable zones are the regions around stars, including our own Sun, where conditions are the most favourable for the development of life on any rocky planets that happen to orbit within them. Generally, they are regions where temperatures allow for liquid water to exist on the surface of these planets and are ideal for “life as we know it.” Specific conditions, due to the kind of atmosphere, geological conditions, etc. must also be taken into consideration, on a case-by-case basis.

Now, by examining trace elements in the host stars, researchers have found clues as to how the habitable zones evolve, and how those elements also influence them. To determine what elements are in a star, scientists study the wavelengths of its light. These trace elements are heavier than the hydrogen and helium gases which the star is primarily composed of. Variations in the composition of these stars are now thought to affect the habitable zones around them.

The study was led by Patrick Young, a theoretical astrophysicist and astrobiologist at Arizona State University. Young and his team presented their findings on January 11, 2012 at the annual meeting of the American Astronomical Society in Austin, Texas. He and his colleagues have examined more than a hundred dwarf stars so far.

An abundance of these elements can affect how opaque a star’s plasma is. Calcium, sodium, magnesium, aluminum and silicon have been found to also have small but significant effects on a star’s evolution – higher levels tended to result in cooler, redder stars. As Young explains, “The persistence of stars as stable objects relies on the heating of plasma in the star by nuclear fusion to produce pressure that counteracts the inward force of gravity. A higher opacity traps the energy of fusion more efficiently and results in a larger radius, cooler star. More efficient use of energy also means that nuclear burning can proceed more slowly, resulting in a longer lifetime for the star.”

The lifetime of a star’s habitable zone can also be influenced by another element – oxygen. Young continues: “The habitable lifetime of an orbit the size of Earth’s around a one-solar-mass star is only 3.5 billion years for oxygen-depleted compositions but 8.5 billion years for oxygen-rich stars. For comparison, we expect the Earth to remain habitable for another billion years or so, for about 5.5 billion years total, before the Sun becomes too luminous. Complex life on Earth arose some 3.9 billion years after its formation, so if Earth is at all representative, low-oxygen stars are perhaps less than ideal targets.”

As well as the habitable zone, the composition of a star can determine the eventual composition of any planets that form. The carbon-oxygen and magnesium-silicon ratios of stars can affect whether a planet will have magnesium or silicon-loaded clay minerals such as magnesium silicate (MgSiO3), silicon dioxide (SiO2), magnesium orthosilicate (Mg2SiO4), and magnesium oxide (MgO). A star’s composition can also play a role in whether a rocky planet might have carbon-based rock instead of silicon-based rock like our planet. Even the interior of planets could be affected, as radiocative elements would determine whether a planet has a molten core or a solid one. Plate tectonics, thought to be important for the evolution of life on Earth, depend on a molten interior.

Young and his team are now looking at 600 stars, ones that are already being targeted in exoplanet searches. They plan to produce a list of the 100 best stars which could have potentially habitable planets.

Posted on by Paul Scott Anderson

How Plants May Have Helped Create Earth’s Unique Landscapes

Credit: Wikimedia Commons

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According to conventional thinking, plant life first took hold on Earth after oceans and rivers formed; the soil produced by liquid water breaking down bare rock provided an ideal medium for plants to grow in. It certainly sounds logical, but a new study is challenging that view – the theory is that vascular plants, those containing a transport system for water and nutrients, actually created a cycle of glaciation and melting, conditions which led to the formation of rivers and mud which allowed forests and farmland to later develop. In short, they helped actually create the landscapes we see today.

The evidence was just published in two articles in a special edition of Nature Geoscience.

In the first article, analysis of the data proposes that vascular plants began to absorb the carbon dioxide in the atmosphere about 450 million years ago. This led to a cooling of temperatures on a global scale, resulting in widespread glaciation. As the glaciers later started to melt, they ground up the Earth’s surface, forming the kind of soils we see today.

The second article goes further, stating that today’s rivers were also created by vascular plants – the vegetation broke the rocks down into mud and minerals and then also held the mud in place. This caused river banks to start forming, acting as channels for water, which up until then had tended to flow over the surface much more randomly. As the water was channeled into more specific routes, rivers formed. This led to periodic flooding; sediments were deposited over large areas which created rich soil. As trees were able to take root in this new soil, debris from the trees fell into the rivers, creating logjams. This had the effect of creating new rivers and causing more flooding. These larger fertile areas were then able to support the growth of larger lush forests and farmland.

According to Martin Gibling, a professor of Earth science at Dalhousie University, “Sedimentary rocks, before plants, contained almost no mud. But after plants developed, the mud content increased dramatically. Muddy landscapes expanded greatly. A new kind of eco-space was created that wasn’t there before.”

The new theory also leads to the possibility that any exoplanets that happen to have vegetation would look different from Earth; varying circumstances would create a surface unique to each world. Any truly Earth-like exoplanets might be very similar in general, but the way that their surfaces have been modified might be rather different.

It’s an interesting scenario, but it also raises other questions. What about the ancient river channels on Mars? Some appear to have been formed by brief catastrophic floods, but others seem more similar to long-lived rivers here on Earth, especially if there actually was a northern hemisphere ocean as well. How did they form? Does this mean that rivers could form in a variety of ways, with or without plant life being involved? Could Mars have once had something equivalent to vascular plant life as well? Or could the new theory just be wrong? Then there’s Titan, which has numerous rivers still flowing today. Albeit they are liquid methane/ethane instead of water, but what exactly led to their formation?

From the editorial in Nature Geoscience:

Without the workings of life, the Earth would not be the planet it is today. Even if there are a number of planets that could support tectonics, running water and the chemical cycles that are essential for life as we know it, it seems unlikely that any of them would look like Earth. Even if evolution follows a predictable path, filling all available niches in a reproducible and consistent way, the niches on any Earth analogue could be different if the composition of its surface and atmosphere are not identical to those of Earth. And if evolution is random, the differences would be expected to be even larger. Either way, a glimpse of the surface of an exoplanet — if we ever get one — may give us a whole new perspective on biogeochemical cycling and geomorphology.

Just as the many exoplanets now being found are of a previously unknown and amazingly wide variety, and all uniquely alien, even the ones that (may) support life are likely to be just as diverse from each other as they are from Earth itself. Earth’s “twin” may be out there, but in terms of outward appearance, it may be somewhat more of a fraternal twin than an exact replica.

Posted on by Amy Shira Teitel

Looks Like We’re Still Looking for Earthly Life Forms on Other Planets

GFAJ-1, the bacterium found in California's Lake Mono. Image credit: Science/AAAS

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In late 2010, NASA set the Internet buzzing when it called a press conference to discuss an astrobiological finding that would impact the search for extraterrestrial life. Many speculated that some primitive life had been found on Mars or one of Saturn’s moons. But the evidence was found on Earth; a strain of bacteria in California’s Lake Mono that had arsenic in its genetic structure. The discovery implied that life could thrive without the elements NASA typically looks for, mainly carbon and phosphorous. But now, a new study challenges the existence of arsenic-based life forms. 

The 2010 paper announcing arsenic based life, “Arsenic-eating microbe may redefine chemistry of life,” was written by a team of scientists led by Felisa Wolfe-Simon. The paper appeared in Science and refuted the long-held assumption that all living things need phosphorus to function, as well as other elements including carbon, hydrogen, and oxygen.

Lake Mono, as seen from Space. Image credit: NASA

The phosphate ion plays several essential roles in cells: it maintains the structure of DNA and RNA, it combines with lipids to make cell membranes, and it transports energy within the cell through the molecule adenosine triphosphate (ATP). Finding a bacteria that uses normally poisonous arsenic in the place of phosphate shook up the guidelines that have structured NASA’s search for life on other worlds.

But microbiologist Rosie Redfield didn’t agree with Wolfe-Simon’s article and published her concerns as technical comments in subsequent issues of Science. Then, she put Wolfe-Simon’s results to the test. She led a team of scientists at the University of British Columbia in Vancouver and tracked her progress online in the name of open science.

Redfield followed Wolfe-Simon’s procedure. She grew GFAJ-1 bacteria, the same strain found in Lake Mono, in a solution of arsenic with a very small amount of phosphorus. She then purified DNA from the cells and sent the material to Princeton University in New Jersey. There, graduate student Marshall Louis Reaves separated the DNA into fractions of varying densities using caesium chloride centrifugation. Caesium chloride, a salt, creates a density gradient when mixed with water and put in a centrifuge. Any DNA in the mixture will settle throughout the gradient depending on its structure. Reaves studied the resulting DNA gradient using a mass spectrometer to identify the different elements at each density. He found no trace of arsenic in the DNA.

Redfield’s results aren’t by themselves conclusive; one experiment isn’t enough to definitively disprove Wolfe-Simon’s arsenic-life paper. Some biochemists are eager to continue the research and want to figure out the lowest possible level of arsenic that Redfield’s method could detect as a way of determining exactly where arsenic from the GFAJ-1 DNA ends up on a caesium chloride gradient.

Dr. Redfield. Image credit: M. Dee/Nature

Wolfe-Simon is also not taking Redfield’s results as conclusive; she is still looking for arsenic in the bacterium. “We are looking for arsenate in the metabolites, as well as the assembled RNA and DNA, and expect others may be doing the same. With all this added effort from the community, we shall certainly know much more by next year.”

Redfield, however, isn’t planning any follow-up experiments to support her initial findings. “What we can say is that there is no arsenic in the DNA at all,” she said. “We’ve done our part. This is a clean demonstration, and I see no point in spending any more time on this.”

It’s unlikely that scientists will conclusively prove or disprove the existence arsenic-based life anytime soon. For the time being, NASA will likely confine its search for extraterrestrial life to phosphorus-dependent forms we know exist.

Source: nature.com

Posted on by Paul Scott Anderson

Key Step in Evolution Replicated by Scientists – With Yeast

Sacharomyces cerevisiae yeast cells. Credit: Wikimedia Commons

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One of the great puzzles in science has been the evolution of single-celled organisms into the incredibly wide variety of flora and fauna that we see today. How did Earth make the transition from an initially lifeless ball of rock to one populated only by single-celled organisms to a world teeming with more complex life?

As scientists understand it, single-celled organisms first began evolving into more complex forms more than 500 million years ago, as they began to form multi-cellular clusters. What isn’t understood is just how that process happened. But now, biologists are another step closer figuring out this puzzle, by successfully replicating this key step – using an ingredient common in the making of bread and beer – ordinary Brewer’s yeast (Saccharomyces cerevisiae). While helping to solve evolutionary riddles here on Earth, it also by extension has bearing on the question of biological evolution on other planets or moons as well.

The results were published in last week’s issue of the Journal Proceedings of the National Academy of Sciences (PNAS).

Yeasts are a microscopic form of fungi; they are uni-cellular but can become multi-cellular through the formation of a string of connected budding cells, like in molds. The experiments were based on this fact, and were surprisingly simple, they just hadn’t been done before, according to Will Ratcliff, a scientist at the University of Minnesota (UMN) and a co-author of the paper. “I don’t think anyone had ever tried it before,” he said, adding: “There aren’t many scientists doing experimental evolution, and they’re trying to answer questions about evolution, not recreate it.”

Sam Scheiner, program director in NSF’s Division of Environmental Biology, also adds: “To understand why the world is full of plants and animals, including humans, we need to know how one-celled organisms made the switch to living as a group, as multi-celled organisms. This study is the first to experimentally observe that transition, providing a look at an event that took place hundreds of millions of years ago.”

It’s been thought that the step toward multi-cellular complexity was a difficult one, an evolutionary hurdle that would be very hard to overcome. The new research however, suggests it may not be that difficult after all.

It took the first experiment only 60 days to produce results. The yeast was first added to a nutrient-rich culture, then the cells were allowed to grow for one day. They were then stratified by weight using a centrifuge. Clusters of yeast cells landed on the bottom of the test tubes. The process was then repeated, taking the cell clusters and re-adding them to fresh cultures. After sixty cycles of this, the cell clusters started to look like spherical snowflakes, composed of hundreds of cells.

The most significant finding was that the cells were not just clustering and sticking together randomly; the clusters were composed of cells that were genetically related to each other and remained attached after cell division. When clusters reached “critical mass,” some cells died, a process known as apoptosis, which allows the offspring to separate.

This then, simply put, is the process toward multi-cellular life. As described by Ratcliff, “A cluster alone isn’t multi-cellular. But when cells in a cluster cooperate, make sacrifices for the common good, and adapt to change, that’s an evolutionary transition to multi-cellularity.”

So next time you are baking bread or brewing your own beer, consider the fact that those lowly little yeast cells hold a lot more importance than just a useful role in your kitchen – they are also helping to solve some of the biggest mysteries of how life started, both here and perhaps elsewhere.

Posted on by Amy Shira Teitel

Rocks From Mars

DARRYL PITT, MACOVICH COLLECTION

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Scientists studying life on Mars got a late Christmas present this year: confirmation that meteorites found in Morocco in December are of Martian origin. It’s a significant discovery; Martian meteorites fall to Earth only about once every 50 years making this a once-in-a-lifetime, and for many a once-in-a-career, event. The Mars rocks are worth more than their weight in gold, but what they can tell us could be even more valuable. 

Astronomers suspect that the meteorite has been wandering around the solar system for millions of years, ever since something big smashed into the red planet and sent debris flying all directions. One of those pieces has wandered its way towards Earth and plunged through the atmosphere.

ALH 84001, the meteorite found in Antarctica in 1984. Evidence of fossilized life inside the rock sparked a search for life on Mars. Image credit: NASA/ JSC

This is only the fifth time scientists have chemically confirmed the Martian origin of meteorites. Rocks found in France in 1815, in India in 1865, in Egypt in 1911, and in Nigeria in 1962 have all been positively identified as being from Mars.

The chemical signature of the Moroccan rocks and the Martian air match said Tony Irving of the University of Washington who did the scientific analysis. But this discovery is different. The rocks weren’t just found, they were seen streaking through the sky in July 2011, which makes them extremely valuable.

These rocks have only had six months to accumulate Earth-based materials and traces of life; typically Martian meteorites found on Earth have been here anywhere from decades to millennia, giving them ample time to become tainted.

These new rocks, while still contaminated because they have been on Earth for months, are relatively pure. “It’s incredibly fresh. It’s highly valuable for that reason,” said Carl Agee, director of the Institute of Meteoritics and curator at the University of New Mexico.

It’s also a rare find. This new sample, about 15 pounds of rocks, brings the total weight of all Martian samples on Earth to just 240 pounds.

Meteorite dealer Darryl Pitt is cashing in on the rocks’ rarity and selling pieces for $11,000 to $22,500 an ounce and has sold most of his supply already. At that price, the Martian meteorite costs about 10 times as much as gold.

An artist's conception of early Mars being hit by an asteroid wider than Texas. Scientists believe the impact melted the planet's crust in its northern hemisphere, flung crust into space, and sent shock wave through the planet's molten core (inset). This explains why Mars' crust is thinner in the northern hemisphere, according to three new studies. Image courtesy Jeff Andrews-Hanna; inset courtesy Francis Nimmo.

Cornell University astronomer Steve Squyres, the principal investigator for NASA’s Mars Exploration Rover Program, is less excited. The rocks, he said, are not the kind scientists are most hoping for. They are hard, igneous or volcanic rock. A softer kind of rock capable of holding water or life would be better. But he also points that these rocks aren’t likely to come streaking through the atmosphere. Any soft rock would be unlikely to survive the fiery entry through Earth’s atmosphere.

Former NASA sciences chief Alan Stern, director of the Florida Space Institute at the University of Central Florida, takes a brighter outlook. “It’s nice to have Mars sending samples to Earth,” he said, “particularly when our pockets are too empty to go get them ourselves.”

Until we manage a sample return mission from Mars, this is the best shot scientists have to study the red planet up close.

Source: physorg.