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  • richardmitnick 5:04 pm on February 8, 2017 Permalink | Reply
    Tags: Ion escape, , Oxygen escape, Planet habitability, Proxima b is subjected to torrents of X-ray and extreme ultraviolet radiation from superflares occurring roughly every two hours., , Stellar eruptions such as flares and coronal mass ejections – collectively called space weather, We have pessimistic results for planets around young red dwarfs in this study   

    From Goddard: “NASA Finds Planets of Red Dwarf Stars May Face Oxygen Loss in Habitable Zones” 

    NASA Goddard Banner

    NASA Goddard Space Flight Center

    Feb. 8, 2017
    Lina Tran
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    Credit: NASA

    The search for life beyond Earth starts in habitable zones, the regions around stars where conditions could potentially allow liquid water – which is essential for life as we know it – to pool on a planet’s surface. New NASA research suggests some of these zones might not actually be able to support life due to frequent stellar eruptions – which spew huge amounts of stellar material and radiation out into space – from young red dwarf stars.

    Now, an interdisciplinary team of NASA scientists wants to expand how habitable zones are defined, taking into account the impact of stellar activity, which can threaten an exoplanet’s atmosphere with oxygen loss. This research was published in The Astrophysical Journal Letters on Feb. 6, 2017.

    “If we want to find an exoplanet that can develop and sustain life, we must figure out which stars make the best parents,” said Vladimir Airapetian, lead author of the paper and a solar scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We’re coming closer to understanding what kind of parent stars we need.”

    To determine a star’s habitable zone, scientists have traditionally considered how much heat and light the star emits. Stars more massive than our sun produce more heat and light, so the habitable zone must be farther out. Smaller, cooler stars yield close-in habitable zones.

    But along with heat and visible light, stars emit X-ray and ultraviolet radiation, and produce stellar eruptions such as flares and coronal mass ejections – collectively called space weather. One possible effect of this radiation is atmospheric erosion, in which high-energy particles drag atmospheric molecules – such as hydrogen and oxygen, the two ingredients for water – out into space. Airapetian and his team’s new model for habitable zones now takes this effect into account.

    In this artist’s concept, X-ray and extreme ultraviolet light from a young red dwarf star cause ions to escape from an exoplanet’s atmosphere. Scientists have developed a model that estimates the oxygen ion escape rate on planets around red dwarfs, which plays an important role in determining an exoplanet’s habitability.
    Credits: NASA Goddard/Conceptual Image Lab, Michael Lentz, animator/Genna Duberstein, producer

    The search for habitable planets often hones in on red dwarfs, as these are the coolest, smallest and most numerous stars in the universe – and therefore relatively amenable to small planet detection.

    “On the downside, red dwarfs are also prone to more frequent and powerful stellar eruptions than the sun,” said William Danchi, a Goddard astronomer and co-author of the paper. “To assess the habitability of planets around these stars, we need to understand how these various effects balance out.”

    Another important habitability factor is a star’s age, say the scientists, based on observations they’ve gathered from NASA’s Kepler mission. Every day, young stars produce superflares, powerful flares and eruptions at least 10 times more powerful than those observed on the sun. On their older, matured counterparts resembling our middle-aged sun today, such superflares are only observed once every 100 years.

    “When we look at young red dwarfs in our galaxy, we see they’re much less luminous than our sun today,” Airapetian said. “By the classical definition, the habitable zone around red dwarfs must be 10 to 20 times closer-in than Earth is to the sun. Now we know these red dwarf stars generate a lot of X-ray and extreme ultraviolet emissions at the habitable zones of exoplanets through frequent flares and stellar storms.”

    Superflares cause atmospheric erosion when high-energy X-ray and extreme ultraviolet emissions first break molecules into atoms and then ionize atmospheric gases. During ionization, radiation strikes the atoms and knocks off electrons. Electrons are much lighter than the newly formed ions, so they escape gravity’s pull far more readily and race out into space.

    Opposites attract, so as more and more negatively charged electrons are generated, they create a powerful charge separation that lures positively charged ions out of the atmosphere in a process called ion escape.

    “We know oxygen ion escape happens on Earth at a smaller scale since the sun exhibits only a fraction of the activity of younger stars,” said Alex Glocer, a Goddard astrophysicist and co-author of the paper. “To see how this effect scales when you get more high-energy input like you’d see from young stars, we developed a model.”

    The model estimates the oxygen escape on planets around red dwarfs, assuming they don’t compensate with volcanic activity or comet bombardment. Various earlier atmospheric erosion models indicated hydrogen is most vulnerable to ion escape. As the lightest element, hydrogen easily escapes into space, presumably leaving behind an atmosphere rich with heavier elements such as oxygen and nitrogen.

    But when the scientists accounted for superflares, their new model indicates the violent storms of young red dwarfs generate enough high-energy radiation to enable the escape of even oxygen and nitrogen – building blocks for life’s essential molecules.

    “The more X-ray and extreme ultraviolet energy there is, the more electrons are generated and the stronger the ion escape effect becomes,” Glocer said. “This effect is very sensitive to the amount of energy the star emits, which means it must play a strong role in determining what is and is not a habitable planet.”

    Considering oxygen escape alone, the model estimates a young red dwarf could render a close-in exoplanet uninhabitable within a few tens to a hundred million years. The loss of both atmospheric hydrogen and oxygen would reduce and eliminate the planet’s water supply before life would have a chance to develop.

    “The results of this work could have profound implications for the atmospheric chemistry of these worlds,” said Shawn Domagal-Goldman, a Goddard space scientist not involved with the study. “The team’s conclusions will impact our ongoing studies of missions that would search for signs of life in the chemical composition of those atmospheres.”

    Modeling the oxygen loss rate is the first step in the team’s efforts to expand the classical definition of habitability into what they call space weather-affected habitable zones. When exoplanets orbit a mature star with a mild space weather environment, the classical definition is sufficient. When the host star exhibits X-ray and extreme ultraviolet levels greater than seven to 10 times the average emissions from our sun, then the new definition applies. The team’s future work will include modeling nitrogen escape, which may be comparable to oxygen escape since nitrogen is just slightly lighter than oxygen.

    The new habitability model has implications for the recently discovered planet orbiting the red dwarf Proxima Centauri, our nearest stellar neighbor. Airapetian and his team applied their model to the roughly Earth-sized planet, dubbed Proxima b, which orbits Proxima Centauri 20 times closer than Earth is to the sun.

    Considering the host star’s age and the planet’s proximity to its host star, the scientists expect that Proxima b is subjected to torrents of X-ray and extreme ultraviolet radiation from superflares occurring roughly every two hours. They estimate oxygen would escape Proxima b’s atmosphere in 10 million years. Additionally, intense magnetic activity and stellar wind – the continuous flow of charged particles from a star – exacerbate already harsh space weather conditions. The scientists concluded that it’s quite unlikely Proxima b is habitable.

    “We have pessimistic results for planets around young red dwarfs in this study, but we also have a better understanding of which stars have good prospects for habitability,” Airapetian said. “As we learn more about what we need from a host star, it seems more and more that our sun is just one of those perfect parent stars, to have supported life on Earth.”

    See the full article here.

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    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.

    NASA Goddard campus
    NASA/Goddard Campus
    NASA image

  • richardmitnick 12:26 pm on May 14, 2016 Permalink | Reply
    Tags: , , Planet habitability   

    From Astronomy: “This map shows where in the sky you might find habitable exoplanets” 

    Astronomy magazine


    May 12, 2016
    John Wenz

    There are 42 worlds that might be Earth-like out there. We can’t see them directly, yet. But here’s where to find out cosmic cousins.

    Location  of the Stars with  Potentially Habitable Planets, Planetary Habitability Laboratory @ UPR Arecibo, 2016
    Location of the Stars with Potentially Habitable Planets, Planetary Habitability Laboratory @ UPR Arecibo, 2016
    The location of all known exoplanets that could potentially harbor life. Imaging them is a whole other matter. PHL / UPRA

    We know of more than 3,000 planets out there in our galaxy, and the list keeps growing. But of all those planets out there, only a small handful are considered habitable. Some exoplanets are too big to have a solid surface. Others are too close in to support life, or too distant not to freeze over.

    The Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo put together a catalog of these scant few planets where we might find life. It also put together the above chart, which shows where in the night sky these exoplanets “live.” Many of the Kepler planets are clustered because the spacecraft looked only at one particular portion of the sky.

    Of course, there are always a few caveats. In our solar system, Venus and Mars both fall in the Sun’s “habitable zone,” but were stripped of water either by a runaway greenhouse effect in the case of Venus or a loss of dense atmosphere in the case of Mars. There are still niches where any life that arose might exist in theory, but no concrete evidence yet. There may be other planets out there that theoretically have the right conditions but either never had the chance to thrive or were stripped of an earlier, balmier atmosphere.

    The PHL catalog also includes catalog planets, those not yet confirmed by other observations to be real. This means there’s the off-chance some of them might not hold up under further scrutiny and could be observational errors, eclipsing binaries, or other non-planetary events. So some of these are strongly suggested to be planets but need more concrete proof.

    Finally, there’s the really disappointing part: any exoplanet much smaller than Jupiter-sized is virtually impossible to see with any current optics, let alone a backyard telescope. Some of the stars are also incredibly faint, too faint to see with many telescopes. With a high-end telescope and some decent software you might be able to detect a transit, but there’s no chance to see the planet itself. The list of directly imaged exoplanets is incredibly small. The tennis court-sized James Webb Space Telescope might be able to finally spot some of these smaller planets, and is set for a 2018 launch.

    With that said, it’s still nice to know where, exactly, to look up and think “there may be life there.”

    See the full article here .

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  • richardmitnick 6:27 pm on April 29, 2016 Permalink | Reply
    Tags: , , Planet habitability   

    From Eos: “Becoming Habitable in the Habitable Zone” 

    Eos news bloc


    Sarah Stanley

    An artist’s rendition of Kepler-186f, an Earth-size planet in the habitable zone of a distant solar system. Little is known about its composition, but if it turns out to be rocky like Earth, it may be subject to climate-mantle-core interactions that determine whether it can actually sustain life. Credit: NASA Ames/SETI Institute/JPL-Caltech

    Day to day, plate tectonics may seem to have little to do with Earth’s habitability. However, over time, interactions between our planet’s climate, mantle, and core have created a suitable home for complex life.

    Techtonic plates, USGS, 1996
    The tectonic plates of the world were mapped in 1996, USGS.

    In a new review paper*, Foley and Driscoll suggest that similar processes could set other rocky planets on very different trajectories, ultimately determining whether they could support life as we know it.

    Cooler climates promote plate tectonics by keeping plate boundaries from fusing and by weakening the crust and outer mantle. In turn, plate tectonics help keep the climate temperate through carbon cycling. On Earth, cold slabs of rock subduct and sink deep into the mantle, drawing heat from the core. Long-term core cooling helps maintain Earth’s magnetic field, which keeps the solar wind from stripping away the atmosphere.

    The authors hypothesize that the climate-mantle-core connection determines whether a young, rocky planet will develop plate tectonics, a temperate climate, and a magnetic field—all of which are thought to be necessary for life. Initial atmospheric composition, timing of the onset of plate tectonics, and other factors can affect how climate-mantle-core dynamics unfold. This means that two similar planets might follow wildly different paths, even if they both reside in a solar system’s habitable zone (where liquid water can exist on the surface).

    The authors also suggest that interactions between the climate, mantle, and core might explain why Earth and Venus are so different, despite their similar sizes and composition: Venus’s hot climate prevents plate tectonics, stifling a sustained magnetic field.

    Scientists don’t yet know enough Venusian history to confirm the authors’ hypothesis. Much more research is also needed to clarify connections between climate, mantle, and core for rocky planets in general, but a better understanding of these dynamics could help predict the likelihood of finding an Earth-like exoplanet. (Geochemistry, Geophysics, Geosystems, doi:10.1002/2015GC006210, 2016).

    *Science paper:
    Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution

    See the full article here .

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    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

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