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  • richardmitnick 9:59 am on October 18, 2015 Permalink | Reply
    Tags: , , Astrobiology Magazine, Zircons   

    From astrobio.net: “Study questions dates for cataclysms on early moon, Earth” 

    Astrobiology Magazine

    Astrobiology Magazine

    Oct 18, 2015
    No Writer Credit

    1
    The deformed lunar zircon at center was brought from the moon by Apollo astronauts. The fractures characteristic of meteorite impact are not seen in most lunar zircons, so the ages they record probably reflect heating by molten rock, not impact. Photo: Apollo 17/Nicholas E. Timms

    Phenomenally durable crystals called zircons are used to date some of the earliest and most dramatic cataclysms of the solar system. One is the super-duty collision that ejected material from Earth to form the moon roughly 50 million years after Earth formed. Another is the late heavy bombardment, a wave of impacts that may have created hellish surface conditions on the young Earth, about 4 billion years ago.

    Both events are widely accepted but unproven, so geoscientists are eager for more details and better dates. Many of those dates come from zircons retrieved from the moon during NASA’s Apollo voyages in the 1970s.

    A study of zircons from a gigantic meteorite impact in South Africa, now online in the journal Geology, casts doubt on the methods used to date lunar impacts. The critical problem, says lead author Aaron Cavosie, a visiting professor of geoscience and member of the NASA Astrobiology Institute at the University of Wisconsin-Madison, is the fact that lunar zircons are “ex situ,” meaning removed from the rock in which they formed, which deprives geoscientists of corroborating evidence of impact.

    “While zircon is one of the best isotopic clocks for dating many geological processes,” Cavosie says, “our results show that it is very challenging to use ex situ zircon to date a large impact of known age.”

    Although many of their zircons show evidence of shock, “once separated from host rocks, ex situ shocked zircons lose critical contextual information,” Cavosie says.

    The “clock” in a zircon occurs as lead isotopes accumulate during radioactive decay of uranium. With precise measurements of isotopes scientists can calculate, based on the half life of uranium, how long lead has been accumulating.

    If all lead was driven off during asteroid impact, the clock was reset, and the amount of accumulated lead should record exactly how long ago the impact occurred.

    Studies of lunar zircons have followed this procedure to produce dates from 4.3 billion to 3.9 billion years ago for the late heavy bombardment.

    2
    This highly shocked zircon, from the Vredefort Dome in South Africa, shows thin, red bands that are a hallmark of meteorite impact. Uranium-lead dating from this zircon matched the age of the rocks exposed at Vredefort, not the more recent age of impact (2 billion years). Credit: Aaron Cavosie

    To evaluate the assumption of clock-resetting by impact, Cavosie and colleagues gathered zircons near Earth’s largest impact, located in South Africa and known to have occurred 2 billion years ago. The Vredefort impact structure is deeply eroded, and approximately 90 kilometers across, says Cavosie, who is also in the Department of Applied Geology at Curtin University in Perth, Australia. “The original size, estimated at 300 kilometers diameter, is modeled to result from an impactor 14 kilometers in diameter,” he says.

    1
    Vredefort Dome

    The researchers searched for features within the zircons that are considered evidence of impact, and concluded that most of the ages reflect when the zircons formed in magma. The zircons from South Africa are “out of place grains that contain definitive evidence of shock deformation from the Vredefort impact,” Cavosie says. “However, most of the shocked grains do not record the age of the impact but rather the age of the rocks they formed in, which are about 1 billion years older.”

    The story is different on Earth, says zircon expert John Valley, a professor of geoscience at UW-Madison. “Most zircons on Earth are found in granite, and they formed in the same process that formed the granite. This has led people to assume that all the zircons were reset by impact, so the ages they get from the Moon are impact ages. Aaron is saying to know that, you have to apply strict criteria, and that’s not what people have been doing.”

    The accuracy of zircon dating affects our view of Earth’s early history. The poorly understood late heavy bombardment, for example, likely influenced when life arose, so dating the bombardment topped a priority list of the National Academy of Sciences for lunar studies. Did the giant craters on the moon form during a brief wave or a steady rain of impacts? “It would be nice to know which,” Valley says.

    “The question of what resets the zircon clock has always been very complicated. For a long time people have been saying if zircon is really involved in a major impact shock, its age will be reset, so you can date the impact. Aaron has been saying, ‘Yes, sometimes, but often what people see as a reset age may not really be reset.’ Zircons are the gift that keep on giving, and this will not change that, but we need to be a lot more careful in analyzing what that gift is telling us.”

    See the full article here .

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  • richardmitnick 8:26 am on October 7, 2015 Permalink | Reply
    Tags: , , , Astrobiology Magazine, Plant life   

    From astrobio.net: “Ancient alga knew how to survive on land before it left water & evolved into first plant” 

    Astrobiology Magazine

    Astrobiology Magazine

    1
    Closterium strigosum is one of the green algae the scientists analyzed. Credit: Michael Melkonian

    A team of scientists led by Dr Pierre-Marc Delaux (John Innes Centre / University of Wisconsin, Madison) has solved a long-running mystery about the first stages of plant life on earth.

    The team of scientists from the John Innes Centre, the University of Wisconsin – Madison and other international collaborators, has discovered how an ancient alga was able to inhabit land, before it went on to evolve into the world’s first plant and colonise the earth.

    Up until now it had been assumed that the alga evolved the capability to source essential nutrients for its survival after it arrived on land by forming a close association with a beneficial fungi called arbuscular mycorrhiza (AM), which still exists today and which helps plant roots obtain nutrients and water from soil in exchange for carbon.

    The previous discovery of 450 million year old fossilised spores similar to the spores of the AM fungi suggests this fungi would have been present in the environment encountered by the first land plants. Remnants of prehistoric fungi have also been found inside the cells of the oldest plant macro-fossils, reinforcing this idea.

    However, scientists were not clear how the algal ancestor of land plants could have survived long enough to mediate a quid pro quo arrangement with a fungi. This new finding points to the alga developing this crucial capability while still living in the earth’s oceans!

    Dr Delaux and colleagues analysed DNA and RNA of some of the earliest known land plants and green algae and found evidence that their shared algal ancestor living in the Earth’s waters already possessed the set of genes, or symbiotic pathways, it needed to detect and interact with the beneficial AM fungi.

    The team of scientists believes this capability was pivotal in enabling the alga to survive out of the water and to colonise the earth. By working with the fungi to find sustenance, the alga was able to buy time to adapt and evolve in a very different and seemingly infertile environment.

    Dr Delaux said: “At some point 450 million years ago, alga from the earth’s waters splashed up on to barren land. Somehow it survived and took root, a watershed moment that kick-started the evolution of life on earth. Our discovery shows for the first time that the alga already knew how to survive on land while it was still in the water. Without the development of this pre-adapted capability in alga, the earth could be a very different place today.

    “This finding has filled a gap in our collective knowledge about the origins of life on earth. None of this would have been possible without the dedication of a world-wide team of scientists including a tremendous contribution from the 1KP initiative led by Gane KS Wong .”

    Professor Jean-Michel Ané, from the University of Wisconsin said: “The surprise was finding the mechanisms in algae which allow plants to interact with symbiotic fungi. Nobody has studied beneficial associations in these algae.”

    See the full article here .

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  • richardmitnick 11:33 am on August 23, 2015 Permalink | Reply
    Tags: , , Astrobiology Magazine,   

    From astrobio.net: “As Ice Age ended, greenhouse gas rise was lead factor in melting of Earth’s glaciers” 

    Astrobiology Magazine

    Astrobiology Magazine

    Aug 23, 2015
    No Writer Credit

    1
    Improved dating methods reveal that the rise in carbon dioxide levels was the primary cause of the simultaneous melting of glaciers around the globe during the last Ice Age. The new finding has implications for rising levels of man-made greenhouse gases and retreating glaciers today. Courtesy: NSF

    A fresh look at some old rocks has solved a crucial mystery of the last Ice Age, yielding an important new finding that connects to the global retreat of glaciers caused by climate change today, according to a new study by a team of climate scientists.

    For decades, researchers examining the glacial meltdown that ended 11,000 years ago took into account a number of contributing factors, particularly regional influences such as solar radiation, ice sheets and ocean currents.

    But a reexamination of more than 1,000 previously studied glacial boulders has produced a more accurate timetable for the pre-historic meltdown and pinpoints the rise in carbon dioxide – then naturally occurring – as the primary driving factor in the simultaneous global retreat of glaciers at the close of the last Ice Age, the researchers report in the journal Nature Communications.

    “Glaciers are very sensitive to temperature. When you get the world’s glaciers retreating all at the same time, you need a broad, global reason for why the world’s thermostat is going up,” said Boston College Assistant Professor of Earth and Environmental Sciences Jeremy Shakun. “The only factor that explains glaciers melting all around the world in unison during the end of the Ice Age is the rise in greenhouse gases.”

    The researchers found that regional factors caused differences in the precise timing and pace of glacier retreat from one place to another, but carbon dioxide was the major driver of the overall global meltdown, said Shakun, a co-author of the report “Regional and global forcing of glacier retreat during the last deglaciation.”

    “This is a lot like today,” said Shakun. “In any given decade you can always find some areas where glaciers are holding steady or even advancing, but the big picture across the world and over the long run is clear – carbon dioxide is making the ice melt.”

    While 11,000 years ago may seem far too distant for a point of comparison, it was only a moment ago in geological time. The team’s findings fix even greater certainty on scientific conclusions that the dramatic increase in manmade greenhouse gases will eradicate many of the world’s glaciers by the end of this century.

    “This has relevance to today since we’ve already raised CO2 by more than it increased at the end of the Ice Age, and we’re on track to go up much higher this century — which adds credence to the view that most of the world’s glaciers will be largely gone within the next few centuries, with negative consequences such as rising sea level and depleted water resources,” said Shakun.

    The team reexamined samples taken from boulders that were left by the retreating glaciers, said Shakun, who was joined in the research by experts from Oregon State University, University of Wisconsin-Madison, Purdue University and the National Center for Atmospheric Research in Boulder, Colo.

    Each boulder has been exposed to cosmic radiation since the glaciers melted, an exposure that produces the isotope Beryllium-10 in the boulder. Measuring the levels of the isotope in boulder samples allows scientists to determine when glaciers melted and first uncovered the boulders.

    Scientists have been using this process called surface exposure dating for more than two decades to determine when glaciers retreated, Shakun said. His team examined samples collected by multiple research teams over the years and applied an improved methodology that increased the accuracy of the boulder ages.

    The team then compared their new exposure ages to the timing of the rise of carbon dioxide concentration in the atmosphere, a development recorded in air bubbles taken from ice cores. Combined with computer models, the analysis eliminated regional factors as the primary explanations for glacial melting across the globe at the end of the Ice Age. The single leading global factor that did explain the global retreat of glaciers was rising carbon dioxide levels in the air.

    “Our study really removes any doubt as to the leading cause of the decline of the glaciers by 11,000 years ago – it was the rising levels of carbon dioxide in the Earth’s atmosphere,” said Shakun.

    Carbon dioxide levels rose from approximately 180 parts per million to 280 parts per million at the end of the last Ice Age, which spanned nearly 7,000 years. Following more than a century of industrialization, carbon dioxide levels have now risen to approximately 400 parts per million.

    “This tells us we are orchestrating something akin to the end of an Ice Age, but much faster. As the amount of carbon dioxide continues to increase, glaciers around the world will retreat,” said Shakun.

    See the full article here.

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  • richardmitnick 2:08 pm on July 29, 2015 Permalink | Reply
    Tags: , , Astrobiology Magazine,   

    From astrobio.net: “‘Carbon sink’ detected underneath world’s deserts” 

    Astrobiology Magazine

    Astrobiology Magazine

    Jul 29, 2015
    No Writer Credit

    1
    Scientists followed the journey of water through the Tarim Basin from the rivers at the edge of the valley to the desert aquifers under the basin. They found that as water moved through irrigated fields, the water gathered dissolved carbon and moved it deep underground. Credit: Yan Li

    The world’s deserts may be storing some of the climate-changing carbon dioxide emitted by human activities, a new study suggests. Massive aquifers underneath deserts could hold more carbon than all the plants on land, according to the new research.

    Humans add carbon dioxide to the atmosphere through fossil fuel combustion and deforestation. About 40 percent of this carbon stays in the atmosphere and roughly 30 percent enters the ocean, according to the University Corporation for Atmospheric Research. Scientists thought the remaining carbon was taken up by plants on land, but measurements show plants don’t absorb all of the leftover carbon. Scientists have been searching for a place on land where the additional carbon is being stored—the so-called “missing carbon sink.”

    The new study suggests some of this carbon may be disappearing underneath the world’s deserts – a process exacerbated by irrigation. Scientists examining the flow of water through a Chinese desert found that carbon from the atmosphere is being absorbed by crops, released into the soil and transported underground in groundwater—a process that picked up when farming entered the region 2,000 years ago.

    Underground aquifers store the dissolved carbon deep below the desert where it can’t escape back to the atmosphere, according to the new study.

    The new study estimates that because of agriculture roughly 14 times more carbon than previously thought could be entering these underground desert aquifers every year. These underground pools that taken together cover an area the size of North America may account for at least a portion of the “missing carbon sink” for which scientists have been searching.

    “The carbon is stored in these geological structures covered by thick layers of sand, and it may never return to the atmosphere,” said Yan Li, a desert biogeochemist with the Chinese Academy of Sciences in Urumqi, Xinjiang, and lead author of the study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union. “It is basically a one-way trip.”

    Knowing the locations of carbon sinks could improve models used to predict future climate change and enhance calculations of the Earth’s carbon budget, or the amount of fossil fuels humans can burn without causing major changes in the Earth’s temperature, according to the study’s authors.

    Although there are most likely many missing carbon sinks around the world, desert aquifers could be important ones, said Michael Allen, a soil ecologist from the Center for Conservation Biology at the University of California-Riverside who was not an author on the new study.

    If farmers and water managers understand the role heavily-irrigated inland deserts play in storing the world’s carbon, they may be able to alter how much carbon enters these underground reserves, he said.

    “This means [managers] can take practical steps that could play a role in addressing carbon budgets,” said Allen.

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    Researchers gathered groundwater flowing under the desert sands. The amount of carbon carried by this underground flow increased quickly when the Silk Road, which opened the region to farming, began 2,000 years ago. Credit: Yan Li

    Examining desert water

    To find out where deserts tucked away the extra carbon, Li and his colleagues analyzed water samples from the Tarim Basin, a Venezuela-sized valley in China’s Xinjiang region. Water draining from rivers in the surrounding mountains support farms that edge the desert in the center of the basin.

    The researchers measured the amount of carbon in each water sample and calculated the age of the carbon to figure out how long the water had been in the ground.

    The study shows the amount of carbon dioxide dissolved in the water doubles as it filters through irrigated fields. The scientists suggest carbon dioxide in the air is taken up by the desert crops. Some of this carbon is released into the soil through the plant’s roots. At the same time, microbes also add carbon dioxide to the soil when they break down sugars in the dirt. In a dry desert, this gas would work its way out of the soil into the air. But on arid farms, the carbon dioxide emitted by the roots and microbes is picked up by irrigation water, according to the new study.

    In these dry regions, where water is scarce, farmers over-irrigate their land to protect their crops from salts that are left behind when water used for farming evaporates. Over-irrigating washes these salts, along with carbon dioxide that is dissolved in the water, deeper into the earth, according to the new study.

    Although this process of carbon burial occurs naturally, the scientists estimate that the amount of carbon disappearing under the Tarim Desert each year is almost 12 times higher because of agriculture. They found that the amount of carbon entering the desert aquifer in the Tarim Desert jumped around the time the Silk Road, which opened the region to farming, begin to flourish.

    After the carbon-rich water flows down into the aquifer near the farms and rivers, it moves sideways toward the middle of the desert, a process that takes roughly 10,000 years.

    Any carbon dissolved in the water stays underground as it makes its way through the aquifer to the center of the desert, where it remains for thousands of years, according to the new study.

    Estimating carbon storage

    Based on the various rates that carbon entered the desert throughout history, the study’s authors estimate 20 billion metric tons (22 billion U.S. tons) of carbon is stored underneath the Tarim Basin desert, dissolved in an aquifer that contains roughly 10 times the amount of water held in the North American Great Lakes.

    The study’s authors approximate the world’s desert aquifers contain roughly 1 trillion metric tons (1 trillion U.S. tons) of carbon—about a quarter more than the amount stored in living plants on land.

    Li said more information about water movement patterns and carbon measurements from other desert basins are needed to improve the estimate of carbon stored underneath deserts around the globe.

    Allen said the new study is “an early foray” into this research area. “It is as much a call for further research as a definitive final answer,” he said.

    See the full article here.

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  • richardmitnick 9:18 am on July 23, 2015 Permalink | Reply
    Tags: astrobio, Astrobiology Magazine, ,   

    From astrobio.net: “Mini-Neptunes Might Host Life Under Right Conditions” 

    Astrobiology Magazine

    Astrobiology Magazine

    Jul 23, 2015
    Amanda Doyle

    1
    Artist’s impression of Roche lobe overflow in a planet. Credit: NASA/GSFC/Frank Reddy

    M-dwarfs, which are cooler than our sun, have habitable zones closer to the stars. As such, any habitable planets orbiting these stars would transit frequently, making the chances of discovery better.

    It sounds promising for astrobiology, yet life on a planet orbiting close to an M-drawf would face hazardous conditions. These stars are extremely active in their early years, and any nearby planet would likely get blasted with high energy radiation that would make it hard for life to take hold.

    Also, such close orbiting planets are unlikely to have water. In the proto-planetary disc that surrounds a young star, ices can only condense at a far enough distance where it is cool. This is what allows gas giants to become so massive, as they can accrete ice as well as gas and dust. With this increased core mass, they can then sweep up hydrogen and helium to create an extensive gas envelope.

    The boundary beyond which ice can form is known as the “snow line,” and planets forming in the habitable zones of some M-dwarfs are so far inside the snow line that they are devoid of water.

    2
    The dashed lines in the image show the Roche lobes of a star and a planet. As a mini-Neptune migrates inwards, the increasing effects of the star’s gravity can cause the planet’s atmosphere to extend beyond the Roche lobe. When this happens, the atmosphere is no longer gravitationally bound to the planet. Credit: Swinburne University of Technology

    But what if a gas giant migrated into the habitable zone? Astronomer Rodrigo Luger of the University of Washington, along with colleagues, have found that a certain kind of planet called a mini-Neptune with its atmosphere removed could, in fact, become a viable planet to life.

    A mini-Neptune is a gaseous planet that is up to ten times the mass of the Earth. Such a planet would be engulfed in a thick atmosphere of gas and then would need to lose its envelope before becoming a water-rich world.

    The research has been published in the journal Astrobiology.

    Losing an atmosphere

    There are two ways in which a mini-Neptune could evict its atmosphere. The first is via a process known as hydrodynamic escape. Extreme radiation from the host star in the form of x-ray and ultraviolet rays bombard the planet, causing the atmosphere to heat up. The upper atmosphere then expands, forcing the gas to accelerate to supersonic speeds. This hydrodynamic wind is fast enough for the atmosphere to escape into space.

    The second way for a mini-Neptune to shed its cloak of gas is for the atmosphere to become so extended that it is no longer gravitationally bound to the planet. The area around a star or planet where material is gravitationally bound is known as the Roche lobe. Once gas reaches the edge the of this teardrop-shaped lobe it can escape, and this is known as Roche lobe overflow. Roche lobe overflow couldn’t occur during planet formation, as it simply wouldn’t accrete the material in the first place. However, a planet migrating inwards will start to feel the effects of the star’s gravity more and more, and this can trigger the overflow.

    From mini-Neptunes to water worlds

    3
    Artist’s impression of a water world, with very few continents showing above the water. Credit: a1Star.com

    Once the initial atmosphere is gone, the solid core left behind becomes a terrestrial planet. Assuming that a secondary atmosphere could form through a process such as volcanic outgassing, this core could become habitable, earning it the name “habitable evaporated core” (HEC).

    The computer simulations run by Luger and colleagues showed that a mini-Neptune with a core mass similar to that of Earth would be the most likely candidate to become a habitable evaporated core. If the core mass was greater than twice the mass of the Earth, it could not become an evaporated core.

    Assuming that the composition of a proto-planetary disc surrounding an M-dwarf is similar to that of our Solar System, then a habitable evaporated core would likely have a lot of water since it would have formed beyond the snow line. These planets would therefore become water worlds, with little or no exposed continents.

    “While water is great for life, this could be tricky for supporting a biosphere, since high pressure ices can form at the bottom of the ocean and interrupt the carbon cycle on these planets,” explains Luger. “But we still have no idea how chemical cycling occurs on water worlds, so we can’t rule out life on these planets just yet.”

    Spot the difference

    If an Earth-mass planet is detected in the habitable zone of an M-dwarf, how will astronomers know if it is a “native” planet, which is dry and barren, or a habitable evaporated core? The key to telling them apart is in their different compositions.

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    A mini-Neptune compared to the size of the Earth. The core of a mini-Neptune can be similar in mass to that of the Earth. Once the hydrogen and helium envelope has been stripped, a water-rich habitable evaporated core is left behind. Credit: Geoff Marcy

    “The easiest way to (potentially) distinguish a HEC from an in-situ Earth would be density,” says Luger. “HECs will have much lower bulk densities due to their higher water fraction.”

    Measurements of the radius and mass of a planet will reveal the density, however we are still a few years away from achieving this precision. With the launch of the James Webb Space Telescope in 2018, it might be possible to detect signatures in the atmosphere of a planet which would reveal it to be an evaporated core.

    NASA Webb Telescope
    NASA/Webb

    See the full article here.

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  • richardmitnick 7:32 pm on April 9, 2015 Permalink | Reply
    Tags: , Astrobiology Magazine, ,   

    From astrobio.net: “Can we find an ancient Earth-like planet with a dying biosphere?” 

    Astrobiology Magazine

    Astrobiology Magazine

    Apr 9, 2015
    Amanda Doyle

    1
    The life cycle of a solar-like star shows how our Sun will expand into a red giant. Credit: ESO/M. Kornmesser

    Our Sun will evolve into a red giant star billions of years from now. The increased heat from the expanding Sun will scorch the Earth with dire effects to life. Climate models can be used to predict how this will happen, but, of course, this cannot be tested out on Earth.

    Jack O’Malley-James of the Institute for Pale Blue Dots at Cornell University, along with colleagues, have been calculating the chances of discovering an old-Earth analog approaching the end of its habitable lifetime. This follows his work on Swansong Biospheres in which the potential bio-signatures of a dying world were assessed. The new paper, In Search of Future Earths: Assessing the possibility of finding Earth analogues in the later stages of their habitable lifetimes, has been accepted for publication in the journal Astrobiology and is available in preprint.

    The far future Earth

    Searches are already in place to find Earth’s twin, a planet with a similar mass and radius as the Earth and orbiting at the same distance as the Earth does from the Sun. However, finding an equivalent of Earth’s much older cousin involves a different set of criteria.

    The “habitable zone” is defined as the region where liquid water can exist on the surface of a planet. Habitable zones move outwards as a star ages, so a planet that was in the zone when the star was younger may not necessarily remain there. An old Earth analogue is one that has been in the star’s habitable zone for the entire main sequence lifetime of the star, known as the continuously habitable zone. As the purpose is to study planets in the final stages of habitability, a far future Earth would also have to be approaching the inner edge of the habitable zone.

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    The habitable zone (in blue) extends to greater distances for stars hotter than the Sun. Similarly, the habitable zone will move outwards as our Sun becomes a red giant. The continuously habitable zone is a smaller region where a planet can remain habitable throughout the main sequence lifetime of the star. Credit: Wikimedia

    As up to one-third of main sequence solar-like stars are thought to be in the later stages of their evolution, it is feasible that old Earth analogues could be detected. If any of these planets exist in the solar neighborhood, then they would be excellent candidates for future space telescopes with the capability to characterize a planet’s atmosphere from its spectrum.

    Searching nearby

    There are six solar-like stars within 10 parsecs of the Sun that are old enough to harbor an old Earth analogue.

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    A parsec is the distance from the Sun to an astronomical object that has a parallax angle of one arcsecond (the diagram is not to scale).

    A parsec is the equivalent of 3.26 light years. O’Malley-James calculated the location of the habitable zone for each star over its entire lifetime. He then placed hypothetical planets in each system at a distance where the planet could remain habitable for billions of years. The temperature changes on the planet over the main sequence lifetime of the star can be modeled by comparing the predicted incoming and outgoing radiation.

    The paper concludes that if Earth-like planets existed around these stars, then the one around 61 Vir would be at the right stage of its lifetime to be considered a far future Earth. Such a planet might be home to a declining microbial population, assuming that life evolved there in a similar manner to the Earth. This hypothetical planet would be akin to the stage in future Earth’s lifetime when the temperature has risen too high for complex life to survive, and microbes are the last lifeforms to cling to existence. Other stars could host planets similar to future Earth where only extremophile microbial life remains in a few select niches, however these biosignatures would be much more difficult to detect than the declining microbial biosphere.

    A Galaxy Teeming with Earth-like Planets?

    If an Earth-like planet existed around 61 Vir, it would provide a good opportunity to study the far future Earth. But what are the actual chances of such planets existing?

    O’Malley-James used previous studies by other scientists in order to find out. One study, based on the number of planets found by NASA’s Kepler mission, predicts that 8.6 percent of solar-like stars could harbor an Earth-like planet orbiting in the habitable zone.

    NASA Kepler Telescope
    Kepler

    A solar-like star is one that is of a similar temperature and mass as our own Star. There are 276 stars like our Sun within 100 parsecs, around half of which are older than six billion years. This means that there should be 11 potential targets.

    3
    61 Vir as seen with a 12.5″ telescope with a field of view of 45.1 arc minutes. Credit: Kevin Heider

    However, another study showed that terrestrial planets are more likely to form less than one astronomical unit (AU), the distance between the Sun and the Earth) from the star. From the six example stars that O’Malley-James studied, the continuously habitable zone is located slightly further from the star than this. Combining these results indicates that there would actually only be one potential old-Earth analogue within the solar neighborhood.

    “It turned out that these planets are probably not that common at all, so in reality any habitable planets in the 61 Vir system will probably not resemble an older version of Earth,” said O’Malley-James. “This study highlights that finding replicas of our own world, in terms of the diversity and complexity of life, is going to be a much harder task than simply finding life.”

    Yet while there may only be one potential old-Earth analogue close enough to be studied in detail, there could still be thousands more in the distant reaches of our Galaxy.

    See the full article here.

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  • richardmitnick 4:22 am on March 21, 2015 Permalink | Reply
    Tags: , Astrobiology Magazine, , Ice Ages   

    From astrobio.net: “International study raises questions about cause of global ice ages” 

    Astrobiology Magazine

    Astrobiology Magazine

    Mar 21, 2015
    No Writer Credit

    1
    Moraines, or rocks and soil deposited by glaciers during the Last Glacial Maximum, are spread across the landscape near Mt. Cook, New Zealand’s tallest mountain, and Lake Pukaki. Credit: Aaron Putnam

    A new international study casts doubt on the leading theory of what causes ice ages around the world — changes in the way the Earth orbits the sun.

    The researchers found that glacier movement in the Southern Hemisphere is influenced primarily by sea surface temperature and atmospheric carbon dioxide rather than changes in the Earth’s orbit, which are thought to drive the advance and retreat of ice sheets in the Northern Hemisphere.

    The findings appear in the journal Geology. A PDF is available on request.

    The study raises questions about the Milankovitch theory of climate, which says the expansion and contraction of Northern Hemisphere continental ice sheets are influenced by cyclic fluctuations in solar radiation intensity due to wobbles in the Earth’s orbit; those orbital fluctuations should have an opposite effect on Southern Hemisphere glaciers.

    “Records of past climatic changes are the only reason scientists are able to predict how the world will change in the future due to warming. The more we understand about the cause of large climatic changes and how the cooling or warming signals travel around the world, the better we can predict and adapt to future changes,” says lead author Alice Doughty, a glacial geologist at Dartmouth College who studies New Zealand mountain glaciers to understand what causes large-scale global climatic change such as ice ages.

    “Our results point to the importance of feedbacks — a reaction within the climate system that can amplify the initial climate change, such as cool temperatures leading to larger ice sheets, which reflect more sunlight, which cools the planet further. The more we know about the magnitude and rates of these changes and the better we can explain these connections, the more robust climate models can be in predicting future change.”

    The researchers used detailed mapping and beryllium-10 surface exposure dating of ice-age moraines – or rocks deposited when glaciers move — in New Zealand’s Southern Alps, where the glaciers were much bigger in the past. The dating method measures beryllium-10, a nuclide produced in rocks when they are struck by cosmic rays.

    The researchers identified at least seven episodes of maximum glacier expansion during the last ice age, and they also dated the ages of four sequential moraine ridges. The results showed that New Zealand glaciers were large at the same time that large ice sheets covered Scandinavia and Canada during the last ice age about 20,000 years ago.

    This makes sense in that the whole world was cold at the same time, but the Milankovitch theory should have opposite effects for the Northern and Southern Hemispheres, and thus cannot explain the synchronous advance of glaciers around the globe. Previous studies have shown that Chilean glaciers in the southern Andes also have been large at the same time as Northern Hemisphere ice sheets.

    The ages of the four New Zealand ridges – about 35,500; 27,170; 20,270; and 18,290 years old — instead align with times of cooler sea surface temperatures off the coast of New Zealand based on offshore marine sediment cores. The timing of the Northern Hemisphere’s ice ages and large ice sheets is still paced by how Earth orbits the Sun, but how the cooling and warming signals are transferred around the world has not been fully explained, although ocean currents (flow direction, speed and temperature) play a significant role.

    See the full article here.

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  • richardmitnick 2:46 pm on March 7, 2015 Permalink | Reply
    Tags: , , Astrobiology Magazine,   

    From astrobio.net: “NASA Ames Reproduces the Building Blocks of Life in Laboratory” 

    Astrobiology Magazine

    Astrobiology Magazine

    Mar 7, 2015
    No Writer Credit

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    Left to right: Ames scientists Michel Nuevo, Christopher Materese and Scott Sandford reproduce uracil, cytosine, and thymine, three key components of our hereditary material, in the laboratory. Image Credit: NASA/ Dominic Hart

    NASA scientists studying the origin of life have reproduced uracil, cytosine, and thymine, three key components of our hereditary material, in the laboratory. They discovered that an ice sample containing pyrimidine exposed to ultraviolet radiation under space-like conditions produces these essential ingredients of life.

    Pyrimidine is a ring-shaped molecule made up of carbon and nitrogen and is the central structure for uracil, cytosine, and thymine, which are all three part of a genetic code found in ribonucleic (RNA) and deoxyribonucleic acids (DNA). RNA and DNA are central to protein synthesis, but also have many other roles.

    “We have demonstrated for the first time that we can make uracil, cytosine, and thymine, all three components of RNA and DNA, non-biologically in a laboratory under conditions found in space,” said Michel Nuevo, research scientist at NASA’s Ames Research Center, Moffett Field, California. “We are showing that these laboratory processes, which simulate conditions in outer space, can make several fundamental building blocks used by living organisms on Earth.”

    An ice sample is deposited on a cold (approximately –440 degrees Fahrenheit) substrate in a chamber, where it is irradiated with high-energy ultraviolet (UV) photons from a hydrogen lamp. The bombarding photons break chemical bonds in the ices and break down the ice’s molecules into fragments that then recombine to form new compounds, such as uracil, cytosine, and thymine.

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    Pyrimidine is a ring-shaped molecule made up of carbon and nitrogen and is the central structure for uracil, cytosine, and thymine, which are found in RNA and DNA. Image Credit: NASA

    NASA Ames scientists have been simulating the environments found in interstellar space and the outer Solar System for years. During this time, they have studied a class of carbon-rich compounds, called polycyclic aromatic hydrocarbons (PAHs), that have been identified in meteorites, and which are the most common carbon-rich compound observed in the universe. PAHs typically are structures based on several six-carbon rings that resemble fused hexagons, or a piece of chicken wire.

    The molecule pyrimidine is found in meteorites, although scientists still do not know its origin. It may be similar to the carbon-rich PAHs, in that it may be produced in the final outbursts of dying, giant red stars, or formed in dense clouds of interstellar gas and dust.

    “Molecules like pyrimidine have nitrogen atoms in their ring structures, which makes them somewhat wimpy. As a less stable molecule, it is more susceptible to destruction by radiation, compared to its counterparts that don’t have nitrogen,” said Scott Sandford, a space science researcher at Ames. “We wanted to test whether pyrimidine can survive in space, and whether it can undergo reactions that turn it into more complicated organic species, such as the nucleobases uracil, cytosine, and thymine.”

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    The ring-shaped molecule pyrimidine is found in cytosine and thymine. Image Credit: NASA

    In theory, the researchers thought that if molecules of pyrimidine could survive long enough to migrate into interstellar dust clouds, they might be able to shield themselves from destructive radiation. Once in the clouds, most molecules freeze onto dust grains (much like moisture in your breath condenses on a cold window during winter).

    These clouds are dense enough to screen out much of the surrounding outside radiation of space, thereby providing some protection to the molecules inside the clouds.

    Scientists tested their hypotheses in the Ames Astrochemistry Laboratory. During their experiment, they exposed the ice sample containing pyrimidine to ultraviolet radiation under space-like conditions, including a very high vacuum, extremely low temperatures (approximately –440 degrees Fahrenheit), and harsh radiation.

    They found that when pyrimidine is frozen in ice mostly consisting of water, but also ammonia, methanol, or methane, it is much less vulnerable to destruction by radiation than it would be if it were in the gas phase in open space. Instead of being destroyed, many of the molecules took on new forms, such as the RNA/DNA components uracil, cytosine, and thymine, which are found in the genetic make-up of all living organisms on Earth.

    “We are trying to address the mechanisms in space that are forming these molecules. Considering what we produced in the laboratory, the chemistry of ice exposed to ultraviolet radiation may be an important linking step between what goes on in space and what fell to Earth early in its development,” said Christopher Materese, another researcher at NASA Ames who has been working on these experiments.

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    An ice sample is held at approximately -440 degrees Fahrenheit in a vacuum chamber, where it is irradiated with high energy UV photons from a hydrogen lamp. The bombarding photons break chemical bonds in the ice samples and result in the formation of new compounds, such as uracil. Image Credit: NASA/Dominic Hart

    “Nobody really understands how life got started on Earth. Our experiments suggest that once the Earth formed, many of the building blocks of life were likely present from the beginning. Since we are simulating universal astrophysical conditions, the same is likely wherever planets are formed,” says Sandford.

    Additional team members who helped perform some of the research are Jason Dworkin, Jamie Elsila, and Stefanie Milam, three NASA scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

    The research was funded by the NASA Astrobiology Institute (NAI) and the NASA Origins of Solar Systems Program. The NAI is a virtual, distributed organization of competitively-selected teams that integrates and funds astrobiology research and training programs in concert with the national and international science communities.

    See the full article here.

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  • richardmitnick 7:03 pm on February 9, 2015 Permalink | Reply
    Tags: , Astrobiology Magazine, ,   

    From astrobio: “Planets Orbiting Red Dwarfs May Stay Wet Enough for Life” 

    Astrobiology Magazine

    Astrobiology Magazine

    Feb 9, 2015
    Charles Q. Choi

    1
    Oceans currents would transport heat to the dark side of tidally-locked exoplanets. Image Credit: Lynette Cook

    Small, cold stars known as red dwarfs are the most common type of star in the Universe, and the sheer number of planets that may exist around them potentially make them valuable places to hunt for signs of extraterrestrial life.

    However, previous research into planets around red dwarfs suggested that while they may be warm enough to host life, they might also completely dry out, with any water they possess locked away permanently as ice. New research published on the topic finds that these planets may stay wet enough for life after all. The scientists detailed their findings online on November 12 in The Astrophysical Journal Letters.

    Red dwarfs, also known as M stars, are roughly one-fifth as massive as the Sun and up to 50 times fainter. These stars comprise up to 70 percent of the stars in the cosmos, and NASA’s Kepler space observatory has discovered that at least half of these stars host rocky planets that are one-half to four times the mass of Earth.

    NASA Kepler Telescope
    Kepler

    Red dwarf planets are potentially key places to search for life as we know it, not just because there are so many of them, but also because of their incredible longevity. Unlike our Sun, which will die in a few billion years, red dwarfs will take trillions of years to burn through their fuel, significantly longer than the age of the Universe, which is less than 14 billion years old. This longevity potentially gives red dwarfs a great deal more time for life to evolve around them.

    Research into whether a distant world might host life as we know it usually focuses on whether or not it has liquid water, since there is life virtually everywhere there is liquid water on Earth, even miles underground. Scientists typically concentrate on habitable zones, the area around a star where it is neither too hot for all its surface water to boil away, nor too cold enough for all its surface water to freeze.

    Recent findings suggest that planets in the habitable zones of red dwarf stars could accumulate significant amounts of water. In fact, each planet could possess about 25 times more water than Earth.

    The habitable zones of red dwarfs are close to these stars because of how dim they are, often closer than the distance Mercury orbits the Sun. This closeness makes them appealing to astrobiologists, since planets near their stars cross in front of them more often, making them easier to detect than planets that orbit farther away.

    However, when a planet orbits very near a star, the star’s gravitational pull can force the world to become “tidally locked” to it. When a planet is tidally locked to its star, it will always show the same side to its star, just as the Moon always shows the same side to Earth. This causes the planet to have one permanent day side and one permanent night side.

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    The extremes of heat and cold that tidally locked planets experience could make them profoundly different from Earth. For example, prior research speculated the dark sides of tidally locked planets would become so cold that any water there would freeze. Sunlight would make water on the sunlit side evaporate, and this water vapor could get carried by air currents to the night sides, eventually leading to sheets of ice miles thick on the night sides and removing all water from the sunlit sides. Life as we know it probably could not develop on the day sides of such planets. Although they would have sunlight for photosynthesis, they would have no water to serve as the primordial soup for life to swim in.

    To see how habitable tidally-locked planets really are, scientists devised a 3D global climate model of planets that simulated interactions between the atmosphere, ocean, sea ice, and land, as well as a 3-D model of ice sheets large enough to cover entire continents. They also simulated a red dwarf with a temperature of about 5,660 degrees Fahrenheit (3,125 degrees Celsius), and investigated whether all the water on these planets would indeed get trapped on their night sides.

    “I’ve been interested in trying to make calculations relevant for M-star planet habitability since being convinced by astronomers that these types of planets will likely be closest (in proximity) to Earth,” said study co-author Dorian Abbot, a geoscientist at the University of Chicago.

    For instance, the nearest known star to the Sun, Proxima Centauri, is a red dwarf, and it remains uncertain whether or not it has a planet. The possibility that red dwarf planets might be relatively near to Earth “means that anything geoscientists can tell astronomers about habitability of these planets will be essential for planning future missions.”

    The researchers simulated planets of Earth’s size and gravity that experienced between 63 percent and 77 percent as much sunlight as Earth. They also modeled a super-Earth planet 50 percent wider than Earth with 38 percent stronger gravity, because astronomers have discovered super-Earth worlds around red dwarfs. For instance, Gliese 667Cb, a super-Earth at least 4.5 times the mass of Earth, orbits Gliese 667C, a red dwarf about 22 light years from Earth. They set this super-Earth on an orbit where it received about two-thirds as much as sunlight as Earth.

    The researchers modeled three different arrangements of continents for all these planets. One was a water world with no continents and global oceans of varying depths. Another involved a supercontinent covering the night side and an ocean covering the day side. The last mimicked Earth’s configuration of continents. The planets also had atmospheres similar to Earth’s, but the researchers also tested lower levels of the greenhouse gas, carbon dioxide, which traps heat and helps keep planets warm.

    When it came to super-Earths covered entirely in water, and super-Earths with continental arrangements like Earth’s, the researchers found it was unlikely that all their water would get trapped on their night sides.

    “This is because surface winds transport sea ice to the day side where it is melted easily,” said lead study author Jun Yang at the University of Chicago.

    Moreover, ocean currents transport heat from the day side to the night side on these planets.

    “Ocean heat transport strongly influences the climate and sea ice thickness on our Earth,” Yang said. “We found this may also work on exoplanets.”

    If a super-Earth has very large continents covering most of its night side, the scientists discovered ice sheets of at least 3,300 feet (1,000 meters) thick could grow on its night side. However, the day sides of these super-Earths would dry out completely only if they received less geothermal heat from volcanic activity than Earth, and had 10 percent of the amount of water on Earth’s surface or less. Similar results were seen with Earth-sized planets.

    “The important implication is that it may be easier than previously thought to keep liquid water on the dayside of a tidally locked planet, where photosynthesis is possible,” Abbot said. “There are many issues that will affect the habitability of M-star planets, but our results suggest at least that water-trapping on the night side will only be a problem for relatively dry planets with large continents on their nightside and relatively low geothermal heat flux.”

    Based on present and near-future technology, Yang said it would be very difficult for astronomers to gauge how thick the sea ice or the ice sheets are on the night sides of red dwarf planets and test whether their models are correct. Still, using current and upcoming technology “it may be possible to know whether the day sides are dry or not,” Yang said.

    See the full article here.

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  • richardmitnick 9:35 am on February 7, 2015 Permalink | Reply
    Tags: Astrobiology Magazine, , , Twinkle project,   

    From astrobio.net: “New Mission, Twinkle, on Fast-Track to Unveil Exoplanet Atmospheres” 

    Astrobiology Magazine

    Astrobiology Magazine

    Feb 6, 2015

    1
    Artist’s impression of a hot Neptune-sized planet orbiting a star beyond our Sun. Credit:NASA/JPL-Caltech

    A team of UK scientists and engineers have announced plans for a small satellite, named “Twinkle,” that will give radical new insights into the chemistry, formation and evolution of planets orbiting other stars.

    The mission, which is being led by University College London (UCL) and Surrey Satellite Technology Ltd. (SSTL), will be launched within four years. An overview of the science case and instrument design will be presented today at an open meeting at the Royal Astronomical Society.

    “Twinkle is a very ambitious mission,” said lead scientist, Prof. Giovanna Tinetti of UCL. “Nearly two thousand exoplanets — planets orbiting stars other than our Sun — have been discovered to date, but we know very little about these alien worlds. We can measure their mass, density and distance from their star. From that, we can deduce that that some are freezing cold, some are so hot that they have molten surfaces, some are vast balls of gas, like Jupiter, or small and rocky, like Earth. But beyond that, we just don’t know. Twinkle will be the first mission dedicated to analyzing exoplanets atmospheres, and will give us a completely new picture of what these worlds are really like.”

    When an exoplanet passes in front of the star that it orbits, a tiny amount of starlight is filtered through the molecules and clouds in the planet’s atmosphere. Twinkle will measure this light and pick out the characteristic spectral “fingerprints” that show if gases like water vapor or methane are present on the planet.

    Tinetti played a key role in the team that pioneered this technique through observations with the Hubble and Spitzer Space Telescopes.

    NASA Hubble Telescope
    Hubble

    NASA Spitzer Telescope
    Spitzer

    Knowledge of the chemical composition of exoplanet atmospheres is essential for understanding whether a planet was born in the orbit in which it is currently observed or whether it has migrated from a different part of its planetary system.

    The make-up, evolution, chemistry and physical processes driving an exoplanet’s atmosphere are strongly affected by the distance from its parent star. The atmospheres of small, terrestrial type-planets may have evolved quite dramatically from their initial composition. The loss of lighter molecules, impacts with other bodies, such as comets or asteroids, volcanic activity, or even life can significantly alter the composition of primordial atmospheres. Atmospheric composition is therefore a tracer of an exoplanet’s history as well as whether it might be habitable — or even host life.

    twinkle
    Rendering of the Twinkle mission spacecraft, which will be built by Surrey Satellite Technology Ltd. Credit: Twinkle/SSTL

    Twinkle will analyze at least 100 exoplanets in the Milky Way. Its infrared spectrograph will enable observations of a wide range of planet types including super-Earths (rocky planets 1-10 times the mass of Earth) and hot Jupiters (gas giants orbiting very close to their suns).

    2

    Some of the target planets are orbiting stars similar to our Sun and some are orbiting cooler red dwarfs. For the largest planets orbiting bright stars, Twinkle will even be able to produce maps of clouds and temperature.

    “The light filtered through the planet’s atmosphere is only about one ten thousandth of the overall light from the star,” said Tinetti. “That’s a big challenge and one that requires a very stable platform outside the screening effects of Earth’s atmosphere.”

    While the construction of Twinkle’s scientific instrument is led by UCL, the spacecraft itself will be built by SSTL, based in Guildford, Surrey. SSTL has innovated the concept of rapid and cost-effective spacecraft development, which has resulted in a significant export market for commercial and government Earth observation missions.

    “This is an exciting opportunity to adapt the high-performance capacity we have developed at SSTL to deliver ground-breaking science,” said Dr. Susan Jason, lead engineer from SSTL.

    Twinkle will be launched into a polar low-Earth orbit. The spacecraft will be built to operate for a minimum of three years, with the possibility of an extended lifetime of five years or more. The mission will be funded through a mixture of private and public sources. With a total mission cost of around £50 million, including launch, Twinkle is a factor of 10 times cheaper to build and operate than other astrophysical spacecraft developed through international space agency programs. The short development timescale and low budget are made possible through expertise already developed at UK institutions and the use of off-the-shelf components.

    “The UK has already made an outstanding contribution to exoplanet detection with the WASP survey program. Twinkle is a unique chance for the UK to build on this and take the world lead in understanding exoplanet science, as well as to inspire the next generation of scientists and engineers,” said Prof. Jonathan Tennyson, senior advisor for the Twinkle mission.

    Twinkle project press release

    See the full article here.

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